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Full text of "Scientific amusements"

Cornell University Library 



arV17317 

Scientific amusements 




,. 3 1924 031 296 126 

olin.anx 




Cornell University 
Library 



The original of this book is in 
the Cornell University Library. 

There are no known copyright restrictions in 
the United States on the use of the text. 



http://www.archive.org/details/cu31 924031 2961 26 



SCIENTIFIC AMUSEMENTS. 



SCIENTIFIC AMUSEMENTS 



Translated from the French of GASTON TISSANDIER. 



By henry frith. 



ffullB jllustcateO. 



LONDON : 

WARD, LOCK & CO., LIMITED, 
NEW YORK & MELBOURNE. 
K 



HALF-HOURS OF SCIENTIFIC 
AMUSEMENT. 



PREFACE. 




jQUNG people of both sexes, and persons ol 
all ages who have leisure and a taste for that 
which is ingenious as well as instructive and 
amusing, may be commended to this remark- 
ably interesting collection of experiments, nearly all of which 
can be readily performed by an iinskilled person who will 
carefully follow out the directions given. It is surprising 
how near we are to the most fundamental principles of 
science when we perform some of the simplest operations. 
The act of balancing oneself on one foot may be made 
to illustrate most instructively the principle of gravitation 
and the centre of gravity. The musical (or unmusical, as ^ 
the case may be) performance of whistling illustrates the 
power of air in motion, and the effects of vibrating cords^ 
(the vocal cords) in a limited space. The toasting of a 
piece of bread is an example of evaporation of water 
change of structure owing to heat, and the appearance 
of a black substance out of a white one by a change' in 
chemical combination. It is so in a multitude of the 
common occupations of life, and especially in the amuse- 
ments in which children take so great a delight. The 
schoolboy's sucker exemplifies the effect of the external 
pressure of the atmosphere ; his top, coerced to move 



vi PREFACE. 

circularly by the effect of a string wound round it in a 
spiral fashion, illustrates the effect of a spinning turn 
long after the force has been applied. A large number 
of experiments with coins— piercing a halfpenny with a 
needle, revolving a penny in a lampshade, catching coins 
held on the elbow in the hand, rotating a coin between 
two pins, and the like, show to how many amusing 
incidents these may give rise. Inertia, the bane of too 
many boys and men, is seen to prevail in the physical 
world in the experiment of projecting one or two draughts 
from a heap of them (page 1 8), and in removing a domino, 
as on page 20. The strange effects which can be produced 
by virtue of the principle of the centre of gravity are seen 
in the pencil and knife balanced on the point of the 
former, the match puzzle (page 30), the poising of a 
tumbler upon three sticks, each having one end in the air, 
the suspension of a bucket of water from a stick resting 
on a table, etc. 

Hydrostatics, the study of the effects of fluids, supplies 
many interesting facts and illustrations to this little book. 
The ascent of wine in an inverted glass of water, the 
floating of a needle, and the lobster syphon, are among 
these. The maintenance of various bodies in the air by 
currents of air, and the phenomena of vortex rings of 
smoke, are equally striking and instructive. Various 
experiments on the pressure of the air and with com- 
pressed air, and the properties of air and gas balloons, 
complete the section dealing with pneumatics. 

The conduction of heat by metals, and their dilatation 
by heat, furr>ish several striking phenomena of which 



PREFACE. vii 

the placing of a red-hot coal on a muslin handkerchief 
encircling a copper globe,' without setting fire to the 
handkerchief, is one of the most notable. Even more 
remarkable, perhaps, are the optical illusions, effects of 
refraction, etc., explained in Chapter VI. How to make 
a florin appear like five shillings and sixpence appeals 
strongly to the cupidity of mankind ; but it must not be 
imagined that this book will enable any one to buy five 
shillings and sixpence worth of goods for a florin. It is 
astonishing how many optical illusions may be produced 
by the varied arrangements of lines, points, and squares, 
and these are here duly set forth. The "imp on the 
ceiling" illustrates the persistence of impressions on 
the retina. 

Eleqtricity and magnetism, as is only to be expected 
in these days of the electric light, supply us with some 
most interesting subjects. The "dance of the paper 
puppets," and the " magnetised magician," are examples of 
these. Chemistry without a laboratory introduces us to the 
air and its elements, the formation of salts, instantaneous 
crystallisation, the "Tree of Saturn," the produ^;tion of 
gas, and the graven eggs. 

Mathematical games, as here expounded, are capable 
of affording no small amusement. Marjy of the best 
mechanical toys invented in recent years are described 
in Chapter XL, such as the acrobatic ape, the magic glass, 
the fantoccini top, the mechanical paper bird, the magic 
picture with three faces, and the mechanical fly. Every 
one may take his friend's portrait by the silhouette process 
given on pages 85, 86, while the formation of typica/ 



Vlll 



PREFACE. 



portrait sketches by the combination of implements used 
in any given craft is amusingly shown on pages 139-141-. 
Thus it will be evident that a vast amount of amusement, 
combined with instruction, is to be got out of the attentive 
perusal of the following pages. 




CONTENTS. 



Chapter i.— properties of bodies. 

PAGE 

STRENGTH — ELASTICITY — POROSITY — PERMEABILITY — RE- 
SISTANCE OF SUBSTANCES — HARDNESS— CENTRIFUGAL 
FORCE— THE PRINCIPLE OF INERTIA .... I 



CHAPTER II.- EQUILIBRIUM OF BODIES. 

THE CENTRE OF GRAVITY 28 

CHAPTER III.— DENSITY, HYDROSTATICS, ETC. 

HYDROSTATICS — THE MOVEMENTS OF GASES — RESISTANCE 

OF THE AIR • 38 

CtlAPTER IV.— PRESSURE OF THE AIR. 

PRESSURE OF THE AIR — EXPERIMENTS WITH COMPRE.SSED 

AIR— ASRONAUTICS 56 

CHAPTER v.— HEAT. 

THE CONDUCTIBILITY OF METALS — DILATATION OF BODIES 

BY HEAT .... 66 



X CONTENTS. 

CHAPTER VI.— LIGHT, OPTICAL ILLUSIONS, ETC. 

PAGV 

REFRACTION— VISIONAND OPTICAL ILLUSIONS— PERSISTENCE 



OF IMPRESSIONS ON THE RETINA 



CHAPTER XI. 

MECHANICAL TOYS, ETC. . 



73' r\ 



CHAPTER VII. 

ELEpTRICITY AND MAGNETISM. . . . , , . .88 

CHAPTER VIII. 

CHEMISTRY WITHOUT A LABORATORY . „ . >q2 

CHAPTER IX.— MATHEMATICAL GAMES. 

THE DICE TRICK , .... 



104 



CHAPTER X. 

NATURAL SCIENCE IN THE COUNTRY . . , , . U3 



»I7 



HALF HOURS OF SCIENTIFIC 
AMUSEMENT. 




CHAPTER I.— PROPERTIES OF BODIES. 

strength elasticity — porositv — permeability — 

resistance of substances— hardness — centri- 
fugal force — the principle of inertiai 

Strength. 

.VERYONE who practises experimental science 
knows how useful it is to unite with his 
theories the manual dexterity which practice 
in experiments gives. Chemists and physicists, 
should in every way be stimulated to construct their own 
apparatus. In numerous cases it will be found possible 
to put together even delicate apparatus at a very small 
cost ; and these will be found quite' as useful as the most 
expensive ones. 

Is it not then even more useful to lay down the 
elements of a course of experimental physics without 
apparatus? This is just what we are about to do in 
a recreative guise. Our first experiment will be on 
falling bodies. 

THE HALFPENNY AND THE PIECE OF PAPER. 

Take a sou — a halfpenny^ — and a piece of paper cut 
into the same shape as the coin. Let these two bodies 
fall at the same moment side by side, aj shown in the 



2 I'kOrERTIES OF BODIES. 

illustration (Fig. i). You will find that the coin will 
reach the ground a long while before the disc of paper. 
But now place the piece of paper upon the upper surface 
of the halfpenny and permit thenn to fall together in a 
horizontal position, as in illustration (Fig. 2). You will 
find that the two bodies will reach the ground at the same 
time ! Why .? Because the piece of paper is protected 
Irom the action of the air by the halfpenny ! 

The weight of the bodies counts for nothing in their 
fall. It is the air only which prevents them from falling 



:■*..."; '■ 




"■- -^ 








^^^^^ 


w ,.;:; 




;■;■ E.liiul:nlll 




I'ig. I.- Fall of a Halfpenny and a Piece of Fig 
Paper cut to same Shape. 



?. — Fall of the ?ame Bodies. The Paper 
placed upon the Coin. 



with the same velocity. Under the receiver of an air- 
pump both bodies would fall with the same speed. 



T//E TWO PIECES OF PAPER. 

Take a sheet of paper, fold it in half, and cut it so 
that you obtain two pieces of exactly the same size and 
weight. Rub one into the shape of a ball, and leave the 
other in its former condition. Then let both fall together. 
The rolled-up paper will reach the ground before the 
other piece ! /.■ 



STRENGTH. 3 

TO BREAK A NUT WITH A FALLING KNIFE. 

Attach, lightly, a penknife to the upper framework of 
a wooden door by inserting its point in the wood as 
shown in the illustration (Fig.' 3) herewith. The knife 
must be suspended so that it can be detached by a blow 
of the^fist on the frame of the door. If a nut be placed 




Fig. 3.— Experiment with Falling Bodies. 

beneath, at the ej^act spot on which the handle of the 
penknife will strike the floor, the nut will be cracked 
immediately. 

"Yes; but how are we to determine the exact spot .' " 
you will say. I will tell you. , 



4 FROPERTIES OF BODIES. 

Moisten the end of the knife-handle with water in a 
glass in the manner shown in the illustration (Fig. 3). 
A drop of water will adhere to the handle and fall to the 
floor. On the spot thus indicated the nut must be placed.' 
The illustration indicates the manner in which this 
experiment should be made. On the left is seen the 
knife suspended above the nut. On the right is the glass 
by which the positions of the two bodies can be ascer-' 
tained. 

Elasticity. 

the unalterable pellet of bread. 

Knead between your fingers, a piece of the crumb of 




Fig. 4.— Pellet of Crumb of Bread modelled for the Demonstration of the Elasticity of Bodies. 



a fresh loaf in such a manner as to impart to it the spiny 
appearance of the figure in illustration (Fig. 4). Place 
this moulded pellet on a wooden table and strike the 
pellet on top with your hand. You will find that you 
caftnot alter its shape! No matter how violent your^ 
blows, the elastic material, for an instant flattened, will 
a:lways return to its formation again. 

Again, take the pellet and throw it violently on the 
ground. The shock will not permanently deform it any^ 



POROSITY. PERMEABILITY. 5 

more than your blows did, and it will resume its shape 
again, because its elasticity has preserved it from injury ! 
The experiment will hot succeed unless the bread be 
perfectly fresh. 

A band of india-rubber gives a very striking illustration 
of the elasticity of bodies. If all bodies are not elastic 
to the same extent, they are, nevertheless, all capable of 
some degree of expansion. If force be applied, they can 
be more or less extended ; they will return again, when 
released, almost to their normal shape. 

Porosity. Permeability, 

a blotting-paper filter. 

Place a piece of blotting-paper on the mouth of a 
tumbler ; pour upon it some water darkened with charcoal 
or other such' substance. The water will filter into the 
tumbler in a perfectly clear condition ; the blotting-paper 
will retain all the solid impurities of the charcoal or coal. 
This experiment -is illustrate;d in Fig. 5. 

TO PASS STEAM THROUGH CARDBOARD, 

lake two tumblers or goblets of equal capacity.; placp 
one of them on the table, and pour into it a small quantity 
of hot, almost boiling, water. Then cover the tumbler 
with a piece of cardboard, and place over the cardboard 
the other tumbler, as in the illustration (Fig. 6). Care 
must be taken that the upper glass, is perfectly clean and 
free from moisture. 

Now wait a while, and you will perceive that the steam 
from the boiling water in the lower vessel will penetrate 
the cardboard, the porosity and permeability of which will 
thus be clearly demonstrated, and the vapour will in time 
fill the upper glass. Wood, cloth, or woollen substances 



PROPERTIES OF BODIES. 



may be experimented upon in succession, and will givej 
the same result. But there are other textures which are 
impermeable, and will not permit the transmission of the 
vapour; such, for instance, as vulcanized india-rubber, 
of which waterproofs are made. 





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1 


1 1 III 
..1 1,1 , 


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<^^B> 


^ 




■'' '|''!I, 


^ 


^ 


rsic 


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^. j' 1 ' 1 ,1 1 




Fig. 5.— The Blotting-paper Filler. 



, This experiment tends to explain w^y fog is, as it is 
well said, " so penetrating." It passe? through the tissue! 
of our cloth coats and our flannels, and thus comes; 
into contact with our bodies. A waterproof will protect 
us from its action. 



resistance of substances. 'j 

Resistance of Substances. 

AT WtilCH SIDE WILL THE MATCH CATCH FIRE? 

Take four " safety " matches from a box, and insert 
two of them in the spaces which are apparent when the 




Fig. 6. — Steam passing thipugh Cardboard. 

box is partly opened ; the third match should be placed 
between the two former, when the whole will appear' as 
in the annexed figure (Fig. 7). Care must be taken that 
the third match is firmly gripped between the other two, 



PROPERTIES OF BODIES. 



which will be bent outwards, but must not be broken, 
by the contact. 

The fourth match should then be struck, and the third 
(the horizontal) match lighted by it in the cetitre. The 
question for the spectators to solve now is : — Which of 




Fig. 7- The Match Problem. 



the two supporting side matches will be fired first.? 
That on the right or that on the left >. Will it be 
that side at which we have two ends tipped with phos-'^ 
phorus, or the side at which there is only one phosphoric ' 
end .? The reply must be— At neither of them. The' 



HARDNESS. 



side matches will not ignite at all, because immediately 
the centre of the horizontal, match is burned, the two side 
matches will spring back and throw off the third match, 
which will fall to the ground and be extinguished. 



Hardness, 
to pierce a halfpenny with a needle, 

Everyone knows that if of two bodies one is harder 
than the other the former will scratch the latter. A 
piece of glass will scratch marble ; a diamond will cut 
glass. The glass is harder than the marble, the diamond 
harder than the glass. A bit of steel — a knife, for 
instance — will scratch copper. It is not impossible to 
pierce a halfpenny with a needle, because it is harder 
than the coin. 

The problem may appear impossible of solution, for if 
we endeavour to drive a needle through a halfpenny as 
we would drive a nail through a board we shall fail every 
time, because we shall break the needle; which, though 
it possesses great durability, is also very brittle. But if 
by some method we can manage to maintain the needle 
in a rigid and upright< position above the halfpenny, we 
can drive it into the coin with a hammer ! 

In order to perform this experiment successfully we 
must have a cork which is of the same height, as the 
needle, and into which the latter must be driven. Thus 
the needle is maintained in a perfectly rigid condition, 
and may be struck violently in the direction of its axis 
without being broken. 

Now place the needle (buried in the cork) above a 
halfpenny, which may rest either upon , a " bolt-washer," 
or even on a wooden table, which will not be injured 



lO 



PROPERTIES OF BODIES. 



by the experiment. Then with a somewhat heavy (lock- 
smith's) hammer strike the cork decidedly. 

If the blow be delivered straight and strong the needle 
will pass right through the halfpenny. 

The experiment can be made equally well with any 




Fig. 8.— How to pierce a Halfpenny with a Needle. 

other piece of money. We must, however, add that the 
experiment may not succeed at the first attempt ; it 
may be necessary to repeat the trial many times ; but - 
it is capable of accomplishment, and we have beside. us 
some coins which have been pierced by needles in the 
manner above described. 



Centrifugal force. 



II 



It will be a very difficult matter to withdraw the needle 
from the coin after the experiment. The adhesion is very 
great. 

Centrifugal Force., 

to keep a penny revolving in a lamp-shade. 

Grasp a lamp-shade in the right hand, as shown in 
the illustration (Fig. 9), Now, with the left hand, tw'iri 




Fig. 9. — Twirling a Penny in a Lamp-shade. 



a coin on its edge into the shade, and at the same 
I moment cause the sha!de to rotate in the right hand in 
the opposite direction. The coin will roll round without 
falling. i 

If the movement of the shade be gradually slackened, 
the coin will by degrees rotate towards the lower part of 
tlje lamp-shade ; if the speed be augmented, the coin will 



12 PROPERTIES OF BODIES. 

by degrees ascend the cone towards the upper circum- 
ference. The movement of the coin will continue just 
as long as the twirling motion of the shade is kept up. 
The money is maintained by the action of centrifugal 
force, and moves in an inclined position similar to that 
of a rider in the circus. With practice one can roll two 
pieces of money in the lamp-shade at the same time. 

The experiment we have described is very easy to 
perform ; only a slight movement of the hand is needed. 
Although some dexterity is required in launching the 
penny into the lamp-shade at first, still no particiilar skill 
on the part of the performer is required. We ourselves 
have done the trick with ease, and have taught many 
persons inexperienced in sleight of hand to perform it. 

If a lamp-shade be not available, we may use a basin, 
or pan, or a salad-bowl ; but the cardboard la np-shade 
is lightest and most handy, and should be diosen in 
preference to all other articles. A Japanese umbrella 
will also suit. 

EFFECTS OF CENTRIFUGAL FORCE. \ 

The effects of centrifugal force are manifested under a 
great variety of circumstances, and we may filequently 
observe them. | 

When a railway is run round a sharp curve, tie outer 
rail is always raised above the inner, so that tne train 
when passing round the curve may retain its position 
on the metals. f 

If you run rapidly round a small circular track you 
will find it necessary to incline your body towards the 
centre, so that your, course may thus become the more 
rapid. 

The effects of centrifugal force are otherwise frequently 
observable, as, for instance, when a carriage-wfieel is 



CENTRIFUGAL FORCE. 



13 



revolving rapidly the mud which adheres to the tire is 
flung away from the wheel by the action of centrifugal 
force. 

It is centrifugal force which sometimes causes mill- 
stones to split when revolving at a high speed. It is 
the same force which causes the tiny drops of water to 




Fig. 10. — The Cane-sling. 

fly out of the wicker basket in which -lettuce is being 
washed, dried, and shaken. 

TffE SLING. 
When one launches a stone from a sling, the stone 



14 PEOPERTIES OF BODIES. 

escapes from the circle which it has been made to describe 
as soon as one string of the sling has been let go, and 
it flies off at a tangent with the same velocity that has 
been imparted to it at the moment it was released. 



TO THROW A POTATO TO A GREAT HEIGHT. 

When the writer was a schoolboy and used to walk 
in the country, he substituted an ordinary walking-stick 
for the sling, and for the stone a potato, and in the 
following manner he succeeded in his experiment. He 
fixed a potato at the end of his cane in a firm way, and 
then, whirling the stick as he would whirl a sling, he 
suddenly stopped the motion when the end of the stick 
pointed upwards. The potato .was thus hurled to an 
immense height in the air. 



The Principle of Inertia. 

In treatises on mechanics and physics, " inertia " is 
defined as a property of matter by which bodies tend 
to preserve a condition of repose, and by which a body,' 
in motion is prevented from modifying of itself the 
movement which has been imparted to it. 

' A PIECE OF MONEY ROLLING ON AN UMBRELLA. ' 

We will first give an illustration of the feat performed 
by some jugglers — viz., the circling of a half-crown upon 
a Japanese umbrella, as shown in the engraving. The 
umbrella is turned rapidly round, and, to all appearance, 
the half-crown is running along the surface ; but it is 
really the umbrella that is moving beneath the piece of 



THE PRINCIPLE OF INERTIA. 



IS 



money. This is an example. of the principle of inertia.- 
The experiment is performed very cleverly by the 
Japanese jugglers. 

to cut A PEACH, WITH ITS STONE, RIGHT THROUGH. 

Take an almost ripe peach, of medium size, and insert 
in it a table-knife so that the blade may be in contact 
with ths edge of the stone. If the peach be too ripe 




Fig. II. — Half-crown rolling over an Umbrella. 



to remain suspended on the blade it can be fastened by 
a thread, but only on the condition that the knife-blade 
remains in contact with the edge of the stone. ^ 

The knife with the peach attached is then grasped in 
the left hand tightly and firmly, and with another table- 
knife a blow is struck by the right hand — a smart, violent 



i6 



PROPERTIES OF BODIES. 



blow — on the knife, close to the fruit. If the knife has 
been properly inserted into the fruit, so that the shock 
is transmitted in the direction of the centre of gravity of 
the peach, the stone will be cut normally to its axis, as 
well as the tissue which encloses it, and moreover in a 
very neat manner indeed. 




Fig. 12. — How to cut through a Peach. 



In performing this experiment it will be well to suspend 
the peach over a table, and to use common knives, which 
are not likely to be damaged. 

Many games based upon " inertia " are practised. One 
of therh consists in placing in the midst of a certain 



THE PRINCIPLE OF INERTIA. 1 7 

circumference a pipe, at the upper end of which some 
pieces of money are placed. The pipe, when thrown at 
with quoits or a stick, lets the coin fall to the ground 
■within the circle ; but if the pieces must be struck beyond 
the circle, it is necessary to avoid hitting the pipe. (On 
this principle the " cocoa-nut throwing " is practised at 
fairs.) 

It is by virtue of the inertia of matter that the par- 
ticles of dust are beaten out of our clothes, every particle 
being in a condition of repose. When the shock of the 
sudden stroke puts in motion the stuff in which the 
particles are resting, they remain behind, and at once 
fall down released from the clothes. 

When a piece of cord is vigorously flourished and then 
suddenly checked in the moment of its greatest impulse, 
the extreme end, which has the greatest velocity, has a 
tendency to escape from the other sections, and in its 
attempt a noise is produced. This is the cracking of the 
whip. It is on the same principle that the drops of 
water will run from the lettuce-leaves when forcibly 
shaken in a wicker basket. In this there is also an 
illustf-ation of ceritrifugal force, as already mentioned. 

Facts of this nature may be multiplied exceedingly. 
A bullet shot from a rifle will go through a pane of glass 
and leave a round hole in it ; but if the ball be thrown 
by the hand, at a much less speed, the glass will be 
shivered into fragments. 

The flexible stem of a plant may be severed by a 
switch horizontally thro-vt^n at it with great force. The 
velocity in this case is very high, and the molecules 
directly struck attain also a speed so great that they 
separate themselves from the surrounding molecules before 
they have ,had time to communicate their velocity to the 
latter. 



PROPERTIES OF BODIES. 



TO PRPJECT ONE OR 2'WO "DRAUGHTSMEN" FROM A 
HEAP OF THEM. 

This experiment is a variation of one which we hav^ 
explained in another place. It is performed by means of 
draughts or backgammon " men," but instead of a piece 
of wbod, another disc is used as a projectile. 

Build up a column of ten or twelve pieces, as in 




Fig. I3-— The Draughtsmen. 



the illustration, and with the thumb and forefinger propel 
the single disc violently against the pile, causing the disc 
to strike the column (Fig. 13). The piece thus launched 

out will strike tangentially the pile in one of two ways 

either it will hit it at the point of contact of two discs,- 
in which case two will be projected from the column- 
or it will strike a single disc, as shown in the illustration' 



THE PRINCIPLE OF INERTIA. 



ig 



in which the black piece only will be projected from the 
pile, without disturbing the stability of the other pieces. 



THE CARD AND THE COIN. 



Place on the forefinger of your left hand, held upright, 
a card ; on the card place a halfcrown or other good- 




Fig. 14.— The Card and the Coin. 



sized coin, and offer to remove the card without disturbing 
the coin. To do this you must " fillip " the card forcibly 
with the middle finger of the right hand ; the pasteboard 
will be propelled across the room, and the coin will remain 
upon the finger. In performing this trick, care must be 
taken to flip the card in a plane perfectly horizontal to 
the coin — as shown in the illustration (Fig. 14). 



io 



TROPERTIES OF BODIES. 



EXPERIMENT OF INERTrA MADE WITH DOMINOES., 

Place two dominoes upright at their highest elevation: 
with their faces towards each other, and then another. piece 
horizontally across them, forming a door. Upon this 
third — the horizontal — domino place a fourth, the black 




B'ig. I5-— Experiment of Inertia. 



surfaces bemg in contact. Finally upon this fourth 
domino set two others in the same manner as the first 
pair, face to face, then a seventh piece over all • as in 
illustration (Fig. 15). ' - 

The experiment consists in detaching rapidly the lowest 



THE PRINCIPLE OF INERTIA. 



21 



horizontal domino from the building, without disturbing 
the remainder of the erection. To do this you must place 
another domino in front of the building lengthwise 
(A-B), at such a distance that it can be conveniently 
reached by the forefinger passing beneath the first storey. 
The epd E of this domino is then sharply pulled down 




Fig. i6.— The Plate and the Coins Experiment. 

backwards, by which movement the corner D describes 
a curve in the direction of the dotted line to C. 
' If this movement be properly accomplished, the angle 
D will suddenly strike the lower horizontal domino and 
project it in the direction of the arrow F. This displace- 



2 2 PROPERTIES OF BODIES. 

ment will be followed by the instantaneous descent of 
the upper horizontal domino upon the two lower perpen- 
dicular pieces, in place of the domino removed, and the 
structure will remain otherwise undisturbed. 



THE PLATE AND THE PILE OF COPPERS. 

Put a dozen coins in a plate and propose to deposit 
them at one movement in the same order upon the table. 
People who have never tried this experiment will essay it 
in vain. To accomplish it you must raise the plate about 
a foot above the table, suddenly depress it, as shown in 
the illustration, and draw it towards you. The coins, 
not finding any support, will fall to the table in the same 
position as they left the plate. 

It is by no means an easy task to let the pile of 
money fall as here described without separating them. 
With practice and skill you will surely accomplish the 
task, in performing which it is best to let the coins fall 
or slide off the plate upon a cloth, which i^ more elastic 
than a bare table. The cloth will lessen the shock of 
propulsion. 

THE MONEY ON THE ELBOW. 

This is another experiment which the writer has fre- 
quently performed. It is managed by holding the arm 
back upwards, the elbow being almost flat and the hand 
open, palm upwards, as in the illustration . (Fig. 17), On 
the arm, close to the joint, place the coin or coins. 
Perhaps one at first will be sufficient, in case of failure 
and possible loss. If the hand be suddenly brought down 
with a circular sweep, the pile of money— or the single 
coin — will be left for an instant in space, and be at once 
clasped in the palm coming down upon it. 



THE PRINCIPLE OF INERTIA. 



23 



It will be found easy and possible to catch a pile of a 
dozen pence or halfcrowns in this way, after a little pre- 
liminary practice, without letting one coin escape. 

Care must nevertheless be taken that no breakable 
articles are in front of you when you are practising this 



m 











\^\ 




Fig. 17. — Catching the Pile of Money. 



experiment, for, if you do not succeed in catching the 
coins, they will be struck by the hand with very con- 
siderable force, and may do damage to the surroundings ; 
they also may roll out of sight ! 



24 



PROPERTIES OF BODIES. 



TO CUT AN APPLE IN A HANDKERCHIEF WITHOUT 
INJURING THE LATTER. 

In this instance the apple is wrapped up in the hand- 
kerchief and suspended by a cord, as indicated in the 




Fig. i8.— The Apple in the Handkerchief. 



illustration (Fig. i8). Take a sabre or a strong knife 
the plan of which is indicated in the right-hand upper 
corner. The edge of the blade should be very sharp, 
the more polished and the sharper the blade the more 



THE PRINCl'PLE OF INERTIA. 2 5 

likely is the experiment to succeed. The cut must be 
given without sawing, and perpendicularly to the point 
of suspension. If the blade be rather thick, the apple 
will jump up slightly and then the handkerchief will enter 
with the blade and be uncut. 

In 1887 there were some clowns at the circus in Paris 
who used to perform this trick very neatly indeed, and 
with great dexterity. 



THE ST0NE'BBE4ICEIi. 

By great acquired force, or inertia in repose, one is 
enabled to break stones with the fist: This feat is 
performed by men at fairs in the manner following : — 

The right hand is carefully wrapped in a bandage, and 
in the left is held a piece of flint of rounded form, which 
the operator places upon a larger stone or upon an 
anvil ; then with the right hand he strikes the flint some 
very powerful blows, always taking care to raise it a little 
from the anvil when he is about to strike. Thus the 
object struck acquires the force of the fist that has 
struck it, and, as it comes , in violent contact with the 
anvil it is quickly broken. Simple as the feat is it 
never fails to evoke great astonishment from the spec- 
tators (Fig. 19). 



II© UNCORK A BOTTLE WITHOUT A CORKSCREW. 

Take a bottle of wine or beer, or any other liquid, and 
having folded a dinner napkin into a pad, strike the 
bottom of the bottle violently against it,, as in the illus- 




Fig. 19. — Experiment of Acquired Force. 



THE PRINCIPLE OF INERTIA. 27 

tration (Fig, 20), on the wall. By virtue of the principle 
of inertia the liquid in the bottle will force out the cork. 
If the contents be beer or gaseous water, it will come out 
with considerable force, and carry some of the liquid 




_ ncorking a Bottle. 



with it over the spectators. This fact will enchance the 
success of the experiment, with which we will end our 
chapter on the inertia of matter. 




CHAPTER 11.— EQUILIBRIUM OF BODIES. 

THE CENTRE OF GRAVITY. 

5dEAS relative to the centre of gravity and to 
the equilibrium of bodies can be demonstrated 
by means of a number of every-day objects. 
When we find a box of soldiers in w^hich each 
warrior is gifted with a small piece of lead at his feet, 
we have an illustration of the centre of gravity. We 
know that the cylinders, roughly representing soldiers, will 
always resume their .upright position when one endeavours 
to overturn them. 

It has been stated that it is possible, with patience and 
lightness of hand, to make an egg stand on one end. To 
accomplish this the egg must be placed upon a perfectly 
plane surface — a marble chimney-piece, for instance. The 
egg must be shaken to mingle the yolk with the white, 
and then if one succeed in making the egg stand upright, 
one of the most elementary principles, of physjics is illus- 
trated thereby ; for the centre of gravity is at the point 
of contact at the end of the egg, and the plane surface on 
which it rests. We will give some illustrations of this. 



TO BALANCE A PENCIL ON ITS POINT. 

The arrangement of the pencil and the knife, the blade 
of which is buried in the wood, is held in equilibrium at 
the point of the finger, becai*se the centre of gravity of 



THE CENTRE OF GRAVJTY. 



29 



the. arrangement is situated in the vertical, beneath the 
point of contact (Fig. 21). 



THE MATCH PUZZLE. 
Slit a match at one end, and insert into the groove 



''/'', 



"/""'t'J't 







Fig. 21. —A Pencil balanced on its Point 



another, so that the pair shall form a certain angle. Place 
them on a table, angle upwards, tent fashion ; and let a 
third match rest against them as in Fig. 22. Now all is 
ready for the experiment, Take a fourth match, and 



30 



EQUILIBRIUM OF BODIES. 



handing It to one of )-our audience, request him to lift the 
three others with it. 

If the Seeker, the interesting paper from which we 
borrow this pleasing problem, be correct, the solution of 
the puzzle will test the patience of many an architect or 



jrr, .-^-M.,^..- . .TTT — -■■,■:.- 








. 


r 


^ 




^1 


/ 


Iv:. 


^^ 


^ ■ 


\ 


* 


i 


1^ 


i 


' 




^ 


^ :■ 


j 


\ 


k 














i 




1 


i 


k ^^^ 


S 


r 


1 


^rjr'i- 




^ 


1 


'J&A 


$ 


w 



Fig. 22. — Problem of the Four TVfatclies. 



builder who is not previously acquainted with the experi- 
ment. 

The upper diagram in the illustration explains the 
mode of proceeding. The way the trick is performed 
is to allow the third match to fall lightly against the 
match you hold, and then lower the hand until this third 



THE CENTRE OF GRAVITY. 



31 



match enters within the angle formed by the first pair ; 
then lift your fourth match and you wpl find that the 
other matches will rest crosswise on your match, No. i 
and 2 on one side, and No. 3 on the other. 




Fig, 23.— The Tumbler and the Sticks. 

TO POISE A TUMBLER UPON THREE STICKS, EACH 
ONE OF WHICH HAS ONE END IN THE AIR. 

Ozanam, in his "Mathematical and Physical Recrea- 
tions in the 1 6th Century," laid down the following 
problem : " Place three sticks on a horizontal plane, so 
that each one shall have one end resting on the plane 
and the other end ^unsupported." 



32 EQUILIBRIUM OF BODIES. 

To perform this experiment, and even to place a 
weight on the sticks thus poised, you must carefully 
proceed as follows : — Place in a sloping position one 
stick with one end resting on the table and the other 
elevated. Put another in a similar fashion above, and 
resting on the first. Then form a triangle by means of 
the third stick poised in the same way but passing under 
one and above the other of the two sticks already laid 
down. The three sticks will in this manner prove o\ 
mutual support to each other, and will not .give way 
even if a tumbler or other weight be placed upon them 
over the points of contact, as in Fig. 2 3. 



THE WATER-BOTTLE AND THE THREE KNIVES. 

In almost the same manner as above illustrated, we can 
place three Itnives upon three wine-glasses as represented 
in Fig. 24. The knives not only support each other 
blade to blade, but they will sustain as heavy an object 
as a filled water,-carafe upon the triangle at their inter- 
sections. 



TO SUSPEND A BUCKET OF WATER FROM A STICK 
RESTING ON A TABLE. 

Here is another very old-fashioned experiment oh the 
" centre of gravity," which consists in suspending by the 
handle a bucket filled with water passed over the stick 
A B, which is laid on the table. To succeed in this 
experiment, which appears almost impossible \o perform. 



THE CENTRE OF GRAVITY. 



33 



we must fix a switch C D oi convenient length between 
the point B of suspension and the bottom of the pail. 
The arrangement thus consolidated forms, virtually, one 
object — a whole, and the pail or bucket is easily main- 




^. 



»•., 







Fig. 24.— The Glasses and the Knives Trick. 



tained in the position shown in the illustration, because 
the centre of gravity of the whole mass is beneath the 
point of suspension situated almost at the centre of the 
stick A B (Fig. 25). f , 



34 



EQUILIBRIUM OF BODIES. 



THE FORKS AND THE COIN. 



Place two forks with their prongs one set over the 
other, and slip a coin — a five-franc piece or a halfcrown" 
— between the middle prongs of the forks. Then place 
the coin flat on the rim of a wineglass or tumbler, 




25— Pail of Water suspended from a Stick. 



pushing it outwards until the two circumferences shall 
be touching externally. In this position, as shown in 
the accompanying engraving, the forks will remain in 
eqiiilibKio,' and the water may be poured steadily from 



THE CENTRE OF GRAVITY. 



35 



the glass into another without disturbing the coin or the 
two forks. (See Fig. 26.) 

We have now indicated almost all the recreative experi- 
ments connected with the centre of gravity and the laws 
of equilibrium. We will, however, explain another problem 
requiring skill, which can be worked out with a box of 
dominoes. 




Fig. 26. — Experiment of Equilibrium on the Centre of Gravity, 



EXPERIMENT WITH DOMINOES. 

The illustration shows how the contents of a box of 
dominoes can be supported upon one of their number. 
We must begin by placing three of the pieces on the 
table so as to form a solid base,; the first domino being 
laid upon three supports. When the edifice is finikhed, 



36 EQUILIBRIUM OF BODIES. 

as in the illustration, the two outside dominoes must' be 
withdrawn and very gently placed upon the top of the 
construction. The" erection will remain in equilibrio 
provided that the perpendicular drawn from the centre 
of gravity of the system passes through the base of 




Experiment of the Centre of Gravity witli Dominoes. ^ 



sustentation of the lowest domino (Fig. 27). 

This experiment should only be attempted upon a 
perfectly firm and level table. 

In our next section we shall deal with Density and the 
Movements of Gases. 



THE CENTRE OF GRAVITY. 



37 



ffOl'F TO SIT WITHOUT CHAIRS. 

I 

This amusing feat can be perforqied by a number of 
persons arranging themselves as ybu see them in the 
illustration, the last in the ring sitting on the knees of 
the first. While the circle is being formed it would be 
advisable for the first to be seated on a chair, which can 



*-."•->•» ^jLi 










ft- 




Hs- J-^' '*'*' 



- / 



I'lg. 28.— S.ttlng withoi t Clla rs 



be slipped away when the ring is completed. This plan^ 
was adopted by French soldiers in Algeria, when they 
found themselves in any place where the soil was marshy, 
and where it would have been unwise for them to sit 
down on the ground. 




CHAPTER III.-^DENSITY, HYDRO- 
STATICS, ETC. 

hydrostatics — the movements of gases — re- 
sistance of the air. 

Hydrostatics. 

HERE is no necessity to dwell upon the density 
of bodies here : it is well known that, con- 
sidered as possessing the same volume, bodies 
have different weights. We shall consider 
this subject at greater length in the subsequent part 
of the work, when dealing with the prope;rties of 
metals. 

The principles of hydrostatics, which we intend to 
consider now, can be easily explained. It is very easy to 
understand the principle of Archimedes^ Take any body 
of irregular form, — a. stone will do, — and having attached 
to it a thread, let it dip into a vessel filled to the brim 
with water. The water will overflow in volume equivalent 
to the bulk of the stone ; as can readily be proved by 
weighing the glass partly emptied of water and the stone 
against another similar glass full of water. 



ASCENT OF WINE IN AN INVERTED GLASS OF 
WATER. 

Dip two wineglasses into a basin of water, and before 
taking them out, place the brims together, so that they 
may remain full, but one over the other. Then move 



ilVUKUbTAllCb. 



39 



them slightly, so that a very small space may intervene 
between the rims. Take a third glass and drip from it 
some wine in such a manner as it may spread slowly 
over the surface of the inverted glass, as shown in the 







Fig. 29. — Experiment on the Density of Liquids. 



illustration (Fig, 29). When the wine has trickled down 
to the line of separation, you will perceive the ruddy 
dfops filtering into the glasses and ascending into the 
upper one, in consequence of the difference in the densities 
of wine and water., 



40 



DENSITY, HYDROSTATICS, ETC. 



THE GRAPE-SEED IN THE CLASS OF CHAMPAGNE. 

If we place a grape-seed, quite dry, at the bottom of a 
glass, and fill it with champagne, we shall see the bubbles 
attaching themselves to the seed, and it will rise to the 







Fig. 30.^The Grape-seed in the Glass of Champagne. ^ 

surface of the wine, where the bubbles burst/and disappear. 
Then the seed will fall to the bottom of the glass again. 
The seed in this instance has been raised to' the surface 
by the aid of the air-bubbles, which play the part 'of little 
balloons in bringing it to the top of the liquid (Fig. 30). 

HOW TO MAKE A SYPHON WITH A COMMON BOILED 
LOBSTER. 

Take a glass filled with water, and attach a lobster to 
it, plunge the tail as far as possible into the liquid, letting 



HYDROSTATICS. 



41 



the body and head hang over the side of the glass ; it is 
necessary also to cut the antennae, so that they shall not 
touch the vessel on which the glass of water stands. The 
moment that the lobster is hooked on to the edge of the 
glass, small globules of water will be seen to form at the 




Fig.' 31. — The Ldbster Syphon. 

end of the antennae, which eventually form themselves into 
a trickling stream, which lasts as long as the tail of the 
lobster remains immersed in the water. 

TO MAKE A NEEDLE FLOAT. 
Take an ordinary needle and put it upon a fork, and 



42 DENSITY, HYDROSTATICS, ETC. 

slowly lower the fork into a tumbler of water ; the needle 
will then float just like a piece of straw. The reason of 
this is that a meniscus, or bed, convex on one side, and 
concave on the other, is formed upon the surface of the 
water ; and the surface of this meniscus being large in 




Fig. 32.— The Floa.ing Needle. 

comparison with that of the needle, the latter is supported 
by it, so that scarcely any part of the needle is touching 
the water ; of course, if the water penetrated the needle's 
eye, the weight of the fluid would cause the thing to sink 
immediately. Another method is to put a leaf of cigarette 
or tissue paper on the surface of a tumbler of water, lay 



THE MOVEMENTS OF GASES. 



43 



a needle very gently upon the paper, which will soon 
become soaked and sink to the bottom of the glass 
leaving the needle floating on the top of the water. 




Fig- 33'— Direction of Candle-flames under the influence of Air-( 



The MOVEMENTS of Gases. 

AERIAL CURRENTS. 

Hot air is much lighter than cold air, and the differ- 
ences in density of the air-strata play a very important 
part in the movements of the atmosphere. Air is warmed 
in the Equatorial, and cooled in the Polar, Regions. 

It is easy to understand the differences in density of 



44 



DENSITY, HYDROSTATICS, ETC. 



the aerial currents if we open the door of a ^ warm room 
which is entered from a cold hall. 

A candle held to the upper part of the open door 
will show the direction of the warm current, while the 
course of the cold air will be demonstrated by the flaring 
flame of a candle placed on the floor. The currents 
pass in opposite directions, out and in (Fig. 33). 




M^^^^ 



Fig. 34. — Extinguisbing a Candle placed behind a Bottle, 

, BLOWING OUT A CANDLE BEHIND A BOTTLE. 

Put a lighted candle on the table, and in front of it, 
about 10 inches removed, a bottle like the one in the 
engraving (Fig. 34). Then blow on the bottle at a 



THE MOX'KMENTS OF GASES. 



45 



distance of 8 or 9 inches, and the light will be extinguished 
just as though there was nothing between it and your 
breath. The breath divides into two currents on the 
smooth surface of the bottle, one going right, the other 
left, 'which join each other just at the flame of the candle. 




Fig. 35* — Rotation of Coin between Two Pins., 

TO REVOLVE A COIN BETWEEN TWO PINS.^ 

It is not necessary to have recourse to the action of 
warm air to produce aerial motion. We have in our- 
selves an apparatus which is capable of producing ■ 
gaseous currents, and which will assist us in Our Scientific 
Amusements — viz., our ittouths ! Place a halfcrown flat 
on the table, then, seize it between two pins held at the 
extremities of the same diameter. You may raise it thus 
with,out any trouble. Blow against the upper surface, 
and you will see the- coin revolving with considerable 
speeid between the pins. The illustration (Fig. 3 5) shows the 



46 



DENSITY, HYDROSTATICS, ETC. 



manner in which this feat can be accomplished. The coin 
can be made to revolve (by blowing on its upper surface) 
with such rapidity as to make it appear a metallic sphere. 
In this we have an illustration of the persistence of impres- 
sions on the retina, of which we shall speak hereafter. ; 

TO KEEP A PEA IN EQUILIBRIUM BY MEANS OF A 
CURRENT OF AIR. 

Choose as rounded a pea as you can find, . and soften 
it, if dry, in water. Then skilfully impale it on a pin, 
so as not to damage its exterior surface and shape. 
Then get a pipe, of very small bore, and place the pea 




Fig. 36.— Pea sustained in the Air by blowing through a Tube. 



on one of its extremities, where it is maintained by the 
pin which has been inserted in the tube. Throw your 
head back until the pipe is in a vertical position, and 
then blow gradually and slowly through it. The pea 
will rise up ; then blow more forcibly, and it will be, 
sustained by the current of air turning on itself when the 
breath strikes the pin (Fig. 36). 



THE MOVEMENTS OF GASES. 



47 



Here is another experiment of the same kind : — 
Take a metallic penholder which is closed at one of 
its ends. At a little distance from the closed extremity 
drill a tiny hole. Then blow up through the aperture, 
thus formed, regularly and steadily. A small bread pellet, 
perfectly round, can then be kept up, as shown in the 
illustration (Fig. 37). 

The pellet should be as spherical as possible, its size 
varying with the density of the material of which it is 




Fig.'37. — Bread Pellet sustained by a Current qf Air. 



composed and the size of the aperture in the tube. 
Many other experiments can be maae by any means 
which will ensure a constant, even, supply of air, or gas, 
or steam from the extremity of a pipe. 

By analogous means an egg-shell can be maintained 
at the upper extremity of a jet of water, on which it will 
revolve without falling off. [A wooden ball can also 
be kept up in revolution in the same manner.] 



48 



DENSITY, HYDROSTATICS, ETC. 



rb MA/CE A PLANK ADHERE TO A TABLE BY MEANS OF 
A NEWSPAPER. 

Take a thin plank; about a quarter of an inch thick, 
and eight inches wide, and twenty-eight in length. Place 
this plank on a table slightly out of the horizontal, and it 




Fig. 38, — Kxperiment in Equilibrium. 

will be evident that the least touch will bring it to the 
ground. On the plank thus balanced place a newspaper 
sheet ; and then if you strike the portion of the plank 
which extends beyond the table you will be surprised to 
find that the plank will resist the blow absolutely, as if it 
had been nailed to the table. If you strike hard you 
will perhaps hurt your hand or break the plank, but you 
will not raise the sheet of newspaper which holds it. 
The quick compression of the air which is exercised on 
a considerable surface is" sufficient to explain this 
phenomenon (Fig. 38),: 



resistance of the air. 49 

Resistance of the Air. 
the australian boomerang. 

Everyone has heard of the Australian boomerang. It 
is a weapon formed in the shape of an arc of hard wood, 
which^ the Aborigines and , inhabitants of Australia throw 
with unerring skill at some object — an enemy or quarry. 
When the boomerang strikes the object aimed at, it 







■'■ ~.\ 



V ^ \ 






Fig. 39. — The Boonieraii'j. 

\ 

returns to the hand which launched it. One may quickly 
learn to throw_this weiapon after a few trials. 

Fifteen years ago M. Marcy, of the Paris Institute, 
published an interesting paper on this subject in the 
A'e'ronaut, in which journal were discussed questions relative 
to the resistance of the air. The learned professor then 
prepared^uncpnsciously— -a little chapter for Scientific 



50 DENSITY, HYDROSTATICS, ETC. 

Amusements, and we will reproduce the gist of his 
remarks. 

A piece of cardboard shaped into a crescent, the corners 
of which are rounded off, should be placed on the, tip of 
the finger, or, still better, supported between the nail and 
the finger tip, so that the cardboard be inclined at an 
angle of 43°, or so. Then, with a vigorous flip of the 
finger of the right hand at the extremity of the toy, it 
is impelled into the air with a rotatory motion. The 
cardboard crescent then appears as a wheel, and moves 
in an oblique ascending direction, stops, and without^ 
turning a somersault, returns in the same trajectory, if 
the experiment be successful, but more frequently it, will 
come back in front or beside the point of departure, and 
always retrograding. The illustration (Fig. 39) will ex- 
plain the method of procedure. We may add that it is 
preferable to place the crescent with its horns tozvards the 
experimentalist, not as in the illustration. 

Now why does the boomerang return thus in the same 
direction with reference to the plane of the horizon .' 
Here come in the notions which Foucault has alreaxily 
given us respecting the preservation of the plane of 
oscillation by the pendulum, and by the plane of gyration 
of the gyroscope. 

"The boomerang receives from the thrower a double 
movement — viz., rapid rotation and a general impulse. 
The rotation given to the implement obliges it to retain 
its plane : it whirls obliquely in the air until its impulse 
is exhausted. At a given moment the weapon turns 
without advancing in space, and then its weight causes it 
to fall. But as the projectile continues to turn, still 
maintaining its inclined plane, the resista,nce of the air 
causes it to fall back in a direction parallel to this plane 
— that is to say, towards its point of departure." 



RESISTANCE OF THE AIR. 



SI 



WHIRLING RINGS. 



If you bore a hole in a box made of playing cards, 
and fill this box from your mouth with tobacco smoke, 
and then tap at the bottom of the box you will cause 
the smoke to -rise in rings from the orifice with remarkable 
regularity (Fig. 40). 




Fig. 40. — Mode of making Smoke-rings. 



Every one has seen smokers making pretty white 
diadems which they watch turning in the air with great 
satisfaction. It is a matter of daily observation that a 
drop of soapy water escaped from the tip of the finger 
enlarges itself in the basin in the form of a perfect ring, 
which slowly grows larger as it reaches the bottom. 



5 2 DENSITY, I-IYDROSTATICS, ETC. 

These observations are applicable to the phenomena of 
whirling rings ; they are not futile, and can be made 
interesting. There is nothing corhmonplace for him who 
can use his eyes,, nothing different to him who is able to 
observe. 

We can also project the rings or diadems of smoke by 




Fig. 41. — Crowns of Tobacco Smoke (after picture by Branwer in the LouVre). 

projecting puffs from a cigarette through a tube. But 
some precautions are necessary to assure the success of 
the experiment. Any draught must be avoided, and to 
prevent the action even of the air currents, which ascend 
in the proximity of the body, we should operate at a 
table as shown in Fig. 44. The rings which float beyond 



RESISTANCE OF THE AIR. 53 

the table will not be sensibly influenced by the warm 




'^'S; 42. Fig. 43. 

Aspects of Smoke-rings (42, genlly emitted ; 43, tmitted with some force). 




Fig. 44. — With a little Smoke some Distance from the Tube. 

air-currents. A tube formed from a sheet of ordinary 

S 



54 



DENSITY, HYDROSTATICS, ETC, 



note-paper will suffice to produce some elegant rings 
(Fig. 44). 




Fig. 45 Dissipation of SmoKe-rings (genera! aspect). 

The better to watch these rings they should be 




Fig. 46.— Dissipation of Smoke-rings (magnified ring). 

propelled to the darker side of the room, towards a dark 



RESISTANCE OF THE AIR. 55 

picture, for instance. The first puffs will not produce a 
ring if the tube has not been previously filled with smoke. 
The rotatory movement will be plainly visible at the end 
of the tube, and even beyond it. The next illustration 
(Fig. 45) gives a clear idea of the more or less rapid 
movements of the smoke-rings. The last illustration of 
all (Fig. 46) shows the way in which th6 rings are dissi- 
pated in a calm atmosphere. The filaments of smoke 
fall, preceded by a kind of skull-cap. These capricious 
forms of smoke in a calm atmosphere are always more 
readily observed when the sun is shining into the'room. 




CHAPTER IV.— PRESSURE OF THE AH^. 



pressure of the air — experiments with com- 
pressed air — aeronautics. 

Pressure of the Air. 
the magdeburg hemispheres. 

Jake two tumblers of the same size. Be 
careful that they fit closely when one is placed 
on top of the other. Light a piece of wax 
candle, and place it within the tumbler on the 





I''ic, 47. — The Adhesive Tumblers. 

table. Place on top of it a piece of rather thick paper ^ 



PRESSURE OF THE ATR. 



5 7 



saturated with water. Then place upon it the other 
tumbler, as in the illustration (Fig. 47). The tumblers 
will then be found to adhere closely. The candle will be 
extinguished ; but while burning it has dilated the air 
contained in the lower tumbler, and this air has, therefore, 




^^ Fig. 48, — The " Sucker.'" 

become rarefied. The exterior pressure of the atmosphere 
will fix the tumblers as closely together as the classical 
Magdeburg hemispheres are united. It is possible to" 
raise the undermost tumbler by holding up the upper one. 
The paper may be scorched on the under side, but the 
success of the experiment is not thereby imperilled. 



58 



!=RESSURE OF THE AIR 



THE •■' sucker:' 



This is a plaything familiai: to all schoolboys, and has, 
no doubt, served as the text for many a dissertation on 
the pressure of the air. Readers are aware that the 
" sucker " is formed of a piece of leather, in the centre 




jH)^ 



Fig. 49. — The Schoolboy Inventor of the Air-pump. 

\ 

of which a cord is fixed. This piece of leather pressed 
upon the pavement forms a kind of " cupping-glass '' 
arrangement, and considerable force must be exercised 
to draw it away from the pavement. Large stones may 
be lifted by these means. The piece of leather should 



EXPERIMENTS WITH COMPRESSED AIR. $g 

be first wetted, and the cord attached to it, so that no 
air may penetrate through the aperture in which the 
string is inserted. A circular piece of leather seems to 
act best. 



Tff£ PENHOLDER AND A VACUUM. 

The schoolboy who first exhausted the air from a 
tube penholder and made it cling to his lip, by reason 
of the exterior pressure of the air, was perhaps the first 
to discover the air-pump. Tq perform this little experi- 
ment, you must have a penholdei" with one closed end. 
Put the open end in the mouth, exhaust the air by aspiring 
it, and then permit the end in the mouth to slide on to 
the lip, which seals it hermetically. 



Experiments with Compressed Air. 

to extinguish a gamble by means of a bottle. 

Take an ordinary bottle, the neck of whicl^ is about 
three-quarters of an inch wide. Hold the bottle in the 
right hand, and cover the neck with the ball of the thumb 
of the left hand, leaving only a small aperture (see A, 
FiS- So)- Care must be taken to leave only a small 
aperture. Then applj' your mouth to the opening, so 
as to cover it completely, and breathe into the bottle 
gradually but forcibly, so as to compress the air in 
it. Under these circumstances it is evident that, in con- 
sequence of the communication which exists between the 
interior of the bottle and the lungs, an equilibrium of 



6o 



Plif.SSURE OF THE AIR. 



pressure will be established. Three or four seconds will 
suffice for the action. At that moment, by a rapid 
movement, close the bottle completely, by applying the 
ball of the thumb to the orifice, displacing, the lips. 

Then place the bottle in an inclined position, as in 




Fig. 50.- -Posilion of the Hartd', before the Compression of the Air by the ^foiith. 



Fig. 5 I , mouth downwards, and bring it within about an 
inch and a half of a lighted candle. Loose the thu'mb, 
and permit the compressed air to escape from the bottle 
through an aperture as nearly the same size as possible 
to the opening through which the bottle was filled. The 



EXrERlMENTS- WITH COMPRESSED AIR. 



6l 



flame of the candle will be blown aside and perhaps 
extinguished. 



THE PAPER BAG FILLED WITH AIR. 
After the experiments with a vacuum, we may next 




Fi^ 5t.--MocIe of holdin^; the Bottle in order to extinguish, or hlow aside, the Flame. 

speak of those which refer to the compression of gases. 
Let us recall the experiment of the bag, full of air, which 
is broken by a blow of the hand. 

The com.pressed air bursts the bag, and produces an 
explosion. 



62 



PRESSURE OF THE AIR 



Aeronautics. 
a montgolfier balloon. 



Make a hollow cylinder, about the size of an ordinary 
cork, with a sheet of silver-paper or cigarette-paper. The 
edges of the cylinder must be somewhat bent over, so as 
to make it retain its form. With a lighted match set f re 




'ig. 52.— Cuniprts.sed A 



to the cylinder at its upper part. The paper will burn, 
and be converted into a thin layer of ashes. This residue 
enclosing rarefied air suddenly rises, and mounts rapidly 
for several feet like a Montgolfier balloon (Fig. 1:3). 



AERONAUTICS. 



63 



AIR AND GAS BALLOONS. 

Take a glass tube, about three-quarters of an inch in 
diameter, and about eight inches long, or, in default of it, 
a roll of ordinary notepaper, which will enable you to 



.^^* 



\ J 






' -ft i 








Fig.'53.— Demonstration of the Principle of the Ascent of Bfilloons by means of 
Heated Air. 



blow bubbles as big as a man's head'. Dip the end 
of the tube in a solution of soap, and blow rapidly and 
strongly through the tube. The bubble, filled with the 
warm air from your lungs, will soon ascend. Without 



64 PRESSURE OF THE AIR. 

letting it go, follow it in its ascending movement, turning 
the end of the tube gradually upwards until you can 
touch off the drop suspended at the bottom of the bubble. 
Your balloon, fully inflated, will only want to be released, 
if it has not already freed itself. If the temperature is 
low, the bubble will break against the ceiling ; in the 
contrary case, it will descend slowly, as soon as it becomes 
somewhat chilled. 




l'''S- 54-— Soap-bubble lifting a Paper Aeronaut. 

Let a small, thin paper-figure be cut out, and fastened 
by a thread to a disc of paper ; it can be made to adhere- 
to the bubble, as shown in Fig. 54. If the bubble then 
be released, it will carry the figure up with it (Fig. 55). 
If smaller tubes be used, bubbles of smaller size will be 
produced. The paper tubes must be replaced by others 
when wet and soddened, but glass tubes are preferable. 



AERONAUTICS. 65 

By inflating soap-bubbles with hydrogen gas we can 




^"io- 55-— Soap-bubble iuJiated with warm Air. Mode of fixing an Aeronaut. 



represent the ascents of gas balloons, which differ from 
warm air balloons. 





CHAPTER v.— HEAT. 

THE CONDUCTIBILITY OF METALS DILATATION OF' 

BODIES BY HEAT. 

>HE art of producing fire or of procuring heat 
artificially is one of the most profitable of 
human industries, since it has given us the 
means of moving machinery in manufactures;, 
locomotives, and steamboats. The impression which 
produces the sensation of heat in our organism is a 
subjective phenomenon, and the impression which we 
convey when we say that a body is hot or cold is 
relative. ,When we enter a cellar in the summer when, 
the exterior air is warm, we find the cellar cold ; if we 
enter during the wintry weather, we find the temperature 
rather warm. Nevertheless it remains about the same 
heat all the while. 

Suppose that we hold the right hand in a vessel con- 
taining hot water, and the left hand in a vessel containing 
cold water ; if we then withdraw our hands at the same 
moment and plunge them together into a third vessel full 
of tepid water, we shall then experience two different 
sensations, heat and cold, proceeding from water of a 
certain temperature. 

The study of heat and caloric can be immediately 
undertaken without any apparatus, as we have seen when 
dealing with other branches of physics. 



THE CONDUCtlBILlTY OF METALS. 



67 



The Conductibility of Metals. 

a burning coal on a muslin hand kerchief. 

Take a globe of copper, about as large as the globular 
ornaments which one sees at the bottom of a staircase, 
and wrap it in muslin or, in a cambric handkerchief. 




Fig. 56. — A Burning Coal placed on a Handkerchief wrapped round a Copper Globe. 
Tne Handkerchief is not scorched. 

Place on this metallic bowl, thus enveloped, a red'hot 
coal, and it will continue to glqw, without in any way 
damaging the muslin wrapper. The reason is this : the 
metal being an excellent conductor absorbs all the heat 



68 



HEAT. 



developed by the combustion of the coal, and as the 
handkerchief has not absorbed any of the heat, it remains 
at a, lower temperatmre to that at which it would be 
injured (Fig. 56). ^ 




f'"'o- 57.— Gas Jet (Metal) wrapped in a Cambric Handkerchief, tightly stretcheijl. The Flame 
will burn above the Handkerchief without injuring it. 



TO MAKE GAS BURN UNDER A HANDKERCHIEF. 

Take a batiste handkerchief, and wrap it round a 
copper gas jet. The jet must be of metal. This is in- 
dispensable. Turn on and light the gas, which will burn 
above the handkerchief without injuring it (Fig. 57). To^ 



THE CONDUCTIBILITY OF METALS. 



69 



succeed in this experiment it is necessary that the hand- 
kerchief should fit I quite closely to the metal without 
any crease whatever. It will be found advantageous to 
tie the batiste with a thin copper wire. 



There 



THE METAL IN THE PENHOLDER. 
„ „.,„fi,=, ,,=.-,, easy way of evidencing the 




F.g. 58. —Carbonization of Paper on llie WooJen Portion of a Penholder, 

conductibility of metals for heat. Take a wooden pen- 
holder with a metallic end, and fix a piece of paper 
partly on the wood and partly on the metal. Heat the 
paper above the flame of a lamp. The paper will 
carbonize at the side on which it adheres to. the wood 
- — a bad conductor of heat — but it will remain un- 
changed, and preserve its whiteness on the side which 
is in contact with the metal. g 



70 



HEAT. 



Metals strike cold when wc place them in our palms ; 
by their conductibility they draw the heat from our hands. 
We do not- experience the same effect when we touch 
wood or cloth. 

A silver spoon will be burning hot after being dipped 
in a cup of boiling coffee, but an ivory or wooden spoon 
will not be so heated. 




tig. 59.— 'ihe CapLivti Imp, 



Dilatation of Bodies by Heat. 
tbe captive imp. 

This consists of a tube of thin glass, like a shade, as 
in illustration, the lower extremity being rendered opaque 
by a coat of black varnish. The iQwer portion being held 
in the hand, the liquid with which the receptacle is filled 



DILATATION OF BODIES BY ^EAT. 



71 



will immediately tise and sustain the small image of blown 
glass which is contained in the tube. 

AH gases expand under the' influence of heat. No>v 
» e perceive in the section of the apparatus (Fig. 59) that 
the upper tube terminates in a caplillary tube which is 




ii ig. 00. — K-xpcrim jnt in Linear Dilatation. 



immersedln the bulb underneath. A certain quantity of 
air is enclosed in the portion A A in the bulb. If this 
supply of air be warmed by the hand it expands, presses 
upon the water in the tube, and it rises with the floating 
imp. 



73 HEAT. 

LINEAR DILATATION. 

Cut a cork in the manner shown in the illustration 
(Fig. 60), so as to form a plane surface, and " scolloped " 
out in a semi-cylindrical form. In one of these hollowed 
spaces at A place a needle A B, the head of which is 
supported at B, and at a slightly less elevation at that 
end. Through the eye of this needle pass another, and 
insert its point lightly in the cork. Parallel to it, and 
behind it, place another needle of the same length. If we 
hold a lighted candle beneath the horizontal needle, we 
shall see the needle B C incline sideways, as in the 
illustration. 





CHAPTER VI.— LIGHT, OPTICAL ILLUSIONS, 

ETC. 

refraction — vision and optical illusions — 
persistence of impressions on the retina. 

Refraction. 

'O illustrate refraction we have only to plunge 
a stick into water and it will appear broken. 
We can also place a piece of money at the 
, bottom of a basin and stoop until the coin is 
no longer visible. If then some one pours water into the 
basin the coin will appear, as if the bottom of the, basin 
had been raised. 

THE MIRAGE. 

Amongst the optical experiments easy to make we 
may instance those relating to the curious phenomenon 
of the mirage. If we warm an iron plate, and look 
beyond the column of heated air which arises from the 
plate, we shall see the object we are gazing at deformed, 
or its image will appear in a different place from the true 
object. These effects are due to the difference in the 
density of the air-strata through which the visual rays 
pass. This is the effect whereby the traveller in the desert 
is deceived when the sun is very hot. 

HOW TO MAKE A FLORIN APPEAR LIKE FIVE SHILLINGS 
AND SIXPENCE. 

This experiment requires for its performance a tum- 



74 LIGHT, 

bier, a plate, a little water, a florin, and a match. With 
these appliances we can solve the astonishing problem of 
how to make a two-shilling-piece appear like iive shillings 
and sixpence. 

Take the florin and place it in the centre of a plate 
containing water just sufficient to cover the money. Then 




Fig. 6i. —Experiment of Refraction and Divergent Lens obtained wiih a Tumbler 



take an ordinary tumbler, and holding it upside-down, 
warm the interior with a lighted match. When the air 
within the tumbler has been well warmed — which will be 
when the tumbler looks steamy — place it over the florin 
in the plate. 



^ VISION AND OPTICAL ILLUSIONS. 75 

The water in the plate will ascend then into the tumbler 
in consequence of the contraction of the cooling air in the 
"glass, and because of the exterior atrnospheric pressure. 
Look at the surface of the water, and you will see that 
the florin is doubled in size by refraction. You will 
distinguish the florin, and a little below it will appear the 
image of a coin as large as a five-shilliiig-piece. Again 
look at the tumbler from the top. The bottom of it 
forms a lens, which gives you the reduced image of the 
florin so that it resembles a sixpence in size. Thus the 
problem is solved, and we have five shillings and sixpence 
for our florin (Fig. 6i); 

Vision AND Optical Illusions. 

The eye is an optical instrument of the greatest 
delicacy, and the phenomena of vision maybe regarded 
as amongst the most complicated and the most worthy 
of the attention of physicists. We cannot here enter 
upon the great theoretical developments of the subject, 
biit will confine ourselvfes specially to the consideration 
of some curious illusions which will be ; fotind , adapted to 
sfmple experiments. 

Let us, in the first place, notice that nature on all sides 
offers to us opportunities to observe these phenomena. 
In the morning we see the sun rise in the east, we notice 
. it on its course across the sky during the day, and watch 
it setting in the west in the evening. This movement 
is an optical illusion ; the sun is immovable as regards the 
earth : it is our globe which turns around the orb in the 
twenty-four hours. 

A somewhat similar phenomenon may be observed in 
a train in motion. The telegraph poles appear to fly 
past with great rapidity, and give the traveller an impres- 
sion of immobility, which is a sensation contrary to fact. 



76 



LIGHT. 



These optical illusions are numerous, and present to 
usmany opportunities for amusement; as follows: — • 

THE WHITE AAD BLACK SQUARES. 

The illustration herewith presents to us (Fig. 62) a 
white square on a black ground, and a black square on a 
w'.iite ground. Although the squares are precisely of the 
same dimensions, the white one appears to be the larger. 





Fig 62. — The White appears larger Ihan the 
Bhick. 



Fig. 63. — The Angles of the White 
Squares seem to Unite. 



For designs formed of white and black squares, like those 
of the draught-board (Fig. 63), the angles of the white 
squares unite by irradiation, and separate the black squares. 
If we look at a draught-board in its entirety the effect will 
be more fully appreciated. 

THE DIVIDED f.TNES. 

We will now show an experiment of another kind 
which gives rise to some comment. 

A divided space appears larger than when it is not 



I I M 1 I I I I I 10 



Fig. 64.— a i appears equal to i c. 



divided. So thus in the cut (Fig. 64) one would say 
that the length a b is equal to b c, while in reality a b is 
longer than be. 



VISION AND OPTICAL ILLUSIONS. 



17 



The reader may satisfy himself of the exactitude of the 
measurement ; when the lines are drawn on a larger scale 
the illusion is more striking. We recommend our readers 
to try the effect for themselves. 

LINES AND ANGLES. 

The illusions relative to parallel lines are appreciable 
when the distances to be compared take different direc- 
tions. If we look at A and B (Fig. 65), which are both 



Fig. 



-A and B are perfect Squares. 



perfect squares, A appears higher than it is wide, and B 
appears wider than it is high. 

It is the same with angles. Look at Fig. 66. The 
angles i, 2, 3, 4, are right angles, and ought to appear 
so when examined with both eyes. But i and 2 seem to 





Fig. 66;— ^The Angles 1—4 are equal. 



be acute, and 3 and 4 obtuse angles. The illusion will be 

intensified if the diagram be looked at with the right eye. 

Certain analogous illusions are daily presented to us.^ 



78 LIGHT, 

For instance, an empty room appears smaller than when 
furnished, a papered wall appears larger than a naked wall, 
a dress striped crossways makes the wearer appear bigger 
than when the dress is striped downwards — lengthway. 




Fig 67.— The Height o( the Hat. 



THE HAT EXPERIMENT. 

A simple amusement consists in requesting some one 
to measure the height of your hat on the wall from the 
floor. Generally the person addressed will indicate one 
and a half times the actual height if unacquainted with 
the trick. In drawing the illustration (Fig. 67) for this 



VISION AND OPTICAL ILLUSIONS. 79 

experiment we were astonished to find that the design 
reproduced the same illusion. The plinth in the illustra- 
tion is exactly the same height as the hat, but one would 
scarcely think so when looking at the two objects. The 
measurement can be verified with a compass.' 

THE THREE GREAT MEN. 

Which is the tallest of the three figures in the annexed 
illustration ? (Fig. 68.) 

If you trust only to your eyes you will certainly .reply, 
" Number 3." Well, then, take a graduated scale and 
measure the figures, and you will ascertain that your 
vision has been playing you a trick, and that Number i 
is the tallest of all. 

M. Viallard, Professor of Physics at Dieppe, who 
brought this curious effect to our notice, gave us at the 
same time the explanation of it, which is as follows : — 

Placed in the midst of carefully calculated vanishing 
lines the three silhouettes are not in perspective. Our 
eyes:, accustomed to perceive objects diminish in propor- 
tion to their distance from us, and believing that Number 
3 is elevated, come therefore to the conclusion that the 
third figure must be the tallest of the three. It is an 
optical delusion. 

There is in this illustration, then, a fault in drawing, 
purposely committed, which deceives the spectator, and 
produce^ in his vision an inverse effect from that which 
would be obtained with a correctly-dr^wn sketch. 

The origin of the design is not less curious than the 
drawing itself. It did not emanate from the portfolio of 
a scientist, but from the warehouse of a firm of Soap- 
makers who printed their name in perspective between 
the vanishing lines, and published the drawing in a 
number of newspapers in Great Britain and America. 



So LIGHT, OPTICAL ILLUSIONS, ETC. 




Fig. 68.— Optical Illusion— Which is the tallest of the Three ? 
{By pcnnisstoji ofRIcssrs. A. ajid F, Pears.) 



VISION AND OPTICAL ILLUSIONS. 



8l 



The Soap-merchants completed this telling advertise- 
ment by giving the three figures the " counterfeit pre- 
sentiments " of Lord Randolph Churchill (i), Lord 
Salisbury (2), and Mr.- Gladstone (3). We have repro- 
duced the illustration by permission of the proprietors 
of the picture. 

THE MAGIC RINGS. 




Fig. 6p. — The Magic Rings. 

The rings, virhich we reproduce from a photo- 
graph, give birth to a curious illusion, which may be 
included in the class of phenomena which we have been 
studying. These rings are made of metallic coils, each 
alternate "strand " being of a golden and silvern hue, and 
brilliantly polished. 

The rings are of equal diameters, the coils of equal 
thickness, and absolutely parallel. Now when we look 



82 LIGHT. 

at one of the rings sideways, the coils seem to come 
closer near the bottom, and the ring appears thinner there 
than at the top, and when the ring is turned round the 
finger the illusion is produced at the same point. The 
ring at the left of the illustration gives some notion of the 
illusion, but the effect is much greater in the real ring. 

In the three-coiled ring shown in the centre of the 
illustration the middle coil appears to lean aside, but the 
design does not reproduce the illusion as it is in actual 
practice. The right-hand ring merely shows the arrange- 
ment of the coils. It is not very easy to give an 
explanation to these facts. 

The phenomenon is in great measure due to the re- 
flection of the light on the rounded threads of the metallic 
coils. The light is reflected on the exterior border of the 
upper part, and in the middle of the coil in the lower part 
of the ring. The left-hand ring shows this plainly. 

Other objects probably would facilitate the study of 
this illusion. Skeins of silk of various colours rolled 
round a hoop or ring would afford the same effect. It 
would be necessary to be careful in the blending of the 
colours so as to produce the proper result. By adoptingt 
this suggestion many amusing experiments may be at- 
tempted. But in any case, the ring represented can be 
obtained at most jewellers' shops at a small cost, and the 
experiment may be tried. 



Persistence of Impressions on the Retina. 

the imp on the ceiling. 

This experiment, which can be performed with the aid 
of the next illustration, is one appertaining to the principle 
of persistence of impressions on the retina, to which must 
be added that of complementary colours. 



' PERSISTENCE OF IMPRESSIONS ON THE RETINA, 83 

Look Steadily wjth both eyes at the white figure in the 
illustration, on a black ground, particularly keeping yoUr 
gaze ^xed on the band in the centre ; then, just when 
your eyes are beginning to feel tired- — say in half a 
minute — look up to the ceiling, and in a few seconds 
you will perceive the outline of the imp, in grey, on the 
ceiling, repeatedly. 

This experiment will gain by being made in a strong 




Fig. 70. —Figure for Experiment of Persistence of Impressions on the Retina. 



light. I If the imp be red m the silhmette the impression 
will come out in green, which is the complementary 
colour of red. It is rather comical when a nuniber of 
people try the experiment simultaneously, all with heads 
in the air waiting for the irtip to appear. A card, such 
as the ace of hearts, may replace the design, and instead 
of the ceiling, a sheet of white paper may be looked at 



84 



LIGHT. 



after the figure has been studied. This experiment can 
be varied to any extent — a white, black, or green image 
will be reproduced in the complementary blue, white, or 
red. If painted green on a red ground the result will 
appear as red on green. The annexed illustration coloured 
will suffice for any experiments. 




Fig. 7i.— The Mule Rigolo. 

THE MULE RIGOLO. 

We have seen on the boulevards a very simple zoo- 
troptic apparatus represented in the cut above (Fig. 71). 
It is composed of four panels of cardboard, mounted at 
a right angle around a hollow axis. This cardboard' 



PERSISTENCE OF IMPRESSIONS ON THE RETINA. 85 

arrangement can be put on a vertical stem, fixed on a 
pedestal, on which it turns >vith ease. Each panel con- 
tains a zpotroptic design, and the impression of each 
figure on the retina gives the spectator the idea of a 
single figure with different action ; at the different periods 
of a movement comprised between its extreme limits. 



Fig. 72. — The Silhouette Portraits. 

THE SILHOUETTE PORTRAITS. 

Take a large sheet of paper, black on one side and 
white on the other. Fix it by means of pins to the wall 
so that the white surface is outermost. On a table close 
by place a good lamp, and let the person whose portrait 

7 



86 



LIGHT. 



you wish to take stand between the lamp and the sheet 
of white paper. You can then outline the proiile with a 
pencil. Cut out the design, and, turning the paper, gum 
the drawing black side outwards on another sheet of 
(white) paper. Your portrait will then be mounted, and 
the sillwttette will show very well in black. 

TO VARY THE SIZE OF A HALFPENNl, 
Take a rectangular box of white wood, and in one side 




Fig 73.- Mode of EquaHzing llie size ot larger and smaller Coins. 



of it fix a nail or bodkin, to which attach, with wax or 
other substance, a halfpenny. Beside this halfpenny, but 
on the surface of the box; fasten a farthing.; If you gaze 
at these two pieces of money through- a small , circular 
hole in a piece of cardboard (as in Fig. 73), you will not 
be able to distinguish one coin from the other. They 
will both appear the same size. 



l'JlK&lSi^lSJ^^CE OF IMPRESSIONS OF THE RETINA. 87 

Of course the distance at which the coin^ must be 
placed will depend upon the powers of vision of the 
spectator. It is as well to fix the cardboard screen, and 
then move the box farther or nearer, as may be desirable. 
A time will come when the two coins will appear of 
equal size ; but by gradually lessening , the distance the 
"farthing will actually appear larger than the halfpenny. 
This experiment demonstrates that the eye under the 
conditions indicated is unable to appreciate the distance 
between two objects. By a similar phenomenon the 
moon, when viewed thi^ough an astronomical telescope, 
appears smaller than it looks to the unaided eye, while 
as a matter of fact it is magnified by the telescope. 





CHAPTER VII.— ELECTRICITY AND 
MAGNETISM. 

E will now reproduce a few experiments in 
electricity, and commence with 

THE ELECTRIFIED PIPE. 




Fig. 74. — Pipe attracted by an EiectriHed Glass. 

Place a clay pipe in equilibrium on the edge of a 



ELECTRICITY AND MAGNETISM. 89 

glass in such a manner that it may oscillate freely. The 
problem now is to make the pipe fall without touching 
it, blowing upon it, or agitating the air, and without 
moving the table. 

Take another glass, similar to that which supports 
the pipe, and rub it rapidly on the sleeve of your coat. 
The glass will % -^^^ectrified by the friction, and when 
you have rubbed, it»Avell bring it close to the pipe with- 
out touching it. You will then see it turn after the glass 
and follow it till it falls from its support. 

• THE PAPER PUPPETS. 

We will now explain the means of obtaining some 
electrical manifestations of great simplicity in performance, 
such as the " dance of the paper puppets." 

Procure a square of glass and two volumes sufficiently, 
large to support the plate of glass in the manner shown 
in the picture (Fig. 75), about an inch from the table. 
Then cut out of rice-paper or silver paper any figures 
you choose — frogs, men, women, children, or any animals. 
These little figures should not exceed three-quarters of 
an inch In height We give some specimens of larger 
size in the upper part of the illustration. They can be 
. cut out of different coloured papers, which will improve 
the experiment. 1 

Place these little people in their ball-room — that is to 
say, beneath the glass which you have supported above 
the table, lying side by side on it. Then rub the plate 
of glass vigorously with a silk rubber (silk is best), and 
after a while you will see the paper figures jump up to 
the celling of their "ball-room,"' attracted by the electricity 
which you have developed in the glass by rubbing. They 
fall again and are again atttacted, impelled to an 
extravagant dance. Even when the rubbing ceases the 



90 



ELECTRICITY AND MAGNETISM. 



dancing will continue for a certain time, and the contact 
of your hand with the glass will be sufficient to animate 
the little dancers. 

To ensure the success of this experiment the glass 
must be perfectly dry, as well as the handkerchief or 




Fig. 75. — The Dance of Dolli. 

rubber with which you operate ; and if the table be 
warmed the manifestation will be ' more successful. Silk 
is better than cloth for rubbing purposes. 

THE MAGICIAN. 
The little toy depicted in the Illustration is based on 



ELECTRICITY AND MAGNETISM. 



91 



the property of repulsion possessed by the opposite poles 
of magnets. It consists of a magician, or " diviner," 
fixed on a pivot upon which he turns easily. A series of 
questions are written on the pieces of cardboard, which 
are introduced into the pedestal on which the magician 
stands. These cards contain magnets properly placeci, 







Fig. 76.— The Magnetized IMagician. 



and when a card is put into the pediment of the figure 
the magician turns the magnet in the form of a horse- 
shoe (U) hidden in his dress, obeys the influence of the 
other magnet in the card, and with his magic wand he 
indicates a number in the circle which surrounds him. 
The number corresponds to those on a list of answers 
supplied with the apparatus. , 




CHAPTER VIII.— CHEMISTRY WITHOUT A 
LABORATORY. 

^E have in foregoing pages shown the possibility 
of practising a course of physics without ap- 
paratus ; we now propose to perform some 
experiments in chemistry without the aid of 
a laboratory, and only with the assistance of a number of 
simple and inexpensive articles. The preparation of 
gases, such as oxygen, hydrogen, and carbonic acid gas, 
is very easy and very inexpensive. We have merely to 
procure some glass tubes, a few phials, and a number of 
sound corks, which we can pierce with a round file 
called a rats tail. 

For " furnace " we can easily make a spirit lamp from 
an ordinary penny glass ink-bottle, which we fill with 
spirits of wine, and fit with a metal top, in which we 
punch a hole to permit the wick to ascend through a 
metallic pen-holden Our heating-apparatus is then 
complete. 

OXYGEN AND HYDROGEN 

The ancients believed that earth, air, fire, and water 
were the four elements ; but they were mistaken, for each 
of these so-called elements is composed of other bodies. 
Thus — water is composed of two gases, oxygen and 
hydrogen, which we may now proceed to prepare. To 
make oxygen it is only necessary to warm in a glass 
tube a mixture of chlorate of potash and the bi-oxide of 
manganese. Oxygen is contained in water, but it is also 



CHEMISTRY WITHOUT A LAEORATORV. 



93 



contained in air; it supports the respiration of animals 
and the combustion of burning substances. After we 
have warmed our glass tube for a while we may perceive 
the escape of the oxygen from it by putting the incan- 
descent point of an extinguished match in the tube : the 
niatch will at once be re-lighted, and burn under the 
influence of the oxygen. 




Fis- 77- — Preparation of Oxygen, 



To prepare hydrogen gas — another of the constitutional 
elements of water^we must decompose the water by a 
metal, such as zinc or iron, under the action of sulphuric 
acid. \Procure a glass vessel with three tubes, which can 
be closed with corks. One of these is furnished with 
a funnel, into which we may pour sulphuric acid and 
water ; another tube is furnished with a removable tube 
with a fine point, through which the hydrogen gas 



94 



CHEMISTRY WITHOUT A LABORATORY. 



escapes. The glass vessel is half filled with zinc filings. 
When the sulphuric acid and water come in contact with 
the zinc filings an effervescence due to the disengagement 
of the gas is produced. ' 

Care must be taken that the air in the glass receptacle 
for' the hydrogen gas is expelled, else there will be an 
explosion, for air and hydrogen gas form an explosive 







Fig. 78. — Iron Filings burning in a Jet of Air. 



mixture. When the air has been withdrawn the hydrogen.' 
gas can be lighted at the extremity of the tube. 

Hydrogen is a combustible gas ; oxygen is a supporter 
of combustion. The latter is the active constituent of the 
air, and by its aid iron filings can be burned in the flame 
of a candle driven by the action of a blow-pipej formed 
by a common clay pipe, as in the foregoing illustration 
(Fig 78). 



CHEMISTRY WITHOUT A LABORATORY. 



95 



AIR AND ITS ELEMENTS— CARBOMC ACID. 

Air contains oxygen and azote (nitrogen), a heavy 
gas which extinguishes bodies in combustion ; the air 
also contains a small quantity of carbonic acid, which we 




Fig. /, 



-ting on the Surface of a Layer of Carbonic Acid Gas, 



can ascertain by a very pleasing experiment, at the same 
time proving the density of gas and the equilibrium of 
floating bodies. 

Take a large glass — a soda-water glass or some wider 
tumbler—and support it on a tripod or in some other 
secure way. At the bottom of the glass vessel put a 



g6 CHEMISTRY WITHOUT A LABORATORY. 

thin layer of bi-carbonate pf soda and tartaric acid, mixed 
in equal quantities. The quantity of the powder em- 
ployed will depend upon the thickness of the carbonic 
acid atmosphere which you wish to produce. One must 
proceed on the basis that the bi-carbonate of soda con- 
tains half its weight of carbonic acid, and consequently 
we must dissolve four grammes of the bi-carbonate to 
produce a litre of carbonic acid gas. 

Over the glass vessel place a cardboard covering so 
as to fit it closely. The centre of this covering should 
be perforated so as to admit a small glass tube long 
enough to reach to the bottom of the vase and rise above 
the cardboard. By this tube and a small funnel we can 
pour in the small quantities of water, which must be 
successively introduced in order that the effervescence may 
not become too violent, and so that the powder may 
be quite covered with water. When the carbonic has 
ceased to disengage itself the glass tube may be with- 
drawn. 

It must be supposed that a good lather of soap has 
been prepared beforehand, and with this mixture a 
bubble some two inches in diameter may be blown ; 
then cdrefully let the bubble fall into the glass vessel 
perpendicularly. If this fall be from a certain height 
the bubble will rebound as if it had been repelled by a 
spring ; then it re-descends and again ascends many times, 
and executes many vertical oscillations before it becomes 
motionless. At that moment the covering should be 
replaced, so that no agitation is produced within the 
vessel. The soap bubble floats upon the stratum of 
carbonic acid gas, which is invisible. 



CHEMISTRY WITHOUT A LABORATORY. 



97 



FORMATION OF SALTS—INSTANTANEOUS 
CRYSTALLIZATION. 

We are aware that caustic soda or oxide of sodium 
is an alkaline , production endowed with very energetic 
properties ; it blisters the skin and destroys organic 
matter. 

Sulphuric acid is endowed with not less destructive 
properties : a drop falling on the hand will produce 
intense pain, and cause a terrible burn ; a piece of wood 
plunged into this acijd is carbonised iriimediately. 

If we mix forty-nine grammes of sqlphuric acid and 



p? 



1 



/ /"^Sv^ 





Fig. 80. — Bottle containing a Saturated Solution of Sulphate of Soda. Crystallization is 
shown in the Decanter to the left of the. Illustration. 

thirty-one grammes of caustic ' soda a most intense re- 
action will set in, accompanied by a considerable increase 
of tehiperature ; after the mass has co9led we find la 
substance which may be hand led with impunity ; the acid 
and the alkali have combined and their properties have 
been reciprocally destroyed. The combination has given 
birth to a salt which is sidphaie of soda. The result of 



98 



CHEMISTRY WITHOUT A LABORATORY. 



the union exercises no action on litmus paper ; it in no 
respect resembles its parents. 

In cliemistry there is an almost infinite number' of 
salts, which result from the combination of an acid with 
an alkali, or base. Some, like the sulphate of copper, or 



:<?'B*'"'3 



«,» 











Fig. 8i.— Preparation of a Saturated Solution of Sulpliate of Soda. 

' I 

the chromate of potash, are coloured ; others, like sulphate 
of soda, are colourless. 

The last-mentioned product, like the majority of salts, 
can assume a crystalline form, and if it be dissolved in 
warm water and the soluti9n be permitted to remain 
undisturbed it will quickly precipitate in remarkable 



CHliMISTRY WITHOUT A LABORATORY. 99 

transparent crystals. ^ This product, discovered by Glauber, 
is called the " admirable " or Glauber salts. 

Sulphate of soda is very soluble in water, and at a 
temperature of thirty-three degrees the best effect is 
obtained. If we pour some oil on a saturated solution of 
Glauber salt and let the liquor remain undisturbed it will ' 
not deposit any crystals ; but if we plunge into the 
solution a glass rod, penetrating the layer of oil, the 
crystallization will be instantaneous. (Fig. 80.) 

This experiment is still more striking when the solu- 
tion is acted on in a tube of glass, hermetically sealed, 
after having exhausted the air by the ebullition of the 
liquid. (Fig 81.) 

As soon as the tube Is closed the crystals will not 
form even at the freezing point ; nevertheless, the salt 
being less soluble in a cold than in a heated atmosphere 
is in proportion ten times stronger than under ordinary 
conditions. If the point of the tube be broken Crystal- 
lization immediately ensues. 

TREE OF SATURN. 

Lead, like tin, is capable of assuming a beautiful 
crystalline form. The crystallization of lead represented, 
in Fig. 82, page 100, is known as the Tree of Saturn. The 
experiment is performed as follows. Form a solution of 
acetate of lead in proportions of thirty grammes of salt to 
a litre of distilled water, and pour the Hquid into a 
icylindrical vase. Into the cork of this vase fit a piece of 
zinc, to. which are attached five or six brass wires separated 
from each other ; plunge these into the solution, and you 
will soon perceive the brass wires becoming covered with 
spangles of scintillating crystals of lead, which increase 
day by day. Alchemists who were aware of the experi- 
ment believed that there was a transformation of copper 



I GO 



CHEMISTRY WITHOUT A LABORATORY. 



to lead, while it is really only a substitution of one metal 
for another. The copper is dissolved in the liquid and is 
replaced by the lead which is deposited, but no meta- 
morphosis takes place. One may vary at will the form 
of the vessel and the disposition of the wires which 




I cc of "^^tu n 



support the crystals of lead, and form letters, figures, etc., 
at pleasure. 



TO PRODUCE GAS FOR LIGHTING PURPOSES. 

If we burn, on a perfectly clean plate, a sheet of paper 
we need no more to convince us of the phenomenon of 



CHEMISTRY WITHOUT A LABORATORY. 



lOI 



carbonization (the paper is transformed into a black mass) 
and the formation of empyreumatic products under the 
action of heat. Beneath the burned paper we shall find a 
yellow deposit, which clings to the fingers, formed by the 
oil of the paper produced in contact with the air by a 
kind of distillation. 

We may produce coal gas very easily by filling a com- 
mon clay tobacco-pipe with small coal dust,, and covering 




Fig 83.— Production of Gas with a Paper Cone. 

the bowl up with fire-clay. Place the bowl ,of the pipe 
in the fire, and after a while the gas will evolve from th^ 
aperture in the stem. It can then be lighted. If the 
pipe be not available you may have recourse to a large 
piece of wrapping paper, which you muSt fold into a 
"horn of plenty" as in illustration. This will suffice for 
your " gasometer." Hold the folded paper by its pointed 
end, after having punctured a small orifice in the cone, 

,8 



I02 CHEMISTRY WITHOUT A LABORATORY. 

near the upper part, of it. Light the paper, it burns ; 
but the heat developed by the flame produces distillation 
of the materials of the paper ; the empyreumatic and 
gaseous products rise into the cone and escape by the 
orifice, where the gas can be lighted by a match. 
(Fig. 83.) 

This experirrient Only lasts a few seconds, but its 
duration, brief as) it is, : will suiKice to demonstrate f the 
production of gks for lighting purposes by the distillation 
of organic matter. Of course fire must be guarded 
against when this experiment is tried, which it should not 
be in the vicinity of any inflammable matter. 

THE GRA VEN EGGS. 

Some time ago a man viras seen selling eggs engraved 
■with names and various devices. This egg-engraving 
recalls to us a curious historical fact. 

In the month of August 1808, during the Peninsular 
War, there was found in the cathedral of Lisbon an egg, 
on the shell of which was engraven a prediction of the 
expulsion of the French, ^ This caused considerable excite- 
ment, and nearly led to a riot. 

The French commander caused a counter irritant to be 
applied, in the shape of thousands of eggs denying the 
prediction. The people did not know what to think ; 
thousands of eggs denied the accuracy of one. Besides 
after a while posters were placarded on the walls giving 
the particulars and directions for working the miracle. 
The means are very simple. 

Write your name or legend on the egg-shell on bees- wax 
or varnish, or even with tallow. Plunge the egg into a 
weak acid — vinegar will do, or diluted hydro-chloric acid, 
or aquafortis. Wherever the shell is not protected by 
the covering material it is decomposed, and the. design 



I' 
chemistry' WITHOUT A LABORATORY. 



IP3 



Stands put in relief. There is no difficulty in this experi- 
ment, but some precautions are necies^ary. > 

As " blown " eggs are generally experipiented upon 
it will be necessary to close up the ends with yellow or 
■white wax ; aild as these eggs are necessarily very light 
they must be weighted to keep them in the acid bath, or 




Fig. 84. — Manner of engraving an Egg. 1 

held down with a glass rod. If the acid be very much 
diluted the operation, although it will occupy more time, 
will be more complete. Two or three hours will be 
sufficient to bring ont th6 tracing. 

Thus the, miracle of the sorcerer has become an 
amusing and easy experiment in chemistry. 




CHAPTER IX.— MATHEMATICAL GAMES. 

The Dice Trick. 

jHIS trick, which always astonishes people who 
have not previously witnessed it, is based upon 
a very simple calculation. Few people know 
that dice are made and " printed " on a cer- 
tain plan, which is that every face with the number of 
dots on the side immediately opposite shall, added to- 
gether, make seven. This is the whole point of the trick. 
If there are two dice the total of the points on the 
opposed faces will be fourteen. 

This ascertained, we may proceed and throw the dice. 
We find six, for instance, and we seize the cubes between 
the thumb and index finger (Fig. 85, No. i)." , The 
performer knows at once that the total of the under faces 
is nine, but he takes good care not to show them. He 
"quickly turns his hand to reach the position shown in 
Fig. 85, No. 2, but during the movement he has taken a 
"quarter turn" of the dice in his fingers, by slightly 
raising the thumb and lowering his fore-finger (as in 
No. 2). He then exhibits to his audience the points, 
eight, for instance, which the spectators think was the 
total underneath, but which is, in truth, the total of one 
of the lateral faces. 

This point established the operator quickly resumes 
position No. i, and replaces the dice in their first position 
by manipulation which is easily acquired by practice- 
Then he says, " I have just shown you that the points 



MATHEMATICAL GAMES. 



105 



underneath are number eight, now I am going to add a 
point." Requesting a spectator to touch the dice so as 
to ensure the addition of the required unit, the operator 
takes his fingers from them to show that he will not alter 
their position (No. s),when the dice are taken up. The 
sub-total is found to be nine instead of eight as before. 

It is evident that in some cases points must be sub- 
tracted and not added. If one has begun with twelve, for 
instance, and that the false total is shown as nine, though 




Fig. 85.— A Trick with Dice by a Turn of tlie Hand. 

the true total is two, the performer must request an 
assistant to efface s6ven points instead of adding any. 

Again,, there are circumstances in which the true and 
false points are equal. - Thus, when the upper total is ten 
the lateral face against the thumb is double ^ve. ; and the 
false total will be four by the double two, while the true 
total will also be four, by three and one. So no addition 



I06 MATHEMATICAL GAMES. 

or subtraction can be requested. In such a case one of 
the thousand deceptions practised by prestidigitators must 
be employed, and by simply letting the dice fall, " by 
accident," you may begin ' over again, and with another 
total. 

THE TOWER OF HANOI AND THE QUESTION OF 
TONQUIN. 

This game, which has attained great success, is in the 
form of a small pasteboard box, on which is inscribed the 
Tower of Hanoi, a real Chinese puzzle, brought from 
Tonquin by Professor Claus of Siam, Mandarin of the 
College of Li-Sou-Stiaq. A real puzzle truly, but in- 
teresting. ]V[. H. de Parville was the first, to introduce it. 
We borrow his lively description of it. 

It is related tha:t, in the great temple at Benares, beneath 
the dome which marks the centre of the world, one may 
see fixed in a brass-plate three diamond needles, a cubit 
high and as thick round as the body of a bee. On one 
of these needles God at the creation placed sixty-four 
discs of pure gold, the largest disc resting on the brass 
slab, and the others smaller and smaller to the top one. 
This is the Tower of Bramah. Night and day the priests 
are continually occupied in transferring the discs from 
the first diamond needle to the third, without infringing 
any of the fixed and immutable laws of Bramah. The 
priest must not move more than one disc at a time, he 
must only place this disc on an unoccupied needle, and 
then only on a disc larger than it.. When according to 
these rules the sixty-four discs shall have been transferred 
from the needle on which the Creator placed them to the 
third needle, the tower and the Brahmins will all crumble 
into dust, and that will be the end of the world. 
, It was, this legend evidently that inspired the Mandarin 
of Li-Sou-Stian. The Tower of Hanoi is the Tower of 



MATHEMATICAL , GAMES. 



107 



Bramab, only the diamond needles are replaced by nails, 
and round blocks of wood substituted for the golden 




Fig. 86. — The Tower of Hanoi". ^ , 

I. Beginning ot'the Game : the Tower complete. Tl.Procefs of TrAnsposition : 
the Discs are placed Successively on the Sticks A, B, C. III. End of the 
Game : the Tower is rebuilt at B. 

discs. The blocks of wood, of decreasing circumferences, 
are only eight in tivimber, and that is quite sufficient. If 



io8 



MATHEMATICAL GAMES. 



the trick were to be attempted in thC' manner of the 
Brahmins, with sixty-four discs, it would be necessary 




^ Fig. 87.— The Question of Tonquin. 

I. Cardboai-d Pyramids i^8 with their Supports A, B. C. II. Course of 
Proceeding, showing the Superposition of the Pyramids, which must take 
place in (Transit. III. End of the Game : the Pyramid is rebuilt at C. 

to move them as many times as expressed in 
the bewildering row of figures following — viz.:-; 



MATHEMATICAL GAMES. 109 

18,446,744,075,709,65 1,615 — a task which would occupy 
more than five thousand millions of centuries in accom- 
plishment. ' 

With eight discs it is necessary to make two hundred 
and five transpositions, and allowing for each movement 
one second of time, four minutes will be required to 
transport the " tower." Let us put this into practice. It 
will be conceded that in order to transfer two discs three 
movements must be made, for three discs seven move- 
ments, that is to say double each number of discs 
moved plus i. For four discs fifteen movements^ — 
double plus i, and so on. So to move all the eight 
blocks we must make two hundred and fifty-five moves. 

This ingenious game is founded upon the elementary 
problem of combinations. Newton gave the world a 
general and now well-known formula^the Binomial 
Theorem. But the ancients long before his time knew 
how to find the correct expression for the number of 
combinations which they could obtain TXrith eleven letters 
of the alphabet^ The number of combinations possible 
with four letters is equal to i* minus i ; with five letters, 
it is equal to 2^ diminished by a unit, and so on. With 
eight letters, or eight discs, the same rule holds ; 2* di- 
minished by one unit is equal to/2X4v A tower of nine 
discs would necessitate the samedouble number of dis- 
placements //mj I, or what is the same thing — 2' — i., 
that is 5 1 3 moves, and so on. 

The Tower of Hanoi brings to our recollection the ring 
puzzle, which appears in a volume which we have already 
mentioned, entitled Mathematical Recreations, by Mr. 
Edward Lucas, Professor at the College of St. Louis. 
This reminiscence comes to me very opportunely, as I 
think I have discovered the name of the Mandarin, the 
inventor of, the Tower of Hanoi. One is only betrayed 
by himself. A Mandarin who conceives a game founded 



I 10 



MATHEMATICAL GAMES. 



on combinations would be perpetually thinking of and 
seeing combinations everywhere. Now, in examining the 
letters inscribed on the box containing the Tqwer of 
Hanoi, it seems to me that without much difficulty we 




Fig. 88.— A Mathematical Game— The Packer's Secret. ' 

can transpose St. Claus (of Siam) Mandarin of the College 
of Li-Sou-Stian, into Lucas d'A miens, Professor of the 
College of Saint Louis ! Have I also solved my problem, 
I wonder ? 



MATHEM-ATICAL. GAMES. I I I 

Since the conception of the Tower ot Hanof we have 
found another analogous game, called the Question of 
Tonquin, a game of Chinese hats., This puzzle is com- 
posed of pasteboard pyramids of decreasing sizes (as in 
Fig. 87 on page io8)j which must be manipulated in the 
manner already related with references to the discs and 
the foregoing illustrations. 




Fig. 8g. — Explanation of Method of Packing. 
THE PACKER'S SECRET. 

This ingenious game consists of a cardboard box con- 
taining twelve wooden discs, which lie loosely in their 
receptacle as on the upper portion of the foregoing illus- 
tration (see Fig. 88, page 1 10). The problem to be solved 
is this. Place the twelve pieces in the box in such a 
manner that, they will remain immovable, and will not 
fall out even when the box is turned upside down without 
the lid. 

The solution consists in placing th^ discs tangentially, 
and the puzzle can be performed by arranging them as 
|shown in the cut above (Fig. 89). All the " men ", thus 
[isustain each other by gentle pressure, and the' box may 
f'be shaken without any one of them falling out. To 
perform this puzzle one must understand, in some mea- 



I 12 



MATHEMATICAL GAMES. 



sure, the packer's secret (see Fig. 89). We place one disc 
(No. i) in the centre, and dispose around it six other 
discs, 2, 3, 4, 5, 6, 7. Steady these with the left hand, 
so that they will not move except en bloc, and then insert 
the remaining pieces 8, 9, 10, 11, 12 around them, next 
the circumference of the box. Then remove the disc 
No. I from the central place, and put it where i''"' is 
resting. The twelve discs will then remain firm in their 
places. The puzzle is solved ! 




CHAPTER X.— NATURAL SCIENCE IN THE 
COUNTRY. 

>HE manner of constructing an aquarium has 
already been described, but we will here show 
a charming apparatus which will be' both 
aviary and aquarium combined. Procure a 
large melon-glass, as shown in Fig. 91, page 114; and into 
it introduce a cylindrical glass vase, in which you have 





Fig. 90; — Aviary Aquarium 



previously placed some pieces of lead or pther metal 
^painted, green, etc., so as to suggest the bed of a fountain 
or a clear stream. Upon the bottom of this vase rest a 
movable " perch " with a foot: — a metal one will serve. 
Over the mouth of the melon-glass place a wfre-work 



114 



NATURAL SCIENCE IN THE COUNTRY 



/ 



/ 







Fig. Qi. — Birds in an Aquarium. 



NATURAL SCIENCE IN THE COUNTRY. 



I '5 



screen, with meshes wide enough to adniit ^ir to the birds, 
and finally place, pots of flowers around the grill to em- 
bellish it. Place the aquarium glass thus prepared on a 
pedestal or rest suitable to your apartment, and when all 
is ready introduce gold and silver fish - into the melon- 
glass and a pair of birds into the cylindrical vase within 
it. The flowers will close the mouth of the glasses, so 
you will possess an aquarium, aviary, and garden in one ; 




Npcklace of Nuts suspended by Hairs. 



and also produce a curious effect, as the birds will be seen 
living apparently in the water with the fishes. 

We can also produce a still more surprising effect 
as shown in Fig. 90. A balloon -glass is reversed ihto an 
ordinary glass aquariunl vase. The neck of the inner 
vase, sufficient to admit air, is concealed at the foot of the 
aquarium by plants and by the opaque base, which 



Il6 NATURAL SCIENCE IN THE COUNTRV. 

seems to support the globe. When the water and the 
glass are clear the illusion is perfect. 

A COLLAR OF NUTS. 

If we closely examine a nut we shall perceive clearly 
some inequalities on its surface which look like little 
cavities. Not only are they cavities, but they also cor- 
respond to small excavations which traverse the nut 
within — little tunnels, in fact. If you scratch the super- 
ficial cavity with a penknife you will open up the entrance 
to the little tunnel, and you will be able to pass a hair 
through it, fastening it by its root, which will not penetrate 
the nut. To pass a hair through a nut, and even to pass 
many hairs through nuts, were problems which we confess 
we at one time regarded as visionary : but we have seen 
them performed by skilful hands. With dexterity and 
patience, with some lady' s hair, we can make collars and 
necklaces like those shown in the illustration. 

This proves that nuts are full of perforations, and 
whether the fact be known or not to botanists, amateurs 
may derive some amusement from the exercise of their 
dexterity on the fruit 





CHAPTER XL— MECHANICAL TOYS, ETC. 

ACROBATIC APE. 

*MONGST the most amusing of modern me- 
chanical toys this takes a foremost place. 
The inventor has succeeded in reproducing 
very effectively all the movements of a >man 
climbing up a rope. Hitherto the puppet has always 
been more or less stiff in his movements, but in the, 
toy under ' notice it is completely independent and 
free. Just suspend the cord or hold it in the left hand 
and pull it with the right hand — the puppet will then 
ascend. Notwithstanding the complicated nature of the 
movements produced the system is ver)' simple : it 
requires only a single articulation at D to permit the 
motions of the limbs. A kind of catch or Spring V, in 
which the cord fixes at certain times, simul,ates the grasp- 
ing of the hands. The movement of the legs towards 
the body is effected by the india-rubber band R (No. 2), 
fixed in the chest and thigh of the figiire. 

We must now proceed to explain the mechanism which 
produces the ascending movement of the puppet. Suppose 
the cord suspended, the figure is at the lower end : we can 
describe the cycle "of ascent in three phases. 

First Phase. — The figu^-e is in the position indicated 
in No. I in the illustration; his limbs are drawn up by 
the tension of the india-rubber band. You will see that 
when the string is pulled the limbs will pivot round the 
points A and B, and the puppets will assume the position 
represented in No. 2, the body having slid along the cord, 

9 



ii8 



MECHANICAL TOYS, ETC. 



which it cannot get away from because of the peg C, 
which only permits a movement along the string.^ It is 
the movement of a climber moving upright on his legs. 
The fork V stops the cord at the end of the climb imitat- 
ing the prehensile movement of hands. 




-Fig., 93- — A Mechanical Toy. The Acrobatic Ape. 



1. Position at starting : pull the Cord and the Puppet will assume Position 2. 

2. End of Ascension Motion. The String is caught at V. The India-rubber 
pulls up the Legs (3). 

3. Puppet suspended by V. Pull the Cord, and the Figure resumes Attitude 
No. I. 

Second Phase. — When we loose the cord the puppet 
remains suspended by V, the limbs being again drawn up 
by the india-rubber, and it assumes the po.sition as in 
No. 3. This is the climber suspended by his hands, and 
gathering up his legs. 



MECHANICAL TOYS, ETC. 



119 



Third Phase. — If we pull the cord again it escapes 
from V and reassumes the position as in No. i , as already 
described. By pulling the string the various motions are 
continued until the puppet has reached the end of his 
tether. 

It is important that the cord should in the first phase 
be pulled until it is finished in V. If not the puppet 
will slide down again as soon as the pull is intermitted, 




because it will have to be in the position of a man who 
has not gripped the rope with his hands. 

THE ROAD LOCOMOTIVE. 

r Every one is aware that to impart a certain velocity to 
a given mass a certain amount of energy must be deve- 
loped — an energy in proportion to the mass and to the 
square of the velocity which is imparted to it. We also 



I20 MECHANICAL TOYS, ETC. 

know that bodies thus animated do not return to a con- 
dition of repose until thpy have exhausted the power or 
force imparted to them, and in the cases of bodies whose 
friction is reduced to a minimum the energy will be 
slowly exhausted ; the motion will continue for a long 
time. 

We can utilize this force by putting in motion a wheel 
by a system of impulse by pulling, finally producing 
progression, as evidenced in the little apparatus illustrated 
(Fig. 94). It is composed of a fly-wheel V, to which a rapid 
rotatory movement is imparted by a thread or string 
wound round it. The wheel acts on the two trailing 
wheels of the engine, furnished with adhering tires. The 
axle which acts on the wheels is about wth of an inch 
in diameter, and the wheel about two inches, so it results 
that the velocity of the small wheel is much greater than 
the larger, and the latter moves only Tuth as fast as the 
former. The initial velocity of the small wheel is, how- 
ever, very great, and the machine moves with considerable 
speed until its impetus dies away. On a level floor it 
will run rapidly and for a long while. The same principle 
has been applied to many other toys popular in England 
and France. The hind wheels are the motive power, the 
others are only supporters. 

TO LIFT A MAN WITH FIVE FINGERS. 

This is a school-boy pastime, and consists in one indi- 
vidual being lifted and sustained by the fingers. Two 
operators put their index fingers under the person's boots, 
two others place their fingers under each elbow, and a 
fifth under the chin of the subject. At a given signal 
each person lifts his hand and the person is easily lifted up 
(Fig. 95 )• The result may seem very surprising, but it is 
only a question of the equal sub-division of weight. The 



MECHANICAL TOYS, ETC. 



121 



average human being weighs about 70 kilogrammes, or 
say eleven stone ; so each finger has only to sustain about 
30 lbs. weight (10 kilogrammes) which is nothing extra- 
ordinary. 




GiLBEf\T. 



, Fig. 95.— A Man held up by Five Fingers. 

ATTJ^ACT/OJV. 

Take a cork and fix in it three hairpins, so as to form 
a species of tripod. In the centre fix a knitting-needle, 
and on this fasten a sheet of paper cut as shown in the 
illustration Fig. 96. 

We have now two surfaces of paper A and B, sus- 



122 



MECHANICAL TOYS, ETC. 



iseptible of turning, at the least wind which blows, around 
the needle which serves as an axis. Well, if we fan one 
of these surfaces with a piece of cardboard or a wooden 
plate .directed normally to the surface, we shall preceive 
that the surface thus fanned, instead of being repelled 
as one would anticipate, is actually attracted. In certain 











A 






B 


















- 


-:~-^- m 


Ll_,- — ^zj: 







Fig. g6, — A Curious Experiment in Rotatory Movement-Attraction. 

cases when a flexible fan is employed there is repulsion. 
We have performed this really curious experiment in the 
presence of many savants, and have arrived at the con- 
clusion that the disc of paper is attracted by the fan-plate, 
Which in its sudden fall creates a vacuum, and the surface 
of the paper is attracted towards the operator. 



MECHANICAL T0Y3, ETC. 
THE MAGIC GLASS. 



123 



A skilful chemist, M. Wideman, has supplied a curiosity. 
It is a square of glass perfectly plain, on which no drawing 
or any lines can be distinguished even after minute investi- 
gation. But if any one breathes on the surface of the 
glass a figure such as in the engraving appears. The 
figure will disappear immediately the breath has evaporated 




Fig. 97.— The Magic Glass. On the Left the Transparent glass ; on the Right the Sanie after 

being breathed on. 

from the glass. You may wash and rub the glass, but 
the image will again appear if the plate be breathed upon. 
The explanation is simple. Prepare the, piece of 
looking-glass, and let the operator draw upon it any 
design he , chooses with some fluor-hydric acid, which is, 
obtained by dissolving some powdered fluor spar in the 



124 



MECHANICAL TOYS, ETC 



ordinary sulphuric acid of commerce. When it is su 
ciently liquefied the figure should be traced on the glass 
with a quill-pen. Leave it for a few minutes— five to ten 
at the most. Wash the glass and dry it well. Then 
when it is breathed upon the figure or design will appear. 




Fig. gS. — Fantoccini Top. 



A little experience will decide the length of time requisite 
for the proper production of the figure ; the acid if left 
too long will eat into the glass, and the design will remain 
visible even on tiie dry surface. 



MECHANICAL TOYS, ETC. 12 5 

A FANTOCCINI TOP. 

This apparatus is composed of foiir small triangular 
mirrors, whose surfaces form a square-based pyramid. 
The sides of this base are precisely double the height of 
the pyramid. The mirrors are set at an inclination 

of 45°; 

At the apex of the pyramid, which is somewhat trun- 
cated, are placed successive discs of cardboard, on which 
are painted divers figures in various attitudes. Rotation 
at a moderate speed, by means of the handle at the upper 
extrernity, will bring the reflections of the figures in 
succession before the eyes of the spectators, and every 
figure will appear to be moving. So a girl skipping, a 
dancer, or a gymnast on a trapeze, a ■ horse leaping a 
bar, etc., may all be seen in rapid succession. 

A SMALL LOOM MADE WITH CARDBOARD. 

When we see a weaving-machine at work we admire 
the ingenious mechanism, but we are unable at first to 
seize the fundamental principles of its working. We will 
now endeavour to show the working of the loom by the 
very best method that can be imagined, viz., that which 
consists in making the apparatus for oneself, and weaving 
a piece of tissue with it. 

Two pencils, a visiting-card or playing-card, some 
thread, a good knife, and, if you please, a wooden paper- 
knife, — that is the whole of the material for our ap- 
paratus. Our loom consists of two pencils, which serve 
for beams ; a comb (or " heddles ") cut out of the card 
by the penknife into a kind of grating, on which longitu- 
dinal openings alternate, with small circular holes. The 
apparatus is completed by two shuttles cut from the same 
cardboard, on which are wound the cotton for the weft 
which is destined to pass across the warp-threads. 



126 



MKCHANICAL TOYS, ETC. 



' Place the pencils at the edge of a table, and, supported 
by some books, as shown in the illustration herewith 
(Fig. lOo). Then you may commence by attaching to 
one of the pencils one end of the thread of the warp, 
and by means of a needle pass it through the first slit 
in the "comb," then turn it around the second pencil, 
returning below it and passing it through the first circular 
hole in the comb. Then around the first pencil and 




Fig. 99. — Shuttles and Comb cut from Card ; above is a Specimen of the Material woven. 



through the second longitudinal opening, and so on, until 
tke last hole in the comb is reached, as represented in the 
illustration (Fig. 100). 

Now, to proceed to our weaving, we have only to raise 
and lower the comb alternately ; and we shall perceive 
that the only threads engaged will be those which are drawn 
through the holes. It now remains for us to pass, be- 
tween each movement, the shuttle full of the thread of 
the weft between the two lines of the warp threads placed 



MECHANICAL TOYS, F.TC. 



127 



at different elevations. We may use the paper-cutter as a 
" batten " to drive home the shot. This little apparatus 
will enable you to comprehend the mechanism of the 
■loom, and may be regarded as at once a medium of 
amusement and of information. With patience we may 
weave some material' by its aid. 




Fig. 100. — The Loo^ ready : showing the " Comb " between the renciis. Ihe' Warp is ex- 
tended between the Pencils : the Thread of the Weft passes transversely by the Aid of the 
Shuttle. 



THE- PAPER RINGS. 

This little arrangement, whichwe are abo ut to explain 
wiir creJate some astonishment amongst those who have 
not been initiated in the manner of performance ; it gives 
rise to' some very interesting geometrical questions. We 
will show how it is done. 

'Look at the illustration (Fig. loi). Here are three 
paper rings. They ought to be in reality of much greater 



128 



MECHANICAL TOYS, ETC. 



diameter in proportion to their length, but in the cut we 
have reduced the circumference so as not to insert such a 
large picture as would be necessary if the true dimensions 



N. 






\ 



\ 




Fjg. loi. — The Papsr Rings. 



Firstly, I give you ring No. i with a pair of scissors, 
and request you to cut it as indicated by the dotted 
line. You will then obtain two rings, as shown under- 



MECHANICAL TOYS, ETC. 129 

neath — No. i'. The dotted line will not be in the paper 
bands in practice. 

Then I request you to cut ring No. 2 in the same 
manner ; but this time you will be surprised to find in 
your hands, when you have finished cutting round the 
ring, not two rings, as at first, but one long ring — 
No. 2'^twice as large as either of the former rings. 

Now for No. 3'. There is another surprise in store. 
As you cut the third ring you will be astonished with the 
result. You will again obtain two rings, but one will 
be^ looped inside the other, as in No. 3'. Let us 
explain this trick. 

You must prepare paper bands 0.05 metre in width, 
and I or li metres in length. Take the first strip, cut 
and join its ends directly in the ordinary manner, as 
shown in fig. i, so that the same side of the paper forms 
the exterior of the ring all round. The second band 
is united after it has been twisted on itself, so that one of 
the ends is united with the opposite surface of the other 
extremity; as for the third band, you must, give it two 
turns before you unite the ends. Let the gum dry, and 
then ydur appa!ratus will be ready. The larger the 
rings are the less apparent will be the turns in them. 



A MECHANICAL PAPER BIRD. 

The art of making paper articles would necessitate a 
long study on our part, and we do not intend to enter on 
the various phases of it here. , We know that many 
things can be made in paper, but the particular object 
which we are about to explain is a mechanical bird 
introduced by the Japanese jugglers — a bird which will 
flap its wings when manipulated. The illustration shows 
the action of the hands, which, approaching arid separating 



I30 



MECHANICAL TOYS, ETC. 



alternately, make the bird flap its wings. The other 
designs indicate the progress of construction as follows : — 
Take a sheet of ordinary writing paper and cut it so 
that it will form a perfect square. Fold this, as indicated 
in No. I, by the middle and the angles, and then turn 
down the angles as in 2, emphasizing the fold strongly, 
following a b only, and operating in this way on both 
sides of the four angles. You will then have turned down 
eight folds like a b, and your paper will have assumed the 




Fig. 102. — The Paper Bird. 

appearance of No. 3 diagram. Then fold the paper as 
No. 4, so as to accentuate the folds, which can be pressed 
with the nail ; it will then be easy by fastening the folds 
around the centre c to obtain fig. 5 from 4. Then turn 
the paper upside down, and bring up the two opposite 
folds as in diagram 6, and proceed to raise the points right 
and left, thus forming diagram 7. By extending the 
points d and / to right and left you will produce the 
appearance of the bird as in diagram 8. The head of 



MECHANICAL TOYS, ETC, 



r ', 1 



the bird can be supplied by turning down the point d. If 
now you hold the figure tenderly by the extremities, ■m 
and /«, you may produce the flapping of the wings. The 






2 


J \/.. .^ 


/ 




/^\ 




Fig. 103. — Mechanical Paper Bird— Manner of Construction. 

same movement may be made by holding the bird at ;//, 
and pulling its tail^ This toy requires little application 
to perfect — anyone hiay succeed in making it. 



132 



MECHANICAL TOYS, tie. 



TO CUT A CORD WITH THE HANDS. 

We have often seen grocers' assistants and others 
breaking the twine which they have tied round parcels 




Fig. 104. — Manner of cutting a Cord with the Hands. 



by a sudden pull, and you may have fancied this jerk 
sufficient to break the' string. Well, try ; you will injure 
or cut your hands and will not break the end. To succeed 
you must get the cord into a certain position, which we 
will tell you. 



MECHANICAL TOYS, ETC. ' 1 33 

Place in the left hand the cord you want to break, and 
pass one end of it over the other in the form of a cross, 
and wind round the fingers the end forming the small arm 
of the cross — you must leave it sufficiently long to make 
several turns. The other end is then wound round the, 
right hand, with some distance between the two hands. 
If your arrangement be correct the string ought to form 
a Y in the centre of the hand, as seen in the lower part of 
the illustration. Then grasping the end tightly in the 
right hand as in the upper part of the cut, bring the, hands 
close and jerk them quickly apart, and the cord will be 
cut at the point of intersection of the arms forming the Y, 
which act as a knife. If the cord be quickly jerked, the 
shock will not have time to communicate itself to the 
hands ; this is an interesting demonstration of the principle 
of inertia. ' 

Cords of considerable thickness can be thus severed 
without any ill effects. The most delicate hands may 
succeed in this experiment, provided the jerk be sudden 
and the twine properly^ arranged. With a little practice 
it can be done , rapidly, and the shop-assistants, who are 
very expert at it, never use knife or scissors. 



THE MAGIC PICTURE WITH THREE FACES. 

The following is the most simple method of making 
the toy. Cut three chromo-lithographs, which we will 
call A B C, on thin paper and of the same size, into 
strips. These strips being numbered right to left, we 
paste them down side by side upon a large sheet of this, 
paper, which is of the same height as one of the chromon 
but as long as all three together. We thus obtain a 
very extraordinary picture, in which are mixed up people 

lO 



134 



MECHANICAL TOYS, ETC. 



landscapes, flowers, and every other detail. The bands 
or strips only appear distinct in this uniform order — 
a\ h\ c\ 3?, b^, c^ and so on (Fig. 105). The gum being 
dry, we fold our picture accordion-fashion as in Fig. 105 ; 
fastening each to each behind, a b, etc., by the edges, the 
dihedral angle also appears, and we have then a series of 
small plans perpendicular to the ground plan. 

Seen full-face this picture presents the plan C, which 
seems to mark somewhat a grille formed by the edges of 
the two other plans. We then step a pace to the left of 





- Fig. 105. — The Magic Picture witli Tliree F^ces. 



the picture, and our eye passes in succession from the 
exterior edge of the facet a^ to the interior edge of the 
other facet a^, from 0? to a^, and so on, and perceive then 
the plan A without dissection, but lightly covered with 
a series of lines which in no wise detracts from its clear- 
One pace to the right and we see in the same 



ness. 



manner the section B — (See Frontispiece). 



IMITATION THUNDER. 

Ask some one to place his hands over his ears and pass 
above the hands around his head a cord in the manner 



MECHANICAL TOYS, ETC. 1 35 

shown in the illustration below (Fig. 106). If you rub 
the string lightly between the finger and thumb, drawing 
the hand along the cord, the subject will hear a loud 
rolling as of thunder. To properly produce the desired 
effect some precautions are necessary. We will mention 
them. Before reaching the end of the string you must 
seize it with the other hand at the point of departure • 




' Fig. loS.— The Rolling of Thunder Imitated. 



by so doing it will be possible to prolong the experiment 
for some time. 

If you grasp the string with the nails and draw the 
hand back by jerks you will produce short sharp peals of 
thunder, which can be changed into rolling peals at will 
by continuous rubbing. 



136 



MECHANICAL TOYS, ETC. 



THE MECHANICAL FLY. 

This fly, made of. polished metal some three inches 
,long, is suspended from the ceihng or chandelier by a 
-long thread. The "animal" contains a band of india- 
rubber, which is twisted round by a kind of handle. The 
untwisting of the india-rubber sets in motion a screw at 




Fig. 107. — The Mechanical Fly. 



the other end, by means of the cogged wheel delineated 
in the lower part of the illustration herewith (Fig. 107). 
A catch permits the release of the machinery at the 
desired moment. The screw imparts a rapid movement 
to the fly, and makes it fly in a circle around the point 
of suspension. 
"v 



MECHANICAL TOYS, ETC. 



137 



THE DOUBLE MARBLE. 

Place the middle finger of the hand under the index, 
and touch a marble with them in the manner shown 
below (Fig. 108). You will then experience the sensa- 
tion of touching two marbles. In normal conditions the 




Fig. 108.— The Dduble' Marble. 



ball cannot be touched at the same time by the exteriors" 
of two fingers of the same hand. When we cross our 
fingers, however, the normal conditions are changed, but 
the instinctive interpretation remains the same, so much 
sp that the frequent repetition of the experiment does not 



138 



MECHANICAL TOYS, ETC. 



confirm the first impressions. In fact, if the experiment 
be frequently repeated the illusion will become less and 
less marked. 

EXPERIMENT IN SOUND— ACOUSTICS. 

Sound is a sensation which affects our ears ; it is pro- 
duced by a cause exterior to the organ itself — generally 
by vibration of a body. This vibration is transmitted by 
the medium serving as a means of communication 
between nerves of hearing and the object vibrating. 

There are three different ways of producing sound, — 
by percussion, when objects strike each other ; by rubbing, 




109. — Wooden Whistle, which a Lad may make for Himself. 



as when a bow of a violin is drawn across the strings ; 
and by twanging the strings of an instrument. 

It is easy to prove that sound is transmitted in a 
perceptible space of time from one place to another. 
When at a distance we see a man hammering a nail, 
we perceive that the noise occasioned by the striking 
of the object does not reach our ears until some seconds 
after the moment of contact. We see the flash of a 
cannon before we hear the sound of the discharge, and 
lightning before thunder. 

We need not give any particular experiments here save 



MECHANICAL TOYS, ETC. 



139 



6ne — the Wooden Whistle, a toy much in vogue amongst 
school-boys. 

Take a piece of lilac or willow-wood, and cut the bark 
round it with a penknife in a circle. Moisten the bark, 
and then beat it on your knee with the handle of the 
knife. Then hollow out the pith, and you will have 
an ordinary whistle, as in a key. A, or by cutting the 





Fig. no. — The Fruiterer. 



Fig. III.— The Cobbler. 



wood (as shown in B and C) a true whistle can be 
fashioned (Fig. 109). 

An excellent whistle can be produced with the cowl of 
an acorn, which forms a small cup. Place this cup 
between the first and middle fingers, and close the fingers 
so that only a very small orifice is left. If you blow 
into this opening a whistle will result. 



I40 



MECHANICAL TOYS, ETC. 



PORTRAITS UNDER TWO ASPECTS. 

Drawings from two points of view, so to speak, have 
already had considerable success ; and chance has recently 
put in our possession a work by an artist named Galliot, 
published in Berlin. The author, under the title Arts 
and Professions, has drawn very amusing figures, which 
are really the result of a combination of the tools and 
utensils belonging to the trades or professions of the 





Fig. 112. — The Alchemist. 



Fig. 113.— The Brewer. 



people they represent.' We reproduce some of these 
essentially original compositions. The Fruiterer (Fig. 1 1 o) 
is composed of a melon, which forms the head ; an arti- 
choke, the stem of which forms the nose in profile ; a 
basket makes the .bust, while some vegetables form a 
collarette, etc. The Cobbler (Fig. in) is likewise repre- 
sented by the tools of his trade, notably the nose and 
chin ; the Alchemist (Fig. 112) is obtained by means 



MECHANICAL TOYS, ETC. 



141 



of a furnace and retorts ; the Brewer (Fig. 1 1 3) with a 
jug, a tub, a cask, and a funnel; the Artist (Fig. 114) 
with the palette and box of colours ; the Sportsman 
(Fig. 1 15) is composed of a gun, a powder-flask, and a 
hunting-horn ; and so on. We have here some amusing 
pictures, with which we may fitly conclude our recreations. 





Fig. 114.— The Artist. 



Fig. 115. — The Sportsman. 



The talented reader can exercise his pencil in other 
compositions. ' 

With these illustrations we bid our friends Farewell, 
We have endeavoured to indicate to them how they can 
occupy their leisure profitably, and with amusement to 
themselves at the same time. 



MARVELS OF TFIE ELEMENTS. 



PREFACE. 



To the child and the savage everything is equally strange 
and unknown. They do not even imagine that there are 
such things as elements and compounds. They see 
certain things, and they perceive or feel certain effects. 
Water boils and steam rises. Fire burns, and if a hot thing 
is touched pain is felt. Heat is the first thing the effects 
of which are noticed, in addition to such things as down- 
pour of rain and brightness of light followed by darkness. 
And from the study of the effects of heat many of our 
most important discoveries have arisen. 

It is very difficult to realise what an enormous step in 
advance was made when mankind first began to have 
some real knowledge about the various substances we see 
around us, to find out their differences, and to learn that 
they can be made to change in some regular ways by 
heat or by letting them mix with each other. The high 
position to which man had advanced before he began to 
find out these things may serve as one measure of the 
difficulty he had experienced in getting at nature's secrets. 
It was not till after the middle of the last century that 
Joseph Black, a professor at Edinburgh, arrived at the 
idea that heat positively disappears in melting ice, leaving 



vi PREFACE. 

the water produced from it no hotter thai; the ice, although 
much heat is needed to melt the ice. The same he found 
to be the case in changing water into steam. From this 
discovery came many others which have revealed new 
worlds to us in the substances which surround us, and 
not only so, but have given us the power of making a 
vast number of new substances previously unknown, some 
of which have proved of the utmost benefit, such as 
chloroform, while others are of much more doubtful value, 
such as dynamite. 

When it was discovered that in the heating of lime- 
stone to make quicklime a particular kind of air was 
given off, which we now call carbonic acid gas, and which 
was found to be poisonous, and that this gas was identical 
with a gas given off in the breath of animals, and which 
will render the air of any room poisonous if the ventila- 
tion is bad, a most important means of advance was put 
in the chemist's hand. What did it mean, that a gas 
could be locked up, as it were, in a solid stone and then 
given out again by heating it, and that the same gas 
should come out of the bodies of men and animals } Till 
those questions were answered there could be no rest for 
the mind anxious to know something of the secrets of 
nature, and the chemist and natural philosopher have 
gone on and on until they have conquered those secrets 
and a multitude more beside. 

By the light of modern chemistry we find a remarkable 
interest attaching to the commonest substances. Our 
table salt is found to be so universally diffused that it is 
scarcely absent anywhere in nature. Its salt taste appears 



PREFACE. vii 

to be far removed from sourness ; yet from it can be got 
one of the sourest of acids, once known as spirit of salt, 
now called muriatic or hydrochloric acid. From the 
tasteless gypsum or alabaster, and also from the un- 
pleasant Epsom salts, can be extracted the terribly 
corrosive oil of vitriol. The purgative calomel and the 
poisonous corrosive sublimate are found to be near neigh- 
bours in composition, simply differing in the proportions 
of their elements. A dull stone yields a bright metal, 
and a light or a heavy gas. The resplendent diamond is 
nothing but a morsel of charcoal in a different condition. 
Water can be split up into two gases, one of which we can 
breathe and the other not. The air is a mixture princi- 
pally of two gases, one of which by itself would hurry 
our life too fast, the other of which is quite inactive upon 
us. This is but a sample of the marvels of chemistry, 
and the list might be indefinitely prolonged. 

And. all these strange phenomena have been brought 
under laws which can be understood as well as we under- 
stand anything. They have their appropriate places in 
the scheme of the universe, and furnish us with endless 
sources of pleasure and profit. Surely even those who 
have least leisure may afford time to enter into conversa- 
tion, as it were, with the Maker of the universe as to the 
laws which it has pleased Him to impose upon ft, and by 
which all things are ordered, a.nd subsist even to this day. 
No more worthy object can be set before the intelligent 
mind than an acquaintance with his Maker's works, which 
in all their forms show, if but partially, and through a veil, 
the impression of ^ marvellous mind and energy, if w? 



vni PREFACE. 

may apply such terms to Him Who " rolls the stars along." 
The very fact that man has been gifted with a mind 
capable of discovering these laws of his Maker proves 
unmistakably that he is intended to know them and to 
make use of them. 

The youth who reads such a work as this should reflect 
that he is here gathering up the knowledge acquired by 
the slow and painful toil and thought of generations of 
the wisest and most patient men who have ever lived. 
Often in poverty, frequently persecuted, thought silly or 
over-presumptuous by their contemporaries, they per- 
severed in spite of all, and found in nature and nature's 
God a rich reward for all their toil. We in the present 
generation reap where we have not sowed ; other men 
have studied, and we derive the profit. The least we can 
do is to endeavour to understand what they so laboriously 
acquired, and in our degree to carry on the work they 
began, not living as if blind in the midst of light, not 
resting content in the material advantages which the 
labours of our predecessors have gained for us, not 
resigning ourselves to disastrous indolence, but rousing 
our manhood, developing our thoughts, raising our ideas 
to the regions which still remain beyond our thought, 
feeding the highest parts of our nature with the thought of 
the marvels which eye hath not seen, ear hath not heard, 
nor hath it yet entered into the heart of man to conceive. 



CONTENTS. 



PAGE 

CHAPTER I. 

INTRODUCTION I 

CHAPTER II. 

CHEMISTRY WITHOUT A LABORATORY 10 

CHAPTER III. 

CHEMISTRY AND ALCHEMY 46 

CHAPTER IV. 

NON-METALLIC ELEMENTS 65 

CHAPTER V. 

NON-METALLIC ELEMENTS {continued) 9^ 

CHAPTER VI. 

THE METALS '^4 

CHAPTER VII. 

pRGAfTIC CPEMIST^Y 1 6° 



THE MARVELS OF THE ELEMENTS. 




CHAPTER I.— INTRODUCTION. 

WHAT CHEMISTRY IS — THE ELEMENTS — METALLIC AND 

NON-METALLIC ATOMIC WEIGHT ACIDS — ALKALIS 

— BASES — SALTS — CHEMICAL COMBINATION AND 
STUDY. 

[KEMISTRY is the science of phenomena which 
are attended by a change of the objects which 
produce them. We know that when a candle 
burns, or when wood is burned, or even a piece 
of metal becomes what we term " rusty," that certain 
chemical changes take place. There is a change by what 
is termed chemical action. Rust on iron is not iron ; it 
is oxide of iron. The oxygen of the air causes it. So 
we endeavour, by Chemistry, to find out the nature of 
various bodies, their changes, and the results. 

In nature we have simple and compound bodies. The 
former are called ELEMENTS. We must not confuse these 
elements with the so-called elements — earth, air, fire, and 
water. Those are really compound bodies. An element 
is a substance or a gas which is not composed of more 
than one constituent ; it is itself — a compound of perfectly 
identical particles. Every " compound " body, therefore, 
must be made up of some of the elements, of which there 
are sixty-five. These bodies are divided into non-metallic 
and metallic elements, and all bodies are composed of 



CHEMISTRY. 



them, or are these bodies themselves. The list is as 
follows. The ^on-metallic elements are " metalloids." 
We have omitted fractions from the weights, on which 
chemists differ. 

TABLE OF ELEMENTS WITH THEIR CHEMICAL 
SYMBOLS AND COMBINING WEIGHTS. 



Non-Metallic 
Elements. 

Oxygen 

Hydrogen 

Nitrogen 

Chlorine 

Iodine 

Fluorine 

Carbon 

Sulphur 

Phosphorus 

Arsenic* 

Silicon 

Boron 

Silenium 

Tellurium 

Bromine . 



Symbols. 

o 

Gaseous < N 

(ci 

/I 
F 

C , 

S , 

P , 

As. 

Si , 

B , 

Se, 

.Te, 

Fluid , 



>• Solid ■{ 



Atomic or 

Combining Derivation of Name. 

Weights. 

. i6 . Gr. Oxus, acid ; gennao, to make. 

I . Gr. Udor, water ; gennao, to make. 

. 14 . Gr. Natron, nitre ; gennao, to make. 

. 35 . Gr. Chloros, green. 

. 127 . Gr. loeides, violet. 

. 19 . Fluor spar, the mineral. 

. 12 . Lat. Carbo, coal. 

, 32 . Lat. Sulphurium. 

31 . Gr. Phos, light ; pherein, to carry. 

75 . Gr. Arsenicon, potent. 

, 23 . Gr. Silex, flint. 

1 1 . Gr. Borax, Arab., baraga, to shine. 

, 79 . Gr. Selene, the moon. 

.129 . Lat. Tellus, the earth. 

. 80 . Gr. Bromos, offensive smell. 



METALS. 



Name. 

Aluminium 

Antimony 

(Stibium) 

[Arsenic] 

Barium 

Bismuth 

Cadmium 

Caesium 

Calcium 

Cerium 

Chromium 

Cobalt 



Atomic or 
Symbols. Combining 
Weights. 



Al 

Sb 

As 
Ba 
Bi 
Cd 
Cs 
Ca 
Ce 
Cr 
Co 



27 
122 

75 
137 
210 
112 

133 

40 

141 

52 

58 



Derivation. 

Lat. Alumen, alum. 

Gr. Anti, against ; minos, one. 

Gr. Barsu, heavy. 

Ger. Weissmuth, white matter. 

Gr. Cadmeia, calamite. 

Lat. Caesius, sky-blue. 

Lat. Calx, lime. 

The planet Ceres. 

Gr. Chroma, colour. 

Ger. Kobald, a sprite. 



* Arsenic is sometimes considered a non-melallic and sometimes a metallic substance. 



THE ELEMENTS. 



METALS (continued). 







Atomic 


or 


Naiae. ! 


Symbols, 


Combining Deriyation. 

Weight" 


Copper • . 


Cu . 


63 . 


Lat. Cuprum (Cyprium), Cyprus. 


Didymium . 


D . 


147 . 


Gr. Didumos, twins. 


Erbium . 


E . 


— . 


Ytterby in Sweden. 


Gallium . 


Ga . 


70 . 


(Not known.) 


Glucinum . . 


Gl . 


9 • 


Gr. Glukos, sweet. 


Gold 


Au , 


197 . 


From Hebrew, to shine (doubtful). 


Indium . . 


In . 


"3 . 


Indigo colour. 


Iridium . • 


Ir . 


198 . 


Gr. Iris, rainbow. 


Iron 


Fe . 


56 . 


Hebrew, to meet (doubtful). 


Lanthanum . 


La . 


139 • 


Gr. Lanthanein, to lie hid. 


Lead . . 


Pb . 


207 , 


(Plumbum) malubodos (galena). 


Lithium . • 


Li . 


7 ■ 


Gr. Lithos, stone. 


Magnesium • 


Mg. 


24 . 


Magnesia, Asia Minor. 


Manganese i 


Mn. 


55 • 


Mangana, E. I. (or Magnesia). 


Mercury . . 


Hg- 


200 . 


Heathen deity (quick). 


Molybdenum . 


Mo . 


96 . 


Gr. Molybdena, lead ore, like lead. 


Nickel . 


Ni . 


58 . 


Ger. Kupfer nikel, false copper. 


Niobium(Columbium) Nb . 


94 . 


Columbite. 


Osmium . 


Os . 


199 . 


Osme, an odour. 


Palladium . 


PI . 


106 . 


Pallas, Minerva. 


Platinum , 


Pt . 


197 . 


Spanish, platina, little silver. 


Potassium (Kalium) 


K . 


39 • 


Potash. 


Rhodium 


Rh . 


104 . 


Gr. Roda, rose. 


Rubidium 


Rb 


85 . 


Lat. Rubidus, red. 


Ruthenium 


Ru . 


104 . 


(Not known.) 


Silver (Argentum) 


Ag 


108 


Hebrew, money. 


Sodium (Natrum) 


Na 


• 23 


Salsoda plant. 


Strontium 


Sr 


. 87 


Strontian, N.B. 


Tantalum 


Ta 


. 182 


Tantalite mineral 


Terbium • 


Tr 


. — 


(Not known.) 


Thallium 


Tl 


. 204 


Gr. Thallos, green twig. 


Thorium . 


Th 


. 230 


. Thor, deity. 


Tin (Stannum) . 


Sn 


. 118 


. (Not known.) 


Titanium 


Ti 


. so 


. Titans. 


Tungsten (Walpam) 


W 


. 184 


. Swedish. 


Uranium . " . 


U 


. 240 


. Urania. 


Vanadium . 


V 


• SI 


. Vanadis, a goddess in Sweden, etc. 


Yttrium . • 


Y 


• 93 


. (Not known.) 


Zinc • • 


Zn 


. 6s 


. Ger. Zinken, nails. 


Zirconium . • 


Zr 


. 89 


. Ger.Zircon,four-cornered(Ceylon) 



4 CHEMISTRY. 

The term " combining weight" requires a little explana- 
tion. We are aware that water, for instance, is made up 
of oxygen and hydrogen in certain proportions. This we 
will prove by-and-by. The proportions are in eighteen 
grains or parts of water, sixteen parts (by weight) of 
oxygen, and two parts (by weight) of hydrogen. These 
are the weights or proportions in which oxygen and 
hydrogen combine to form water, and such weights are 
always the same in these proportions. Chemical com- 



li. 



Liwii '<«■;>, w'lpu^^f HI 









It EM 
i; RK., 

'' J i "^' 1 



^**^'^4?* t i^ 1' 



Xil 






II 



The Laboratory. 



bination always occurs for certain substances in certain 
proportions which never vary in those compounds, and if 
we wish to extract oxygen from an oxide we must take 
the aggregate amount of the combining weights of the 
oxide, and we shall find the proportion of oxygen ; for 
the compound always weighs the same as the sum of the 
elements that compose it. To return to the illustration 
of water. The molecule of water is made up of one 
atom of oxygen and two atoms of hydrogen. One atom 



ATOMS AND MOLECULES. 5 

of the former weighs sixteen times the atom of the latter. 
The weights given in the foregoing table are atomic 
weights, and the law of their proportions is called the 
Atomic Theory. 

An atom in chemistry is usually considered the smallest 
quantity of matter that exists, and is indivisible. A 
molecule is supposed to contain two or more atoms, and 
is the smallest portion of a compound body. The standard 
atom is hydrogen, which is put down as i, because we 
find that when one part by weight of hydrogen is put in 
combination, it must have many more parts by weight of 
others to form a compound. Two grains of hydrogen, 
combining with sixteen of oxygen, make eighteen of 
water, as we have already seen. 

Take an example so plainly given by Professor Roscoe, 
remembering that the numbers" in our table represent the 
fixed weight or proportion by weight in which the simple 
body combines. The red oxide of mercury contains six- 
teen parts by weight of oxygen to two hundred parts by 
weight of mercury (we see the same numbers in the table) ; 
these combined make two hundred and sixteen parts of 
oxide. So to obtain i6 lbs. of oxygen we must get 
216 lbs. of the powder. It is the same all through, and 
it will be found by experiment that if any more parts than 
these fixed proportions be taken to form a compound, 
some of that element used in excess will remain free. 
Lime is made up of calcium and oxygen. We find calcium 
combining weight is forty, oxygen sixteen. Lime is oxide 
of calcium in these proportions (by weight). 

When we wish to express the number of atoms in a 
compound we write the number underneath when more 
than one; thus water is Hp. Sulphuric acid H^SO^. As 
we proceed we will give the various formula when con- 
sidering the chief elements. 

In chemistry we have acids, alkalis, and salts, with 



6 CHEMISTRY. 

metallic oxides, termed bases, or bodies, that when com- 
bined with acids form salts. Alkalis are bases. 

Acids are compounds which possess an acid taste, im- 
part red colour to vegetable blues, but lose their qualities 
when combined with bases. Hydrogen is present in all 
acids. There are insoluble acids. Silicic acid, for instance, 
is not soluble in water, has no sour taste, and will not 
redden the test litmus paper. On the other hand, there 
are substances (not acids) which possess the characteristics 
of acids, and most acids have only one or two of these 
characteristics. 

Thus it has come to pass that the term " acid" has in a 
measure dropped out from scientiiic nomenclature, and salt 
of hydrogen has been substituted by chemists. For 
popular exposition, however, the term is retained. 

Alkalis are bases distinguished by an alkaline taste. 
The derivation is from Arabic, al-kali. They are charac- 
terized by certain properties, and they change vegetable 
blues to green, and will restore the blue to a substance 
which has been reddened by acid. They are soluble in 
water, and the solutions are caustic in their effects. Potash, 
soda, and ammonia are alkalis, or chemically, the oxides of 
potassium ; sodium, ammonium, lithium, and caesium are all 
alkalis. Potash is sometimes called "caustic" potash. 
There are alkaline earths, such as oxides of barium, stron- 
tium, etc. Bases may be defined as the converse of acids. 

Acids and alkalis are then evidently opposite in char- 
acter, and yet they readily combine, and in chemistry we 
shall find that unlike bodies are very fond of combining 
(just as opposite electricities attract each other), and the 
body made by this combination differs in its properties 
from those of its constituents. 

Salts are composed of acids and bases, and are con- 
sidered neutral compounds, but there are other bodies not 
salts, which likewise come under that definition — sugar^ for 



PliEPARAtlOlSfS. 7 

« 
instance. As a rule, when acids and alkalis combine salts 

are found. 

Chemical phenomena are divided into two groups, called 
inorganic and organic, comprising the simple and com- 
pound aspects of the subject, the elementary substances 
being in the first, and the chemistry of animals or vege- 
tables, or organic substances, in the latter. In the inorganic 
section we shall become acquainted with the elements and 




IHTj. ■[_ 



I 



. Laboratory furnace. 

their combinations so often seen as minerals in nature. 
Chemical preparations are artificially prepared. To con- 
sider these elements we must have certain appliances, and 
indeed a laboratory is needed. Heat, as we very commonly 
see, plays a great part in developing substances, and by 
means of heat we can do a great deal in the way of 
chemical decomposition. It expands, and thus diminishes 
cohesion ; it counteracts the chemical attraction. Light 



8 CHEMISTRY. 

and electricity also decompose chemical combinations. But 
before proceeding it will be as well to notice a few facts 
showing how Nature has balanced all things. 

The earth, and its surrounding envelope, the atmo- 
sphere, consist of a number of elements, which in myriad 
combinations give us everything we possess, — the air we 
breathe, the water we drink, the fire that warms us, are all 
made up of certain elements or gases. Water, hydrogen 
and oxygen ; air, oxygen and nitrogen. Fire is combus- 
tion evolving light and heat. Chemical union always 
evolves heat, and when such union proceeds very rapidly 
fire is the result. 

In all these combinations we shall find when we study 
chemistry that not a'particle or atom of matter is ever lost. 
It may change or combine or be " given' off," but the 
matter in some shape or way exists still. We may burn 
things, and rid ourselves, as we think, of them. We do rid 
ourselves of the compounds, the elements remain some- 
where. We only alter the condition. During combustion, 
as in a candle or a fire, the simple bodies assume gaseous 
or other forms, such as carbon, but they do not escape far. 
True they pass beyond our ken, but nature is so nicely 
balanced that there is a place for everything, and every- 
thing is in its place under certain conditions which never 
alter. We cannot destroy and we cannot create. We 
may prepare a combination, and science has even suc- 
ceeded in producing a form like the diamond — a crystal 
of carbon which looks like that beautiful of all crystals, 
but we cannot make a diamond after all. ' We can only 
separate the chemical compounds. We can turn diamonds 
into charcoal it is true, but we cannot create " natural " 
products. We can take a particle of an element and hide 
it, or let it pass beyond our ken, and remain incapable of 
detection, but the particle is there all the time, and when 
we retrace our steps we shall find it as it was before. 



A PASTIME. 9 

This view of chemistry carries it as a science beyond 
the mere holiday amusement we frequently take it to be. 
It is a grand study, a study for a lifetime. Nature is 
always willing, like a kind, good mother as she is, to render 
us up her secrets if we inquire respectfully and lovingly. 
The more we inquire the more we shall find we have to 
learn. In these and the following pages we can only tell 
you a few things, but no one need be turned away because 
he does not find all he wants. We never do get all we 
want in life, and there are many first-rate men — scientists 
— who would give " half their kingdom " for a certain bit 
of knowledge concerning some natural phenomena. There 
are numerous excellent treatises on chemistry, and exhaus- 
tive as the}' are, at present they do not tell us all. Let 
these popular pages lead us to the study of nature, and we 
shall find our labour far from onerous and full of interest, 
daily increasing to the end, when we shall know no more 
of earth, or chemistry. 

As a preliminary we will put our workshop aside, and 
show you something of Chemistry ivithout a Laboratory. 





CHAPTER II.— CHEMISTRY WITHOUT A 
LABORATORY. 

AMMONIUM — PHARAOH'S SERPENTS SALTS AND 

ACIDS VARIOUS EXPERIMENTS. 

fE have elsewhere shown the possibility of 
going through a course of physics without any 
special apparatus ; we shall now endeavour to 
show our readers the method of performing 
some experiments in chemistry without a laboratory, or at 
any rate with only a few simple and inexpensive appliances. 
The preparation of gases, such as hydrogen, carbonic acid, 
and oxygen, is very easily accomplished, but we shall here 
point out principally a series of experiments that are not 
so much known. We will commence by describing an in- 
teresting and rather dangerous experiment which often 
occurs in a course of chemistry. Ammoniacal gas combined 
with the elements of water is analogous to a certain metallic 
oxide which includes a metallic root, ammonium. This 
hypothetically composed metal may be in a manner per- 
ceived, since it is possible to amalgamate it with mercury by 
operating in the following manner : — We take a porcelain 
mortar, in which we pour a quantity of mercury, and then 
cut some thin strips of sodium, which are thrown into the 
mercury. By stirring it about with the pestle a "loud 
cracking is produced, accompanied by a flame, which bears 
evidence to the union of the mercury and the sodium, and 
the formation of an amalgam of sodium. If this amalgam 
of sodium is put into a slender glass tube containing a 
concentrated solution of hydrochlorate of ammonia in 



AMMONIUM. 



I I 



water, we see the ammonia expand in an extraordinary- 
manner, and spout out from the end of the tube, which is 
now too small to contain it, in the form of a metallic 
substance (see below). In this case, the ammonium, the 
radical which exists in the ammoniacal salts, becomes 
amalgamated with the mercury, driving out the sodium 
with which it had previously been combined ; the am- 
monium thus united with the mercury becomes decomposed 
in ammoniacal gas and hydrogen, the mercury assuming 




Experiment with ammonium. 

its ordinary form. Phosphate of ammonia is very valuable 
from its property of rendering the lightest materials, such 
as gauze or muslin, incombustible. Dip a piece of muslin 
in a solution of phosphate of ammonia, and dry it in con- 
tact with the air ; that done, you will find it is impossible 
to set fire to the material ; it will get charred, but you 
cannot make it burn. It is to be wished that this useful 
precaution were oftener taken in the matter of ball-dresses, 



1 2 CHEMISTRY. 

which have so frequently been the cause of serious acci- 
dents. There is no danger whatever with a dress that 
has been soaked in phosphate of ammonia, which is very 
inexpensive, and easily procured. 

For preparing cool drinks in the summer ammoniacal 
salts are very useful ; some'nitrate of ammonia mixed with 
its weight in water, produces a considerable lowering of the 
temperature, and is very useful for making ice. Volatile 
alkali, which is so useful an application for stings from 
insects, is a solution of ammoniacal gas in water, and sal- 
volatile, which has such a refreshing and reanimating 
odour, is a carbonate of ammonia. We often see in 
chemists' shops large glass jars, the insides of which are 
covered with beautiful transparent white crystals, which 
are formed over a red powder placed at the bottom of the 
vase. These crystals are the result of a combination of 
cyanogen and iodine. Nothing is easier than the prepara- 
tion of iodide of cyanogen, a very volatile body, which 
possesses a strong tendency to assume a definite crystalline 
form. We bruise in a mortar a mixture of fifty grams of 
cyanide of mercury, and one hundred grams of iodine ; 
under the pestle, the powder, which was at first a 
brownish colour, assumes a shade of bright vermilion red. 
The cyanogen combines with the iodine, and transforms 
itself into fumes with great rapidity. If the powder is 
placed at the bottom of a stoppered glass jar, the fumes 
of the iodide of cyanogen immediately condense, thereby 
producing beautiful white crystals which often attain a large 
size (page 1 3). Cyanogen forms with sulphur a remarkable 
substance, sulpho-ryanogen, the properties of which we can- 
not describe without exceeding the limits of our present 
treatise ; we shall therefore confine ourselves to pointing 
out one of its combinations, which is well known at the 
present day, owing to its singular properties. This is 
sulpho-cyanide of mercury, with which small combustible 



PHARAOH'S SERPENTS. 



13 



cones are made, generally designated by the pompous title 
of Pliaraolis serpents. For making these, some sulpho- 
cyanide of potassium is mixed into a solution of nitric 
acid on mercury, which forms a precipitate of sulpho- 
cyanide of mercury. This is a white, combustible powder, 
which after passing through a filter, should be trapsformed 
into a stiff paste by means of water containing a solution of 
gum. The paste is afterwards mixed with a small quantit}- 
of nitrate of potash, and fashioned into cones or cylinders 



^5: ■ ' ^ iCn^ 




Iodide of cyanogen. 

of about an inch and a quarter in length, which should be 
thoroughly dried. The "egg" thus obtained can be hatched 
by the simple application of a lighted match, and gives 
rise to the phenomenon. The sulpho-'cyanide slowly ex- 
pands, the cylinder increases in length, and changes to a 
yellowish substance, which dilates and extends to a length 
of twenty* or five-and-twenty inches. It has the appear- 
ance of a genuine serpent, which has jiist started into 



14 



CHEMISTRY. 



existence, and stretches out its tortuous coils, endeavour- 
ing to escape from its narrow prison (see below). Ihe 
residue— which all readers should be careful about where 




Pharaoh's serpent. 



children are — constitutes a very poisonous substance, 
which should be immediately thrown away or burned. It 
can be easily powdered into dust in the fingers. During 



SALT. 



IS 



the decomposition of the sulpho-cyanide of mercury, 
quantities of sulphurous acid are thrown off, and it is to be 
regretted that Pharaoh's serpent should herald his appear- 
ance by such a disagreeable, suffocating odour. 

After these few preliminary experiments, we will en- 
deavour to show the interest afforded by the study of 
chemistry in relation to the commonest substances of 
every-day life. We will first consider the nature of a few 
pinches of salt. We know that kitchen salt, or sea salt, 
is white or greyish, according to its degree of purity ; that 
it has a peculiar flavour, is soluble in water, and makes a 
peculiar crackling when thrown in the fire. But though 
its principal physical properties may be familiar enough, 
many people are entirely ignorant of its chemical nature 
and elementary composition. . Kitchen salt contains a 
metal, combined with a gas possessing a very suffocating 
odour ; the metal is sodium, the gas is cJilorine. The 
scientific name for the substance is chloride of sodium 
(salt).* The metal contained in common salt in no way 
resembles ordinary metals ; it is white like silver, but tar- 
nishes immediately in contact with air, and unites with 
oxygen, thus transforming itself into oxide of sodium. To 
preserve this singular metal it is necessary to protect it 
from the action of the atmosphere, and to keep it in a 
bottle containing oil of naphtha. Sodium is soft, and it is 
possible with a pair of scissors to cut it like a ball of soft 
bread that has been kneaded in the hand. It is lighter 
than water, and when placed in a basin of water floats on 

* It is the same with a number of other common products, such as 
clay, sandstone, etc., the composition of which chemistry has revealed. 
Argil, or clay, slate, and schist all contain a metal — aluminium, which 
has become most valuable for industrial purposes. Stones for building 
are composed of a metal combined with carbon and oxygen — calcium s 
sandstone is composed of silicium, a metallic body united with oxygen ; 
and sulphate of magnesia, which enters into the composition of a pur- 
gative drink, also contains a m^tA— magnesium. 



i6 



CHEMISTRY. 



the top like a piece of cork ; only it is disturbed, and takes 
the form of a small brilliant sphere ; great effervescence is 
also produced as it floats along, for it reduces the water 
to a common temperature by its contact. By degrees the 
small metallic ball disappears from view, after blazing into 
flame (see below). 

This remarkable experiment is very easy to carry out, 
and sodium is now easily procured at any shop where 
chemicals are sold. The combustion of sodium in water 
can be explained in a very simple manner. Water, as we 
know, is composed of hydrogen and oxygen. Sodium, by 
reason of its great affinity for the latter gas, combines 

with it, and forms a very 
soluble oxide ; the hydrogen 
is released and thrown off, 
as we shall perceive by 
placing a lighted match in 
the jar, when the combus- 
tible gas ignites. 

Oxide of sodium has a 
great affinity for water ; it 
combines with it, and absorbs 
it in great quantities. It is 
a solid, white substance, which burns and cauterizes the 
skin ; it is also alkaline, and brings back the blue colour 
to litmus paper that has been reddened by acids. 

Sodium combines easily also with chlorine. If plunged 
into a jar containing this gas it is transformed into a sub- 
stance, which is sea salt. If the chlorine is in excess a 
part of the gas remains free, for simple substances do not 
mingle in undetermined ratios ; they combine, on the con- 
trary, in very definite proportions, and 35-5 gr. of dry 
chlorine always unites with the same quantity of soda 
equal to 23 grams. A gram of kitchen salt is formed, 
therefore, of o'6o6 gr. of chlorine, and 0*394 gr. of sodium. 




Combustion of sodium in water. 



GLAUBER'S SALTS. 1 7 

Besides sea salt, there are a number of different salts which 
may be made the object of curious experiments. We 
know that caustic soda, or oxide of sodium, is an alkaline 
product possessing very powerful properties ; it burns the 
skin, and destroys organic substances. 

Sulphuric acid is endowed with no less powerful pro- 
perties ; if a little is dropped on the hand it produces great 
pain and a sense of burning ; a piece of wood plunged into 
this acid is almost immediately carbonized. If we mix 
forty-nine grams of sulphuric acid and thirty-one grams of 
caustic soda a very intense reaction is produced, accom- 
panied by a considerable elevation of temperature ; after it 
has cooled we have a substance which can be handled with 
impunity ; the acid and alkali have combined, and their 
properties have been reciprocally destroyed. They have 
now originated a salt which is sulphate of soda. This 
substance e3?ercises no influence on litmus paper, and re- 
sembles in no way the substances from which it originated. 

There are an infinite number of salts which result in 
like manner from the combination of an acid with an 
alkali or base. Some, such as sulphate of copper, or 
chromate of potash, are coloured ; others, like sulphate of 
soda, are colourless. The last-mentioned salt, with a 
number of others, will take a crystalline form ; if dissolved 
in boiling water, and the solution left to stand, we shall 
perceive a deposit of transparent prisms of very remark- 
able appearance. This was discovered by Glauber, and 
was formerly called Glauber's salts. 

Sulphate of soda is very soluble in water, and at a tem- 
perature of thirty-three (Centigr.) water can dissolve it in 
the greatest degree. If we pour a layer of oil on a solution 
saturated with Glauber's salts, and let it stand, it will not 
produce crystals ; but if we thrust a glass rod through the 
oil into contact with the solution, crystallization will be 
instantaneous. This singular phenomenon becomes even 



i8 



CHEMISTRY. 



more striking when we put the warm concentrated solution 
into a slender glass tube, A B, which we close after having 
driven out the air by the bubbling of the liquid (see below). 
When the tube has been closed, the crystals of sulphate 
of soda will not form, even with the temperature at zero ; 
nevertheless the salts, being less soluble cold than hot, are 
found in the fluid in a proportion ten times larger than 
they would contain under ordinary conditions. If the end 




Pveparation of a solution saturated with sulphate of soda. 

of the tube be broken the salt will crystallize immediately 
We will describe another experiment, but little known and 
very remarkable, which exhibits in a striking manner the 
process of instantaneous crystallizations. Let one hundred 
and fifty parts of hyposulphite of soda be dissolved in 
fifteen parts of water, and the solution slowly poured into 
a te.st-glass, previously warmed by means of boiling wa^er 
until the vessel is about half-full. One hundred parts of 
acetate of soda is then dissolved in fifteen parts of water 



CRYSTALLIZATION. 



19 



and poured slowly into the first solution, so that they form 
two layers perfectly distinct from each other. The two 
solutions are then covered with a little boiling water, 
which, however, is not represented in our illustration. 
After it has been left to stand and cool slowly, we have 
two solutions of hyposulphite of soda and acetate of soda 




Expenment of instantaneous crystallization. 

superposed on each other. A thread, at the end of which 
is fixed a small crystal of hyposulphite of soda, is then 
lowered into the test-glass ; the crystal passes through the 
solution of acetate without disturbing it, but it has scarcely 
reached the lower solution of hyposulphite when the salt 
crystallizes instantaneously. {See the test-glass on the left 



20 CHEMISTRY. 

of page 1 9.) , We then lower into the upper solution a 
crystal of acetate of soda, suspended from another thread. 
This salt then crystallizes also. {See experiment glass on 
the right of page 19.) This very successful experiment 
is one of the most remarkable belonging to the subject 
of instantaneous crystals. The successive appearance of 
crystals of hyposulphite of soda, which take the form of 
large, rhomboidal prisms, terminating at the two extremi- 
ties with an oblique surface, and the crystals of acetate 
of soda, which have the appearance of rhomboidal, oblique 
prisms, cannot fail to strike the attention and excite the 
interest of those who are not initiated into these kinds of 
experiments. 

Another remarkable instantaneous crystallization is that 
of alum. If we leave standing a solution of this salt it 
gradually cools, at -the same time becoming limpid and 
clear. When it is perfectly cold, if we plunge into it a 
small octahedral crystal of alum suspended from a thread, 
we perceive that crystallization instantly commences on 
the surface of the small crystal ; it rapidly and perceptibly 
increases in size, until it nearly fills the whole jar. 

Common Metals and Precious Metals, 

How many invalids have swallowed magnesia without 
suspecting that this powder contains a metal nearly as 
white as silver, and as malleable, and capable of burning 
with so intense a light that it rivals even the electric light 
in brilliancy ! If any of our readers desire to prepare 
magnesium themselves it can be done in the following 
manner : — Some white magnesia must be obtained frbm 
the chemist, and after having been calcined, must be sub- 
mitted to the influence of hydrochloric acid and hydro- 
chlorate of ammonia. A clear solution will thus be 
obtained, which by means of evaporation under the in- 
fluence of heat, furnishes a double chloride, hydrated and 



MAGNESIA. 2 1 

crystallised. This chloride, if heated to redness in an 
earthenware crucible, leaves as a residue a nacreous pro- 
duct, composed of micaceous, white scales, chloride of 
anhydrous magnesium. 

If six hundred grams of this chloride of magnesium are 
mixed with one hundred grams of chloride of sodium, or 
kitchen salt, and the same quantity of fluoride of calcium 
and metallic sodium in small fragments, and the mixture 




Group of alum crystals. 

is put into an earthenware crucible made red-hot, and 
heated for a quarter of an hour under a closed lid, we shall 
find on pouring out the fluid on to a handful of earth, 
that we have obtained instead of scoria, forty-five grams of 
metallic magnesium. The metal thus obtained is impure, 
and to remove all foreign substances it must be heated in a 
charcoal tube, through which passes a current of hydrogen. 
Magnesium is now produced in great abundance, and 
is very inexpensive. It is a metal endowed with a great 



2 2 CHEMISTRY. 

affinity for oxygen, and it is only necessary to thrust it 
into the flame of a candle to produce combustion ; it burns 
with a brightness that the eye can scarcely tolerate, and is 
transformed into a white powder — oxide of magnesium, or 
magnesia. Combustion is still more active in oxygen, 
and powder of magnesium placed in a jar filled with this 
gas produces a perfect shower of fire of very beautiful 
effect. To give an idea of the lighting power of mag- 
nesium, we may add that a wire of this metal, which is 
^^Q of a millimetre in diameter, produces by combustion 
a light equal to that of seventy-four candles. 

The humble earth of the fields — the clay which is used 
^,.,,, in our potteries,alsocontains aluminium, 

f^'""' Ia that brilliant metal which is as malle- 

\ \ able as silver, and unspoilable as gold. 

When clay is submitted to the influence 
of sulphuric acid and chloride of pota- 
sium, we obtain alum, which is a sul- 
phate of alumina and potash. Alum 
is a colourless salt, which crystallizes 
on the surface of water in beautiful 
octahedrons of striking regularity. The 
Calcined alum. |^g_ ^^ page 21 represents a group of 
alum crystals. This salt is much used in the colouring of 
fabrics ; it is also used for the sizing of papers, and the 
clarification of tallow. Doctors also use it as an astrin- 
gent and caustic substance. When alum is submitted to 
the action of heat in an earthenware crucible, it loses the 
water of crystallization which it contains, and expands in 
a singular manner, overflowing from the jar in which it is 
calcined (see above). Iron, the most important of common 
metals, rapidly unites with oxygen, and, as we know, when 
a piece of this metal is exposed to the influence of damp 
air, it becomes covered with a reddish substance. In the 
well-known experiment of the formation of rust, the iron 




IRON. 



23 



gradually oxidises without its temperature rising, but this 
combination of iron with oxygen is effected much more 
rapidly under the influence of heat. If, for example, we 
redden at the fire a nail attached to a wire, and give it a 
movement of rotation as of a sling, we see flashing out 
from the metal a thousand bright sparks due to the com- 
bination of iron with oxygen, and the formation of an 
oxide. Particles of iron burn spontaneously in contact 
with air, and this property for many centuries has been 
utilized in striking a tinder-box ; that is to say, in sepa- 




Preparation of metallic iron. 

rating, by striking a flint, small particles of iron, which ignite 
under the influence of the heat produced by the friction. 
We can prepare iron in such atoms that it ignites at an 
ordinary temperature by simple contact with the^air. To 
bring it to this state of extreme tenuity, we reduce its 
oxalate by hydrogen. We prepare an apparatus for 
hydrogen as shown above, and the gas produced at A 
is passed through a desiccative tube, B, and finally reaches 
a glass receptacle, c, in which some oxalate of iron is placed. 
The latter salt, under the combined influence of hydrogen 
and heat, is reduced to metallic iron, which assumes the 



24 



CHEMISTRY. 



appearance of a fine black powder. When the experiment 
is completed the glass vessel is closed, and the iron, thus 
protected from contact with the air, can be preserved in- 
definitely ; but if it is exposed to the air by breaking off 
the end of the receptacle (see below), it ignites immediately, 
producing a shower of fire of very beautiful effect. Iron 
thus prepared is known under the name oi pyrophoric iron. 
Iron is acted upon in a very powerful manner by most 




Pyrophoric iron. 

acids. If some nitric acid is poured on iron nails, a stream 
of red, nitrous vapour is let loose, and the oxidised iron is 
dissolved in the liquid to the condition of nitrate of iron. 
This experiment is very easy to perform, and it gives an 
idea of the energy of certain chemical actions. We have 
endeavoured to represent its appearance on page 25. 
Fuming nitric acid does not act on iron, and prevents it 
being attacked by Ot-dinary nitHb acid. This property has 



NITRIC ACID. 



25 



given rise to a very remarkable experiment on passive 
iron. It consists in placing some nails in a glass, into 
which some fuming nitric acid is poured, which produces 
no result ; the fuming acid is then taken out, and is re- 
placed by ordinary nitric acid, which no longer acts on 




Iron and nitric acid. 



the iron rendered passive by the smoking acid. After this, 
if the nails are touched by a piece of iron, which has not 
undergone the action of nitric acid, they are immediately 
acted upon, and a giving off of nitrous vapour is manifested 
with great energy. ' Lead is a verj'- soft metal, and can 
even be scratched by the nails. It is also extremely 



26 



CHEMISTRY. 



pliable, and so entirely devoid of elasticity that when bent 
it has no tendency whatever to return to its primitive form. 
Lead is heavy, and has a density represented by 11-4; 
that is to say, the weight of a quart of water being one 
kilogram, that of the same volume of lead is 1 1 -400 k. 
The figure below represents cylindrical bars of the 

best known metals, all weighing the 
Platinum Density 21 '50 same, showing their -omparative 

density. 

1 GoldD. 19-25 ^^^^^ j.j^^ ^.^^ .^ ^^p^j^jg ^f ^^^j^g 

a Mercury D. 13-66 a beautiful crystalline form when 

placed in solution by a metal that 
is less oxydisable. The crystalliza- 
siiverD. 10-47 tion of lead, represented on page 27, 

is designated by the name of the Tree 
oj Saturn. This is how the experi- 
ment is produced : Thirty grams of 
acetate of lead are dissolved in a 
quart of water, and the solution is 
poured into a vase of a spherical 
shape. A stopper for this vase is 
made out of a piece of zinc, to which 
five or six separate brass wires are 
attached ; these 
Aluminium D. 2-56 are plunged into 



) Lead D. 11'35 



S Bismuth D. 9-82 



I Copper D. 8-78 



t Nickel D. 8-27 



STinD. 7 29 



I Iron D. 7'20 



I Zinc D 6*86 



Uaeneeium D. 1*43 

Sodiom D. ( 



Representation of bars of metal, all of the same weight. 

the fluid, and we see the wires become immediately covered 
with brilliant crystallized spangles of lead, which continue 
increasing in size. 

The alchemists, who were familiar with this experiment, 
believed that it consisted in a transformation of copper 



TREE OF SATURN. 



27 



into lead, while in reality it only consists in the substitu- 
tion of one metal for another. The copper is dissolved 
in the liquid, and is replaced by the lead, but no meta- 
morphosis is brought about. We may vary at will the 
form of the vase or the arrangement of the wire ; thus it 
is easy to form letters, numbers, or figures, by the crystal- 
lization of brilliant spangles. 

Copper, when it is pure, has a characteristic red colour, 
which prevents it being confounded with any other metal ; 
it dissolves easily in nitric acid, and with considerable 
effervescence, giving off vapour very abundantly. This 
property has been put to good use in engraving with aqua 
fortis. A copper plate 
is covered with a layer 
of varnish, and when it 
is dry some strokes are 
made on it by means of 
a graver ; if nitric acid 
is poured on the plate 
when thus prepared, the 
copper is only acted on 
in the parts that have 
been exposed by the 
point of steel. By afterwards removing the varnish, we 
have an engraved plate, which will serve for printing 
purposes. 

Among experiments that may be attempted with com- 
mon metals, we may mention that in which salts of tin are 
employed. Tin has a great tendency to assume a crystal- 
line form, and it will be easy to show this property by an 
interesting experiment A concentrated solution of proto- 
chloride of tin, prepared by dissolving some metallic tin in 
hydrochloric acid, is placed in a test glass ; then a rod of 
tin is introduced, as shown on page 28. Some water is 
next slowly poured on the I'od, so that it gradually trickles 




Tree of Saturn, 



28 



CHEMISTRY. 



down, and prevents the mingling of the proto-chloride of 
tin. The vessel is then left to stand, and we soon see 
brilliant crystals starting out from the rod. This crystal- 
lization is not effected in the water ; it is explained by an 
electric influence, into the details of which we cannot enter 




Jupiter's Tree. 



without overstepping our limits ; it is known as " Jupiter's 
Tree." It is well known that alchemists, with their strange 
system of nomenclature, believed there was a certain mys- 
terious relation between the seven metals then known and 
the seven planets ; each metal was dedicated to a planet ; 



METALS. ig 

tin was called Jupiter ; silver, Luna ; gold, Sol ; lead, 
Saturn ; iron, Mars ; quicksilver. Mercury ; and copper, 
Venus. The crystallization of tin may be recognised also 
by rubbing a piece of this metal with hydrochloric acid ; 
the fragments thus rubbed off exhibit specimens of branch- 
ing crystals similar to the hoar-frost which we see in 
severe winter weather. If we bend a rod of tin in our 
hands the crystals break, with a peculiar rustling sound. 

When speaking of precious metals, we may call to mind 
that the alchemists considered gold as the king of metals, 
and the other valuable ones as noble metals. This defini- 
tion is erroneous, if we look upon the useful as the most 
precious ; for, in that case, iron and copper would be 
placed in the first rank. If gold were found abundantly 
on the surface of the soil, and iron was extremely rare, we 
should seek most eagerly for this useful metal, and should 
despise the former, with which we can neither make 
a ploughshare nor any other implement of industry. 
Nevertheless, the scarcity of gold, its beautiful yellow 
colour, and its unalterability when in contact with air, 
combine to place it in the first rank in the list of precious 
metals. Gold is very heavy ; its density is represented by 
the figure I9'S. It is the most malleable and the most 
ductile of metals, and can be reduced by beating to such 
thin sheets that ten thousand can be laid, one over the 
other, to obtain the thickness of a millimetre. With a 
grain of gold a thread may be manufactured extending a 
league in length, and so fine that it resembles a spider's 
web. When gold is beaten into thin sheets it is no longer 
opaque ; if it is fastened, by means of a solution of gum, 
on to a sheet of glass, the light passes right through it, and 
presents a very perceptible green shade. Gold is some- 
times found scattered in sand, in a condition of impalpable 
dust, and, in certain localities, in irregular lumps of varying 
size, called nuggets. Gold is the least alterable of the 



30 CHEMISTRY. 

metals, and can be exposed, indefinitely, to the contact of 
humid atmosphere without oxidizing. It is not acted on 
by the most powerful acids, and only dissolves in a mixture 
of nitric acid and hydrochloric acid. We can prove that 
gold resists the influence of acids by the following 
operation : — 

Some gold-leaf is placed in two small phials, the first 
containing hydrochloric acid, and the second nitric acid. 
The two vessels are warmed on the stove, and whatever 
the duration of the ebullition .of the acids, the gold-leaf 
remains intact, and completely resists their action. If we 
then empty the contents of one phial into the other, the 
hydrochloric and nitric acids are mixed, and we see the 
gold-leaf immediately disappear, easily dissolved by the 
action of the liquid {aqua regid). Gold also changes when 
in contact with mercury; this is proved by suspending 
some gold-leaf above the surface of this liquid (page 31); 
it quickly changes, and unites with the fumes of the mer- 
cury, becoming of a greyish colour. 

Silver is more easily affected than gold, and though 
so white when fused, tarnishes rapidly in contact with air. 
It does not oxidize, but sulphurizes under the influence of 
hydro-sulphuric emanations. Silver does not combine 
directly with the oxygen of the atmosphere ; but under 
certain conditions it can dissolve great quantities of this 
gas. If it is fused in a small bone cupel, in contact with 
the air, and left to cool quickly, it expands in a remark- 
able manner, and gives off oxygen. 

Nitric acid dissolves silver very easily, by causing the 
formation of abundant fumes. When the solution evapo- 
rates, we perceive white crystals forming, which are nitrate 
of silver. This fused nitrate of silver takes the name of 
lunar caustic, and is employed in medicine. Nitrate of 
silver is very poisonous ; it possesses the singular property 
of turning black under the action of the sun's rays, and is 



LUNAR CAUSTIC. 



3.1 



used in many curious operations in photography. It is 
also employed in the manufacture of dyes for the hair ; it 
is applied to white hair with gall-nut, and under the in- 
fluence of the light it turns black, and gives the hair a 
very dark shade. Salts of silver in solution with water 
have the property of forming a precipitate under the in- 
fluence of chlorides, such as sea salt. If a few grains of 
common salt are thrown into a solution of nitrate of silver, 




Gold-leaf exposed to the fumes of mercury. 



it forms an abundant precipitate of chloride of silver, 
which blackens in the light. This precipitate, insoluble in 
nitric acid, dissolves very easily in ammonia. 

Platinum, which is the last of the precious metals that 
we have to consider, is a greyish-white colour, and like 
gold is only affected by a mixture of nitric acid and hydro- 
chloric acid. It is the heaviest of all the ordinary metals; 
its density is 21 '50. It is very malleable and ductile, 



32 CHEMISTRY. 

and can be beaten into very thin sheets, and into wires as 
slender as wires of gold. Platinum wires have even been 
made so fine that the eye can scarcely perceive them ; 
these are known as Wollaston's invisible wires. Platinum 
resists- the action of the most intense fire, and we can only 
luse it by means of a blow-pipe and hydro-oxide gas. 
Its unalterability and the resistance it opposes to fire render 
it very valuable for use in the laboratory. Small crucibles 
are made of it, which are used by chemists to calcine 
their precipitates in analytical operations, or to bring about 
reactions under the infl.uence of a high temperature. 
Platinum may be reduced to very small particles ; it then 
takes the form of a black powder. In this pulverulent 
condition it absorbs gases with great rapidity, to such an 
extent that a cubic centimetre can condense seven hundred 
and fifty times its own volume of hydrogen gas. It also 
condenses oxygen, and in a number of cases acts as a 
powerful agent. Platinum is also obtained in porous 
masses ("spongy platinum"), which produce phenomena 
of oxidation. 

A very ingenious little lamp may be constructed which 
lights of itself without the help of a flame. It contains a 
bell of glass, which is filled with hydrogen gas, produced 
by the action exercised by a foundation of zinc on acidu- 
lated water. If the knob on the upper part of the 
apparatus is pressed, the hydrogen escapes, and comes in 
contact with. a piece of spongy platinum, which, acting by 
oxidation, becomes ignited. The flame produced sets fire 
to a small oil lamp, which is opposite the jet of gas. 
This very ingenious lamp is known under the name of 
Gay-Lussac's lamp. Platinum can also produce, by mere 
contact, a great number of chemical reactions. Place in a 
test glass an explosive mixture formed of two volumes of 
hydrogen and one volume of oxygen ; in this gas plunge a 
small piece of spongy platinum, and the combination of the 



FLAMELESS LAMP. 



33 



two bodies will be instantly brought about, making a violent 
explosion. Make a small spiral of platinum red-hot in the 
flame of a lamp, having suspended it to a card ; then 
plunge it quickly into a glass containing ether, and you 
will see the metallic spiral remain red for some time, while 




Discolouration of periwinkles by sulphuric acia. 

in the air it would cool immediately. This phenomenon 
is due to the action of oxidation which the platinum 
exercises over the fumes of ether. This curious experi- 
ment is known under the name of the lamp without a 
flame. This remarkable oxidizing power of platinum, which 
has not yet been explained, was formerly designated by 



34 



CHEMISTRY. 



the title of catalytic action. But a phrase is not a theory, 
and it is always preferable to avow one's ignorance than 
to simulate an apparent knowledge. Science is powerful 
enough to be able to express her doubts and uncertainties 
boldly. In observing nature we find an experience of this, 








Experiment for turning columbines a green colour with ammoniacal ether 

and often meet with facts which may be put to profit, and 
become useful in application ; nevertheless it is often the 
case that the why and the wherefore will for a long time 
escape the most penetrating eye and lucid intelligence. 
It is true the admirable applications of science strike us 
with the importance of their results, and the wonderful 



COLOURING OF FLOWERS. 35 

inventions they originate ; but if they turn to account the 
observed facts of nature, what do they teach us as to the 
first cause of all things, the wherefore of nature ? — Almost 
nothing. We must humbly confess our powerlessness, and 
say with d'Alembert: "The encyclopaedia is very abun- 
dant, but what of that if it discourses of what we do not 
understand 1 " 

Artificial Colouring of Flowers. 

In a course of chemistry, the action exercised by sul- 
phurous acid on coloured vegetable matter is proved by 
exposing violets to the influence of this gas, which whitens 
them instantaneously. Sulphurous acid, by its disoxi- 
dating properties, destroys the colour of many flowers, 
such as roses, periwinkles, etc. The experiment succeeds 
very readily by means of the little apparatus which we 
give on 'page 33. We dissolve in a small vessel some 
sulphur, which ignites in contact with air, and gives rise, 
by its combination with oxygen, to sulphurous acid ; the 
capsule is covered with a conical chimney, made out of a 
thin sheet of copper, and at the opening at the top the 
flowers that are to be discoloured are placed. The action 
is very rapid, and a few seconds only are necessary to 
render roses, periwinkles, and violets absolutely white. 

M. Filpol, a distinguished savant, has exhibited to the 
members of the Scientific Association, Paris, the results 
which he obtained by subjecting flowers to the influence of 
a mixture of sulphuric ether and some drops of ammonia ; 
he has shown that, under the influence of this liquid, a 
great number of violets or roses turn a deep green. We 
have recently made on this subject a series of experiments 
which we will here describe, and which may be easily 
attempted by those of our readers who are interested in 
the question. Some common ether is poured into a glass, 
and to it is added a small quantity of liquid ammonia 



36 CHEMISTRY. 

(about one-tenth of the volume). The flowers with which 
it is desired to experiment are then plunged into the 
fluid (page 34). A number of flowers, whose natural 
colour is red or violet, take instantaneously a bright green 
tint ; these are red geranium, violet, periwinkle, lilac, red 
and pink roses, wall-flower, thyme, small blue campanula, 
fumeter, myosotis, and heliotrope. Other flowers, whose 
colours are not of the same shade, take difierent tints when 
in contact with ammoniacal ether. The upper petal of 
the violet sweet-pea becomes dark blue, whilst the lower 
petal turns a bright green colour. The streaked carnation 
becomes brown and bright green. White flowers gener- 
ally turn yellow, such as the white poppy, the variegated 
snow-dragon, which becomes yellow and dark violet, the 
white rose, which takes a straw colour, white columbine, 
camomile, syringa, white daisy, potato blossom, white 
Julian, honeysuckle, and white foxglove, which in contact 
with ammoniocal ether assume more or less deep shades 
of yellow. White snap-dragon becomes yellow and dark 
orange. Red geranium turns blue in a very remarkable 
fashion ; with the monkey-flower the ammoniacal ether 
only affects the red spots, which turn a brownish green ; 
red sna-p-dragon turns a beautiful brown ; valerian takes 
a shade of grey ; and the red corn-poppy assumes a dark 
violet. Yellow flowers are not changed by ammoniacal 
ether ; buttercups, marigolds, and yellow snap-dragon pre- 
serve their natural colour. Leaves of a red colour are 
instantly turned green when placed in contact with am- 
moniacal ether. The action of this liquid is so rapid that 
it is easy to procure green spots by pouring here and there 
a drop of the solution. In like manner violet flowers, 
such as periwinkles, can be spotted with white, even with- 
out gathering them. We will complete our remarks on 
this subject with a description of experiments performed 
by M. Gabba in Italy by means of ammonia actintj on 



PHOSPHORESCENCE. 37 

flowers. M. Gabba simply used a plate, in which he 
poured a certain quantity of solution of ammonia. He 
placed on the plate a funnel turned upside down, in the 
tube of which he arranged the flowers on which he wished 
to experiment. He then found that under the influence 
of the ammonia the blue, violet, and purple flowers became 
a beautiful green, red flowers black, and white yellow, etc. 
The most singular changes of colour are shown by 
flowers which are composed of different tints, their red 
streaks turning green, the white yellow, etc. Another 
curious example is that of red and white fuchsias, which, 
through the action of ammonia, turn yellow, blue, and 
green. When flowers have been subjected to these 
changes of colour, and afterwards plunged into pure water, 
they preserve their new tint for several hours, after which 
they gradually return to their natural colour. Another 
interesting observation, due to M. Gabba, is that asters, 
which are naturally inodorous, acquire an agreeable aro- 
matic odour under the influence of ammonia. Asters of a 
violet colour become red when wetted with nitric acid 
mixed with water. On the other hand, if these same 
flowers are enclosed in a wooden box, where the)- are ex- 
posed to the fumes of hydrochloric acid, they become, in 
six hours' time, a beautiful red colour, which they preserve 
when placed in a dry, shady place, after having been pro- 
perly dried. Hydrochloric acid has the effect of making 
flowers red that have been rendered green by the action of 
ammonia, and also alters their appearance very sensibly. 
We may also mention, in conclusion, that ammonia, com- 
bined with ether, acts much more promptly than when 
employed alone. 

Phosphorescence. 

Artificial flowers are frequently to be seen prepared 
in a particular manner, which have the property of be- 



38 CHEMISTRY. 

coming phosphorescent in darkness, when they have been 
exposed to the action of a ray of light, solar or electric. 
These curious chemical objects are connected with some 
very interesting phenomena and remarkable experiments 
but little known at the present time, to which we will now 
' draw the reader's attention. 

The faculty possessed by certain bodies of emitting 
light when placed in certain conditions, is much more 
general than is usually supposed. 

M. Edmond Becquerel, to whom we owe a remarkable 
work on this subject, divides the phenomena of phos- 
phorescence into five distinct classes : — 

1. Phosplwrescence through elevation of temperature. 
Among the substances which exhibit this phenomenon in 
a high degree we may mention certain diamonds, coloured 
varieties of fluoride of calcium, some minerals ; and sulphur, 
known under the name of artificial phosphorus, when it 
has previously been exposed to the action of the light. 

2. Phosphorescence through mecJianical action. This is 
to be observed when we rub certain bodies together, or 
against a hard' substance. If we rub together two quartz 
crystals in the dark, we perceive red sparks ; and when 
pounding chalk or sugar, there is also an emission of 
sparks. 

3. Phosphorescence through electricity. This is mani- 
fested by the light accompanying disengagement of elec- 
tricity, and when gases and rarefied vapours transmit 
electric discharges. 

4. Spontaneous Phosphorescence is observed, as every one 
knows, in connection with several kinds of living creatures, 
— glow-worms, noctilucids, etc., and similar phosphorescent 
efiTects are produced also with organic substances, animal 
or vegetable, before putrefaction sets in. It is manifested 
also at the flowering time of certain plants, etc. 

5. Phosphorescence through insolation and the action of 



PHOSPHORESCENCE. 



39 



light. "It consists," says M. Edmond Becquerel, "in ex- 
posing for some instants to the action of the sun, or to 
that of rays emanating from a powerful luminous source, 
certain mineral or organic substances, which immediately 




Artificial flower coated with phosphorescent powder, exposed 
to the light of magnesium wire. 

become luminous, and shine in the dark with a light, the 
colour and brilliancy of which depend on their nature and 
physical character ; the light gradually diminishes in 
intensity during a period varying from some seconds to 

4 



40 CHEMISTRY. 

several hours. When these substances are exposed anew 
to the action of light, the same effect is reproduced. The 
intensity of the light emitted after insolation is always 
much less than that of the incidental hght." These 
phenomena appear to have been first observed with pre- 
cious stones ; then, in 1604, in calcined Bologna stone, 
and later, in a diamond by Boyle, in 1663; in 1675 it 
was noticed in Baudoin phosphorus (residuum of the cal- 
cination of nitrate of lime), and more recently still in con- 
nection with other substances which we will mention. 
The substances most powerfully influenced by the action 
of light are sulphates of calcium and barium, sulphate of 
strontium, certain kinds of diamonds, and that variety of 
fluoride of calcium, which^ has received the name of 
chloropkane. 

Phosphorescent sulphate of calcium is prepared by 
calcining in an earthenware crucible a mixture of flowers 
of sulphur and carbonate of lime. But the preparation 
only succeeds with carbonate of lime of a particular cha- 
racter. That obtained from the calcination of oyster shells 
produces very good results. Three parts of this substance 
is mixed with one part of flowers of sulphur, and is made 
red-hot in a crucible covered in from contact with the air. 
The substance thus obtained gives, after its insolation, a 
yellow light in the dark. The shells of oysters, however, 
are not always pure, and the result is sometimes not very 
satisfactory ; it is therefore better to make use of some 
substance whose composition is more to be relied on. 

" When we desire to prepare a phosphorescent sulphate 
with lime, or carbonate of lime," says M. E. Becquerel, 
" the most suitable proportions are those which in a 
hundred parts of the substance are composed of eighty to 
a hundred of flowers of sulphur in the first case, and forty- 
eight to a hundred in the second, that is, when we employ 
the quantity of sulphur which will be necessary for burning 



SULPHATES. 4 r 

with carbonate of lime to produce a monosulphate.* It 
is necessary to have regard to the elevation of the tem- 
perature in the preparation. By using lime procured 
from arragonite, and reducing the temperature below five 
hundred degrees for a sufficient time for the reaction 
between the sulphur and lime to take place, the excess of 
sulphur is eliminated, and we have a feebly luminous mass, 
of a bluish tint ; if this mass is raised to a temperature of 
eight hundred or nine hundred degrees, it will exhibit a 
very bright light." 

Sulphate of calcium possesses different phosphorescent 
properties according to the nature of the salt which has 
served to produce the carbonate of lime employed. If we 
transform marble into nitrate of lime, by dissolving it in 
water and nitric acid, and form a precipitate with carbonate 
of ammonium, and use the carbonate of lime thus obtained 
in the preparation of sulphate of calcium, we have a pro- 
duct which gives a phosphorescence of a violet-red colour. 
If the carbonate of lime used is obtained from chloride of 
calcium precipitated by carbonate of ammonia, the phos- 
phorescence is yellow. If we submit carbonate of lime, 
prepared with lime water and carbonic acid, to the in- 
fluence of sulphur, we obtain a sulphur giving a phos- 
phorescent light of very pure violet. Carbonate of lime 
obtained by forming a precipitate of crystallized chloride 
of calcium with different alkaline carbonates also gives 
satisfactory results. 

Luminous sulphates of strontium may be obtained, like 
those of calcium, by the action of sulphur on strontia or 
the carbonate of this base, by the reduction of sulphates 
of strontia with charcoal. Blue and green shades are the 
most common. Sulphates of barium also present very 
remarkable phenomena of phosphorescence ; but to obtain 
very luminous intensity a higher temperature is needed 
* These substances must be finely powdered and thoroughly mixed. 



42 



CHEMISTRY. 



than with the other substances mentioned, and we have the 
same result when we reduce native sulphate of baryta with 
charcoal ; that is to say, when the reaction takes place 
which produces the phosphorus formerly known as phos- 
phorus of Bologna. Preparations obtained from baryta 
have a phosphorescence varying from orange-red to green. 




Phosphorescent flower emitting hght in a daric rooui. 

The preparation of such substances as we have just 
enumerated afford an easy explanation of the method of 
manufacturing the luminous flowers which we describdd 



LUMINOUS fLOWEllS. 43 

at the commencement of this chapter. We obtain some 
artificial flowers, cover them with some liquid gum, sprinkle 
with phosphorescent sulphur, and let them dry. The pul- 
verulent matter then adheres to them securely, and it is 
only necessary to expose the flowers thus prepared to the 
light of the sun, or the rays emanating from magnesium 
wire in a state of combustion (page 39), to produce im- 
mediate phosphorescent effects. If taken into a dark room 
page 42) they shine with great brilliancy, and give off very 
exquisite coloured rays. Phosphorescent sulphates are used 
also in tracing names or designs on a paper surface, etc., 
and it can easily be conceived that such experiments may 
be infinitely varied according to the pleasure of the ex- 
perimenter. 

But let us ask ourselves if these substances are not 
capable of being put to more serious uses, and of being 
classed among useful products. To this we can reply very 
decidedly in the affirmative. With phosphorescent matter 
we can obtain luminous faces for clocks placed in dark, 
obscure spots, and it is not impossible to use it for making 
sign-boards for shops, or numbers of houses, which can be 
lit up at night. Professor Norton even goes so far as to 
propose in the "Journal of the Franklin Institute," not 
only coating the walls of rooms with these phosphorescent 
substances, but also the fronts of houses, when he considers 
it would be possible to do away entirely with street lights, 
the house-fronts absorbing sufficient light during the day 
to remain luminous the whole of the night. 

Chemistry Applied to Sleight of Hand. 

While physics has provided the species of entertainment 
called "sleight of hand " with a number of interesting 
effects, chemistry has only offered it very feeble contribu- 
tions. Robert Houdin formerly made use of electricity 
to move the hands of his magic clock, and the electric 



44 



CHEMISTRY. 



magnet in making an iron box so heavy instantaneously 
that no one could lift it. Robin has made use of optics 
to produce the curious spectacle of the decapitated man, 
spectres, etc. Those persons who are fopd of this kind of 
amusement may, however, borrow from chemistry some 
original experiments, which can be easily undertaken, and 
I will conclude this chapter by describing a juggling feat 




Amusing experiment in chemistry. 

which I have seen recently executed before a numerous 
audience by a very clever conjurer. 

The operator took a glass that was perfectly trans- 
parent, and placed it on a table, announcing that he should 
cover the glass with a saucer, and then, retiring to some 
distance, would fill it with the smoke from a cigarette. 
And this he carried out exactly, standing smoking his 



SLEIGHT OF HAND. 45 

cigarette in the background, while the glass, as though by 
enchantment, slowly filled with the fumes of the smoke. 
This trick is easily accomplished. It is only necessary to 
pour previously into the glass two or three drops of hydro- 
chloric acid, and to moisten the bottom of the saucer with 
a few drops of ammonia. These two liquids are unper- 
ceived by the spectators, but as soon as the saucer is 
placed over the glass, they unite in forming white fumes 
of hydrochlorate of ammonia, which bear a complete re- 
semblance to the smoke of tobacco. 

This experiment excited the greatest astonishment 
among the spectators present on the occasion, but under- 
standing something of chemistry myself, I easily guessed 
at the solution of the mystery. The same result is 
obtained in a course of chemistry in a more simple manner, 
and without any attempt at trickery, by placing the open- 
ing of a bottle of ammonia against the opening of another 
bottle containing hydrochloric acid. 





CHAPTER III. 

CHEMISTRY AND ALCHEMY CHEMICAL COMBINATION.! 

THE ATMOSPHERIC AIR. 

, E have in the foregoing pages given some 
experiments, and considered several of the 
metals, but there are numerous very interest- 
ing subjects still remaining ; indeed, the num- 
ber is so great that we can only pick and choose. All 
people are desirous to hear something of the atmosphere, 
of water, and the earth ; and as we proceed to speak of 
crystals and minerals, and so on to rocks, we shall learn 
a good deal respecting our globe — its conformation and 
constituents. But the atmospheric air must be treated of 
first. This will lead us to speak of oxygen and nitrogen. 
Water will serve to introduce hydrogen with a few experi- 
ments, and thus we shall have covered a good deal of 
ground on our way towards various other elements in 
daily use and appreciation. Now let us begin with a few 
words concerning Chemistry itself 

At the very outset we are obliged to grope in the dark 
after the origin of this fascinating science. Shem, or 
" Chem," the son of Noah, has been credited with its in- 
troduction, and, at any rate, magicians were in Egypt in 
the time of Moses, and the lawgiver is stated by ancient 
writers to have gained his knowledge from the Egyptians. 
But we need not pursue that line of argument. In more 
modern times the search for the Philosopher's Stone and 
..he Elixir of Life, which respectively turned everything to 



ALCHEMY. 47 

gold, and bestowed long life upon the fortunate finder, 
occupied many people, who in their researches no doubt 
discovered the germs of the popular science of Chemistry 
in Alchemy, while the pursuit took a firm hold of the 
popular imagination for centuries; and even now chemistry 
is the most favoured science, because of its adaptability to 
all minds, for it holds plain and simple truths for our 
every-day experience to confirm, while it leads us step by 
step into the infinite, pleasing us with experiments as we 
proceed. 

Alchemy was practised by numerous quacks in ancient 
times and the Middle Ages, but all its professors were not 
quacks. Astrology and alchemy were associated by the 
Arabians. Geber was a philosopher who devoted himself 
entirely to alchemy, and who lived in the year 730 A.u. 
He fancied gold would cure all disease, and he did actually 
discover corrosive sublimate, nitric acid, and nitrate of 
silver. To give even a list of the noted alchemists and 
magicians would fill too much space. Raymond Sully, 
Paracelsus, Friar Bacon, Albertus Magnus, Thomas 
Aquinas, Flamel, Bernard of Treves, Doctor Dee, with his 
assistant Kelly, and in later times Jean Delisle, and 
Joseph Balsamo (Cagliostro), who was one of the most 
notorious persons in Europe about one hundred years ago 
(1765-1789), are names taken at random ; and with the 
older philosophers chemistry was an all-absorbing occupa- 
tion — not for gold, but knowledge. 

The revelation was slow. On the temperature of bodies 
the old arts of healing were based — for chemistry and 
medicine were allies. The elements, we read, existed on 
the supposition "that bodies were hot or cold, dry or 
moist " ; and on this distinction for a long time " was 
.based the practice of medicine." The doctrine of the 
" three principles" of existence superseded this, — the prin- 
ciples being salt, mercury, and sulphur. Metals had been 



48 CHEMISTRY. 

regarded as living bodies, gases as souls or spirits. The 
idea remained that the form of the substance gave it its 
character. Acid was pointed ; sweet things were round. 

Chemistry, then, has had a great deal to contend against. 
From the time of the Egyptians and Chinese, who were 
evidently acquainted with various processes, — dyeing, etc., 
— the science filtered through the alchemists to Beecher 
and Stahl, and then the principle of affinity — a disposi- 
tion to combine — was promulgated, supplemented in 1 674 
by Mayow, by the theory of divorce or analysis. He con- 
cluded that where union could be effected, separation was 
equally possible. In 171 8 the first " Table of Affinities " 
was produced. Affinity had been shown to be elective, for 
Mayow pointed out that fixed salts chose one acid rather 
than another. Richter and Dalton made great advances. 
Before them Hales, Black, Priestley, Scheele, Lavoisier, 
and numerous others penetrated- the mysteries of the 
science whose history has been pleasantly written by more 
than one author whom we have not been able to consult, 
and have no space to do more than indicate. In later 
days Faraday, De la Rive, Roscoe, and many others have 
rendered chemistry much more popular, while they have 
added to its treasures.. The story of the progress of 
chemistry would fill a large volume, and we have regret- 
fully to put aside the introduction and pass on. 

Before proceeding to investigate the elements, a few 
words concerning the general terms used in chemistry 
will be beneficial to the reader. If we look at the list 
of the elements, pp. 2-3, we shall see various termina- 
tions. Some are apparently named from places, some 
from their characteristics. Metals lately discovered by the 
spectroscope (and recently) end in iuni ; some end in 
"ine," some in " on." As far as possible in late years a 
certain system of nomenclature has been adhered to, but 
the old popular names have not been interfered with. 



COMPOUNDS. 49 

When elements combine together in certain proportions 

of each they receive certain names. The following table 

will explain the terms used ; for instance, we find that — 

Compounds of Oxygen are termed Oxides, as oxide of copper. 

Hydrogen „ Hydrides,as hydride of potassium. 

Chlorine „ ' Chlorides, as chloride of sodium. 

Nitrogen „ Nitrides, as nitride of boron. 

Bromine „ Bromides, asbromide of potassium. 

Iodine „ Iodides, as iodide of potassium. 

Sulphur „ iSjSs."} laf '''""* °' 

Selenium „ Selenides, as selenide of mercury. 

P , Carbides, or i as carbide of nitro- 
" Carburets, I gen, and so on. 

The above examples refer to the union in single pro- 
portion of each and are called Binary Compounds. When 
more than one atom of each element exists in different 
proportions we have different terms to express such union. 
If one atom of oxygen be in the compound it is called a 
"monoxide," or "protoxide"; two atoms of oxygen in 
combination is termed " dioxide," or " binoxide " ; three, 
" trioxide," or " tritoxide " ; four is the " tetroxide," or 
" per-oxide," etc. When more than one atom, but not 
two atoms is involved, we speak of the sesgui-oxide (one- 
and-a-half), — "oxide" being interchangeable for "sulphide" 
or " chloride," according to the element. 

There are other distinctions adopted when metals form 

two series of combinations, such as ons and zc, which apply, 

as will be seen, to acids. Sulphur«V and sulphurous acids, 

mtric and nitrous acid are familiar examples. In these 

cases we shall find that in the acids ending in " ous " 

oxygen is present in less quantity than in the acids ending 

in ic. The symbolic form will prove this directly, the 

number of atoms of oxygen being written below, 

Sulphurous Acid = HoSOj. Nitrous Acid = HNOj. 

Sulphuric Acid = H2SO4. Nitric Acid = HNO3. 

Whenever a stronger compound of oxygen is discovered 

than that denominated by ic, chemists adopt the plan of 



so CHEMISTRY. 

dubbing it the per {vtrep, over), as per-chloric acid, which 
possesses four atoms of oxygen (HCIO4), chloric acid being 
HCIO3. The opposite Greek term, vtto {/mp9, below), is 
used for an acid with less than two atoms of oxygen, and 
in books is written "hypo "-chlorous (for instance). Care 
has been taken to distinguish between the higher and 
lower; for "hyper" is used in English to denote excess, as 
hyper-critical ; and hypo might to a reader unacquainted 
with the derivation convey just the opposite meaning to 
what is intended. 

While speaking of these terminations we may show how 
these distinctive endings are carried out. We shall find; 
if we pursue the subject, that when we have a salt of any 
acid ending in ic the salt terminates in " ate." Similarly 
the salts of acids ending in otis, end in " ite." To continue 
the same example we have — 

Sulphuro«j- Acid, which forms salts called SulphzV«. 
Sulphur/c Acid, „ „ Sulphates. 

Besides these are s\i\^\iides, which are results of the 



o© 






Combinations of elements. 



unions or compounds of elementary bodies. SulphzV^j are 
more complicated unions of the compounds. Sulphates 
are the salts formed by the union of sulphuric acid with 
bases. Sulphides or sulphurets are compounds in which 
sulphur forms the electro- negative element, and sulphites 
are salts formed by the union of sulphur^wj acids with 
bases, or by their action upon them. 

The symbolical nomenclature of the chemist is worse 
than Greek to the uninitiated. We frequently see in so- 
called popular chemical books a number of hieroglyphics 
and combinations of letters with figures very difficult to 



CHEMICAL UNION. 5 i 

decipher, much less to interpret. These symbols take the 
place of the names of the chemical compounds. Thus 
water is made up of oxygen and hydrogen in certain pro- 
portions ; that is, two of hydrogen to one of oxygen. The 
symbolic reading is simple, H2O, = the oxide of hydrogen. 
Potassium again mingles with oxygen. Potassium is K 
in our list ; KO is oxide of potassium (potash). Let us 
look into this a little closer. 

The union of one particle of a simple body with a par- 
ticle of another simple body can be easily understood ; 
but, as we have seen, it is possible to have substances con- 
sisting of four or five different particles, though the 
greater number of chemical combinations consist of two 
or three dissimila'r ones. In the diagram (page 50) we 
have some possible combinations. 



0) 


(=) 


(3) 


©0 


(2& 


®So) 


(i) Hydrosulphurous Acid. 


(2) Sulphurous Acid. 


(3) Sulphuric Acid. 



In these combinations we may have one particle of a 
in combination with one, two, three, four, or five of b, and 
many particles of a can unite with various molecules of b. 
Suppose we have oxygen and sulphur compounds as 
follows : — 

Thus there are three different compounds of these two 
elements — SO, SO2, SO3 (without water). 

A compound body may combine with another com- 
pound body, and this makes a complicated compound. 
Suppose we have a mixture of sulphuric acid and potash. 
We have a sulphate of potassium (K2S0^ and combinations 
of these combinations may likewise be formed. We must 
read these symbols by the light of the combining weights 
given in the table, and then we shall find the weight of 



5 2 CHEMISTRY. 

oxygen or other elements in combination. Thus when we 
see a certain symbol (Hg.S for instance), we understand 
that they form a compound including so many parts of 
mercury and so many of sulphur, which is known as ver- 
milion. Hg.O is oxide of mercury, and by reference to 
the table of Atomic Weights, we find mercury is Hg., and 
its combining weight is 200 ; while oxygen is O, and its 
weight is i6. Thus we see at once how much of each 
element is contained in oxide of mercury, and this propor- 
tion never varies ; there must be 200 of one and 16 of 
the other, by weight, to produce the oxide. So if the 
oxygen has to be separated from it, the sum of 2 1 6 parts 
must be taken to procure the 1 6 parts of oxygen. When 
we see, as above, O2 or O3, we know that the weight must 
be calculated twice or three times, O being 16 ; O3 is 
therefore 32 parts by weight. So when we have found 
what the compounds consist of, we can write them sym- 
bolically with ease. 

Composition of the Atmospheric Air. 
We have elsewhere communicated a variety of facts 
concerning the air.* We have seen that it possesses 
pressure and weight. We call the gaseous envelope of 
the earth the atmosphere, and we are justified in con- 
cluding that other planets possess an atmosphere also, 
though of a different nature to ours. We have seen 
how easy it is to weigh the air, but we may repeat the 
experiment. We shall find that a perfectly empty glass 
globe will balance the weights in the scalepan ; admit 
the air, and the glass globe will sink. So air possesses 
weight. We have mentioned the Magdeburg hemi- 
spheres, the barometer, the air-pump, and the height and 
the pressure of the atmosphere have been indicated. 
The density of the atmosphere decreases as we ascend " 
* See " Marvels of Earih, Air, and Water." 



THE AIRv 53 

for the first seven miles the density diminishes one-fourth 
that of the air at the sea-level, and so on for every suc- 
ceeding seven. 

In consequence of the equal, if enormous, pressure 
exercised in every direction, we do not perceive the incon- 
venience, but if the air were removed from inside of a 
drum, the parchment would quickly collapse. We feel 
the air when we move rapidly. We breathe the air, and 
that statement brings us to consider the composition of the 
atmosphere, which, chemically speaking, may vary a little (as 
compared with the whole mass) in consequence of changes 
which are continually taking place, but to all intents and 
purposes the air is composed as follows, in loo parts : 

Nitrogen . . .79 parts. 

Oxygen . . . 20 „ 

Carbonic Acid. . . '04 „ 

with minute quantities of other ingredients, such as 
ammonia, iodine, carbonetted hydrogen, hydrochloric acid, 
sulphuretted hydrogen, nitric acid, carbonic oxide, and 
dust particles, as visible in the sunbeams, added. 

The true composition of the atmosphere was not known 
till Lavoisier demonstrated that it consisted of two gases, 
one of which was the vital fluid, or oxygen, discovered by 
Priestley. To the other gas Lavoisier gave the name of 
Azote, — an enemy of life, — because it caused death if in- 
haled alone. The carbonic acid in the air varies very 
much, and in close, heated, and crowded rooms increases 
to a large quantity, which causes lassitude and headache. 

We can easily prove the existence of carbonic acid gas 
as exhaled from the lungs. Suppose we take a glass and 
fill it partly with clear lime-water; breathe through a glass 
tube into the water in the glass, and very quickly you will 
perceive that the lime-water is becoming cloudy and 
turbid. This cloudiness is due to the presence of chalk, 
which has been produced by the action of the carbonic 



54 CHEMISTRY. 

acid gas in the lime-water. This is a well known and 
always interesting experiment, because it leads up to the 
vital question of our existence, and the functions of breath- 
ing and living. ,u ^ 

A popular writer once wrote a bo&J< entitled, " Is Life 
Worth Living ?" and a witty coraime|itator replied to the 
implied question by saying, '''rt"aepends*'upon,the liver" 
This was felt to be true by many people who^siiffer, but 
the scientific man will go farther, and tell you it depends 
upon the air you breathe, and on the carbonic acid you 
can raise to create heat, — animal heat, — which is so essen- 
tial to our wfcll-being. We are always burning ; a furnace 
is within us, never ceasing to burn without visible combus- 
tion.' We are generating heat by means of the blood. We 
know that we inhale air into the lungs, and probably are 
aware that the air so received parts with the oxygen to 
renew the blood. The nitrogen dilutes the oxygen, fpr 
if we inhaled a less-mixed air we should either be burnt 
up or become lunatics, as light-headed as when inhaling 
"laughing-gas." This beautifully graduated mixture is 
taken into our bodies, the oxygen renews the blood and 
gives it its bright red colour ; the carbon which exists in 
all our bodies is cold and dead when not so vivified by 
oxygen. The carbonic acid giren off produces heat, and 
our bodies are warm. But when the action ceases we 
become cold, we die away, and cease to live. Man's life 
exemplifies a taper burning ; the carbon waste is con- 
sumed as the wax is, and when the candle burns away 

— it dies ! It is a beautiful study, full of suggestiveness to 
all who care to study the great facts of Nature, which works 
by the same means in all matter. We will refer to plants 
presently, after having proved by experiment the existence 
of nitrogen in the air. 

Rutherford experimented very cruelly upon a bird 
which he placed beneath a glass shade, and there let it 



CARBONIC ACID. 



55 



remain in the carbonic acid exhaled from its lungs, till the 
oxygen being at length all consumed by the bird, it died. 
When the atmosphere had been chemically purified by a 
solution of caustic potash, another bird was introduced, but 
though it lived for some time, it did not exist so long as 
the first. Again the. air was deprived of the carbonic acid, 
and a third bird was introduced. The experiment was 
thus repeated-, till at length a bird was placed beneath the 




Rutherford's experiment. 

receiver, and it perished at once. This is at once a cruel 
and clumsy method of making an experiment, which can 
be more pleasantly and satisfactorily practised by burning 
some substance in the air beneath the glass. Phosphorus, 
having a great affinity for oxygen, is usually chosen. The 
experiment can be performed as follows with a taper, but 
the phosphorus is a better exponent. 

Let us take a shallow basin with some water in it, a 



56 CHEMISTRY. 

cork or small plate floating upon the water, and in the 
plate a piece of phosphorus.. We must be careful how we 
handle phosphorus, for it has a habit, well known, but 
sometimes forgotten by amateur chemists, of suddenly 
taking fire. Light this piece of phosphorus, — a small 
piece will do if the jar be of average " shade " size,^ — and 
place the glass over it, as in the illustration (page 57). 
The smoke will quickly spread in the jar, and the entry 
of air being prevented, because the jar is resting under 
water, phosphoric acid will be formed, and the oxygen 
thereby consumed. The water, meanwhile, will rise in the 
jar, the pressure of the air being removed. The burning 
phosphorus will soon go out, and when the glass is cool, 
you will be able to ascertain what is inside the jar. Put 
a lighted taper underneath, and it will go out. The taper 
would not go out before the phosphorus was burnt in the 
glass, and so now we perceive we have azote in the 
receptacle — that is, nitrogen. The other, the constituent 
of our atmosphere, carbonic acid, as we have seen, is very 
injurious to the life of animals, and as every animal breathes 
it out into the air, what becomes of it ? Where does all 
this enormous volume of carbonic acid, the quantities of 
this poison which are daily and nightly exhaled, where do 
they all go to .' We may be sure nature has provided for 
the safe disposal of it all. Not only because we live and 
move about still, — and of course that is a proof, — but 
because nature always has a compensating law. Remem- 
ber nothing is wasted ; not even the refuse, poisonous air 
we get rid of from our lungs. Where does it go .? 

It goes to nourish the plants and trees and vegetables 
that we delight to look upon and to eat the fruit of. 
Thus the vegetable world forms a link between the animals 
and the minerals. Vegetables obtain food, so to speak, 
and nourishment from water, ammonia, and carbonic acid, 
all compound bodies, but inorganic. 



WATER. 



57 



Water consists of oxygen and hydrogen, carbonic acid 
of carbon and oxygen, and ammonia of hydrogen and 
nitrogen. Water and ammonia are present in the air ; so 
are oxygen and nitrogen. Water falls in the form of rain, 
dew, etc. So in the atmosphere around us we find 
nearly every necessary for plant-life ; and in the ground, 
which supplies some metallic oxides for their use, we find 
the remainder. From the air, then, the plant derives its 
life. 




Drawing the oxygen from air by combustion. 

The vegetable kingdom in turn gives all animals their 
food. This you will see at a glance is true. Certainly 
animals live on animals. Man and wilder animals live on 
the beasts of the field in a measure, but those beasts 
derive their nourishment from vegetables — the vegetable 
kingdom. So we live on the vegetable kingdom, and it 
separates the carbonic acid from the air, and absorbs it. 
What we do not want it takes. What we want it gives. 



5 8 CHEMISTRY. 

Vegetables give out oxygen, and we consume it gladly. 
We throw away carbonic acid, and the plants take it 
greedily ; and thus the atmosphere is retained pure for 
our use. We can, if desirable, prove that plants absorb 
carbonic acid and give out oxygen by placing leaves of a 
plant in water, holding the acid in solution, and let the 
sun shine upon them. Before long we shall find that the 
carbonic acid has disappeared, and that oxygen has come 
into the water. 

Carbonic acid is sufficiently heavy to be poured from 
one vessel to another ; and if we have obtained some in a 
glass, we can extinguish a taper by pouring the invisible 
gas on to the lighted taper, when it will be immediately 
extinguished. 

From the foregoing observations it will be perceived how 
very desirable it is that ventilation should be attended to. 
People close up windows ami doors and fireplaces, and go 
to bed and sleep. In the morning they complain of head- 
ache and lassitude ; they wonder what is the matter, and 
why the children are not well. Simply because they have 
been rebreathing the carbonic acid. Go into a closed 
railway carriage which is nearly filled (and it is astonishing 
to us how people can be so foolish as to close every out- 
let), and you will recoil in disgust. These travellers shut 
the ventilators and windows " because of the cold." A 
very small aperture will ventilate a railway carriage ; but 
a close carriage is sickening and enervating, as these kind 
of travellers find out by the time they reach their journey's 
end. Air was given us to breathe at night as well as by 
day ; and though from man's acts or omissions there may 
be circumstances in which "night" air may affect the health, 
we maintain that air is no more injurious naturally than 
■' day " air. Colder it may be, but any air at night is 
" night " air, in or out of doors at night ; and we are 
'-crtain that night air in itself never hurt any healthy 



OZONE. 59 

person. It is not nature's plan to destroy, but to save 
If a person delicate in constitution gets hot, and comes 
out into a colder atmosphere, and defy nature in that way, 
he (or she) must take the consequences. But air and 
ventilation (not draught) are necessaries of health, and to 
say they injure is to accuse nature falsely. There are 
many impurities in the air in cities, and in country places 
sometimes, but such impurities are owing to man's acts and 
omissions. With average sanitary arrangements and ap- 
pliances in a neighbourhood no one need be afraid to 
breathe fresh air night or day ; and while many invalids 
have, we believe, been retarded in recovery from being 
kept in a close room, hundreds will be benefited by plenty 
of fresh air. We should not so insist upon these plain 
and simple truths were there not so many individuals 
who think it beneficial to close up every avenue by which 
air can enter, and who then feel ill and out of spirits, blam- 
ing everything but their own short-sightedness for the effect 
of their own acts. An inch or two of a window may be 
open at night in a room, as the chimney register should 
be always fully up in bedrooms. When there are fires the 
draught supplies fresh air to the room with sufficient 
rapidity. But many seaside journeys might be avoided if 
fresh air were insisted on at home. 

There is another and an important constituent of the 
atmosphere called OzONE, which is very superior oxygen, 
or oxygen in what is termed the " AUotropic " state, and 
is distantly related to electricity, inasmuch as it can be pro- 
duced by an electrical discharge. This partly accounts for 
the freshness in the air after a thunderstorm, for we are all 
conscious that the storm has " cleared the air." The fresh, 
crisp ozone in the atmosphere is evident. Ozone differs 
from oxygen in possessing taste and smell, and it is heavier 
by one-half than the oxygen gas. There is a good deal 
of ozone in the sea breeze, and we can, though not infal- 



6o 



CHEMISTRY. 



llbly, detect its presence by test-paper prepared with 
iodide of potassium, which, when ozone is present, will 
turn blue. We have still something to learn about ozone, 
which may be considered as "condensed oxygen." 




Development of gas by combustion. 



We have frequently mentioned " combustion," and as 
under ordinary circumstances siich effects cannot take 
place without atmospheric. air, we will consider it. Com- 
bustion is chemical action accompanied by light and heat. 



COMBUSTION. 



6l 



Chemical union is always attended by the development of 
heat, not always by light, because the union varies in inten- 
sity and quickness. But when a candle is burning we can 
study all the interesting phenomena of combustion. We 
have elsewhere spoken of Heat and Light, so we need 
only refer the readers to those subjects in the former parts 
of this series. Heat is referable to chemical action, and 
varies according to the energy of union. Heat is always 
present, remember, in a greater or less degree ; and when 




Gas evolved from flame. 



visible combustion takes place we see light. Invisible 
combustion goes on in our bodies, and we feel heat ; when 
we get cold we feed the fire by eating, or blow it by 
exercise and air in our lungs. 

We shall speak, however, of combustion now as it affects 
us in daily life ; our fires, our candles, gas, etc., and under 
these ordinary circumstances hydrogen and carbon are 
present. (We shall hear' rnore' about carbon presently.) 
These unite with the oxygen to form water and carbonic 
acid ; the water being visible as we first put the cold shade 



62 



CHEMISTRY. 



upon the lighted lamp, and the carbonic acid renders the air 
impure. 

In the case of a common candle, or lamp, combustion 
takes place in the same way. The wick is the inter- 
mediary. The oil mounts in the lamp wick, where it is 




Davy's safety lamp. Davy lamp (section). 

converted into a gas by heat; it then "takes fire," and 
gives us light and heat. The candle-flame is just the 
same with one exception : the burning material is solid, 
not liquid, though the difference is only apparent, for the 
wax is melted and goes up as gas. The burning part 



FLAME. 63 

of the wick has a centre where there is no combustion, and 
contains carbon. We can prove this by placing a bent 
tube, as in the illustration (page 60), one end in the un- 
burning part of the flame. We shall soon see a dark 
vapour, come over into the receiver. This is combustible, 
for if we raise the tube without the glass we can light 
the gas. If we insert the end of the tube into the 
brilliant portion of the flame we shall perceive a black 
vapour, which will extinguish the combustion, for it is a 
mixture of carbonic acid gas and aqueous vapour, in 
which (page 61) particles of carbon are floating. 
When we proceed to light our lamps to read 
or to write by, we find some difficulty in making 
the wick burn at first. We present to it a 
lighted taper, and it has no immediate effect. 
Here we have oil and cotton, two things which 
would speedily set a warehouse in flanies from 
top to bottom, but we cannot even ignite them, 
try all we can. Why ? — Because we must first 
obtain a gas, oil will not bui^i liquid ; it must 
be heated to a gaseous point before it will burn, 
as all combustion depends upon that, — so flames 
mount high in air. Now in a candle-flame, as ^Sr/flamef 
will be seen in the accompanying diagram, there 
are three portions, — the inner dark core, which consists of 
unburnt gas ; the outer flame, which gives light ; and the 
outside rim of perfect combustion non-luminous. In the 
centre. A, there is no heat. If we place a piece of- gauze 
wire over the flame at a little distance the flame will not 
penetrate it. It will remain underneath, because the wire, 
being of metal, quickly absorbs the heat, and consequently 
there is no flame. This idea led to the invention of the 
" safety " lamp by Sir Humphrey Davy, which, although 
it is not infallible, is the only lamp in general use in 
mines (page 62). 



64 



CHEMISTRY. 



Mines must have light, but there is a gas in mines, a 
"marsh'' gas, which becomes very explosive when it mixes 
with oxygen. Of course the gas will be harmless till it 
meets oxygen, but, in its efforts to meet, it explodes the 
moment the union takes place ; instead of burning slowly 
like a candle it goes off all at once. This gas, called "fire 
damp," is carburetted hydrogen, and when it explodes it 
develops into carbonic acid gas, which suffocates the 
miners. 




CHAPTER IV.— NON-METALLIC ELEMENTS. 



OXYGEN— SYMBOL ; ATOMIC WEIGHT 16. 

I XYGEN is certainly the most abundant element 
in nature. It exists all around us, and the 
animal and vegetable worlds are dependent 
upon it. It constitutes in combination about 
one-half of the crust of the earth, and composes eight- 





Oxygen from oxide of mercury. 

ninths of its weight of water. It is a gas without taste 
or colour. Oxygen was discovered by Priestley and 
Scheele, in 1774, independently of each other. 

Oxygen can be procured from the oxides of the metals, 
particularly from gold, silver, and platinum. The noble 
metals are reducible from their oxides by heat, and this 
fact assists us at once. If we heat chlorate of potash, 
mixed with binoxide of manganese, in a retort in a furnace, 



66 CHEMISTRY. 

the gas will be given off. There are many other ways of 
obtaining oxygen, and we illustrate two (pages 65, 67). 

The red oxide of mercury will very readily evolve 
oxygen, and if we heat a small quantity of the compound 
in a retort as per illustration (page 65) we shall get the 
gas. In a basin of water we place a tube test-glass, and 
the gas from the retort will pass over and collect in the 
test-tube, driving out the water. 

The other method mentioned above, — viz., by heating 
chlorate of potash, etc., in a furnace, is shown in the follow- 
ing illustration. Oxygen, as we have said, is a colourless 
and inodorous gas, and for a long time it could not be 
obtained in any other form ; but lately both oxygen and 
..^ hydrogen have been liqui- 

^^^~s fied under tremendous 

:^^f^ pressure at a very low 

S^^ I temperature. Oxygen 

'' - '' " *- causes any red-hot sub- 

stance plunged into it to 
^ burn brightly ; a match 
will readily inflame if a 
Showing retort placed in furnace. spark be remaining, while 

phosphorus is exceedingly brilliant, and these appearances, 
with many others equally striking, are caused by the 
affinity for those substances possessed by the gas. Com- 
bustion is merely oxidation, just as the process of rusting 
is, only in the latter case the action is so slow that no 
sensible heat is produced. But when an aggregate of 
slowly oxidising masses are heaped together, heat is gene- 
rated, and at length bursts into flame. This phenomenon 
is called " spontaneous combustion." Cases have been 
known in which the gases developed in the human body by 
the abuse of alcoholic drinks have ended fatalh' in like 
manner, the body being completely charred. (Combustion 
must not be confounded with ignition, as in the electric 




OXYGEN. 



67. 



light.) Oxygen then, we see, is a great supporter of com- 
bustion, though not a combustible itself as coal is. When 
the chemical union of oxygen with another substance is 
very rapid an explosion takes place. 

Oxidation occurs in various ways. Besides those 
already mentioned, all verdigris produced on copper, all 
decays of whatever kind, disintegration, and respiration, are 
the effects of oxygen. The following experiment for the 
extraction of oxygen directly from the air was made by 




The generation of oxygen from oxide of manganese and potash. 

M. Boussingault, who passed the gas upon a substance at 
a certain temperature, and released it at a higher. The 
illustration on page 69 will show the way in which the 
experiment was performed. 

Boussingault permitted a thin stream of water to flow 
into a large empty flask, and by this water the air was 
gradually driven out into a flask containing chloride of 
calcium and sulphuric acid, which effectually dried it 
This dry air then passed into a large tube inside the 



68 



CHEMISTRY. 



revcrberatory furnace, in which tube were pieces of caustic 
baryta. Heated to a dull redness this absorbs oxygen, 

and when the heat is increased 
to a bright red the superabun- 
dant gas is given off. Thus 
the oxygen was permitted to 
pass from the furnace-tube into 
the receiving glass, and so pure 
oxygen was obtained from the 
air which had been in the 
glass bottle at first (page 69). 




HYDROGEN— SYMBOL H; ATOMIC 
WEIGHT I. 



Phosphorus burning- in oxygen. HYDROGEN is abundaOt iu 

nature, but never free. United with oxygen it forms water, 
hence its name, "water-former." It is to Parcelcus that its 
discovery is due, for he found that oil of vitriol in contact 
with iron disengaged a gas 
which was a constituent of | 
water. This gas was subse- 
quently found to be inflam- 
mable, but it is to Cavendish 
that the real explanation of I 
hydrogen is owing. He ex- 
plained his views in 1766. 

Hydrogen is obtained in the 
manner illustrated in the cut, 
by means of a furnace, as on 
page 70, or by the bottle 
method, as per page 71. The I 
first method is less convenient ' 
than the second. A gun- 
barrel or fire-proof tube is passed through the furnace, and 
filled with iron nails or filings ; a delivery tube is at the 





1 


1 




F^^ 


Kwi^fti 1 1 |B 


W»m 


^^^^ 


S^^H^^siw! '' ^^M 


JISi'JM 


^^^S 




■ 


1 


1 



Magnesium wire burning in oxygen. 



HYDROGEN. 



69 



farther end, and a flask of water boiling at the other. The 
oxygen combines with the iron in the tube, and the 
hydrogen passes over. The second method is easily 
arranged. A flask, as in the cut, is provided, and in it 
some zinc shavings are put. Diluted sulpuric acid is then 
poured upon the metal. Sulphate of zinc is formed in the 
flask, and the hydrogen passes off". 




Extraction of oxygen from air. 

Hydrogen being the lightest of all known bodies, its 
weight is put as i, and thus we are relatively with it 
enabled to write down the weights of all the other 
elements. Hydrogen is fourteen-and-a-half times lighter 
than atmospheric air, and would do admirably for the in- 
flation of balloons were it not so expensive to procure in 



70 



CHEMISTRY. 



such large quantities as would be necessary. Ordinary 
coal gas, however, contains a great deal of hydrogen, and 
answers the same purpose. 

A very pretty experiment may be made with a bladder 
full of hydrogen gas. If a tube be fitted to the bladder 
already provided with a stop-cock, and a basin of ordinary 
soap-suds be at hand, by dipping the end of the tube in 




Preparation of hydrogen with furnace. 

the solution and gently expressing the gas, bubbles will be 
formed which are of exceeding lightness (page 72). They • 
can also be fired with a taper. 

Another experiment may be made with hydrogen as 
follows : — If we permit the gas to escape from the flask, 
and light it, as in the illustration, and put a glass over it, 
we shall obtain a musical note, higher or lower, according 
to the length, breadth, and thickness of the open glass- 



WATER. 



71 



\ tube (page 73). If a number of different tubes be 
t employed, we can obtain a musical instrument — a gas 
harmonium. 

Hydrogen burns with a blue flame, and is very inflam- 
mable. Even wa:ter sprinkled upon a fire will increase its 
fierceness, because the hydrogen burns with great heat, 
and the oxygen is liberated. Being very light, H can be 
transferred from one vessel to ' another if both be held 
upside down. Some mixtures of H and O are very explo- 
sive. The oxyhydrogen blow-pipe is used with a mixture 
of O and H, which is forcibly blown through a tube and 
then ignited. The flame thus produced has a most intense 
heating-power. 




Apparatus for generating hydrogen by flask. 

A very easy method of producing hydrogen is to put a 
piece of sodium into an inverted cylinder full of water, 
^standing in a basin of water. The sodium liberates the 
hydrogen by removing the oxygen from the liquid. 

WATER-SYMBOL HoO ; ATOMIC WEIGHT 18. 
At page 4 of this volume we said something about 
water, and remarked (as we have since perceived by ex- 
periment) that "water is composed of oxygen and hydrogen 
in proportions, by weight, of eight of the former to one 
of the latter gas ; in volume, hydrogen is two to one " ; 



72 



CHEMISTRY. 



and we saw that " volume and weight were very different 
things.'' This we will do well to bear in mind, and that, 
to quote Professor Roscoe, "Water is always made up of 
sixteen parts of oxygen to two parts of hydrogen by 
weight " ; sixteen and two being eighteen, the combining 
weight of water is eighteen. 

We can prove by the Eudiometer that hydrogen when 
burnt with oxygen forms water ; and here we must 




Blowing bubbles with hydrogen gas. 

remark that water is not a mere mechanical mixture of 
gases, as air, is. Water is the product of chemical com- 
bination, and as we have before said, is really an oxide of 
hydrogen, and therefore combustion, or electricity, must be 
called to our assistance before we can form water, which is 
the result of an explosion, the mixture meeting with an 
ignited body — the aqueous vapour being expanded by heat. 
The ancients supposed water to be a simple body, but 
Lavoisier and Cavendish demonstrated its true character. 



WATER. 



73 



Pure water, at ordinary temperatures, is devoid of taste 
and smell, and is a transparent, nearly colourless, liquid. 
When viewed in masses it is blue, as visible in a marked 
degree in the Rhone and Rhine, at Geneva and Bale 
respectively. Its specific gravity is i, and it is taken as 
the standard for Sp. Gravity, as hydrogen is taken as the 
standard for Atomic Weight. The uses of water and the 
very important part it plays 
in the arrangements of 
nature as a mechanical agent, 
geology can attest, and me- 
teorology confirm. It com- 
poses the greater portions of 
animals and plants ; without 
water the world would be a 
desert — a dead planet. 

We sometimes speak of 
" pure " spping water, but 
such a fluid absolutely pure 
can scarcely he obtained ; 
and though we can filter 
water, there will always re- | 
main some foreign substance ^ 
or substances in solution. It ^ 
is well known that the action 
of water wears away and 
rounds off hard rocks, and this 
power of disintegration is 
supplemented by its strength as a solvent, which is very 
great. Rain-water is purest in the country as it falls from 
the clouds. In smoky towns it becomes sooty and dirty. It 
is owing to the solvent properties of water, therefore, that 
we have such difficulty in obtaining a pure supply. There 
is hard water and soft water. The former is derived from 
the calcareous formations, and contains lime, like the Kent 




Experiment with hydrogen. 



74 



CHEMISTRY. 



water. This can be ascertained by noticing the incrusta- 
tions of the vesselj wherein the water is boiled. But water 
rising from hard rocks, such as granite, can do little to 
disintegrate them at the moment, and therefore the water 
rises purer. Springs from a great depth are. warm, and 
are known as "thermal springs"; and when they come in 
contact with carbonic acid and some salts in their passage 
to the surface, they are known as "mineral waters." These 




The composition of water. 

waters hold in solution salts of lime and magnesia, or car- 
bonates of soda with those of lime and magnesia; salts 
of iron, and compounds of iodine and bromine are found 
in the natural mineral waters also, as well as sulphurous 
impregnations, instances of which will occur to every 
reader. 

We mentioned the Eudiometer just now, and we give 
an illustration of it. This instrument is used to ascertain 
the proportions in which the elements of water are com- 



THE EUDIOMETER. 



75 



posed by synthesis, or a putting together of the constituents 
of a body to make it up. This is distinguished from analysis, 
which means separating the compound body into its 
elements, as we do when we pass the electric current 
through water. 

The Eudiometer consists of a stout glass tube sealed 
hermetically at one end ; two platinum wires are pushed 
in through the glass just before the end is sealed. The 
tube is now filled with mercury, and inverted in a bowl of 




The Eudiometer. 

the same metal. Hydrogen, and then oxygen, are admitted 
through the mercury in the recognised proportion of two 
to one. By the time the mercury is somewhat more than 
half displaced, the tube should be held upon a sheet of 
india-rubber at the bottom of the vessel to keep the metal 
in the tube,, for when the necessary explosion takes place 
the mercury might also be driven out. A spark from the 
electrophorus or from a Leyden ,jar may now be passed 



^6 CHEMISTRY. 

through the gases in the tube. The explosion occurs, and 
water is formed inside. If the mercury be again admitted 
it will rise nearly to the very top of the tube, driving the 
bubble up. Thus we find we have formed water from the 
two gases. 

The decomposition of water is easily affected by elec- 
tricity, and if a little sulphuric acid be added to the water, 
the experiment will be thereby facilitated. Two wires 
from a battery should be inserted through a glass filled with 
the water, and into two test tubes also filled. The wires 




Decomposition of water. 



terminate in platinum . strips, and are fastened at- the other 
end to the positive and negative poles of the galvanic 
battery. The gases will collect in the test tubes, and will 
be found in proper proportions when the current passes. 

So much for water in its liquid stSte. The solid con- 
dition of water (ice) is equally interesting. When we 
apply heat to water, we get a vapour called "steam"; when 
we cool water to 32° Fahr., we get a solid mass which 
weighs just the same as the liquid we have congealed, or 
the steam we have raised from an equal amount of water. 
But water expands while in the process of solidification 



ICE CRYSTALS. -jy 

just as it does when it bfecomes gaseous, and as we have 
i-etnarked before, our water-pipes bear full testimony to this 
scientific fact. When ice forms it has a tendency to 
crystallize, and some of these ice crystals are, as we see, 
very beautiful. Snow is only water in a nearly solid form, 
and the crystals are extremely elegant, appearing more 




Snow crystals. 

like flowers than congealed water, in tiny six-pointed ice 
crystals. Many philosophers of late years have written 
concerning these tiny crystals, which, in common with all 
crystals, have their own certain form, from which they 
never depart. Snowflakes are regular six-sided prisms 
grouped around a centre forming angles of 60° and 120°. 
There are a number of forms, as will be seen from the 



78 CHEMISTRY. 

accompanying illustrations, and at least ninety-six varieties 
have been observed. One snowflake, apparently so like 
all other flakes that fall, can thus be viewed with much 
interest, and yet, while so very various, snowflakes never 
get away from their proper hexagonal structure. It has 
been, remarked that snowflakes falling at the same time 
have generally the sanje form. 

Of the latent heat of ice, etc., we have already spoken 
in our article upon Heat, and therefore it will be sufficient 
to state that the latent heat of water is 79 thermal units, 
because when passing from the liquid to the solid state a 




j^istilling water. 

certain amount of water absorbs sufficient heat to raise an 
equal quantity of the liquid 79°. This can be proved by 
taking a measured quantity (say a pint) of water at 79° 
and adding ice of the same weight to the water. The 
mixture will be found to be at zero. Therefore the ice 
has absorbed or rendered latent 79" of heat which the 
water possessed. If we melt ice until only a trace of it is 
left, we shall still find the water as cold as the ice was ; 
all the latent heat is employed in melting the ice. So it 
will take as much heat to bring a pound of ice at zero to 
a pound of water at zero, as it would to raise 79 pounds 
of water 1°. The same law applies to steam. 

Water can be distilled in small quantities by an ap- 



DISTILLATION. 



79 



paratus, as figured in the illustration, and by these means 
we get rid, of all impurities which are: inseparable from the 
liquid otherwise. When it is desirable to distil large 
quantities of water a larger apparatus is used, called an 
" Alembic." The principle is simply to convert the liquid 
by , heat into vapour, then cool it, by condensation, in 
another vessel. 







The evaporation .of water, with its effects upon our 
globe, belong more to the study of Meteorology. 

Rain-water is the purest, as we have said, because it 
goes through the process of distillation by nature. The 
sua takes it up, by evaporation, into the air, where it is 
condensed, and falls as rain-water. Water containing 
carbonate of lime will petrify or harden, as in stalactite 



8o 



CHEMISTRY. 



caverns. The carbonic acid escapes from the dripping 
Water, the carbonate in solution is deposited as a stalactite, 
and finally forms pillars in the cave. Sea-water contains 




StalacuLe Cavern. 



many salts; its composition is as follows, according to 
Dr. Schwertzer, of Brighton : — 



Water . . 






96474372 grs 


Chloride of sodium (salt) . 






2805948 , 


Chloride of potassium 






076552 , 


Chloride of magnesium 






3-66658 , 


Brorriide of magnesium 






0-02929 


Sulphate of magnesia 






229578 . 


Sulphate of lime 






o'4o662 , 


Carbonate of lime 






0-03301 , 


(With traces of iodine and arr 


imon 


a). 





jooo'ooooo grains. 



NITROGEN. 



8i 



There fs much more oxygen in water than in air, as can 
be ascertained by analysis of these compounds. This great 
proportion in favour of water enables fish to breathe by 
passing the water through the gills. Marine animals (not 
fishes), like the whale, — which is a warm-blooded creature, 
and therefore not suited to exist without air, — are obliged 
to come to the surface to breathe. The density of salt 
water is much greater than that of fresh water, and there- 
fore swimming and flotation arc easier in the sea than in 
a river. We shall have more to say of water by-and-by. 

NITROGEN— SYMBOL- N ; ATOMIC WEIGHT 14. 
We have already made some reference to this gas when 




Obtaining nitrogen. 

speaking of the atmospherfe and its constituents, of which 
nitrogeh is the principal. From its life-destroying pro- 
perties it is called "azote" by French chemists, and when 
we wish to obtain a supply of nitrogen all we, have to do 
is to take away the oxygen from the air by burning phos- 
phorus on water under a glass. Nitrogen is not found 
frequently in solid portions of the globe. It is abundant 
in ahimals. It is without colour or smell, and can be 
bi-eathed in air without danger. It is heavy and sluggish ; 



82 CHEMISTRY. 

but if we put a taper into a jar of nitrogen it will go out, 
and animals die in the gas for want of oxygen, as nitrogen 
alone cannot support life. 

The affinity of nitrogen for other substances is not 
great, but it gives rise to five compounds, which are as 
below, in the order they are combined with oxygen : — 



Nitrous oxide (" 


laughing gas ") 


(Monoxide; 


NjO. 


Nitric oxide. 


• ■ • 


Dioxide 


N,0,. 


Nitrous acid . 


• • • 


Trioxide 


N,0,. 


Nitric peroxide 


* • ■ 


Tetroxide 


N^O^. 


Nitric acid 


• ■ . 


Pentoxide 


NjOs. 



These compounds are usually taken as representative 
examples of combining weight, and as explanatory of the 
symbolic nomenclature of chemistry, as they advance in 
such regular proportions of oxygen with nitrogen. The 
combining weight of nitrogen is 14, and when two parts 
combine with five of oxygen it makes nitric acid, and we 
put it down as NjOg ; on adding water, 'HNOg, as we can 
see by eliminating the constituents and putting in the pro- 
portions. Actually it is HgNgOo, or, by division, HNO3. 

Nitrogen plays a very important part in nature, par- 
ticularly in the vegetable kingdom. Nitric acid has been 
known for centuries. Geber, the alchemist, was acquainted 
with a substance called " nitric," which he found would 
yield a dissolvent under certain circumstances. He called 
it " dissolving fluid." At the end of the twelfth century 
Albert Magnus investigated the properties of this acid, and 
in 1235 Raymond Lully prepared nitre with clay, and 
gave the liquid the name of " aqua-fortis." But till 1 849 
nitric acid was only known as a hydrate, — that is, in com- 
bination with water, — but now we have the anhydrous acid. 

Oxygen and nitrogen combine under the influence of 
electricity, as shown by Cavendish, who passed a current 
through an atmospheric mixture of oxygen and nitrogen, 
in a tube terminating in a solution of potash, lime, and 



NITROGEN. 



83 



soda. Every time the spark passed, the volume of ga.-, 
diminished, and nitric acid was formed, as it is in thunder- 
storms, when it does not remain free, but unites with 
ammonia, and forms a highly useful salt, which promotes 
vegetable growth. Here is another instance of the useful- 




Apparatus for obtaining nitrogen by using metal to absorb the oxygen of the air 

ne=s of thunderstorms, and of the grand provisions of 
nature for our benefit. Nitric acid is obtained by distilling 
nitre with sulphuric acid. The liquid is, when pure, 
colourless, and is a powerful oxidizer. : It dissolves most 
metals, and destroys vegetable and animal substances. 



84 



CHEMISTRY. 



By an addition of a little sulphuric acid the water is taken 
from the nitric acid, and a very powerful form of it is the 
resijlt. The acid is of great use in medicine, and as an 
application to bites of rabid animals or serpents. It con- 
verts cotton waste into " gun-cotton " by a very simple 
process of steeping, washing, and pressing. From the 
hydraulic press it comes in discs like " quoits," which will 
burn harmlessly and smoulder away, but if detonated they 




lllljTHFf' 

^"WuifcliCTli I 1 1 I I 

Nitric apid obtained from nitric and sulphuric acid. 

explode with great violence. As a rule, when damp, it is 
not dangerous, but it can be fired even when wet. It 
will explode at a less temperature than gunpowder, and, 
moreover, yields, no smoke, nor does it foul a gun. Gun- 
cotton, when dissolved in ether, gives us collodion for 
photographic purposes. 

In speaking farther of the compounds of nitrogen with 
oxygen, we will limit ourselves to the monoxide, or laugh- 



nl.1 jtvlVj At^lJJ. 



85 



ing gas. This is now used as an anaesthetic in dentistry, 
etc., and is quite successful, as a rule. People afflicted 




Cavendish's experiment. 

with heart disease should not use it without advice, how- 
ever. When inhaled into the lungs it makes the subject 
very hilarious, and the effect is rather nojsy, It is obtained 




Experiment to obtain nitric aqid. 

from the nitrate of ammonia, which, on the application of 
heftt, decomposes into nitrous oxide and vapour. Warm 



86 



CHEMISTRY. 



water should be used for the trough. The gas is a 
powerful supporter of combustion. 

Binoxide of nitrogen is of importance in the manufac- 
ture of sulphuric acid. 

Nitrogen combines with hydrogen, forming various 
compounds. These are the " amines," also ammonia, and 
ammonium. Ammonia possesses the properties of a base. 
Its name is derived from Jupiter Ammon, near whose 
temple it was prepared, from camels' dung. But bodies 
containing nitrogen give off ammonia in course of dis- 
tilling, and hartshorn is the term applied to horn-cuttings, 




Apparatus for obtaining laugiiing-gas. 

which yield ammonia, which is a colourless gas of strong 
odour and taste now obtained from gas-works. 

To obtain AMMONIA heat equal parts of chloride of 
ammonia (sal ammoniac) and quick-lime powdered (see 
page 87). The gas must be collected over mercury, be- 
cause it is very soluble in water. Ammonia is useful to 
restore tipsy people and fainting ladies. A solution of 
ammonia is used for cauteries. Ammoniacal gas is re- 
markable for its solubility in water. To prepare the 
solution the gas is forced thmugh a series of flasks. The 
tubes carrying the gas should be continued to the bottoms 
of the flasks, else Ae solution, being lighter than water 



LAUGHING GAS. 



87 



the upper portion alone would be saturated. The tubes 
carrying away the solution are raised a little, so that the 




Inhaling laughing gas. 

renewal is continually proceeding. The gas liquifies under 
a pressure of six atmospheres, at a temperature of 10^ 




Cieneration of ammonia. 



Cent. This experiment can be artificially performed by 



88 



CHEMISTRY. 



heating chloride of silver saturated with ammonia, and 
the silver will part with the gas at a temperature of 40° C. 
The gas will then condense in a liquid form in the tube. 
The experiment may be facilitated by placing the other 
extremity of the tube in snow and salt, and by the liquid 
we can obtain intense cold. This experiment has been 
made use of by M. Carre in his refrigerator (which was 
described in the Physics' section), by which he freezes 




Liquefaction of ammania. 

water. We may however, just refer to the process. 
Whenever the condition of a body is changed from that 
of liquid to a -gas, the temperature is greatly lowered, 
because the heat becomes "latent." The latest freezing 
machine consists of an apparatus as shown in the illustra- 
tions on pages 89 and 90. The machine is of- wrought 
iron, and contains, when ready for action, a saturated solu- 
tion of ammonia at zero. This is in communication with 
another and an air-tight vessel, of which the centre is 



REFRIGERATION. 



89 



hollow. The first process is to heat the solution, and the 
gas escapes into the second " vase," which is surrounded 
by cold water, and quite unable to escape. A tremendous 
pressure is soon obtained, and this, added to the cold 
water, before long liquifies the ammonia, and when the 
temperature indicates 130' the hot vessel is suddenly 
cooled by being put into the water. The gas is thus sud- 
denly converted into a liquid, the water in the second hollow 
vase is taken out, and the bottle to be frozen is put into 




Carre's refrigerator (first action). 

the cavity. The cold is so great, in consequence of the 
transformation of the liquid ammonia into a gas, that it 
freezes the water in any vessel put into the receiver. 
The ammonia can be reconverted into liquid and back 
again, so no loss is occasioned by the process, which is 
rapid and simple. This is how great blocks of ice are 
produced in water-bottles. 

The one important point upon which care is necessary 
is the raising of the temperature. If it be elevated beyond 



90 



CHEMISTRY. 



130° C, the pressure will be too great, and an explosion 
will occur. 

The abundant formation of ammonia from decaying 
animal matter is evident to everyone, and depends upon 
the presence of moisture to a great extent. Chloride of 
ammonia is called sal-ammoniac, and the carbonate of 
ammonia crystallizes from the alkaline liquid produced by 
the distillation of certain animal matter. The compounds 
of ammonia are easily recognized by a certain sharp taste. 




Carre's refrigerator (second action). 

They are highly valuable remedial agents, acting particu- 
larly upon the cutaneous system, and when taken internally,, 
produce the effect of powerful sudorifics. Their volatility,. 
and the facility with which they are expelled from other 
substances, render them of great importance in chemistry,, 
and peculiarly fit them for the purposes of many chemical 
analyses. The ammonia compounds display a remarkable 
analogy to the corresponding combinations of potash and' 
soda. The compounds of ammonia are highly important 
in their relation to the vegetable kingdom. It may be- 



AMINES. 



91 



assumed that all the nitrogen of plants is derived from 
the ammonia which they absorb from the soil, and from 
the surrounding atmosphere. 

The similarity of ammonia to the metallic oxides has 
led to the conjecture that all its combinations contain a 
compound metallic body, which has received the name 
ammoninm (NH_j) ; but no one has yet succeeded in its 
preparation, although by peculiar processes it may be 
obtained in the form of an amalgam. 

Ammonias, in which one or more atoms of hydrogen 
are replaced by basic radicals, are termed Amides, or 
A mines. 








CHAPTER v.— NON-METALLIC ELEMENTS. 
{Continued^ 

(..HLORXNE— BROMINE — IODINE — FLUORINE — CAR150N — 
SULPHUR — PHOSPHORUS — SILICON — BORON — TELLU- 
RIUM ARSENIC. 

HLORINE (CI.) is usually found with sodium 
in the mineral kingdom, and this chloride of 
sodium is our common salt. Chlorine can be 
obtained by heating hydrochloric acid with 
binoxide of manganese. (Atomic weight 3 5'5.) 

Chlorine possesses a greenish-yellow colour, hence its 
name " Chloros," green. " It should be handled carefully, 
for it is highly injurious and suffocating. It possesses a 
great affinity for other substances, and attacks the metals. 
For hydrogen it has a great affection, and when hydrogen 
is combined with any other substances chlorine imme- 
diately attacks them, and in time destroys them. But 
even this destructive and apparently objectionable quality 
makes chlorine very valuable ; for if we carry the idea to 
its conclusion, we shall find that it also destroys offensive 
and putrid matter, and purifies the atmosphere very much. 
Most colouring matters include hydrogen, and therefore 
they are destroyed by chlorine, which is a great " bleacher " 
as well as a purifier. If we dip any vegetable dyes into a 
jar of chlorine, they will become white if the dyed sub- 
stances are damp. 

Hydrochloric acid is known as muriatic acid and spirits 



CHLORINE. 



93 



of salt. It is obtained when salt' is treated with sulphuric 
acid and the gas comes off into water. Equal parts of 
the acid and the salt are put into a flask as in the cut on 
page 94, and diluted with water. The mixture is then 
heated. The gas is condensed in the bottles half-full of 
•water. The result gives sulphate of soda and hydrochloric 



L -i-^lL _ 




T 



i?J«»'^ -" 



■*-*■*" "■"= I 



J. ''Sj 



t < A" _ f (^ '«>ij 



*?^ a> 



^^> 






g f ip^^"'^- 1^ 




Generation of chlorine. 

acid. This acid is procured in soda manufactories, and 
with nitric acid is called "aqua regia," a solvent for gold. 
When chlorine and hydrogen are mixed in equal propor- 
tions they explode in sunlight. In the dark or by candle- 
light they are harmless. Dry chlorine gas can be obtained 
by interpo.sing a glass filled with some chloride of calcium. 



94 



CHEMISTRY. 



The gas being heavier than air (about 2i times), displaces 
it in the flask, and when it is filled another can be placed 
in position. This mode causes a little waste of gas, which 
should not be breathed. 

Chlorine possesses a great affinity for certain bodies. 
If the gas be thrown upon phosphorus, the latter will burn 
brilliantly. Arsenic, tin, and antimony when powdered 
and poured from a shoot into a vase of chlorine will burst 
into briUiant sparks, and other metals will glow when in- 
troduced to this gas. Chlorine forms many unstable com- 




Productioii cf hytlrcjcliloric acid, _ -^ 

binations with oxygen. Its combination with hydrogen 
has already been referred to. 

Bromine is a rare element. (Symbol Br. Atomic 
weight 80.) 

It is deep brownish red, very volatile, and of a peculiar 
odour. Bromine unites with the elementary bodies, and 
forms some oxygen compounds. It resembles chlorine- 
in its properties, and is used in medicine and in photo- 
graphy. It is found in saline springs and in salt water, 
combined with soda and magnesium. The presence of 



lODINK. 



95 



bromine may easily be detected in tlie strong smell of sea 
weed. Its combinations with metals are termed bromides. 
It is a powerful poison. 

Iodine is another relative of chlorine. It is found in 
seaweed, which by burning is reduced to kelp. When 
iodine is heated a beautiful violet vapour comes off, and 
this characteristic has given it its name ("iodes," violet). 




Apparatus for obtaining dry chlorine gas. 

Iodine was discovered by Courtojs, of Paris, and in 1813 
Gay^Lussac made it a special study. It is solid at ordinary 
temperatures, and assumes crystallized forms in plates of 
metallic lustre. It is an excellent remedy in "goitre" and 
such afifections. (Symbol I. Atomic weight 127.) 

Fluorine is very difficult to prepare. Fluor spar is 
a compound of fluorine and calcium. This element is 
gaseous, and combines so rapidly that it is very difficult 



96 , CHEMISTRY. 

to obtain in a free state. Etching on glass is accomplished 
by means of hydrofluoric acid, for fluorine has a great 
affinity for silicic, acid, which is contained in glass. The 
glass is covered with wax, and the design is traced with 
a needle. The acid attacks the glass and leaves the wax, 
so the design is eaten in. (Symbol F. Atomic "weight 19.) 

Chlorine, fluorine, bromine, and iodine are termed 
" Halogens " (producers of salts). They appear, as we 
have seen, in a gaseous, liquid, and solid form respectively. 

Carbon is the most, or one of the most, largely dif- 




Facets of a brilliant. 

fused elements in nature, and claims more than a passing 
notice at our hands, though even that must be brief. We 
may put down carbon next to oxygen as the most im- 
portant element in the world. The forms assumed by 
carbon are very variable, and pervade nature in all its 
phases. We have carbon in crystals, in the animal and 
vegetable kingdoms, and amongst the chief minerals a solid, 
odourless, tasteless, infusible, and almost insoluble body. 
In various combinations carbon meets us at every turn ; 
united with oxygen it forms carbonic acid, which we 
exhale for the plants to imbibe. We have it in coal, 



CARBON. 



97 



with hydrogen and oxygen. We have it building up 
animal tissues, and it is never absent in two out of the 
three great divisions of nature — the plants and the animals 
(Symbol C ; Atomic W. 1 2). 

We have carbon in three different and well-known con- 
ditions ; as the diamond, as graphite, or black-lead, and 
as charcoal. The properties of the diamond are well 
known, and we shall, when we get to Crystallography, 
learn the forms of diamond or crystals of carbon. At pre- 
sent we give an illustration or two, reserving- all explana- 
tion for the present.. Diamond cutting is a matter of some 




Facets of a rose diamond. 



difficulty, and it requires, skill to cut in the' proper direction. 
Diamonds are found in India, Brazil, and at the Cape of 
Good Hope, in alluvial soil. The identity of diamond and 
char(!oal was discovered accidentally. An experiment to 
fuse at few small diamonds resulted in their disappearance, 
and when the residue was examined it was found that the 
diamonds had been burned, that they had combined with 
oxygen and formed carbonic acid, just as when coal burns. 
The diamond is the hardest of all substances, the most 
valuable of gems, and the purest condition in which carbon 
appears. 



9- 



CHEMISTRY. 



' black-lead," and is 
It crystallizes and 
In Cumberland it is 



Graphite (Plumbago) is termed 
the next purest form of carbon, 
belongs to the primitive formations, 
dug up and used to make pencils; the operations can be 
seen at Keswick. It has other uses of a domestic character. 

Charcoal is the third form of carbon, and as it possesses 
no definite form, is said to be amorphous. Charcoal is 




Coke ovens. 



prepared in air-tight ovens, so that no oxygen can enter 
and burn the wood thus treated. Coke is the result of 
the same process applied to coal. The gas manufactories 
are the chief depots for this article, and it is used in 
locomotive engines. The various smokeless coals and 
prepared fuels, however, are frequently substituted. 

Coke ovens were formerly much resorted to by the rail- 
way companies, who found the ordinary coal too smoky 



CHARCOAL. 99 

for locomotive purposes, and apt to give rise to complaints 
by passengers and residents near^the line. 

The origin of wood charcoal we have seen. All vege- 
table substances contain carbon. When we burn wood, in 
the absence of air as far as possible, oxygen and hydrogen 
are expelled. The wood is piled in layers as in the illus- 
tration below, covered over with turf and mould, with 
occasional apertures for air. This mass is ignited, the 
oxygen and hydrogen are driven off, and carbon remains. 
(Animal charcoal is obtained from calcining bones). Wood 
charcoal attracts vapours, and water, if impure, can be 
purified by charcoal, and any impure or tainted animal 
matter can be rendered inoffensive by reason of charcoal 
absorbing the gases, while the 
process oFdecay goes on just 
the same. Housekeepers 
should therefore not always 
decide that meat is good 
because it is not offensive to 
the olfactory nerves. Char- 
coal will, remove the aroina, 
but the,- meat may be never- charcoai burning. 

theless bad. The use of charcoal in filters is acknowledged 
universally, and as a constituent of gunpowder it is im- 
portant. 

Carbon is not easily affected by the atmospheric air, 
or in the earth; so in many instances wood is charred 
before being driven into the ground ; and casks for water 
are prepared so. Soot is carbon in a pulverised condition, 
and Indian ink is manufactured with its assistance. 

The preparation of wood charcoal gives occupation to 
men who are frequently wild and untutored, but the results 
of their labour are very beneficial. Care should be taken 
not to sleep in a room with a charcoal stove burning, 
unless there is ample vent for the carbonic acid gas, for it 




lOO 



chemistrv 



will cause suffocation. Lampblack is obtained by holding 
a plate over the flame of some resinous substance, which 
deposits the black upon it. There is a special apparatus 
for this purpose. 

Carbon combines with oxygen to make carbonic acid 
gas, as we hav.e already mentioned, and in other propor- 
tions to form a more deadly compound than the other. 
The former is the dioxide (COJ, the latter the monoxide, 
or carbonic oxide (CO). The dioxide is the more im- 



=--.,?Sa^s 






"^3 




Wood piles of charcoal burners. 



portant, being held in the atmosphere, and combined with 
lime in chalk. All sparkling beverages contain carbonic, 
acid, to which their effervescence is due. The soda and 
other mineral waters owe their sparkle to this gas. Soda- 
water consists of a weak solution of carbonate of soda and 
the acid. There is a vessel holding chalk and water, and 
another containing some sulphuric acid. When the sul ■ 
phuric acid is permitted to unite with the chalk and water,, 
carbonic acid is liberated. A boy turning a wheel forces 



SODA WATER. 



roi 



the gas into the water in the bottles, or the water and 
carbonate of soda is drawn off thus impregnated into 







fc:-^s^ 







Seltzer-water manufactory. 

bottles and corked down, in the manner so familiar to all. 



I02 



CHEMISTRY. 



The bottles are made of the shape depicted, so that the 
bubble of air shall be at the top when the bottle lies down. 
If it be not kept so, the air will eventually escape, no 
matter how tightly the cork be put in. The ordinary 
" soda-water " contains scarcely any soda. It is merely 
water, chalk, and carbonic acid. The " Gazogene " is 
made useful for small quantities of soda-water, and is 
arranged in the following manner. The appearance of 
it is familiar to all. It consists of a double vessel, into 
the upper part of which a solution of any kind — wine and 
water, or even plain water— ^is put, to 
be saturated with carbonic acid, or 
"aerated," and into the lower one 
some carbonate of soda and tartaric 
acid. A tube leads from this lower 
to the top of the upper vessel, which 
screws on and off. By shaking the 
apparatus when thus charged and 
screwed together, some of the liquid 
descends through the tube into the 
lower vessel and moistens the soda 
and acid, which therefore act on each 
other, and cause carbonic acid to be 
disengaged ; this, rising up through 
Gazogene. ^^6 tubc (which is perforated with 

small holes at the upper part), disperses itself through 
the liquid in small bubbles, and causes sufficient pressure 
to enable the liquid to absorb it, which therefore effervesces 
when drawn off by the tap. 

Carbonic acid can be liquified, and then it is colour- 
less. In a solid form it resembles snow, and if pressed 
with the fingers it will blister them. Being very heavy 
the gas can be poured into a vase, and if there be a light 
in the receptacle the flame will be immediately extinguished. 
That even the gas introduced into seltzer-water is 




CARBONIC ACID GAS. 



103 



capable of destroying life, the following experiment will 
prove. Let us place a bird within a glass case as in the 




Soda-water apparatus. 

illustration (page 104), and connect the glass with a bottle 
of seltzer-water or a siphon. As soon as the liquid enters 
the carbonic acid will ascend, and this, 
if continued for a long time, would 
suffocate the bird, which soon begins 
to develop an appearance of restless- 
ness, 

We have already remarked upon 
the important part taken by this gas 
in nature, so we need only mention its 
existence in pits and caves. There 
are many places in which the vapour 
is so strong as to render the localities 
uninhabitable. In the Middle Ages 
the vapours were attributed to the 
presence of evil spirits, who were supposed to extinguish 
miners' lamps, and suffocate people who ventured into the 




Pouring out the carbonic 
acid gas. 



I04 



CHEMISTRY, 



caves. In the Grotto Del Cane there is still an example, 
and certain caves of Montronge are often filled with the 
gas. A lighted taper held in the hand will, by its ex- 
tinction, give the necessary warning. Oxygen and carbon 
are condensed in carbonic acid, for the gas contains a 
volume of oxygen equal to its own. If we fill a glass 
globe, as per illustration (page los), with pure oxygen, 
and in the globe insert two carbon points, through which 
we pass a current of electricity, we shall find, after the ex- 




Experiment with carbonic acid. 

periment, that if the stop-cock be opened, there is no 
escape of gas, and yet the mercury does not rise in the 
tube, so the oxygen absorbed has been replaced by an 
equal volume of carbonic acid. 

The other combination of carbon with oxygen is the 
carbonic oxide (CO), and when a small quantity of oxygen 
is burnt with it, it gives a blue flame, as on the top of the 
fire in our ordinary grates. This gas is present in lime 
kilns, and is a very deadly one. We must now pass rapidly 



COAL. 



105 



through the compounds of carbon with hydrogen, merely 
referring to coal for a moment as we go on. 

Coal, of which we shall learn more in Mineralogy and 
Geology, is a combination, mechanical or otherwise, and is 
the result of the decomposition of vegetable matter in re- 
■ mote ages, — the so-called " forests," which were more like 
the jungles than the woods of the present day. Moss and 
fern played prominent parts in this great transformation, 




Experiment showing that carbonic acid contains oxygen and carbon. 

as we can see in the Irish peat-bogs, where the first steps 
to the coal measures are taken. 

The compounds of carbon with hydrogen are important. 
There is the " light " carburetted hydrogen (CH^), which 
is usually known as fire-damp in coal mines. It is highly 
inflammable and dangerous. The safety-lamp invented 
by Davy is a great protection against it, for as the gas 
neters it is cooled by the wire, and burns within harmlessly. 



io6 



CHEMISTRY. 



The explosion warns the miner. " Heavy " carburetted 
hydrogen possesses double the quantity of carbon (C^H^). 
It is also explosive vifhen mixed with oxygen. 

The most useful compound is coal-gas, and though its 




Temperature reduced by contact with wire. 

principal function appears to be in some manner super- 
seded by electricity, " gas " is still too important to be put 
aside. It can easily be obtained by putting small frag- 
ments of coal into the bowl of a tobacco-pipe, closing the 

bowl with clay, and putting 
it in the fire. Before long 
the gas will issue from the 
stem of the pipe, and may 
either be lighted or col- 
lected in a bladder. For 
the use of the " million," 
however, gas is prepared 
upon a very large scale, 
and is divided into three 
processes — its " forma- 
tion," " purification," and 
its " collection " for dis- 
tribution to consumers. 
The first process is carried on by means of retorts shown 
in the illustration above. The first portion of the next 
figure is a section of a furnace, the other part shows two 
furnaces from the front. The following is the nr.ode em- 




Retorts. 



COAL-GAS. 



10/ 



ployed. The coal is put into retorts fitted to the furnace, 
so that they are surrounded by the flames, and terminating 
in a horizontal tube called the hydraulic main, E, which is 
in its turn connected with a pit or opening for the recep- 
tion of the tar and ammoniacal liquor, etc., which con- 




Sectioa. 



front vie 



denses from the gas. It then passes up and down a 
series of tubes in water, called a " condenser," and in this 
are reservoirs or receptacles for any tar and ammonia that 
remain. But sulphur is still present, so the gas is carried 
to the purifying apparatus (D in fig. below), which consists 




Condens 



of a large cylindrical vessel air-tight, with an inverted 
funnel, nearly filled with a mixture of lime and water. 
The gas bubbles in, and the sulphur unites with the lime, 
while the gas rises to the top (trays of lime are used when 
the gas enters from the bottom). The Gasometer, a large 



io8 



CHEMISTRY. 



vessel closed at the top and open below, dips into a large 
trough of circular shape. The gasometer is balanced by 
weights and chains, and may be raised {see illustration). 

When quite empty the top rests 
upon the ground, and when the 
gas enters it is raised to the top 
of the frame which supports it. 
We have now our Gasometer full. 
When the time comes to fill the 
pipes for lighting purposes, some 
of the weights are removed, the 
Gasometer falls down slowly, and 
forces the gas through the tubes 
■ into the main supply to be dis- 
tributed. About four cubic feet 
of gas is obtained from every pound of coal. When gas 
and air become mixed; the mixture is very explosive. In 
a house where an escape of gas is detected let the windows 




Gasometer. 




be opened at the top, and no light introduced for several 
minutes. 



Coal-gas 



109 



It has been calculated that one ton of good coal pro- 
duces the following : — 



I Chaldron of coke . . . 
12 Gallons of tar . . . . 
12 Gallons of ammoniacal liquor 
5,900 Cubic feet of gas 

Loss (water) . , . , 



weighing 



1,494 lbs. 
„ 135 lbs. 

„ 100 lbs. 

„ 291 lbs. 

I, 220 lbs. 

Total 2,240 lbs. 



We can thus estimate the profits of our gas companies 
at leisure. The analysis of gas made by Professor Bunsen 
is as under, iri 100 parts. 



Hydrogen . . 
Marsh gas . , 
Carbonic oxide . 
defiant gas . 
Bufyline 

Sulphide of hydrogen 
Nitrogen 
Carbonic acid . 



45-58 

34-90 

6-64 

4-08 

2-38 

0'29 
2 '46 
3-67 



Gas, therefore, is very injurious, for it rapidly vitiates 
the atmosphere it burns in, and is very trying to the eyes, 
as well as destructive to gilt ornaments. 

Tar is familiar to all readers, and though unpleasant to 
handle or to smell, it produces the beautiful aniline dyes. 
Tar pills are very efficacious for some blood disorders, 
and will remove pimples, etc., from the face, and cure 
" boils " eff( ctually. If a dose of five be taken first, in a 
day or two four, and so on, no second remedy need be 
applied. We have known cases finally cured, and no 
recurrence of boils ever ensued after this simple remedy. 

Tar is one of the results left in the distillation both of 
wood and coal : in places where wood is plentiful and tar 
in request, it is produced by burning the wood for that 



no 



CHEMISTRY. 



purpose ; and in some of the pits in which charcoal is 
produced,' an arrangement is made to collect the tar also. 
Coal-tar and wood-tar are different in some respects, and 
are both distilled to procure the naphthas which bear their 
respective names. From wood-tar creosote is also ex- 
tracted, and it is this substance which gives the peculiar 
tarry flavours to provisions, such as ham, bacon, or herrings, 
cured or preserved by being smoked over wood fires. Tar 
is used as a sort of paint for covering wood-work and 




Tar manufactory. 

cordage when much exposed to wet, v;hich it resists better 
than anything else at the same price ; but the tar chiefly 
used for these purposes is that produced by burning fir or 
deal wood and condensing the tar in a pit below the stack 
of wood ; it is called Stockholm tar, as it comes chiefly 
from that place. 

Carbon only combines with nitrogen under peculiar cir- 
cumstances. This indirect combination is tei-med cyanogen 
(CN). It was discovered by Gay-Lussac, and is used for 



SULPHUR. 



II I 



the production of Prussian blue. Hydrocyanide of potas- 
sium (Prussia acid) is prepared by heating cyanide of 
potassium with sulphuric acid. It is a deadly poison, and 
found in peach- stones. Free cyanogen is a gas. The 
bisulphide of carbon is a colourless, transparent liquid. It 
will easily dissolve sulphur and phosphorus and several 
resins. When phosphorus is dissolved in it, it makes a 




Sulphur furnace. 

very dangerous " fire," and one difficult to extinguish. We 
must now leave carbon and its combinations, and come to 
sulphur. 

Sulphur is found in a native state in Sicily and many 
other localities which are volcanic. It is a yellow, solid 
body, and as it is "f>ver perfectly free from earthy matter. 



I I 2 CHEMISTRY. 

it must be purified before it can be used. It possesses 
neither taste nor smell, and is insoluble in water. Sulphur 
is purified in a retort, C D, which communicates with- a brick 
chamber, A. The retort is placed over a furnace, K, and 
the vapour passes into the chimney through the tube, D, 
where it condenses into fine powder called "flowers of 
sulphur'' (brimstone). A valve permits the heated air 
to pass off, while no exterior air can pass in, for explosions 
would take place were the heated vapour to meet the 
atmospheric air. The danger is avoided by putting an air 
reservoir outside the chimney which is heated by the 
furnace. The sulphur is drawn out through the aperture, 
r, when deposited on the floor of the chamber. The 
sulphur is cast into cylinders and sold. Sulphur is soluble 
in bisulphide of carbon, and is used as a medical agent. 

The compounds of sulphur with oxygen form an 
interesting series. There are two anhydrous oxides 
(anhydrides), — viz., sulphurous and sulphuric anhydride 
(SOj and SO3). There are two notable acids formed by 
the combination with water, sulphurous and sulphuric, and 
some others, which, as in the case of nitrogen, form a series 
of multiple proportions, the oxygen being present in an 
increasing regularity of progression, as follows : — 

Name of Acid. Chemical Formula. 

Hypo-sulphurous acid H2SO2 

Sulphurous acid HjSO, 

Sulphuric acid H2S04 

Thio-sulphuric, or hypo- sulphuric acid . . H2S2O3 

Dithionic acid . . .... HjSsOs 

Trithionic acid HvSsOs 

Tetrathionic acid HjSiOe 

Pcntathionic acid H2S5O5 

The last four are termed " polythionic," because the pro- 
portions of sulphur vary with constant proportions of the 
other constituents. 

The sulphurous anhydride mentioned above is produced 



SULPHURIC ACID. 



113 



when we burn sulphur in the air, or in oxygen ; it may be 
obtained in other ways. It is a colourless gas, and when 
subjected to pressure may be liquified, and crystallized at 
very low temperature. It was formerly called sulphuric 




Liquefaction of sulphuric acid. 

acid. It is a powerful "reducing agent," and a good anti- 
septic. It dissolves in water, and forms the H^SO now 
known as sulphurous acid. 

Sulphuric acid is a most dangerous agent in wicked or 
inexperienced hands, and ama- 
teurs should be very careful 
when dealing with it. It takes 
the water from the moist air, 
and from vegetable and animal 
substances. It carbonizes and 
destroys all animal tissues. Its 
discovery is due to Basil Valen- 
tine, in 1440. He distilled 
sulphate of iron, or green vitriol, and the result was " oil 
of vitriol." It is still manufactured in this way in the 
Hartz district, and the acid passes by retorts into receivers. 
The earthen retorts, A, are arranged in the furnace as in 




Retorts and receivers for acid. 



114 



CHEMISTRY. 



the illustration, and the receivers, B, containing a little 
sulphuric acid, are firmly fixed to them. The oily brown 
product fumes in the air, and is called " fuming sulphuric 
acid," or Nordhausen acid. Sulphuric acid is very much 
used in chemical manufactures, and the prices of many 
necessaries, such as soap, soda, calico, stearin, paper, etc., 
are in close relationship with the cost and production of 
sulphur, which also plays an important part in the making 




„ ,(|l!l]klfMrJJJrfl.im 






ii-tperimcnt to show the existence of gases in solution. 

of gunpowder. The manufacture of the acid is carried on 
in platinum stills. 

Sulphuretted hydrogen, or the hydric sulphide (HjS), is 
a colourless and horribly-smelling gas, and arises from 
putrefying vegetable and animal matter which contains 
sulphur. The odour of rotten eggs is due to this gas, 
which is very dangerous when breathed in a pure state in 
drains, etc. It can be made by treating a sulphide with 



PHOSPHORUS. 1 I 5 

sulphuric acid. It is. capable of precipitating the metals 
when in solution, and so by its aid we can discover the 
metallic ingredient if it be present. The gas is soluble in 
water, and makes its presence known in certain sulphur- 
springs. The colour imparted to egg-spoons and fish- 
knives and forks sometimes is due to the presence of metallic 
sulphides. The solution is called hydro- sulphuric acid. 

Phosphorus occurs in very small quantities, though in 
the form of phosphates we are acquainted with it pretty 
generally, and as such it is absorbed by plants, and is 
useful in agricultural operations. In our organization — in 
the brain, the nerves, flesh, and particularly in bones — 
phosphorus is present, and likewise in all animals. Never- 
theless it is highly poisonous. It is usually obtained from 
the calcined bones of mammalia by obtaining phosphoric 
acid by means of acting upon the bone-ash with sulphuric 
acid. Phosphorus when pure is colourless, nearly trans- 
parent, soft, and easily cut. It has a strong affinity for 
oxygen. It evolves white vapour in atmospheric air, and 
is luminous ; to this element is attributable the luminosity 
of bones of decaying animal matter. It should be kept 
in water, and handled — or indeed not handled but 
grasped with a proper instrument — carefully. 

Phosphorus is much used in the manufacture of lucifer 
matches, and we are all aware of the ghastly appearance 
and ghostly presentment it gives when rubbed upon the 
face and hands in the dark. In the ripples of the waves 
and under the counter of ships at sea, the phosphorescence 
of the ocean is very marked. In Calais harbour we have 
frequently noticed it of a very brilliant appearance a.s the 
mail steamer slowly came to her moorings. This appear- 
ance is due to the presence of phosphorus in the tiny 
animalculse of the sea. It is also observable in the female 
glow-worm, and the " fire-fly." Phosphorus was discovered 
by Brandt in 1669. 



Ii6 



CHEMISTRY. 



It forms two compounds with oxygen — phosphorous 

acid, H,PO^, and 
phosphoric acid, 
H PO,. The com- 

3 4 

pound with hydrogen 
is well marked as 
phosphuretted hydro- 
gen, and is a product 
of animal and veget- 
able decomposition. 
It may frequently be 
observed in stagnant 
pools, for when emit- 
ted it becomes lumi- 
nous by contact with 
atmospheric air. 
There is a very pretty 
but not altogether 
safe experiment to be 
performed when phos- 
phuretted hydrogen 
has been prepared in 
the following manner. 
Heat small pieces of 
phosphorus with milk 
of lime or a solution 
of caustic potash ; or 
make a paste of quick- 
lime and phosphorus, 
and put into the flask 
with some quick-lime 
powdered. Fix a tube 
to the neck, and let 
the other end be 
inserted in a basin of water. (^See illustration, page i i8.) 




" WILL-O'-THE-WISP. 



117 



Apply heat; the phosphuretted hydrogen will be given off, 
and will emerge from the water in the basin in luminous 




rings of a very beautiful appearance. The greatest care 
Should be taken in the performance of this very simple 



ii8 



CHEMISTRY. 



experiment. No water must on any account come in con- 
tact ivith the mixture in the flask. If even a drop or two 
find its way in through the bent tube a tremendous explo- 
sion will result, and then the fire generated will surely 
prove disastrous. The experiment can be performed in a 
cheaper and less dangerous fashion by dropping phosphate 
of lime into the basin. We strongly recommend the latter 
course to the student unless he has had some practice in 
the handling of these inflammable substances, and learnt 
caution by experience. The effect, when the experiment 
is properly performed is very good, the smoke rising in a 
succession of coloured rings. 




Experiment with phospiiuretted hydrogen. 

Silicon is not found in a free state m nature, but, 
combined with oxygen, as Silica it constitutes the major 
portion of our earth, and even occurs in wheat stalks and 
bones of animals. As flint or quartz (see Mineralogy), it 
is very plentiful, and in its purest form is known as rock 
crystal, and approaches the form of carbon known as 
diamond. When separated from oxygen, silicon is a 
powder of greyish^brown appearance, and when heated in 
an atmosphere- of oxygen forms silicic " acid " again, 
which, however, is not acid to the taste, and is also termed 
"silica," or "silex." It is fused with great difificulty, but 



GLASS. 1 1 9 

enters into the manufacture of glass in the form of sand. 
The chemical composition of glass is mixed silicate of 
potassium or sodium, with silicates of calcium, lead, etc. 
Ordinary window glass is a mixture of silicates of sodium 
and calcium ; crown glass contains calcium and silicate of 
potassium.. Crystal glass is a mixture of the same silicate 
and lead. Flint glass is of a heavier composition. Glass 
can be coloured by copper to a gold tinge, blue by cobalt, 
green by chromium, etc. Glass made on a large scale is 
composed of the following materials, according to the kind 
of glass that is required. 

Flint glass (" crystal ") is very heavy and moderately 
soft, very white and bright. It is essentially a table-glass, 
and was used in the construction of the Crystal Palace. 
Its composition is — pure white sea-sand, 52 parts, potash 
14 parts, oxide of lead, 34 parts = 100. 

Plate Glass. Crown Glass. Green (Botlle) Glass. 

Parts. Parts.- Parts. 

Pure white sand. . 55 Fine sand . . . 63 Sea sand . . . 80 

Soda 35 Chalk .... 7 Salt 10 

Nitre 8 Soda .... 30 Lime .... 10 

Lime 2 

loo 100 100 

The ingredients to be made into glass (of whatever kind 
it may be) are thoroughly mixed together and thrown from 
time to time into large crucibles placed in a circle, A A 
(page 120), in a furnace resting on buttresses, BB, and 
heated to whiteness by means of a fire in the centre, c, 
blown by a blowing machine, the tube of which is seen at 
D. This furnace is shown in perspective in page 120. 
The ingredients melt and sink down into a clear fluid, 
throwing up a scum, which is removed. This clear glass 
in the fused state is kept at a white heat till all air- 
bubbles have disappeared ; the heat is then lowered to a 
bright redness, when the glass assumes a consistence and 
ductility suitable to the purposes of the " blower." 

9 



I20 



CHEMISTRY. 




Crucibles. 



Glass blowing requires great care and dexterity, and is 

done by twirling a hollow rod of iron on one end of which 

is a globe of melted glass, the workman blowing into the 

other end all the time. By reheating and twirling a sheet 

of glass is produced. Plate glass is 

formed by pouring the molten glass upon 

a table with raised edges. When cold 

it is ground with emery powder, and 

*B then polished by machinery. 

Many glass articles are cast, or 
" struck-up," by compression in moulds, 
and are made to resemble cut-glass, but 
they are much inferior in appearance. The best are first 
blown, and afterwards cut and polished. Of whatever 
kind of glass the article may be, it is so brittle that the 
slightest blow would break it, a bad quality which is got 
rid of by a process called " annealing," that is, placing it 
while quite hot on the floor of an 
oven, which is allowed to cool very 
gradually. This slow cooling takes 
off the brittleness, consequently 
articles of glass well annealed are 
very much tougher than others, 
and will scarcely break in boiling 
water. 

The kind generally used for 
ornamental cutting is flint-glass. 
Decanters and wine-glasses are 
therefore made of it ; it is very 
bright, white, and easily cut. The 
cutting is performed by means of 
wheels of different sizes and materials, turned by a treadle 
as m a common lathe, or by steam power ; some wheels 
are made of fine sandstone, some of iron, others of tin or 
copper; the edges of some are square, or round, or sharp. 




Plate-glass casting -bringing 
out the pot. 



SELENIUM. 



121 




They are used with sand and water, or emery and water, 
stone wheels with water only. 

In a soluble form silicic acid is found in springs, and 
thus enters into the composi- 
tion of most plants and 
grasses, while the shells and 
scales of " infusoria " consist 
of silica. As silicate of alu- 
mina, — i.e., clay, — it plays a 
very important role in our 
porcelain and pottery works. 

Boron is found in volcanic 
districts, in lakes as boracic 

acid, in combination with Glass flimace (see also page 120 for detail). 

oxygen. It is a brownish-green, insoluble powder, in a 
free state, but as boracic acid it is white. It is used to 
colour fireworks with the beautiful green tints we see. 

Soda and boracic acid combine to 
make borax (or biborate of soda). 
Another and inferior quality of 
this combination is tinkal, found 
in Thibet. Borax is much used 
in art and manufactures, and in 
glazing porcelain. (Symbol B, 
Atomic Weight 1 1.) 

Selenium is a very rare ele- 
ment. It was found by Berzelius 
in a sulphuric-acid factory. It is 
[not found in a free state in nature.. 
It closely resembles sulphur in its 
properties. Its union with hydro- 
Giass-cutting. ggjj produccs a gas, seleniuretted 

hydrogen, which is even more offensive than sulphuretted 
hydrogen. (Symbol Se, Atomic Weight 79.) 

Tellurium is also a rare substance generally found 




122 



CHEMISTRY. 



in combination with gold and silver. It is like bismuth, 
and is lustrous in appearance. Telluretted hydrogen is 
horrible as a gas. Tellurium, like selenium, sulphur, and 
oxygen, combines with two atoms of hydrogen. (Symbol 
Te, Atomic Weight 129.) 

Arsenic, like tellurium, possesses many attributes of a 
metal, and on the other hand has some resemblance to 
phosphorus. Arsenic is sometimes found free, but usually 
combined with metals, and is reduced from the ores by 




Casting plate-glass. 

roasting ; and uniting with oxygen in the air, is known 
as •' white arsenic." The brilliant greens on papers, etc., 
contain arsenic, and are poisonous on that account. 
Arsenic and hydrogen unite (as do sulphur and hydrogen, 
etc.), and produce a foetid gas of a most deadly quality. 
This element also unites with sulphur. If poured into a 
glass containing chlorine it will sparkle and scintillate. 
(Symbol As, Atomic Weight 75.) 

Before closing this division, and passing on to a brief 



METALLOIDS. 



123 



review of the Metals, we would call attention to a few 
facts connected with the metalloids we have been consider- 
ing. Some, we have seen, unite with hydrogen only, as 
chlorine ; some with two atoms of hydrogen, as oxygen, 
sulphur, etc., and some with three, as nitrogen and phos- 
phorus ; some again with four, as carbon and silicon. It 




The manufacture qt porcelain in China. 

has been impossible in the pages we have been able to 
devote to the Metalloids to do more than mention each 
briefly and incompletely, but the student will find sufficient, 
we trust, to interest him, and to induce him to search 
farther, while the general reader will have gathered some 
few facts to add to his store of interesting knowledge. 
We now pass on to the Metals. 





CHAPTER VI.— THE METALS. 

WHAT METALS ARE CHARACTERISTICS AND GENERAL 

■PROPERTIES OF METALS CLASSIFICATION SPECIFIC 

GRAVITY DESCRIPTIONS. 

[E have learnt that the elements are divided into 
metalloids and metals, but the line of demarca- 
tion is very faint. It is very difficult to define 
what a metal is, though we can say what it is 
not. It is indeed impossible to give any absolute defini- 
tion of a metal, except as " an element which does not 
unite with hydrogen, or with another metal to form a 
chemical compound." This definition has been lately given 
by Mr. Spencer, and we may accept it as the nearest 
affirmative definition of a metal, though obviously not 
quite accurate. 

A metal is usually supposed to be solid, heavy, opaque, 
ductile, malleable, and tenacious ; to possess good con- 
ducting powers for heat and electricity, and to exhibit a 
certain shiny appearance known as " metallic lustre." 
These are all the conditions, but they are by no means 
necessary, for very few metals possess them all, and many 
non-metallic elements possess several. The " alkali " 
metals are lighter than water ; mercury is a fluid. The 
opacity of a mass is only in relation to its thickness, for 
Faraday beat out metals into plates so thin that they 
became transparent. All metals are not malleable, nor 
are they ductile. Tin and lead, for example, have veiy 



THE METALS. 



125 



little ductility or tenacity, while bismuth and antimony 
have none at all. Carbon is a much better conductor of 
electricity than many metals in which such power is ex- 
tremely varied. Lustre, again, though possessed by metals, 
is a characteristic of some non-metals. So we see that 
while we can easily say what is not a metal, we can 
scarcely define an actual metal, nor depend upon unvary^ 
ing properties to guide us in our determination. 

The affinity of metals for oxygen is in an inverse ratio 
to their specific gravity, as can be ascertained by experi- 
ment, when the heaviest 
metal will be the least ready 
to oxidise. Metals differ 
in other respects, and thus 
classification and division 
become easier. The fusi- 
bility of metals is of a very 
wide range, rising from a 
temperature below zero to 
the highest heat obtainable 
in the blow-pipe, and even 
then in the case of osmium 
there is a difficulty. While 
there can be no question 
that certain elements, iron, 
copper, gold, silver, etc., are Laminate, 

metals proper, there are many which border upon the line 
of demarcation very closely, and as in the case of arsenic 
even occupy the debatable land. 




Specific Gravity is the relation which the weight of 
substance bears to the weight of an equal volume of water, 
as already pointed out in Phvsics. The specific gravities 
of the metals vary very much, as will be seen from the 
table following — water being, as usual, taken as i : — 



126 



CHEMISTRY. 



Aluminium , 






2"S6 


Antimony 
Arsenic 






67 
6- 


Bismuth . 






97 


Cadmium 






8-6 


Calcium . 






I'S 


Chromium 






6'8 


Cobalt . 






8-9 


Copper , 






8-9 


Gold 






19-3 


Indium . 






Ti 


Iridium . 






2I'I 


Iron 






7-8 


Lead 






113 


Lithium . 






•593 


Magnesium 






174 


Manganese 






8- 


Mercury 






13-5 


Molybdenum 






8-6 



Nickel . 

Osmium . 

Palladium 

Platinum 

Potassium 

Rhodium 

Rubidium 

Ruthenium 

Silver 

Sodium . 

Strontium 

Thallium . 

Tin. 

Titanium 

Tungsten 

Uranium 

Zinc 

Zircon 



8-8 

21'4 

11-8 

21-5 

•86s 

12'I 

"■4 

lo-s 
•972 

2-5 
11-8 

7-2 

5'3 

17-6 

18-4 

7'i 

4'3 



Some metals are therefore lighter and some heavier than 
water. 

The table underneath gives the approximate fusing 
points of some of the metals (Centigrade Scale) — 

(Ice melts at o°.) 



Platinum* . 


about isoo° 


Zinc . . 


about 400 


Gold . 


„ 1200° 


Lead . 


„ 330° 


Silver . 


„ 1000° 


Bismuth 


„ 26s^ 


Cast iron 


1000-1200° 


Tin . 


« 23s' 


Wrought iron , 


„ isoo° 


Sodium 


» 97= 


Copper 


„ I loo" 


Potassium . 


„ 6o' 


Antimony . 


>, 432° 


Mercury 


„ 40= 



There are some metals which, instead of fusing, — that is, 
passing from the solid to the liquid state, — go away in 
vapour. These are volatile metals. Mercury, potassium, 
and sodium, can be thus distilled. Some — antimony and 
bismuth for instance, — do not expand with heat, but con- 
tract (like ice) ; while air pressure has a considerable effect 



Reauires oxy-liydrogen blow-pipe. 



ALLOYS. 



127 



upon the fusing point. Some vaporise at once without 
hquefying ; others, such as iron, become soft before melting. 

Alloys are combinations of metals which are used for 
many purposes, and become harder in union. Amalgams 
are alloys in which mercury is one constituent. Some of 
the most useful alloys are under-stated : — 



Name of Alloy. 

Aluminium bronze 

Bell metal . 

Bronze . . 

Gun metal . 

Brass . 

Dutch metal. 

Mosaic gold. 

Ormolu 

Tombac 

German silver 

Britannia metal 

Solder . 

Pewter . 

Type metal . 

Shot . 

Gold currency 

Silver currency 

Stereotype metal 
Metals combine 
Metals „ 
Metals „ 



Composition. 
Copper and aluminium. 
Copper and tin. 



Copper and zinc 



Copper, nickel, and zinc. 
Antimony and tin. 

Tin and lead. 

Lead and antimony (also copper at times). 

Lead and arsenic. 

Gold and copper. 

Silver and copper. 

Lead, antimony, and bismuth, 
with chlorine, and produce chlorides, 
„ sulphur „ „ sulphides, 

„ oxygen „ „ oxides, and so on. 



The metals may be classed as follows in divisions : — 

., , ^^. „ ,. > Potassium, Sodium, Lithium, Am- 

Metals of the alkalies . as ^ ^.^„„-,^. 

) MONIUM. 

Metals of the alkaline ) Barium, Calcium, Magnesium, Stron- 
earths as j tium. 

•i Aluminium, Cerium, Didymium, Erbium, 
Metals of the earths . as [ Glucinium, Lanthanum, Terbium, Tho- 

) rium, Yttrium, Zirconium. 



128 CHEMISTRY. 

Metals proper — 

y Iron, Manganese, Cobalt, Nickel, 

Common Metals . . as | Copper, Bismuth, Lead, Tin, Zinc, 
' Chromium, Antimony. 
1 Mercury, Silver, Gold, Platinum, 

Noble Metals ... as [ Palladium, Rhodium, Ruthenium, 
) Osmium, Iridium. 

We cannot attempt an elaborate description of all the 
metals, but we will endeavour to give a few particulars 
concerning the important ones, leaving many parts for 
Mineralogy to supplement and enlarge upon. We .shall 
therefore mention only the most useful of the metals in 
this place. We will commence with POTASSIUM. 

Metals of the Alkalies. 

Potassium has a bright, almost silvery, appearance, and 
is so greatly attracted by oxygen that it cannot be kept 
anywhere if that element be present — not even in water, 
for combustion will immediately ensue on water ; and in 
air it is rapidly tarnished. It burns with a beautiful 
violet colour, and a very pretty experiment may easily be 
performed by throwing a piece upon a basin of water. 
The fragment combines with the oxygen of the water, 
the hydrogen is evolved, and burns, and the potassium 
vapour gives the gas its purple or violet colour. The 
metal can be procured by pulverizing carbonate of potas- 
sium and charcoal, and heating them in an iron retort. 
The vapour condenses into globules in the receiver, which 
is surrounded by ice in a wire basket. It must be collected 
and kept in naphtha, or it would be oxidised. Potassium 
was first obtained by Sir Humphrey Davy in 1807. 
Potash is the oxide of potassium, and comes from the 
" ashes " of wood. 

The compounds of potassium are numerous, and exist 
in nature, and by burning plants we can obtain potash 
(" pearlash "). Nitrate of potassium, or nitre (saltpetre), 



POTASSIUM. 



129 



(KNO3), is a very important salt. It is found in the East 
Indies. It is a constituent of gunpowder, which consists 
of seventy-five parts of nitre, fifteen of charcoal, and ten 
of sulphur. The hydrated oxide of potassium, or " caustic 
potash " (obtained from the carbonate), is much used in 
soap manufactories. It is called " caustic " from its pro- 
perty of cauterizing the tissues. Iodide, bromide, and 
cyanide of potassium, are used in medicine and photography. 
Soap is made by combining soda (for hard soap), or 




Preparation of potassium. 

potash (for soft soap), with oil or tallow. Yellow soap has 
turpentine, and occasionally palm oil, added. Oils and 
fats combine with metallic oxides, and oxide of lead with 
olive oil and resin forms the adhesive plaster with which 
we are all familiar vi'hen the mixture is spread upon linen. 
Fats boiled with potash or soda make soaps ; the glycerine 
is sometimes set free and purified as we have it. Some- 
times it is retained for glycerine soap. Fancy soap is 
only common soap coloured. White and brown Windsor 
are the same soap — in the latter case browned to imitate 



130 



CHEMISTRY. 



age ! Soap is quite soluble in spirits, but in ordinary 
water it is not so greatly soluble, and produces a lather, 
owing to the lime in the water being present in more or 
less quantity, to make the water more or less " hard." 



Sodium is not unlike potassium, not only in appear- 
ance, but in its attributes ; it can be obtained from the 
carbonate, as potassium is obtained from its carbonate. 
Soda is the oxide of sodium, but the most common and 
useful compound of sodium is the chloride, or common salt, 
which is found in mines in England, Poland, and elsewhere. 
Salt may also be obtained by the evaporation of sea water. 

Rock salt is got at Salz- 
burg, and the German salt 
mines and works produce 
a large quantity. The 
Carbonate of Soda is 
manufactured from the 
chloride of sodium, al- 
though it can be procured 
from the salsoda plants by 
burning. The chloride of 
sodium is converted into 




Machine for cutting soap in bars. 



sulphate, and then ignited with carbonate of lime and 
charcoal. The soluble carbonate is extracted in warm 
water, and sold in crystals as soda, or (anhydrous) "soda 
ash." The large quantity of hydrochloric acid produced 
in the iirst part of the process is used in the process of 
making chloride of lime. A few years back, soda was 
got from Hungary and various other countries where it 
exists as a natural efflorescence on the shores of some 
lakes, also by burning sea-weeds, especially the common 
bladder wrack {Fiicus vesiculosus), the ashes of which were 
melted into masses, and came to market in various states 
of purity. The bi-carbonate of soda is obtained by pass- 



LITHIUM. 



131 



ing carbonic acid gas over the carbonate crystals. Soda 
does not attract moisture from the air. It is used in wash- 
ing, in glass manufactories, in dyeing, soap-making, etc. 

Sulphate of Soda is "Glauber's Salt"; it is also employed 
in glass-making. Mixed with sulphuric acid and water, 
it forms a freezing mixture. Glass, as we have seen, is 
made with silicic acid (sand), soda, potassa, oxide of lead, 
and lime, and is an artificial silicate of soda. 



Lithium is the lightest of metals, and forms the link 




Soap-boiling house. 

between alkaline and the alkaline earth metals. The salts 
are found in many places in solution. The chloride when 
decomposed by electricity yields the metal. 

CESIUM and Rubidium require no detailed notice 
from us. They were first found in the solar spectrum, 
and resemble potassium. 

Ammonium is only a conjectural metal. Ammonia, of 



132 



CHEMISTRY. 




which we have already treated, is so like a metallic oxide 
that chemists have come to the conclusion that its com- 
pounds contain a metallic body, which they have named 

hypothetically AMMONIUM. 
It is usually classed amongst 
the alkaline metals. The salts 
of ammonia are important, 
and have already been men- 
tioned. Muriate (chloride) of 
ammonia, or sal-ammoniac, is 
analogous to chloride of 
sodium and chloride of potas- 
sium. It is decomposed by 
Mottled soap-frames. heating it with slakcd lime 

and then gaseous ammonia is given off. 

The Metals of the Alkaline Earths. 

Barium is the first of the four metals we have to notice 
in this group, and will not detain 
us long, for it is little known in a 
free condition. Its most im- 
portant compound is heavy spar 
{sulphate of baryta), which, when 
powdered, is employed as a white 
paint. The oxide of barium, 
BaO, is termed baryta. 

Nitrate of Baryta is used for 
" green fire," which is made as 
follows : — Sulphur, twenty parts ; 
chlorate of potassium, thirty-three 
parts ; and nitrate of baryta, 
eighty parts (by weight). 

Soda furnace. 

Calcium forms a considerable quantity of our earth's 
crust. It is the metal of lime, which is the oxide of 




CHALK. I 3 3 

calcium. In a metallic state it possesses no great interest, 
but its combinations are very important to us. Lime is, 
of course, familiar to all. It is obtained by evolving the 
carbonic acid from carbonate of lime (CaO). 

The properties of this lime are its white appearance, 
and it develops a considerable amount of heat when mixed 
with water, combining to make hydrate of lime, or " slaked 
lime." This soon crumbles into powder, and as a mortar 
attracts the carbonic acid from the air, by which means 
it assumes the carbonate and very solid form, which 
renders it valuable for cement and mortar, which, when 
mixed with sand, hardens. Caustic lime is used in white- 
washing, etc. 

Carbonate of Lime (CaCOj) occurs in nature in various 
forms, as lime-stone, chalk, marble, etc. Calc-spar (arra- 
gonite) is colourless, and occurs as crystals. Marble is 
white (sometimes coloured by metallic oxides), hard, and 
granular. Chalk is soft and pulverizing. It occurs in 
mountainous masses, and in the tiniest shells, for carbonate 
of lime is the main component of the shells of the Crus- 
tacea, of corals, and of the shell of the egg ; it enters like- 
wise into the composition of bones, and hence we must 
regard it as one of the necessary constituents of the food 
of animals. It is an almost invariable constituent of the 
waters we meet with in Nature, containing, as they always 
do, a portion of carbonic acid, which has the power of 
dissolving carbonate of lime. But when gently warmed, 
the volatile gas is expelled, and the carbonate of lime is 
deposited in the form of white incrustations upon the 
bottom of the vessel, which are particularly observed on 
the bottoms of tea-kettles, and if the water contains a large 
quantity of calcareous matter, even our water-bottles and 
drinking-glasses become covered with a thin film ot car- 
bonate of lime. These depositions may readily be removed 
by pouring into the vessels a little dilute hydrochloric acid, 



134 CHEMISTRY. 

or some strong vinegar, which in a short time dissolves the 
carbonate of lime. 

Sulphate of Lime (CaSO^ is found in considerable 
masses, and is commonly known under the name of 
Gypsum. It occurs either crystallized or granulated, and 
is of dazzling whiteness ; in the latter form it is termed 
Alabaster, which is so soft as to admit of being cut with 
a chisel, and is admirably adapted for various kinds of 
works of art. Gypsum contains water of crystallization, 
which is expelled at a gentle heat. But when ignited, 
ground, and mixed into a paste with water, it acquires the 
property of entering into chemical combination with it, 
and forming the original hydrate, which in a short time 
becomes perfectly solid. Thus it offers to the artist a 
highly valuable material for preparing the well-known 
plaster of Paris figures, and by its use the noblest statues 
of ancient and modern art have now been placed within 
the reach of all. Gypsum, moreover, has received a valu- 
able application as manure. In water it is slightly soluble, 
and imparts to it a disagreeable and somewhat bitterish, 
earthy taste. It is called " selenite " when transparent. 

Phosphate of Lime constitutes the principal mass of the 
bones of animals, and is extensively employed in the pre- 
paration of phosphorus ; in the form of ground bones it is 
likewise used as a manure. It appears to belong to those 
mineral constituents which are essential to the nutrition 
of animals. It is found in corn and cereals, and used in 
making bread ; so we derive the phosphorus which is so 
useful to our system. 

Chloride of Lime is a white powder smelling of chlorine, 
and is produced by passing the gas over the hydrate of 
lime spread on trays for the purpose. It is the well-known 
"bleaching powder." It is also used as a disinfectant. 
The Fluoride of Calcium is Derbyshire spar, or " Blue 
John.'' Fluor spar is generally of a purple hue. We 



MAGNESIUM. I 3 5 

may add that hard water can be softened by adding a 
Httle powdered lime to it. 

Magnesium sometimes finds a place with the other 
metals, for it bears a resemblance to zinc. Magnesium 
may be prepared by heating its chloride with sodium. Salt 
is formed, and the metal is procured. It burns very 
brightly, and forms an oxide of magnesia (MgO). Magne- 
sium appears in the formation of mountains occasionally. 
It is ductile and malleable, and may be easily melted. 

Carbonate of Magnesia, combining with carbonate of 
lime, form the Dolomite Hills. When pure, the carbonate 
is a light powder, and when the carbonic acid is taken 
from it by burning it is called Calcined Magnesia. 

The Sulphate of Magnesia occurs in sea-water, and in 
saline springs such as Epsom. It is called " Epsom Salts." 
Magnesium wire burns brightly, and may be used as an 
illuminating agent for final scenes in private theatricals. 
Magnesite will be mentioned among Minerals. 

Strontium is a rare metal, and is particularly useful 
in the composition of " red fire." There are the carbonate 
and sulphate of strontium ; the latter is known as Celesiine, 
The red fire above referred to can be made as follows, in a 
dry mixture. Ten parts nitrate of strontia, \\ parts 
chlorate of potassium, 3 J parts of sulphur, i part sulphide 
of antimony, and \ part charcoal. Mix well without mois- 
ture, enclose in touch paper, and burn. A gorgeous 
crimson fire will result. 

Metals of the Earths. 

Aluminium (Aluminum) is like gold in appearance 

when in alloy with copper, and can be procured from its 

chloride by decomposition with electricity. It occurs 

largely in nature in composition with clays and slates. 

10 



1 36 CHEMISTRY. 

Its oxide, alumina (Al^Oj), composes a number of mine- 
rals, and accordingly forms a great mass of the earth. 
Alumina is present in various forms {see Minerals) in the 
earth, all of which will be mentioned under Crystallo- 
graphy and Mineralogy. The other nine metals in this 
class do not call for special notice. 

Heavy Metals. 

Iron, which is the most valuable of all our metals, may 
fitly head our list. So many useful articles are made of it, 
that without consideration any one can name twenty. 
The arts of peace and the glories of war are all produced 
with the assistance of iron, and its occurrence with coal 
has rendered us the greatest service, and placed us at 
the head of nations. It occurs native in meteoric stones. 

Iron is obtained from certain ores in England and 
Sweden, and these contain oxygen and iron {see Miner- 
alogy). We have thus to drive away the former to obtain 
the latter. This is done by putting the ores in small 
pieces into a blast furnace (page 137) mixed with lime- 
stone and coal. The process of severing the metal from 
its ores is termed smelting, the air supplied to the furnace 
being warmed, and termed the "hot blast." The "cold 
blast" is somefhnes used. The ores when dug from the 
mine are generally stamped into powder, then " roasted," 
- — that is, made hot, and kept so for some time to drive off 
water, sulphur, or arsenic, which would prevent the "fluxes" 
acting properly. The fluxes are substances which will mix 
with, melt, and separate the matters to be got rid of, the 
chief being charcoal, coke, and limestone. The ore is then 
mixed with the flux, and the whole raised to a great heat; 
as the metal is separated it melts, runs to the bottom 
of the " smelting furnace," and is drawn off into moulds 
made of sand ; it is thus cast into short thick bars called 
"pigs," so we hear of pig-iron, and pig-lead. Iron is 



HEAVY METALS. 



137 



smelted from " ironstone," which is mixed with coke and 
limestone. The heat required to smelt iron is so very 
great, that a steam-engine is now generally employed to 
blow the furnace. (Before the invention of the steam- 
engine, water-mills were used for the same purpose.) The 




Blast furnace. 

smelting is conducted in what is called a blast furnace. 
When the metal has all been " reduced," or melted, and 
run down to the bottom of the furnace, a hole is made, 
out of which it runs into the moulds ; this is called 
"tapping the furnace." 



138 



CHEMISTRY. 



Smelting is often confounded with melting, as the 
names are somewhat alike, but the processes are entirely- 
different ; in melting, the metal is simply liquefied, in 
smelting, the metal has to be produced from ores which 
often have no appearance of containing any, as in the 
case of iron-stone, which looks like brown clay. 

The cone of the furnace. A, is lined with fire-bricks, ii, 
which is encased by a lining, //; outside are more fire- 
bricks, and then masonry, fn-n ; C is the throat of the fur- 




General foundry, Woolwich Arsenal. 



nace ; D the chimney. The lower part, B, is called the 
boshes. As soon as the ore in the furnace has become 
ignited the carbon and oxygen unite and form carbonic 
acid, which escapes, and the metal fuses at last and runs 
away. The coal and ore are continually added year after 
year. The glassy scum called " slag " protects the molten 
iron from oxidation. 

The metal drawn from the blast furnace is "pig" iron 
or "cast" iron, and contains carbon. This kind of iron is 



WIRE DRAWING. 



139 




used for casting operations, and runs into sand-moulds 
It contracts very little when cooling. It is hard and 
brittle. 

Bar Iron is the almost pure 
metal. It is remarkably tena- 
cious, and may be drawn into 
very fine wire or rolled. But it 
is not hard enough for tools. It 
is difficult to fuse, and must be 
welded by hammering at a red 
heat. Wire-drawing is per- 
formed by taking the metal as a 
bar, and passing it between 
rollers, which flatten it, and then 
between a new set, which form 
cutting edges on the rolled plate, 
the projections of one set fit- 
ting into the hollows of the wire rollers. 

other closely as in the two illustrations on this page. 
The strips of metal come out at the aperture seen at A, in 
illustration on next page. These rods are drawn through 
a series of diminishing holes in a steel plate, 
occasionally being heated to keep it soft and 
ductile. When the wire has got to a certain 
fineness it is attached to a cylinder and 
drawn away, at the same time being wound 
round the cylinder over a small fire. Some 
metals can be drawn much finer than others. 
Gold wire can be obtained of a " thickness " 
(or thinness) of only the 5,000th part of an 
JiJ inch, 550 feet weighing one grain! But 
Cutting edges. platiuum has exceeded this marvellous thin- 
ness, and wire the 30,000th part of an inch has been 
produced. Ductility and malleability are not always 
fpund in the same metal in proportion. The sizes of" 




I40 



CHEMISTRY. 



wires are gauged by the instrument shown in the margin. 

The farther the wire will go into 
the groove the smaller its " size." 
Steel contains a certain 
amount of carbon, generally 
about I 
to 2 per 
cent. 
Cast 
steel is 

prepared from cast iron. Steel 
from bar-iron has carbon added, 
and is termed bar-steel. The 
process is called " cementation," 
and is carried on by packing the bars of iron in brick- 
work boxes, with a mixture of salt and soot, or with char- 




.H^IH-H'-'HHH- 


- 




' 1 1 1 1 1 1 1 1 







Wire size. 



Rollers. 




Coarse wire-drawing. 

coal, which is termed " cement." Steel js really a carbide 



BESSEMER STEEL. 



141 



of iron, and Mr. Bessemer founded his process of making- 
steel by blowing out the excess of carbon from the 
iron, so that the proper amount — 1-$ per cent. — should 
remain. 

A brief summary of the Bessemer process may be 
interesting. If a bar of steel as soft as iron be made red- 
hot and plunged into cold water, it will become very hard. 
If it be then gently heated it will become less hard, and is 
then fitted for surgical instruments. The various shades 
of steel are carefully watched, — the change of colour being 




Fine wire-drawing. 



due to the varying thickness of the oxide ; for we know 
that when light falls upon very thin films of a substance, — 
soap-bubbles, for instance, — the light reflected from the 
under and upper surfaces interfere, and cause colour, 
which varies with the thickness of the film. These 
colours in steel correspond to different temperatures, and 
the " temper " of the steel depends upon the tempera- 
ture it has reached. The following table extracted from 
Haydn's " Dictionary of Science " gives the " temper,'' the 
colour, and the uses of the various kinds of steel. 



142 



CHEMISTRY. 



Cent. Fahr. 


Colour. 


Uses of Steel. 


220° = 430" 


Faint yellow 


Lancets. 


232° = 450° 


Pale straw . 


Best razors and surgical instruments. 


243° = 470° 


Yellow 


Ordinary razors, pen-knives, etc. 


2S4° = 490° 


Brown 


Small shears, scissors, cold chisels, etc. 


265° = 510° 


Brown and purple 






spots 


"Vxes, pocket-knives, plane-irons, etc. 


277° = 530° 


Purple 


Table-knives, etc. 


288° = 550° 


Light blue . 


Swords, watch-springs, etc. 


293' = 560° 


Full blue . 


Fine saws, daggers, etc. 


316° = 600° 


Dark blue . 


^and and pit saws. 



The Bessemer process transfers the metal into a vessel 
in which there are tubes, through which air is forced, which 
produces a much greater heat than a bellows does. Thus 
in the process the carbon of the iron acts as fuel to main- 
tain the fusion, and at the same time by the bubbling of 
the carbonic acid mixes the molten iron thoroughly. 

During the bubbling up of the whole mass of iron, and 
the extreme elevation of temperature caused by the union 
of the carbon of the impure iron with the oxygen of the 
air, the oxide of iron is formed, and as fast as it forms 
fuses into a sort of glass ; this unites with the earthy 
matters of the " impure" iron, and floats on the upper part 
as a flux, thus ridding the " cast iron" of all its impurities, 
with no other fuel than that contained in the metal itself, 
and in the air used. When the flame issuing from the 
" converter " contracts and changes its colour, then the 
time is known to have arrived when the iron is " de- 
carbonked." The amount of carbon necessary is arti- 
ficially added, ebullition takes place, a flame of carbonic 
oxide comes out, and the metal is then run into ingots. 

The compounds of iron which are soluble in water 
have a peculiar taste called chalybeate (like ink). Many 
mineral springs are so flavoured, and taste, as the immortal 
Samuel Weller put it, "like warm flat-irons." Iron is fre- 
quently used as a medicine to renew the blood globules. 



OXIDES OF IRON. 



143 



Protoxide of Iron is known only in combination. 

Sesqui-Oxide of Iron is "red ironstone." Powdered it 
is called English rouge, a pigment not altogether foreign 
to our use. In a pure state it is a remedy for arsenical 
poisoning, and is really the " rust " upon iron. 

Bisulphide of Iron is iron pyrites, and is crystalline. 




Bessemer's process. 

Chloride of Iron is dissolved from iron with hydro- 
chloric acid. It is used in medicine. 

Cyanide of Iron makes, with cyanide of potassium, the 
well-known prussiate of potash (ferro-cyanide of potas- 
sium), which, when heated, precipitates Prussian blue 
(cyanogen and iron). 

The Sulphate of the Protoxide is known as copperas, or 
green vitriol, and is applied to the preparation of Prussian 
blue. 



144 CHEMISTRY. 

Manganese is found extensively, but not in any large 
quantities, in one place ; iron ore contains it. It is very 
hard to fuse, and is easily oxidised. The binoxide is 
used to obtain oxygen, and when treated with potassium 
and diluted, it becomes the permanganate of potassium, 
and is used as "Condy's fluid." It readily oxidizes organic 
matters, and is thus a disinfectant. It cry.stallizes in long, 
deep, red needles, which are dissolved in water. It is a 
standard laboratory test. There are other compounds, but 
in these pages we need not detail them. 

Cobalt and Nickel occur together. They are hard, 
brittle, and fusible. The salts of cobalt produce beautiful 
colours, and the chloride yields an "invisible" or sympa- 
thetic ink. The oxide of cobalt forms a blue pigment for 
staining glass which is called " smalt." Nickel is chiefly 
used in the preparation of German silver and electro- 
plating. The salts of nickel are green. Nickel is difficult 
to melt, and always is one of the constituents of meteoric 
iron, which falls from the sky in aerolites. It is magnetic 
like cobalt, and is extracted from the ore called kupfer- 
nickel. A small United-States coin is termed a " nickel." 

Copper is the next metal we have to notice. It has 
been known for centuries. It is encountered native in 
many places. The Cornish copper ore is the copper 
pyrites. The fumes of the smelting works are very 
injurious, containing, as they do, arsenic and sulphur. Tiie 
ground near the works is usually bare of vegetation in 
consequence of the " smoke." Sheet copper is worked 
into many domestic utensils, and the alloy with zinc, 
termed Brass, is both useful and ornamental. Red brass 
is beaten into thin leaves, and is by some supposed to be 
"gold leaf"; it is used in decorative work. Bronze is also 
an alloy of copper, as are gun-metal, bell-metal, etc. 



LEAD. 1 4 5 

Next to silver, copper is the best conductor of electricity 
we have. It is very hard and tough yet elastic, and 
possesses malleability and ductility in a high degree. It 
forms two oxides, and there are several sulphides ; the 
principal of the latter are found native, and worked as 
ores. The sulphate of copper is termed blue vitriol, and 
is used in calico-printing, and from it all the (copper) 
pigments are derived. It is also used in solution by 
agriculturists to protect wheat from insects. When copper 
or its alloys are exposed to air and water, a carbonate of 
copper forms, which is termed verdigris. All copper salts 




Native copper. 

are poisonous; white of eggs is an excellent remedy in 
such cases of poisoning. 

Lead is obtained from galena, a sulphide of lead. It 
is a soft and easily-worked metal. When freshly cut it 
has quite a bright appearance, which is quickly tarnished. 
Silver is often present in lead ore, and is extracted by 
Pattison's process, which consists in the adaptation of the 
knowledge that lead containing silver becomes solid, after 
melting, at a lower temperature than lead does when pure. 
Pure lead therefore solidiiies sooner. 

One great use of lead is for our domestic water-pipes, 



146 



CHEMISTRY. 



which remind us in winter of their presence so disagreeably. 
Shot is made from lead, and bullets are cast from the same 
metal. Shot-making is very simple, and before the days 
of breech-loading guns and cartridges, no doubt many 
readers have cast bullets in the kitchen and run them into 
the mould over a basin of water or a box of sand. For 
sporting purposes lead is mixed with arsenic, and when it 




Shot tower. 

is melted it is poured through a sort of sieve (as in the 
cut) at the top of a high tower. (See pages 146 and 148). 
The latter illustration gives the section of the shot tower ; 
A IS the furnace, b is the tank for melting the lead, and 
the metal is permitted by the workman ate to run through 
the sieve in fine streams. As the lead falls it congeals 
into drops, which are received in water below to cool them, 



TIN. 147 

They are, of course, not all round, and must be sorted. 
This operation is performed by placing them on a board 
tilted up, and under which are two boxes. The round 
shot rush over the first holes and drop into the second 
box, but the uneven ones are caught lagging, and drop 
into box No. i. They are accordingly sent to the furnace 
again. 

The next process is to sort the good shot for size. This 
is done by sieves — one having holes a little larger than 
the size of shot required. This sieve passes through it 
all of the right size and smaller, and keeps the bigger 
ones. Those that have passed this examination are then 
put into another sieve, which has holes in it a little smaller 
than the size of shot wanted. This sieve retains the right 
shot, and lets the smaller sizes pass, and so on. The shot 

are sized and numbered, ■ s,^^ 

glazed by rolling them 'in a ^^ — !-'~T"'^A JL. 

barrel with graphite, and =---:'JJW 1 

then they are ready for use. 

Bullets are made by ma- .sieve for sizeing shot. 

chinery by the thousand, and made up into cartridges with 
great speed. 

The compounds of lead are also poisonous, and •pro- 
duce " colic," to which painters are subject. Red lead, or 
minium, is a compound of the protoxide and the binoxide, 
and may be found native. The former oxide is litharge ; 
white lead, or the carbonate of lead^ is a paint, and is easily 
obtained by passing a stream of carbonic acid into a solu- 
tion of acetate of lead. It is used as a basis of many 
paints. 

Tin is another well-known metal. It is mentioned by 
Moses. It possesses a silver-like lustre, and is not liable 
to be oxidised. The only really important ore is called 
Tinstone, from which the oxygen is separated, and the 



148 



CHEMISTRY. 



^\^\-j— 



metal remains. Cornwall has extensive tin mines. Tin 
is malleable and ductile, and can be beaten into /oil or 
'• silver leaf," or drawn into wire. It prevents oxidation 
of iron if the latter be covered with it, and 
for tinning copper vessels for culinary pur- 
poses. The Romans found tin in Cornwall, 
and the term "Stanneries" was applied to 
the courts of justice among the tin miners 
in Edward the First's time. We have already 
mentioned the alloys of tin. The oxides of 
tin, " Stannous " and " Stannic," are useful 
to dyers. The latter is the tin-stone (SnO^). 
Sulphide of tin is called " Mosaic gold," and 
is much used for decorative purposes. 

Zinc is procured from calamine, or car- 
bonate of zinc, and blende, or sulphide of 
zinc. It has for some years been used for 
many purposes for which lead was once 
employed, as it is cheap and light. Zinc is 
a hard metal of a greyish colour, not easily 
bent, and rather brittle; but when made 
nearly red-hot, it can be rolled out into 
sheets or beaten into form by the hammer. 
Zinc is about six-and-three-quarter times 
heavier than water. Like many other 
metals, it is volatile (when heated to a 
certain extent it passes off into vapour), and 
the probable reason that it was not known 
or used of old is that it was lost in the 
attempt to smelt its ores. Zinc is now 
obtained by a sort of distillation ; the ores 

are mixed with the flux in a large earthen crucible or pot. 
We have already noticed the alloy of zinc with copper 

(brass), and the use of zinc to galvanize iron by covering 



!ll:l 



Secrion of shot tower. 



CHROMIUM. 



149 



the latter with a coating of zinc in a bath is somewhat 
analogous to electro-plating. The metal is largely used 
as the positive element in galvanic batteries, and for the 
production of hydrogen in the laboratory. Zinc forms one 
oxide (ZnO), used for zinc-white. The sulphate of zinc is 
white vitriol, and the chloride of zinc is an "antiseptic." 
Certain preparations of the metal are used in medicme, as 
"ointments" or "'washes," and are of use in inflammation 
of the eyelids. 




Preparing lead for bullets. 

Chromium. This "metallic element" is almost un- 
known in the metallic state. But although little known, 
the beautiful colours of its compounds make it a very 
interesting study. The very name leads one to expect 
something different to the other metals — chroma, colour. 
The metal is procured from what is known as chrome- 
ironstone, a combination of protoxide of iron and sesqui- 
oxide of chromium (FeOCr,03). By ignition with potas- 
sium we get chromic acid and chromate of potassium, a: 



ISO 



CHEMISTRY. 



yellow salt which is used to make the other compounds of 
chromium. The metal is by no means easy to fuse. 

Sesqui-Oxide of Chromium is a fine green powder em- 
ployed in painting porcelain. 

Chromate of Lead is termed " chrome yellow," and in 
its varieties is employed as a paint. 




Type-casting 

Chromate of Mercury is a beautiful vermilion. There 
are numerous other combinations which need not be men- 
tioned here. 



Antimony was discovered by Basil Valentine. The 
Latin term is Stibium, hence its symbol, Sb. It is very 
crystalline, and of a peculiar bluish-white tint. It will 
take fire at a certain high temperature, and can be used 
for the manufacture of "Bengal Lights," with nitre and 



ANTIMONY. I 5 I 

sulphur in the proportions of antimony " one," the others 
two and three respectively. 

The compounds of antimony are used in medicine, and 
are dangerous when taken without advice. They act as 
emetics if taken in large quantities. Our "tartar emetic" 
is well known. 

Antimony, in alloy with lead and a little tin, form the 
ype metal to which we are indebted for our printing. 
Type-casting is done by hand, and requires much dexterity. 
A ladle is dipped into the molten metal, and the mould 
jerked in to fill it properly, and then the type is removed 
and the mould shut ready for another type ; and a skilful 
workman can perform these operations five hundred times 
in an hour, — rather more than eight times a minute, — 
producing a type each time ; this has afterwards to be 
finished off by other hands. The metal of which type is 
made consists of lead and antimony ; the antimony hardens 
it and makes it take a sharper impression. The letters are 
first cut in steel, and from these "dies " the moulds are 
made in brass, by stamping, and in these the types are cast 

Stereotype consists of plates of metal taken, by casting, 
from a forme of type set up for the purpose : an impression 
was formerly carried on by plaster-of-Paris moulds, but 
lately what is termed the papier-macM process is adopted. 
The paper used is now made in England, and the pre- 
pared sheet is placed upon the type and beaten upon it. 
Paste is then filled in where there are blanks, and another 
and thicker sheet of the prepared paper is placed over all, 
dried, and pressed. When this is properly done the paper 
is hardened, and preserves an impression of the type set 
up. The paper mould is then put into an iron box, and 
molten metal run in. In a very short time a "stereotype" 
• plate is prepared from the paper, which can be used again 
if necessary. The metal plate is put on the machine. 

There are several compounds of antimony, which, 



I 5 2 CHEMISTRY. 

though valuable to chemists, would not be very interesting 
to the majority of readers. We will therefore at once pass 
to the Noble Metals. 

The Noble Metals. 

There are nine metals which rank under the above 
denomination : — Mercury, Silver, Gold, Platinum, Palla- 
dium, Rhodium, Ruthenium, Osmium, Iridium. We will 
confine ourselves chiefly to the first four on the list. 

Mercury, or Quicksilver, is the first of the metals 
which remain unaltered by exposure to atmospheric air, 
and thus are supposed to earn their title of nobility. 
Mercury is familiar to us in our barometers, etc., and is 
fluid in ordinary temperatures, though one of the heaviest 
metals we possess. It is principally obtained from native 
cinnabar, or sulphide of mercury (vermilion), and the pro- 
cess of extraction is very easy. Mercury was known to 
the ancients, and is sometimes found native. In the mines 
the evil effects of the contact with mercury are apparent 

This metal forms two oxides, — the black (mercurous) 
oxide, or sub-oxide (Hg^O), and the red (mercuric) oxide, 
or red precipitate. The chlorides are two, — the sub- 
chloride, or calomel, and the perchloride, or corrosive 
sublimate. The sulphides correspond with the oxides ; 
the mercuric sulphide has been mentioned. Its crimson 
colour is apparent in nature, but the Chinese prepare it in 
a particularly beautiful form. Many amalgams are made 
with mercury, which is useful in various ways that will at 
once occur to the reader. 

Silver is the whitest and most beautiful of metals, and 
its use for our plate and ornaments is general. It is 
malleable and ductile, and the best conductor of electricity 



SILVER. 



153 



and heat that we have. It is not unfrequently met with 
in its native state, but more generally it is found in com- 
bination with gold and mercury, or in lead, copper, and 
antimony ores. The mines of Peru and Mexico, with other 
Western States of America, are celebrated — Nevada, 
Colorado, and Utah in particular. The story of the silver 
mine would be as interesting as any narrative ever printed. 
The slavery and the death-roll would equal in horror and 
in its length the terrible records of war or pestilence. We 
have no opportunity here to follow it, or its kindred metals 
with which- it unites, on the sentimental side ; but were 
the story of silver production 
written in full, it would be 
most instructive. 

Silver is found with lead 
(galena), which is then smelted. 
The lead is volatilized, and 
the silver remains. It is also 
extracted by the following 
process, wherein the silver 
and golden ore is crushed and 
washed, and quicksilver, salt, 
and sulphate of copper added, 
while heat is applied to the 
mass. From tank to tank 
the slime flows, and deposits the metals, which are put' 
into retorts and heated. The mercury flies off ; the silver' 
and gold remain in bars. 

In some countries, as in Saxony and South America,- 
recourse is had to another process, that of amalgamation, 
which depends on the easy solubility of silver and other 
metals in mercury. The ore, after being reduced to a fine- 
powder, is mixed with common salt, and roasted at a low' 
red heat, whereby any sulphide of silver the ore may 
contain is converted into chloride. The mixture is then! 




Native silver. 



154 CHEMISTRY. 

placed, with some water and iron filings, in a barrel which 
revolves round its axis, and the whole agitated for some 
time, during which process the chloride of silver becomes 
reduced to the metallic state. A portion of mercury is 
then introduced, and the agitation continued. The mer- 
cury combines with the silver, and the amalgam is then 
separated by washing. It is afterwards pressed in woollen 
bags to free it from the greater part of the mercury, and 
then heated, when the last trace of mercury volatilizes and 
leaves the silver behind. 

Nitrate of Silver is obtained when metallic silver is dis- 
solved in nitric acid. It is known popularly as lunar 
caustic, and forms the base of " marking inks." Chloride 
of silver is altered by light, but the iodide of silver is even 
more rapidly acted on, and is employed in photography. 
Fulminating silver is oxide of silver' digested in ammonia. 
It is very dangerous in inexperienced hands. It is also 
prepared by dissolving silver in nitric acid, and adding 
alcohol. It cools in crystals. Fulminating mercury is 
prepared in the same way. 

Gold is the most valuable of all metals, — the " king 
of metals," as it was termed by the ancients. It is always 
found "native," frequently with silver and copper. Quartz 
is the rock wherein it occurs. From the disintegration of 
these rocks the gold sands of rivers are formed, and 
separated from the sands by "washing." In Australia 
and California "nuggets" are picked up of considerable 
size. 

It is a rather soft metal, and, being likewise costly, is 
never used in an absolutely pure state. Coins and jewel- 
lery are all alloyed with copper and silver to give them 
the requisite hardness and durability. Gold is extremely 
ductile, and very malleable. One grain of gold may be 
drawn into a wire five hundred feet in length; and the 



GOLD. I 5 5 

metal may be beaten into almost transparent leaves ^o(/ooo 
of an inch in thickness ! 

Aqua-regia, a mixture of hydro-chloric and nitric 
acids, is used to dissolve gold, though free chlorine, or 
selenic acid individually, will dissolve it. Faraday made 
many experiments as to the relation of gold to light. 
{See "Phil. Trans.," 1857, p. 145.) The various uses of 
gold are so well known that we need not occupy time and 
space in recording thenr . Gilding can be accomplished 
by immersing the article in a hot solution of chloride of 
gold and bicarbonate of potash mixed ; but the electro 




Native gold. 

process is that now in use, by which the gold precipitates 
on the article to be plated. 

We have already described the process of electro-plating 
in the case of silvered articles, and we need only mention 
that electro-gilding is performed very much in the same 
way. But gilding is also performed in other ways ; one 
of which, the so-called water gilding, is managed as follows. 
Gilding with the gold-leaf is merely a mechanical opera- 
tion, but water-gilding is effected by chemistry. 

Water-gilding is a process (in which, however, no water 
is used) for covering the surface of metal with a thin 



156 CHEMISTRY. 

coating of gold ; the best metal for water-gilding is either 
brass, or a mixture of brass and copper. A mixture of 
gold and mercury, in the proportion of one part of gold to 
eight of mercury, is made hot over a fire till they have 
united ; it is then put into a bag of chamois-leather, and 
the superfluous mercury pressed out. What remains is 
called an " amalgam " ; it is soft, and of a greasy nature, 
so that it can be smeared over any surface with the fingers. 
The articles to be gilt are made perfectly clean on the 
surface, and a liquid, made by dissolving mercury in nitric 
acid (aqua-fortis), is passed over them with a brush made 
of fine brass wire, called a " scratch-brush." The mercury 
immediately adheres to the surface of the metal, making it 
look like silver ; when this is done, a little of the amalgam 
is rubbed on, and the article evenly covered with it. It 
is then heated in a charcoal fire till all the mercury evapo- 
rates, and the brass is left with a coating of gold, which is 
very dull, but may be burnished with a steel burnisher and 
made bright iif necessary. In former times articles were 
inlaid with thin plates of gold, which were placed in hollows 
made with a graver, and melted in, a little borax being 
applied between. 

When a solution of " chloride of gold " is mixed with 
ether, the ether takes the gold away from the solution, and 
may be poured off" the top charged with it. " This solution, 
if applied to polished steel by means of a camel-hair pencil, 
rapidly evaporates, leaving a film of gold adhering to the 
steel, which, when burnished with any hard substance, has 
a very elegant appearance. In this way any ornamental 
design in gold may be produced, but it is not very durable. 
The gilt ornaments, scrolls, and mottoes on sword-blades, 
are sometimes done in this way. 

Platinum is the heaviest of all metals, gold being next. 
Platinum is practically infusible, and quite indifferent to 
reagents. It is therefore very useful in certain manufac- 



PLATINUM. 



157 



tories, and in the laboratory. It can be dissolved by 
aqua-regia. The stills for sulphuric acid are made of 
platinum, and the metal is used for Russian coinage, but 
must be very difficult to wor'k on account of its infusible 
property. 

In the finely-divided state it forms a gray and very 
porous mass, which is known as spongy platinum, and pos- 
sesses the remarkable property of condensing gases within 
its pores. Hence, when a jet of hydrogen is directed upon 
a piece of spongy platinum, the heat caused by its con- 
densation suffices to inflame the gas. This singular power 
has been applied to the construction of a very beautiful 
apparatus, known as Dobereiner's lamp, 
which consists of a glass jar, a, covered by 
a brass lid, e, which is furnished with a suit- 
able stop-cock, c, and in connection with a 
small bell jar, /, in which is suspended, by 
means of a wire, a cylinder of metallic zinc, 
z. When required for use, the outer jar is 
two-thirds filled with a mixture of one part 
sulphuric acid and four parts water, and the 
stop-cock opened to allow the escape of 
atmospheric air, the spongy platinum con- 
tained in the small brass cylinder, d, being covered by a 
piece of paper. The stop-cock is then closed, and the bell 
jar, /, allowed to fill with hydrogen, and after it has been 
filled and emptied several times, the paper is removed 
from the platinum and the cock is again opened, when the 
gas, which escapes first, makes the metal red-hot and 
finally inflames. This property of platinum is also used 
in the " Davy " lamp. 

The remaining metals do not call for detailed notice. 

In conclusion, we may refer to the following statement, 
which in general terms gives the properties of the metal •, 
their oxides and sulphides for ordinary reader^, 




Dobereiner's lamp. 



158 



CHEMISTRY. 



General Classification of the Metals. 

The metals admit of being really distinguished by the 
following table, in which they are presented in several 
groups, according to their peculiar properties, and each 
distinguished by a particular name : — 



Metals. 



CA.) Light Metah. 

Specific gravity from o'8 
to I ; never occur in 
the uncombined state. 



(a.) Alkaline Metals. 

1. Potassium. 

2. Sodium. 

(Ammonium.) 



(b.) Metals of the Alkaline 
Earths. 

3. Calcium. 

4. Barium. 

5. Strontium, 



Properties of the 



Oxides. 



Powerful bases ; posses 
sing a strong affinity for 
water, and form with it 
hydrates. They yield 
their oxygen to carbon 
only at a white heat. 



Powerful bases, which 
oxidize in the air, and 
form sulphates ; when 
treated with acids 
evolve hydrosulphuric 
acid. 



Highly caustic ; powerful 
bases, separate all other 
oxides from their com- 
binations with acids ; 
are very soluble 
water, and do not lose 
their water of hydra- 
tion at the highest tem- 
peratures; attract car- 
bonic acid rapidly from 
the air. 



Caustic ; strong bases ; 
very soluble in water, 
and dissolve a large 
quantity of sulphur, 
wliich is separated on 
addition of an acid as a 
white powder, termed 
milk of sulphur ; they 
were formerly termed 
iiver of sulphur. 



Caustic ; strong bases ; 
slightly soluble in 
water ; lose their water 
of hydration at a mode- 
rate heat, and power- 
fully absorb carbonic 
acid. 



(c.) Metals of the Earths 
proper, 

(6.) Magnesium. 
(7.) Aluminium. 



(B.) Heavy Metals. 

Specific gravity from 5 to 
21 ; are found chiefly in 
combination with oxy 
gen, and frequently 
with sulphur and ar- 
senic ; some are native. 



Feebly caustic. 
Not caustic. 



iWea k 
bases 
insolu- 
ble in 
water. 



Feebler bases than the 
foregoing, some are 
acids ; insoluble in 
water, and lose their 
water of hydration at 
a moderate heat. 



Sulphides. 



Caustic ; strong bases ; 
dissolve sulphur, and 
are partly soluble in 
water, and partly in- 
soluble. 



Insoluble in water. 



Neutral compounds ; in- 
soluble in water ; anti- 
mony and several of 
the rarer metals pro- 
duce compounds with 
sulphur, which deport 
themselves as acids. 



LIST OF METALS. 



IS9 



Metals. 



Properties of the 



(a.) Common Metals. 

Become oxidized in the 
air. 

8. Iron. 

9. Manganese. 

10. Cobalt. 

11. Nickel. 

12. Copper. 

13. Bismuth. 

14. Lead. 

15. Tin. 

16. Zinc. 

17. Chromium. 

18. Antimony. 



With few .exceptions, are 
soluble in acids, and, 
when ignited with car- 
bon at a red heat, yield 
their oxygen ; are, for 
the most part, fusible 
and non-volatile. 



(b.) Noble Metals. 
Unchangeable in the air. 
19 Mercury. 

20. Silver. 

21. Gold. 

22. Platinum. 



Oxides. 



Those occurring in nature 
aresomewhatbrass-like 
in appearance, and are 
termed pyrites and 
blendes. Those which 
are artificially prepared 
have peculiar colours ; 
by heat they are con- 
verted into sulphates. 



Have more the properties 
of acids than of bases 
are decomposed by 
ignition into oxygen 
and metal. 



Sulphides. 



With the exception of 
sulphide of mercury, 
they leave the pure 
metal when ignited. 





CHAPTER VII.— ORGANIC CHEMISTRY. 

RADICALS ACIDS BASES N EUTRALS. 

: N the introduction to these brief chapters upon 
Chemistry, we said that the science was divided 
into two sections, the first section consisting 
of the simple combinations, and the other o^ 
compound combinations. The latter being met with 
chiefly in animal and vegetable matter, as distinguished 
from dead or inert matter, was termed Organic. This 
distinction will be seen below. 

COMBINATIONS OF SIMPLE GROUPS. 
Inorganic. 
I. Elements and their Combinations, 
(i) Non-Metallic. 
(2) Metallic. 
II. Peculiar Decompositions of the above, 
(i) By Electricity. 
(2; By Light. 

COMBINATIONS OF COMPOUND GROUPS. 
Organic 
I. Compound Radicals and their Combinations. 
II. Peculiar Decompositions of the above, 
(i) Spontaneous. 
(2) Dry Distillation. 

.Ve have already placed before our readers the elements 
and their simple combinations, and have incidentally men- 
tioned the decomposition by electricity and by light. In 
marvels of Electricity the positive and negative poles 



RELATION OF ELEMENTS. 



i6i 



are explained. Oxygen appears always at the positive 
pole, potassium at the negative. The other simple bodies 
vary. Chlorine, in combination with oxygen, is evolved 
at the negative pole, but when with hydrogen at the posi- 
tive pole. In the series below each element behaves 
e\&ctro-negatively to those following it, and &\cztro-positivefy 
to those above it; and the farther they are apart the 
stronger their opposite affinities are. 

Electrical Relation of the Elements. 



Oxygen. 


Carbon. 


Copper. 


Aluminium. 


Sulphur. 


Chromium. 


Bismuth. 


Magnesium. 


Nitrogen. 


Boron. 


Lead. 


Calcium. 


Chlorine. 


Antimony. 


Cobalt. 


Strontium. 


Bromine. 


Silicium. 


Nickel. 


Barium. 


Iodine. 


Gold. 


Iron. 


Sodium. 


Fluorine. 


Platinum. 


Zinc. 


Potassium. 


Phosphorus. 


Mercury. 


Hydrogen. 




Arsenic. 


Silver. 


Manganese. 





The importance of these facts to science is unmistak- 
able, and, indeed, many attempts hafve been made to 
explain, from the electrical condition of the elements, the 
nature of chemical affinity, and of chemical phenomena in 
general. 

Electrotyping is another instance of decomposition by 
means of electricity, and respecting decomposition by light 
we know how powerful the action of the sun's rays is 
upon plants, and for the evolution of oxygen. The 
daguerreotype and photographic processes are also in- 
stances which we have commented upon. So we can 
pass directly to the consideration of the compound groups. 

In nearly every complex organic compound we have a 
relatively simple one of great stability, which is termed 
the radical, which forms, with other bodies, a compound 
radical.* In these complex groups we find certain 

*• Cyanogen, ethyl, and cacodyl, are compound radicals. 



1 62 CHEMISTRY. 

elements generally, — viz., carbon, hydrogen, nitrogen, sul- 
phur, and phosphorus. Some compounds may consist of 
two of these, but the majority contain three (hydrogen, 
oxygen, and carbon). Many have four (carbon, oxygen, 
hydrogen, and nitrogen), and some more than four, in- 
cluding phosphorus and sulphur. Others, again, may con- 
tain chlorine and its relatives, arsenic, etc., in addition. 
Now we will all admit that in any case in which carbon 
is present in composition with other simple bodies forming 
an organic body, and if that body be ignited in the air, it 
burns and leaves (generally) a black mass. This is a sure 
test of the presence of carbon, and forms an organic com- 
pound. Similarly in decomposition nitrogen and sulphur 
in combination inform us they are present by the odour 
they give off. We need not go farther into this question 
of radicals and compound radicals than to state that a 
compound radical plays the part of an element in com- 
bination. We iind in alcohol and ether a certain combi- 
nation termed Ethyl. This "compound radical" occurs in 
same proportions in ether, chloride of ethyl, iodide of ethyl, 
etc., as C2H5 ; so it really acts as a simple- body or element, 
though it is a compound of carbon and hydrogen. A 
simple radical is easily understood ; it is an element, like 
potassium, for instance. We may now pass to the organic 
combinations classified into AciDS, BASES, and INDIF- 
FERENT, or Neutral, Bodies. 

I. Acids. 

There are several well-known organic acids, which we 
find in fruits and in plants. They are volatile and non- 
volatile ; acids are sometimes known as " Salts of Hydro- 
gen." We have a number of acids whose names are 
familiar to us, — viz., acetic, tartaric, citric, malic, oxalic, 
tannic, formic, lactic, etc. 



ACIDS. 



163 



Acetic acid (HCgH^O^) is a very important one, and is 
easily found when vegetable juices, which ferm ent, are 
exposed to the air, or when wood and othe r vegetable 
matter is subjected to the process of " dry distillation." 
Vinegar contains acetic acid, which is distilled from wood, 
as we shall see presently. Vinegar is made abroad by 
merely permitting wine to get sour ; hence the term 
Vin-aigre. In England vinegar is made from " wort," of 
malt which is fermented for a few days, and then put into 
casks, the bung-holes of which are left open for several 




vinegar ground. 

weeks, until the contents have become quite sour. The 
liquid is then cleared by isinglass. The vinegar of com- 
merce contains about 6 per cent, of pure acetic acid, and 
some spirit, some colouring matter, and, of course, water. 
Wood vinegar (pyroligneous acid) is used for pickles. 
The ordinary vinegar when distilled is called white vinegar, 
and it may also be obtained from fruits, such as goose- 
berries or raspberries. 

Acetic acid, or " wood vinegar/' is prepared as follows ; 



1 64 



CHEMISTRY. 



. There are some large iron cylinders set in brickwork 

over furnaces, and these cylinders have each a tube leading 
to a main pipe in which the liquid is received for conden- 
sation. The cylinders, which 
contain about seven or eight 
hundredweight, are filled with 
logs of wood, either oak, beech, 
birch, or ash, the door is closely 
fastened, and the joints smeared 
with clay ; the fires are now 
lighted and kept up all day, till 
the cylinders are red-hot ; at 
night they are allowed to cool. 
In the morning, the charcoal, into 
which the wood is now converted, 



is withdrawn, and a fresh charge 



supplied ; it is then found that 
Boiler or copper. about thirty or forty gallons of 

liquid has condensed in the main tube from each cylinder, 
the remainder being charcoal and gases which pass off; 
the liquid is acid, brown, and very offensive, and contains 
, acetic acid, tar, and several 
other ingredients, among 
which may be named creo- 
sote ; it is from this source 
all the creosote, for the 
cure of toothache, is ob- 
tained. To purify this 
liquid it is first distilled, 
and this separates much 
of the tar ; it is then mixed 
with lime, evaporated to 





vinegar-cooling process. 



dryness, and heated to expel the remaining tar and other 
impurities ; it is next mixed with sulphate of soda and 
water, and the whole stirred together ; the soda, now in 



CITRIC ACID. 165 

union with the acetic acid, is washed out from the lime 
and strained quite clear ; it is afterwards evaporated till it 
crystallises, and vitriol (sulphuric acid) then added; finally 
the acetic acid is distilled over, and the sulphuric acid left 
in union with the soda, forming sulphate of soda, to be 
used in a similar process for the next batch of acid. The 
acetic acid is now quite colourless, transparent, and very 
sour, possessing a fragrant smell. This is not pure acetic 
acid, but contains a considerable quantity of water. The 
acetic acid of commerce, mixed with seven times its bulk of 
water, forms an acid of about the strength of malt vinegar, 
perfectly wholesome, and agreeable as a condiment. 

Pure acetic acid may be made by mixing dry acetate of 
potash with oil of vitriol in a retort, and distilling the 
acetic acid into a very cold receiver ; this, when flavoured 
with various volatile oils, forms the aromatic vinegar sold 
by druggists. It is a very strong acid, and if applied to 
the skin will quickly blister it. 

Acetate of lead, or sugar of lead, is obtained by dis- 
solving oxide of lead in vinegar. A solution of this salt 
makes the goulard water so familiar to all. Acetate of 
lead is highly poisonous. 

Acetate of copper is verdigris, and poisonous. Other 
acetates are used in medicine. 

We may pass quickly over some other acids. They, arc 
as follows: — 

Tartaric Acid (C^H^Og) is contained in grape juice, 
and crystallizes in tabular form. The purified powdered 
salt is creani of Tartar. 

Citric Acid (CsHgO^) is found native in citrons and 
lemons, as well as in currants and other fruits. It is an 
excellent anti-scorbutic. 



1 66 



CHEMISTRY. 



Malic Acid (C^HjOj) is found chiefly in apples, as its 
name denotes {malum, an apple). It is prepared from 
mountain-ash berries. 

Oxalic Acid (C^H.O^). If we heat sugar with nitric 
acid we shall procure this acid. It is found in sorrel plants. 

Tannic Acid (Q^N^.O^^). It is assumed that all 




Tan-yard and pits. 

vegetables with an astringent taste contain this acid. 
Tannin is known for its astringent qualities. The name 
given to this acid is derived from the fact that it possesses 
a property of forming an insoluble compound with water, 
known as leather. Tanning is the term employed. Tannin 
is found in many vegetable substances, but oak bark is 
usually employed, being the cheapest. The " pelts " hides 
or skins, have first to be freed from all fat or hair by 



TANNIC ACID. 167 

scraping, and afterwards soaking them in lime and water. 
Then they are placed in the tan-pit between layers of the 
bark, water is pumped in, and the hides remain for weeks, 
occasionally being moved from pit to pit, or relaid, so as 
to give all an equal proportion of pressure, etc. The 
longer the leather is tanned — it may be a year — the 
better it wears. 

Skins for gloves and binding are tanned with " sumach," 
or alum and salt. Sometimes the leather is split by 
machinery for fine working. Parchment is prepared from 
the skins of asses, sheep, goats, and calves, which are 
cleaned, and rubbed smooth with pumice stone. 

Tannic acid, with oxide of iron, 
produces Ink, for the gall-nut con- 
tains a quantity of the acid. All 
the .black inks in use generally are 
composed of green vitriol (sulphate 
of iron) in union with some astrin- 
gent vegetable matter ; the best is 
the gall-nut, although, for cheap- 
ness, logwood and oak bark have 
each been used. An excellent black 
ink may be made by putting into a Unhairing .he hide. 

gallon stone bottle twelve ounces of bruised galls, six 
ounces of green vitriol, and six of common gum, and 
filling up the bottle with rain water ; this should be kept 
three or four weeks before using, shaking the bottle from 
time to time. 

Blue ink has lately been much used ; it is made by 
dissolving newly-formed Prussian blue in a solution of 
oxalic acid. To make it, dissolve some yellow prussiate 
of potash in water in one vessel, and some sulphate of iron 
in another, adding a few drops of nitric acid to the sulphate 
of iron ; now mix the two liquids, and a magnificent blue 
colour will appear, in the form of a light sediment ; this is 

12 




1 68 



CHEMISTRY. 



to be put upon a paper filter, and well washed by pouring 
over it warm water, and allowing it to run through ; a 
warm solution of oxalic acid should now be mixed with 
it, and the Prussian blue will dissolve into a bright blue 
ink. 

Red ink is made by boiling chips or raspings of Brazil 
wood in vinegar, and adding a little alum and gum ; it 
keeps well, and is of a good colour. A red ink of more 
beautiful appearance, but not so durable, may be made by 
dissolving a few grains of carmine in two or three tea- 
spoonfuls of spirit of hartshorn. 




Drying rooms for hides. 

Marking ink is made by dissolving nitrate of silver in 
water, and then adding some solution of ammonia, a little 
gum water, and some Indian ink to colour it. Printers' 
ink is made by grinding drying oil with lamp-black. 

The powdered gall-nut is an excellent test for iron in 
water. It will turn violet if any iron be present. 



Formic Acid (C H,0 J is the caustic means of defence 
employed by ants, hence the term formic. It can be 
artificially prepared by distilling a mixture of sugar, 
binoxide of manganese, and sulphuric acid. On the skin 
it will raise blisters. 



BASES. 1 09 

Lactic Acid (CgH^Oj) is present in vegetable and 
animal substances. Sour whey contains it, and the 
presence of the acid in the whey accounts for its power 
of removing stains from table-linen. When what is called 
" lactic fermentation " occurs, milk is said to be " turned." 

II. 

Bases. 

The definition of a base is not easy. We have de- 
scribed bases as substances which, combining with acids, 
form salts, but the definition of a base is as unsatisfactory 
as that of acid or salt. All vegetable bases contain nitro- 
gen, are usually very bitter, possess no smell or colour, and 
are insoluble in water. They are usually strong poisons, 
but very useful in medicine. 

The most important are the following bases : — 

Quinine is contained in the cinchona (yellow) bark. 
One hundred parts of the bark have been calculated to 
yield three of quinine. 

Morphine is the poisonous base of opium, which is 
the juice of the poppy, and is prepared chiefly in India 
and China. 

Nicotine is the active principle of tobacco, and varies 
in quantity in different tobaccos. Havannah tobacco 
possesses the least. It is a powerful poison, very oily, 
volatile, and inflammable. 

CONIA is prepared from the hemlock. It is fluid and 
volatile. It is also a deadly poison, and paralyses the 
spine directly. 

Strychnine is found in poisonous trees, particularly 



I70 



CHEMISTRY. 




Hemlock. 



in the nux-vomica seeds of Coromandel. It produces lock- 
jaw and paralysis. There is no 
antidote for strychnine ; emetics 
are the only remedy. 

The above are chiefly remarkable 
for their uses in medicine, and in 
consequence of their highly poison- 
ous character are best left alone by 
unpractised hands. 

A German chemist, named Ser- 
turner, was the first to extract the 
active principle from Opium. The 
question of opium importation has 

lately been attracting much attention, and the opinions con- 
cerning its use are divided. 

Probably in moderation, 

and when used by ordinary 

people (not demoralized 

creatures), it does little 

harm. 

Opium is the juice of the 

"common" poppy, and de- 
rives its name from the 

Greek opos, juice. The 

plant is cultivated in India, 

Persia, and Turkey. After 

the poppy has flowered the 

natives go round, and with 

a sharp instrument wound, 

or puncture, every poppy 

head. This is done very 

early in the morning, and 

under the influence of the 

sun during the day the 

juice oozes out. Next morning the drops are scraped off 




The Poppy. 



STARCa. 



i;t 



The juice is then placed in pots, dried, and sent for export. 
The "construction" of opium is very complicated, for it 
contains a number of ingredients, the most important 
being morphia, narcotine, meconic acid, and codeia. It is 
to the first-named constituent that the somnolent effect of 
opium is due. 

III. 

Indifferent Substances. 

There are a great number of so-called "indifferent" sub- 
stances to which we cannot be indifferent. Such bodies 
as these have neither acid nor basic properties, and stand 
no comparison with salts. They are of great importance, 
forming, as they do, the principal nutriment of animals. 
Some contain nitrogen, some do not ; they may therefore 
be divided into nitrogenous and non-nitrogenous sub- 
stances ; the former for solid portions of the body, the 
latter for warmth. 

We will take the latter first, and speak of some of 
them — such as starch, gum, sugar, etc. 

Starch is found in the roots of grain, in the potato, 
dahlia, artichoke, etc., and by crushing the parts of the 
plant, and washing them, the starch can be collected as a 
sediment. In cold water and in spirits of wine starch is 
insoluble. The various kinds of starch usually take their 
names from the plants whence they come. Arrowroot is 
obtained from the West Indian plant Maranta Arundinacea. 
Cassava and tapioca are from the manioc ; sago, from 
the sago palm ; wheat starch, and potato starch are other 
examples. 

If starch be baked in an oven at a temperature of about 
300° it becomes, to a great extent, soluble in cold water, 
forming what is called "British gum"; this is largely used 



I 7 2 CHEMISTRY. 

for calico printing and other purposes ; if boiled in water 
under great pressure, so that the temperature can be raised 
to the same degree, it is also changed into an adhesive 
sort of gum, " mucilage " ; this is the substance made use 
of by the government officials to spread over the backs 
of postage and receipt stamps to make them adhere. The 
starch of grain, during germination, or growth, contains 




Plantation of sugar-canes. 



diastase, which converts the starch into gum and sugar ; 
the same effect can be produced by heating starch with 
diluted sulphuric acid. 

Gum found in plants is chiefly procured from the 
Mimosa trees, from which it flows in drops, and is called 
Gum Arabic. There are other so-called " gums," but this 
is the one generally referred to. 



SUGAR. 



173 



Sugar exists in fruits, roots, and in the stalks of plants, 
in the juice of the cane, maple, and beet-root particularly. 
The canes are crushed, the juice is clarified with lime to 
prevent fermentation, and the liquid is evaporated. It is 
then granulated and cleared from the molasses. Sugar, 
when heated, becomes dark, and is called " caramel." It 
is used for colouring brandy, and gives much diiificulty to 
the sugar refiners. 

Sugar refining is conducted as follows. The raw (brown) 



li 



^<T - 



:!^'<i 










Refining vacuum pan. 



sugar is mixed into a paste with water, and allowed to 
drain. The sugar thus becomes white. It is then dis- 
solved in water, with animal charcoal and bullocks' blood. 
The liquid is boiled, and put into a dark cistern with holes 
at the bottom, and cotton fibres being fastened in the holes, 
are hung into another dark cistern, into which the liquid 
runs pure and-white. It is then pumped into a copper 
vessel, — vacuum pan, — and condensed to the proper con- 
sistence. Subsequently it is poured into conical moulds, 



i;4 



CHEMISTRY. 



and pure syrup poured upon the crystal shapes. The 
caramel is then removed through a hole at the end. The 
moulds or loaves are then dried, and if not even or elegant 
they are turned in a lathe. Finally they are packed up 

as " loaf sugar." Sugar under- 
goes no decomposition, and is the 
cause of non-decomposition in 
other substances. For this reason 
it is employed in "preserving" 
fruit, etc. Sugar is obtained from 
beet by crushing and rasping the 
roots, as the cane is treated. 




Sugar moulds. 



Spirit of Wine, or Alco- 
hol, is not a natural product. 
It is found by the decomposition of grape-sugar by fer- 
mentation. There is a series of alcohols which exhibit a 
regular gradation, founded, so to speak, upon one, two, or 
three molecules of water. They are called respectively 
alcohols, glycols, and glycerins. Thus we have — 

Alcohols. 
Methylic alcohol. 
Ethylic „ 
Prophylic „ 
Amylic „ 

Glycols. 
Enthelein glycol. 
Prophylene „ 
Butylene „ 
Amylene „ 

Glycerins. 

(Ordinary Glycerine is the only one 

known.) 

The cetyl and melissylic alcohols are contained in sper- 
maceti and bee£;-wax respectively. The usual alcohol is 
the Vinic, a transparent, colourless liquid which is the 




Turning the loaves. 



ALCOHOL. 



175 



spirituous principle of wine, spirits, and beer, and, when 
sugar is fermented the alchol and carbonic acid remain. 

Spirits of wine has a very powerful affinity for water, 
and thus the use of stimulants in great quantity is to be 
deprecated, for alcohol absorbs the water from the mucous 
membranes of the stomach and the mouth, making them 
dry and hard. The state of "intoxication," 
unfortunately so familiar, is the effect produced 
by alcohol upon the nerves. We append a list 
of the beverages which are most in use, and the 
percentage of alcohol in each according to Pro- 
fessor Hart : — 



Port . . 


15 per cent. 


Claret . 


. 8 


Madeira. 


14-5 


Ale . . 


. 6 


Sherry . 


14 


Porter . 


• 5 



per cent. 



Spirit of wine is contained in many mixtures, 
and for the purpose of ascertaining how much 
alcohol may be in wine, or any other liquid, a 
hydrometer is used (see cut). This instru- 
ment consists of a glass tube with a bulb at the 
end. It is put into water, and the place the 
water "cuts" is marked by a line on the stem, 
and called zero 0°. Spirit of wine has less 
specific gravity than water, so in absolute alcohol 
the instrument will sink lower than in water, 
and will descend to a point which is marked 
100.° In any mixture of alcohol and water, 
of course the hydrometer will rise or sink 
between the extreme points according as the mixture 
may contain less alcohol or more. So a scale can be 
furnished. The instrument, as described, was invented by 
MM. Gay-Lussac and Tralles, and called the " percentage" 
hydrometer. There are many other instruments marked 
in a more or less arbitrary manner. We append a com- 
parative table of a few hydrometers. {See page 176.) 




Hydrometer. 



176 



CHEMISTRY. 



Ether, or sulphuric ether, is a mixture of spirits of wine 
with sulphuric acid, and distilled. It loses water, and the 
product is ether, which is volatile, and transparent, with a 
peculiarly penetrating odour. It will not mix with water, 
and if inhaled will produce a similar effect to chloroform. 
Comparative Table or Hydrometers. 



Specific 
Gravity. 


Percentage 


Percentage 


Degree, 


Degree, 


Degree, 


Volume 


Weight, 


according 


according 


according 


(Trallcs). 


at6o°F. 


to Cartier. 


to Beck. 


to Baume. 


I'OOO 








10 





10 


0-991 


5 


4-0 


... 


... 


... 


0-985 


lo 


8-0 


12 


... 


... 


0-980 


15 


I2-I 


... 


3 


13 


0-975 


20 


1 6-2 


... 


... 


... 


0-970 


25 


20-4 


14 


5 


... 


0-964 


30 


24-6 


IS 


6 


15 


0-958 


35 


289 




... 


16 


0-951 


40 


33'4 


... 


9 


17 


0-942 


45 


37-9 


18 


... 


... 


0933 


50 


42-5 




12 


20 


0-923 


|S 


47-2 


21 


14 


... 


0-912 


60 


52-2 


... 


16 


24. 


0-901 


65 


57-2 


24 


19 




o'889 


70 


62-5 


27 




28 


0-876 


75 


67-9 


... 


24 




0-863 


80 


73-5 


30 


27 


32 


0-848 


85 


79'5 


35 


30 


35 


0-833 


90 


857 


... 


34 


38 


0-815 


95 


92-4 


40 


38 


42 


0-793 


100 


loo'o 


44 


44 


48 



Chloroform is transparent, and will sink in water. 
Diluted alcohol, with hypo-chloride of lime, will produce it. 
When inhaled, chloroform produces a pleasing insensibility, 
to pain, and is useful in surgery. 

A certain compound of alcohol with mercury dissolved 
m nitric acid will cause decomposition, and white crystals 
will eventuate. These compound crystals are termed 
fiibninating mercury. 

We must now pass rapidly over the few remaining sub- 



OILS. 



177 



jects we have to notice, such as fats and soaps, wax, oils, 
etc. 

Fats are of the greatest use to man, particularly in cold 
climates, for upon them depends the heat of the body. 
Fatty acid, if liquid, is known as oleic acid ; if solid, stearic 
acid. Soaps are compounds of fatty acids. Many " fats " 
are consumed as food, others as fuel or for lighting pur- 
poses, in the shape of oils. Such oils are not primarily 
useful for burning. Petroleum and other mineral oils are 
found in enormous quantities in America. 

There are what we term fixed oils, and essential or 
volatile oils. A list is annexed as given by " Haydn's 
Dictionary of Science " : — 



Fixed Oils. 



Drying. 
Linseed oil. 
Poppy oil. 
Sunflower oiL 
Walnut oil. 
Tobacco-seed oil. 
Cress-seed oil. 

Oil of anise. 
Oil of bergamot. 
Oil of carraway. 
Oil of cassia. 
Oil of cedar. 
Oil of cloves. 
Oil of lavender. 



Essential Oils. 



Non-Drying, 
Almond oiL 
Castor oil. 
Colza oil. 
Oil of mustard. 
Rape-seed oil. 
Olive oil, etc. 

Oil of lemon. 
Oil of mint. 
Oil of myrrh. 
Oil of nutmeg. 
Oil of peppermint. 
Oil of rose. 
Oil of turpentine. 



Vegetable oils are obtained by crushing seeds ; animal 
oils come from the whale and seal tribe. Paraffin oil comes 
from coal. Linseed is a very drying oil, and on it depends 
the drying power of paint. We know olive oil will not 
dry on exposure to the air. Oiled silk is made with lin- 
seed oil. When oil is drying in the air considerable heat 
is evolved, and if oiled substances be left near others 



178 



CHEMISTRY. 



likely to catch fire, spontaneous combustion may ensue 
Oil of turpentine is found in the pine and fir trees, and 
many of the oils above mentioned are used by perfumers, 
etc., the rose oil, or attar of roses, being an Eastern com- 
pound. 

Allied to the volatile oils are the RESINS, which are 
non-conductors of electricity. They are vegetable pro- 
ducts. They are soluble in alcohol, in the volatile oils, or 
in ether, and these solutions are called varnishes; the 
solvent evaporates and leaves the coating. Turpentine, 

■ copal, mastic, shellac, caoutchouc, 

and gutta-percha are all resinous 
bodies. Amber is a mineral resin, 
which was by the ancients sup- 
posed to be the " tears of birds" 
dropped upon the seashore. 
Moore refers to this in his poetic 
"Farewell to Araby's Daughter" — 

" Around thee shall glisten the loveliest 
amber 
That ever the sorrowing sea-bird has 
wept." 

Amber is not soluble either in 
water or alcohol ; it is, however, 
Crushing mill. soluble in sulphuric acid. It 

takes a good polish, and when rubbed is very electrical. 
It is composed of water, an acid, some oil, and an inflam- 
mable gas which goes off when the amber is distilled. 

The well-known camphor is got from a tree called the 
"Laurus Camphora"; it is a white, waxy substance, and 
can be obtained by oxidizing certain volatile oils. It is 
generally produced from the Laurus Camphora in a " still." 
The behaviour of a piece of camphor in pure water is 
curious, but its motions can be at once arrested by touching 
the water or dropping oil on the surface. This pheno- 




ALBUMEN. 179 

menon is due to the surface tension of the liquid, which 
diminishes when it is in contact with the vapour of the 
substance. 



Nitrogenous Substances. 

There are certain albuminous compounds which we 
must mention here. These are albumen, fibrine, and 
caseine. Albumen is the white of egg ; fibrine is, when 
solid, our flesh and muscular fibre, while caseine is the 
substance of cheese. These are very important com- 
pounds, and the albuminous bodies are of the very highest 
importance as food, for the solid portion of blood, brain, 
and flesh consist, in a great measure, of them. Albumen, 
fibrine, and caseine contain carbon, hydrogen, nitrogen, and 
oxygen, with sulphur and phosphorus. 

Albumen. The most familiar and the almost pure 
form of albumen is in the white of eggs, which is albumi- 
nate of sodium. It also exists in the serum of the blood, 
and therefore it is largely found in the animal kingdom. 
It can also be extracted from seed or other vegetable sub- 
stances, but it is essentially the same. Albumen is very 
useful as an antidote to metallic poisons. It forms about 
7 per cent, -of human blood. It is soluble up to about 
1 40° Fah. ; it then solidifies, and is precipitated in a white 
mass. Albumen is used in the purification of sugar, etc. 

Fibrine is found in a liquid condition in blood. The 
vegetable fibrine (gluten) is prepared by kneading wheat 
flour in a bag till the washings are no longer whitened. 
Like albumen it is found both in a solid and liquid state. 

Caseine is seen in the skin which forms upon milk 
when heated, and forms about 3 per cent, of milk, where 
it exists in a soluble state, owing to the presence of alkali; 



1 80 CHEMISTRY. 

but caseine, like albumen, is only soluble in alkaline solu- 
tions. As we have said, it is the principal constituent of 
cheeses. Caseine is precipitated by the lactic acid of milk, 
which is produced by keeping the milk too warm. Caseine, 
or curds, as they are called, are thus precipitated. The 
milk is said to be " sour," or turned. 

Milk, the food of the young of all mammalia, is com- 
posed chiefly of water, a peculiar kind of sugar, butter, and 
caseine. It is this sugar in milk which causes the lactic 
acid mentioned above. The actual constituents of milk 
are as follows : — • 

Water 873"oo 

Butter 30"oo 

Sugar 4390 

Caseine . 48'2o 

Calcium (phosphate) 2"3i 

Magnesia o'42 

Iron o"07 

Potassium (chloride) i'44 

Sodium . o'24 

Soda (with caseine) 0*42 

lOOO'OO 

The sugar of milk is non-fermenting, and can be procured 
from whey by evaporation. 

Decomposition. 

We have seen that animals and plants are composed of 
many different substances, and so it will be at once under- 
stood that these substances can be separated from each 
other, and then the decomposition of the body will be com- 
pleted. When the sap sinks or dries up in plants they are 
dead. When our heart ceases to beat and our blood to 
flow we die, and then, gradually but surely, decay sets in, 
There is no fuel left to keep the body warm ; cold results, 



FERMENTATION. I 8 I 

and the action of oxygen of the air and light or water 
decays the body, according to the great and unalterable 
laws of Nature. " Dust thou art, and unto dust shalt thou 
return," is an awful truth. The constituents of our bodies 
must be resolved again, and the unfailing law of dwmical 
attraction is carried out, whereby the beautiful organism, 
deprived of the animating principle, seeks to render itself 
into less complicated groups and their primary elements. 

This resolution of the organic bodies is decomposition, 
or " spontaneous decomposition," and is called decay, 
fermentation, or putrefaction, according to circumstances, 
The Egyptians, by first drying the bodies of the dead (and 
then embalming them), removed one great source of decay 
— viz., water, and afterwards, by the addition of spices, 
managed to arrest putrefaction. 

Fermentation is familiar in its results, which may be 
distilled for spirituous liquors, or merely remain fermented, 
as beer and wine. Fusel oil is prepared from potatoes, 
rum from cane sugar, arrack from rice. The power of 
fermentation exists in nature everywhere, and putrefaction 
is considered to be owing to the presence of minute germs 
in the atmosphere, upon which Professors Tyndall and 
Huxley have discoursed eloquently. 

Plants are subjected to a process of decomposition, 
which has been termed " slow carbonization," under certain 
circumstances which exclude the air. The gases are given 
off, and the carbon remains and increases. Thus we have 
a kind of moss becoming peat, brown coal, and coal. 
The immense period during which some beds of coal must 
have lain in the ground can only be approximately ascer- 
tained, but the remains found in the coal-measures have 
guided geologists in their calculations. 

Having already mentioned some products of distillation, 
we may now close this portion of the subject. Coal is 
compact, black, and shining, and if compared with the 



l82 



CHEMISTRY. 



density of wood and of charcoal it becomes evident that 
the same bulk of coal contains a far larger quantity of 
combustible matter. On this account it is an excellent 
fuel, but, being denser, it requires a greater supply of air 
to keep it in combustion than either wood or charcoal. 

We are not, however, entitled to consider coal as pure 
carbon. It always contains oxygen, hydrogen, and a 
small quantity of nitrogen. Moreover, we meet with 
certain mineral constituents, particularly sulphur, in com- 
bustion with iron. In the process of carbonization the 
sulphur, which is so prejudicial to the use of coal, is 
separated from it : the product obtained is called coke. 
As this material, with the exception of its mineral con- 
stituents, consists entirely of carbon, and possesses a 
great density, it forms the most valuable of all fuels when 
a high degree of heat is required in a small space. We 
have left many things unnoticed, which in the limited 
space at our disposal we could not conveniently include 
in our sketch of chemistry and chemical phenomena, but 
we trust we have said enough to interest the reader and 
induce him to search farther into chemistry. 




MARVELS OF HEAT, LIGHT, 
AND SOUND. 



INTRODUCTION. 




HE discovery in recent times of the intimate 
connection between all the great manifes- 
tations of energy, which we call the physical 
forces, has been one of the most fruitful 
results of modern thought. Formerly it was believed 
that the forces in action around us — of gravity, heat 
light, sound, electricity — were so many distinct powers 
not directly connected with one another, and certainly 
not interchangeable. Little could it be guessed that 
we should now be teaching that energy, the power of 
doing work, is in its essence one thing, which may 
have many manifestations ; that all these manifestations 
are but temporary, and that they never disappear 
without a quantity of some other force appearing or 
becoming active ; that, in fact, no form of energy ever 
disappears without giving rise or being converted into 
an equivalent quantity of some other force or forces. 
But by the experiments of Joule and Mayer, followed 
by others, it has been proved that this is the case ; 
and the grand principle of the convertibility of energy 
into different and equivalent forms, which can be 
reckoned, has been established. 

From this has been deduced the great generalisation 
of the conservation of energy, which asserts that the 
sum total of energy in the universe is constant, and 
that it simply varies in the situation and form of its 
manifestations. Now it is evident that this, theory 
cannot be absolutely proved, because it is impossible 



VI INTRODUCTION. 

for us to measure the total quantity of energy in the 
universe at different times, and see whether it is always 
the same. So that we must be content to have made 
this great assumption without absolute proof, and to 
gain from its use some advantage as to the phenomena 
with which we are brought into contact. 

Certain observations, however, do give strong support 
to this view. For instance, in every case in which we 
can trace the appearance or the changes of the forms 
of energy, either an exact equivalent is found to have 
appeared and disappeared, or something so near, that 
we may well consider that the difference is due to 
our imperfect observation. The more nearly we are 
able to approach to a completely accurate mode of 
estimating energy, the more closely do we find that 
the quantities of energy disappearing and appearing 
are equal. By studying different changes we are enabled 
to reckon absolutely what is the equivalent between 
energy in one form and in another, and it is possible 
to predict to a large extent what changes will take 
place when we transform one force into another. And 
thus the assumption that ho energy entirely disappears 
or is created anew, but simply that it changes its 
manifestation, allows us to predict new results from 
new combinations of force and material, by assuring 
us of the absence of such disturbances as must vitiate 
our calculations if they occurred, and throw worldly 
events into confusion. Such a principle as the con- 
servation of energy is as valuable to us for practical 
purposes as the certainty that two and two make four, 
and will always make four. 

The germ of this discovery might have been found 
in the old savage method of obtaining fire by rubbing 
two sticks together. The friction of one against the 
other was in process of time attended by the production 



INTRODUCTION, vii 

of heat enough to kindle a flame ; but from the remote 
period when this was first done to the late date when 
men have realised what it meant, how many genera- 
tions have been unconscious of the fact that the energy 
of man's body in producing the friction was transformed 
into the mechanical motion of the wood, and that into 
the heat which at last kindled the flame. How many 
people have watched ice melt or water boil without 
knowing that a quantity of heat was entirely disap- 
pearing as heat in these changes, and that the energy 
which was previously manifest as heat was afterwards 
occupied in keeping the particles of matter in the liquid 
and in the gaseous states respectively. Even when 
the last-mentioned fact was realised, and people began 
to talk of " latent heat," they were far from the con- 
ception implied in Professor Tyndall's title " Heat 
considered as a Mode of Motion." We now regard 
the minute particles of matter as continually vibrating, 
and being capable of various kinds of vibration at 
different rates. One kind of vibration brings about 
the solid, liquid, or gaseous states ; another is manifest 
to us as heat ; a further degree of heat-vibrations 
occasions light ; the sensation of sound is produced by 
more or less regular waves affecting material objects ; 
electricity is another condition affecting material par- 
ticles ; and thus the whole round of forces of nature 
is concerned with the changes of vibration or condition 
of the particles of matter. 

A great number of the changes of matter attended 
by heat, or following on the application of heat; will 
be found detailed in the succeeding pages. Then follow 
some of the most interesting and important facts and 
experiments connected with light. Very few subjects 
can have so great an influence on our welfare and 
happiness. Without light how limited would be our 



viii INTRODUCTION. 

knowledge of nature, how limited the sphere of our 
activity. We should only have touch, taste, and 
mechanical force to give us knowledge of the material 
■world, and thus our ideas and thoughts would be very 
greatly restricted. Few, however, are conscious how 
much we are dependent upon touch and mechanical 
considerations for effects which we refer to sight alone. 
And without the brain, and its faculties of memory, 
comparison, and judgment, light alone would be of 
very little use to us. 

The large space given to light in this book, and the 
great amount of knowledge to which it is the key, 
should serve to show how important a part it has played 
in developing our brain and our nature to their present 
level In fact, apart from our memory, we have no 
perfectly distinct impressions. Our ideas of external 
■ things are compounded of all our past impressions as 
contrasted with the present ones. We combine the 
two pictures made upon our two eyes, so that they 
appear one ; and, this is not the only complex operation 
which we have to perform to get correct ideas. There 
is a muscular adjustment of the eye-lens for near or 
distant vision, which affords us a mechanical means 
of judging of distance, and consequently of the size 
of objects. When it is necessary to move the entire 
eyeball to take in a view, we get an additional muscular 
sensation involved ; and then, when the whole head or 
the body must be moved to see an object, we use that 
sensation of movement to give us information about 
the position of external objects. 

Indeed, it is remarkable how complex most of our 
visual judgments are, whether of distance, size, or solidity. 
All previous sights are brought into comparison. We 
unconsciously compare the intensity of light given out 
by objects, the size, the colour, the distances we may 



INTRODUCTION. IX 

have hr^d to walk to get to them, the movements we 
have had to make in feeling them, the pressures they 
have exerted, the warmth they have imparted. The 
youngest child, grasping at things aimlessly, as it seems, 
is really making a multitude of experiments to correct 
its unaided vision, is ascertaining that "things are not 
what they seem," or, at any rate, are not where they 
seem to be. Our early years are by no means useless ; 
they are perhaps those most full of important lessons 
to us. The store of knowledge we then lay up influences 
every judgment of after-life. 

How extremely important to our practical life is a 
comprehension of the laws of light ! A study of the 
simple laws of reflection and refraction will enable us 
to understand the nature of mirrors and lenses of all 
kinds, and very considerably improve our judgment 
in buying the one or the other. This study will also 
largely help us to preserve good sight in youth, to save 
it from the injury of imperfectly lighted rooms, too 
small print, too great nearness of the eyes to objects, 
and many other causes of damage. It can be scarcely 
expected that human nature will be able to dispense 
hereafter with spectacles. Modern civilisation has intro- 
duced such grave departures from the primeval state, 
when a man's safety depended upon his long sight, 
his being able to track an enemy or a beast of prey 
afar off, that it is very doubtful whether nature will 
give us the microscopic eye required for reading badly 
printed newspapers, or the minute type of cheap Bibles 
and hovels. It is fortunate for us that we are enabled to 
correct to some extent by spectacles the damage we have 
done to our eyesight in the progress of civilisation. 

We must not dwell on the marvels of the spectro- 
scope, the telescope, and the microscope, but refer our 
readers to the sections dealing with them. In drawing 



X INTRODUCTION. 

attention to the subject of sound, we come to that 
which needs no recommendation to the majority of 
people ; for music's charms soothe even the most savage 
of mankind, though apparently they do not interest 
a small minority of the civilised. To those who will 
study them, we can promise a rich store of interest 
in the laws of sound. How simple they are, and what 
astonishing results they produce ; how slight is the 
boundary between noise and music, and how profound 
is the difference to our brain ! 

Independent of the organ, the piano, the violin, and 
other musical instruments which depend for their influence 
upon us, on the quality of sound emitted or reflected 
by the material of which they are constructed, acoustics 
has presented us with many interesting inventions. Of 
these the telephone — in which electrical currents combine 
with sound to almost annihilate distance, so that man 
may .speak to man, not merely telegraph to him, at the 
distance of thousands of miles — is among the most inter- 
esting. But the phonograph, a still simpler invention, is 
perhaps more wonderful, enabling us, as it does, to register 
and then reproduce at any distance of time every con- 
dition of the human voice, the whole world of expression 
in speech and song. The time may come v.'hen the 
whole world may literally hear by telephone the speeches 
and sermons of the greatest men, the songs of the 
greatest singers ; and when our descendants shall listen 
to the voices and hear again the speeches of their 
ancestors, and so gain an infinitely better idea of their 
personal qualities than we can of our ancestors'. Heat, 
light, sound, great as are the parts played by them 
in the past, seem destined to very much greater influence 
in the future upon man's knowledge, power, and well- 
being. 



CONTENTS. 



CHAPTER I.— HEAT. 

WHAT IS HEAT? — THEORY OF HEAT THE THERMOMETER — 

EXPANSION BY HEAT — ^EBULLITION, EVAPORATION, AND DIS- 



TILLATION 



CHAPTER II.— HEAT (continued). 

SPECIFIC HEAT — FUSION — LATENT HEAT — CONDUCTION AND CON- 
VECTION OF HEAT — CALORESdENCE lb 



CHAPTER III.— LIGHT. 

SOURCES OF LIGHT WHAT IS LIGHT? — VELOCITY OF LIGHT — 

REFLECTION AND REFRACTION— RELATIVE VALUE OF LIGHTS 34 

CHAPTER IV.— VISION. 

VISION AND OPTICAL ILLUSIONS — THE EYE DESCRIBED — ACCOMMO- 
DATION OF THE EYE— CHROMATIC ABERRATION — SPINNING 
TOPS 48 

CHAPTER v.— OPTICAL ILLUSIONS. 

OCULAR ESTIMATION — ZOLLNER'S DESIGNS — THE THAUMATROPE 

PHENAKISTOSCOPE THE ZOOTROPE — THE PRAXINOSCOPE 

THE DAZZLING TOP 70 

CHAPTER VI.— OPTICAL ILLUSIONS {contimied). 

EXPERIMENTS — THE TALKING HEAD — GHOST ILLUSIONS . . 9O 



xii CONTENTS. 

CHAPTER VII.— OPTICAL APPARATUS. 

FAGS 
THE EYE— THE STEREOSCOPE — SPECTRUM ANALYSIS — THE SPEC- 
TROSCOPE THE TELESCOPE AND MICROSCOPE PHOTOGRAPHY 

—DISSOLVING VIEWS — LUMINOUS PAINT Io5 

CHAPTER VIII.— SPECTRAL ILLUSIONS. 

A SPECTRE VISIBLE — CURIOUS ILLUSIONS— GHOSTS . , . I4I 

CHAPTER IX.— ACOUSTICS. 

THE EAR, AND HEARING — PHYSIOLOGY OF HEARING AND SOUND 
— SOUND AS COMPARED WITH LIGHT — WHAT IS SOUND? — 
VELOCITY OF SOUND CONDUCTIVITY THE HARMONOGRAPH 1 49 

CHAPTER X.— ACOUSTICS {continued). 

THE TOPOPHONE — THE MEGAPHONE — THE AUTOPHONE — THE 

AUDIPHONE THE TELEPHONE — THE PHONOGRAPH — THE 

MICROPHONE 170 

CHAPTER XL— ACOUSTICS (continued:). 

THE TUNING-FORK — THE SYREN — SOUND FIGURES — SINGING 

FLAMES 191 




CHAPTER I.— HEAT. 

WHAT IS HEAT ? — THEORY OF HEAT — THE THER- 
MOMETER — EXPANSION BY HEAT — EBULLITION, EVAPO- 
RATION, AND DISTILLATION. 

HAT is Heat ? — We will consider this question, 
and endeavour to explain it before we speak of 
its effects on water and other matter. 

Heat is now believed to be the effects of the 
rapid motion of all the particles of a body. It is quite 
certain that a heated body is no heavier than the same 
body before it was made " hot," so the heat could not have 
gone into it, nor does the " heat " leave it when it has 
become what we call "cold," which is a relative term. 
Heat is therefore believed to be a vibratory motion, or 
the effects of very rapid motion of matter. 

The Science of Heat, as we may term it, is only in its 
infancy, or certainly has scarcely come of age. Formerly 
heat was considered a chemical agent, and was termed 
caloric, but now heat is found to be motion, which affects 
our nerves of feeling and sight ; and, as Professor Stewart 
tells us, " a heated body gives a series of blows to the 
medium around it ; and although these blows do not affect 
the ear, they affect the eye, and give us a sense of light." 

Although it is only within a comparatively few years 



2 HEAT. 

that heat has been really looked upon as other than matter, 
many ancient philosophers regarded it as merely a quality 
of matter. They thought it the active principle of the 
universe. Epicurus declared that heat was an effluxion of 
minute spherical particles possessing rapid motion, and 
Lucretius maintained that the sun's light and heat are the 
result of motion of primary particles. Fire was worshipped 
as the active agent of the universe, and Prometheus was 
fabled to have stolen fire from heaven to vivify mankind. 
The views of the ancients were more or less adopted in 
the Middle Ages ; but John Locke recognized the theory 
of heat being a motion of matter. He says : " What in 
our sensation is heat, in the object is nothing but motion" 

Gradually two theories arose concerning heat ; — one, the 
Material theory — the theory of Caloric or Phlogiston ; the 
other, the Kinetic theory. Before the beginning of the 
present century the former theory was generally accepted, 
and the development of heat was accounted for. by asserting 
that friction or percussion altered the capacity for heat of 
the substances acted upon. The heat was squeezed out 
by the hammer, and the amount of heat in the world was 
regarded as a certain quantity, which passed from one 
body to another, and that some substances contained, or 
could " store away," more of the material called heat than 
other substances. Heat was the material of fire — the 
principle of it, or materia ignis ; and by these theories Heat, 
or Caloric, was gradually adopted as a separate material 
agent — an invisible and subtle matter producing certain 
phenomena when liberated. 

So the two theories concerning heat arose at the end of 
the last century. One, as we have said, is known as the 
Material, the other as the Kinetic theory. The latter is 
the theory of motion, so called from the Greek kinesis 
(motion), or sometimes known as the Dynamic theory of 
heat from dunamis (force) : or again as Thermo-dynamics. 



THEORIES OF HEAT. 3 

But any possibility of producing a new supply of heat 
was denied by the materialists. They knew that some 
bodies possessed a greater capacity for heat than others ; but 
Count Rumford, at Munich, in 1 797, astonished an audience 
by making water boil without any fire ! He had observed 
the great extent to which a cannon became heated while 
being bored in a gun factory, and influenced by those who 
maintained the material theory of heat, paid great attention 
to the evolution of heat. He accordingly endeavoured to 
produce heat by friction, and by means of horse power he 
caused a steel borer to work upon a cylinder of metal. 
The shavings were permitted to drop into a pan of water 
at 60° Fahrenheit. In an hour after the commencement 
of the operation the temperature of the water had risen to 
107° : in another half hour the heat of it was up to 142° : 
and in two hours had measured 1 70°. Upon this he says : 
" It is hardly necessary to add that anything which any 
insulated body or system of bodies can continue to furnish 
without limitation cannot possibly be a materiail substance, 
and it appears to me to be extremely difficult, if not quite 
impossible, to form any distinct idea of anything capable 
of being excited and communicated in these experiments 
except by motion!' 

A few years later Sir Humphrey Davy made his 
conclusive experiments, and the Material theory of heat 
received its death-blow. 

Sir Humphrey Davy — referring to the fact that water 
at a freezing temperature has " moi-e heat in it " (as it was 
believed) than ice at the same temperature — said : " If I, 
by friction, liquify ice, a substance will be produced which 
contains a far greater absolute amount of heat than ice. In 
this case it cannot reasonably be affirmed that I merely 
render sensible heat which had been previously insensible in 
the frozen mass. Liquification will conclusively prove the 
(generation of heat. 



4 HEAT. 

This reasoning could not be doubted. Sir Humphrey 
Davy made the experiment. He rubbed together two 
pieces of ice in the air, and in a vacuum surrounded by 
a freezing mixture. The ice became Hquified, and so the 
generation of heat by "mechanical means" was proved. 
Its immateriality was demonstrated, but the Material theory 
was not even then abandoned by its adherents. 

So things continued, until in 1 842-3, Doctor Julius Meyer, 
of Heilbronn, and Doctor Joule, of Manchester, separately, 
and by different means, arrived at the conclusion that a 
certain definite amount of mechanical work corresponds 
to a certain definite amount of Heat, and vice versA. Thus 
was a great support afforded to the Dynamic theory. 
This fact Doctor Joule communicated to the Philosophical 
Magazine in 1 843, and the conclusions he came to were — 

1. "That the quantity of heat produced by the friction 

of bodies, whether solid or liquid, is always in 
proportion to the force expended ; 

2. " That the quantity of heat capable of increasing the 

temperature of a pound of water (weighed in 
vacuo and taken at between 55° and 60° Fahr.) 
by 1° Fahr., requires for its evolution the ex- 
penditure of a mechanical force represented by 
the fall of 772 lbs. through the space of one 
foot. 
This is the " mechanical equivalent of heat." The first 
paper written by Mr. Joule demonstrated that the tempera- 
ture of water rises when forced through narrow tubes ; and 
to heat it one degree, the force of 770 foot pounds was 
necessary, which means that the i lb. of water falling 770 
feet, got hotter by one degree when it reached the earth. 
He subsequently arrived at the more exact conclusions 
quoted above. 

So heat is now known to be a series of vibrations, or 
vibratory motions, as sound vibrations, which we cannot 



MECHANICAL EQUIVALENT. 5 

hear nor see, but the effects of which are known to us as 
light and heat. 

In considering heat we naust put aside the idea of warmth 
and cold, for they are only different degrees of heat, not 
the absence of it. 







^f^nr,. 



Melting a piece of tin on a card. 

The study of heat can be briefly undertaken without any 
complicated apparatus. If we desire a proof of the great 
conducting power of metals, let us place a fine piece of 
muslin tightly stretched over a lump of polished metal. 
On the muslin we put a burning ember, and excite 
combustion by blowing on it ; the muslin is not burned 
in the least, the heat being entirely absorbed by the metal, 



6 HEAT. 

which draws it through the material into itself. The 
foregoing cut represents a similar experiment : it consists 
of melting some tin on a playing card, held over the flame 
of a spirit lamp. The metal becomes completely melted 
without the card being burnt. It is through a similar 




Boiling water in a paper case. 

effect that metals appear cold to us when we take them 
in our hands ; by their conductivity they remove the 
heat from our hands, and give us the peculiar impression 
which we do not experience when in contact with sub- 
stances that are bad conductors, such as wood, woollen 
materials, etc. 



REFREEZING OF ICE. 7 

The illustration shows the method of boihng water in 
paper. We make a small paper box, such as those made 
by school-boys,, and suspend it by four threads to a piece 
of wood held horizontally at a suitable height. We fill this 
improvised vessel with water, and place it over the flame of 
a spirit lamp. The paper is not burnt, because the water 
absorbs all the heat into itself. After a few minutes the 
water begins to boil, sending forth clouds of steam, but the 
paper remains intact. It is well to perform this operation 
over a plate, in case of accident, as the water may be spilt. 
We may also make use of an egg-shell as a little vessel 
in which to heat the water, by resting it on a wire ring over 
the flame of the spirit lamp. 

We can easily arrange a very remarkable experiment, 
but little known, on the refreezing of ice. A block of ice 
is placed on the edge of two iron chairs, and ife encircled 
by a piece of wire, to which is suspended the weight of say 
five pounds. The wire penetrates slowly, and in about an 
hour's time has passed completely through the lump of ice, 
and the weight, with the piece of wire, falls to the ground. 
What happens then to the block of ice ? — You imagine, 
doubtless, that it is cut in two. No such thing ; it is intact, 
and in a single lump as it was previous to the experiment. 
In proportion as the wire was sunk through the mass, 
the slit has been closed again by refreezing. Ice or snow 
during the winter may serve for a number of experiments 
relating to heat. If we wish to demonstrate the influence 
of colours on radiation, we take two pieces of cloth of the 
same size, — one white, and the other black, — and place 
them both on the snow, if possible, when there is a gleam 
of sunlight. In a short time it will be found that the 
snow underneath the black cloth has melted to a much 
greater extent than that beneath the white cloth, because 
black absorbs heat more than white, which, on the contrary, 
has a tendency to reflect it. We perceive very plainly the 



8 HEAT. 

difference in temperature by touching the two cloths. The 
white cloth feels cold in comparison with the black cloth. 
It is hardly necessary to point out experiments on the 
expansion of bodies. They can be performed in a number 
of different v/ays ; by placing water in a narrow-necked 




Experiment on the regelation of ice. 

bottle, and warming it over the fire, we can ascertain the 
expansion of liquids under the inflxience of heat. We 
may in this way construct a complete thermometer. 

We may now consider the Sources of Heat, or cau.ses of 
its development, which are various, and in many cases 
apparent. The first great source is the Sun, and it has 



SOURCES OF HEAT. 9 

been calculated that the heat received by the earth in one 
year is sufficient to melt an envelope of ice surrounding it 
one hundred and five feet thick. Of course the heat at 
the surface of the sun is enormously greater than this, 
about one-half being absorbed in the atmosphere before it 
reaches us at all. In fact, it is impossible to give you an 
idea of the enormous heat given out by the sun to the 
earth (which is a very small fraction indeed of the w^hole), 
stars, and planets, all of which give out heat. We know 
that heat is stored in the earth, and that it is in a very 
active condition we can perceive from the hot springs, 
lava, and flame which are continually erupting from the 
earth in various places. These sources of heat are beyond 
our control. 

But apart from the extra and intra-terrestrial sources of 
heat there are mechanical causes for its generation upon 
our globe, such as friction, percussion, or compression. 
The savage or the woodman can procure heat and fire by 
rubbing a pointed stick in a grooved log. The wooden 
" breaks " of a locomotive are often set on fire by friction 
of the wheels, so they require' grease, and the wheels on 
the rails will develop heat and sparks. Our matches, 
and many other common instances of the generation of 
heat (and fire) by friction, will occur to every reader. 
Water may be heated by shaking it in a bottle, taking 
care to wrap something round it to keep the warmth of 
the hand from the glass. By percussion, such as hammer- 
ing a nail or piece of iron, the solid bar may be made 
" red-hot " ; and when cannon are bored at Woolwich the 
shavings of steel are too hot to hold even if soap-and-water 
has been playing upon the boring-machine. 

The production of heat by chemical action is termed 
combustion, and this is the means by which all artificial 
heat for our daily wants is supplied. We can also pro- 
duce heat by electricity. A familiar and not always 



lO HEAT 

pleasant instance of this is seen in the flash of lightning 
which will fuse metals, and experiment may do the same 
upon a smaller scale. These are, in brief, the Sources of 
Heat, and we may speak of its effects. 

We may take it for granted that no matter from what 
source heat is derived, it exhibits the same phenomena in 
its relation to objects. One of the most usual of these 
phenomena is expansion. Let us take water; and see the 
effect of heat upon it. 

We know that a certain weight of water under the same 
conditions has always the same volume ; and although 
the attributes of the liquid vary under different circum- 
stances, under the same conditions its properties are exactly 
the same. Now, water expands very much when under 
the influence of heat, like all liquids ; solids and gases 
also expand upon the application of heat. 

We can easily establish these statements. A metallic 
ring when heated is larger than when cool. A small 
quantity of air in a bladder when heated will fill the 
bladder, and water will boil over- the vessel, or expand 
into steam, and perhaps burst the boiler. So expansion 
is the tendency of what we term heat. 

We make use of this quality of heat in the thermometer, 
by which we can measure the temperature not only of 
liquids or solids, but of the atmosphere. The reading of 
the thermometer varies in different countries, for the 
degrees are differently marked, but the construction of the 
instrument is the same. It is called thermometer from 
two Greek words signifying the measure of heat. It is a 
notable fact that Castelli, writing in 1638, says to 
Ferdinand Csesarina : " I remembered an experiment 
which Signer Galileo had shown me more than thirty-five 
years ago. He took a glass bottle about the size of a 
hen's egg, the neck of which was two palms long, and as 
narrow as a straw. Having well heated the bulb in his 



THE THERMOMETER. I I 

hands, he placed its mouth in a vessel containing water, 
and withdrawing the heat of his hand from the bulb, the 
water instantly rose in the neck more than a palm above 
the level of the water in the vessel." 

Here, then, we have an air-thermometer, but as it was 
affected by the pressure as well as the temperature of the 
atmosphere, it could not be relied upon as a " measurer 
of heat." 'Until Torricelli propounded the principle of 
the barometer, this " weather-glass " of Galileo was used, 
for the philosopher divided the stem into divisions, and 
the air-thermometer served the purpose of our modern 
instruments. 

The actual inventor of the thermometer is not known. 
It has been attributed to Galileo, to Drebbel, and to 
Robert Fludd. There is little doubt, however, that Galileo 
and Drebbel were both acquainted with it, but whether 
either claimed the honour of the invention, whether they 
discovered it independently, or together, we cannot say. 
Sanctorio, of Padua, and Drebbel have also been credited 
with the invention. We may add that the spirit ther- 
mometer was invented in 1655-1656. It was a rough 
form of our present thermometer, and roughly graduated. 
But it was hermetically closed to the air, and a great 
improvement on the old " weather-glass." Edward Halley 
introduced mercury as the liquid for the instrument in 
1680. Otto von Guerike first suggested the freezing 
point of water as the lowest limit, and Renaldini, in 1694, 
proposed that the boiling and freezing points of water 
should be the hmit of the scale. 

Let us now explain the construction and varied markings 
of the three kinds of thermometers in use. By noting the 
differences between the scales every reader will be able to 
read the records from foreign countries noted upon the 
Centigrade and Rdaumur instruments, which are all based 
upon the theory that heat expands liquids. 



12 HEAT. 

[We used to hear the expression, " Heat expands, and 
cold contracts," but we trust that all our readers have now 
learnt that there is no such thing as cold. It is only a 
negative term. We feel things cold because they extract 
some warmth from our fingers, not because the substances 
have no heat.] 

Thermometers are made of very fine bore glass tubes. 
One end has a bowl, or bulb, the other is af first open. 
By heating the bowl the air in the tube is driven away by 
the open end, which is quickly dipped in a bowl of mer- 
cury. The mercury will then occupy a certain space in 
the tube ; and if it be heated till the liquid boils, all the 
air will be driven out by the mercurial vapour. By once 
again dipping the tube in the quicksilver the glass will be 
filled. Then, before it cools, close the open end of the 
tube, and the thermometer is so far made. Having now 
caught our thermometer we must proceed to mark it, 
which is an easy process. By plunging the mercury into 
pounded melting ice we can get the freezing point, and 
boiling water will give us the boiling point. The inter- 
mediate scale can be then indicated; 

If mercury and glass expanded equally there would be 
no rise in the latter. Extreme delicacy of the ther- 
mometer can be arrived at by using a very fine tube, 
particularly if it be also flat. 

The freezing point in Fahrenheit's scale is 32° ; in the 
Centigrade it is 0°, and the boiling point 100°. This 
was the scale adopted by Celsius, a Swede, and is much 
used. Reaumur called the freezing point o", and the 
boiling point 80°. There is another scale, almost obso- 
lete, — that of Del isle, who called boiling point zero, and 
freezing point 150°. 

There is no diiificulty in converting degrees on one 
scale into degrees on the other. Fahrenheit made his 
zero at the greatest cold he could get ; viz., snow and 



MEASURING HEAT. 



13 



salt. The freezing point of water is 32° above his zero' 
Therefore 212 — 32 gives 180°, the difference between 
the freezing and boiling points of water. So 180° Fahr. 
corresponds to 100° Cent, and to 80° Reaumur, reckoning 
from freezing point. 

The following tables will explain the differences : — 

Table i. 

1° Fahr. = 0*55° Cent., or 0'44° Reaumur. 
1° Cent. = '80° Reaumur, or i'8o° Fahr. 

1° Reaumur = i'25° Cent., or 2'25° Fahr. 

Table ii. 





Fahr. 


Cent. 


R(!aumur. 



80 


Coiling point , 


212 


100 




194 
176 
158 
140 


90 
80 
70 
60 


72 
64 
56 
48 




122 


50 


40 




86 
68 


40 
20 


32 
24 
16 




50 


10 


8 


Freezing point of water 


32 
14 




— 10 




—8 




—4 


— 20 


-16 


Freezing pjint of mercury . 


—40 


—40 


-32 



Alcohol is used in thermometers in very cold districts, 
as it does not freeze even at a temperature of — 132° 
Fahr. 

We have now explained the way in which we can 
measure heat by the expansion of mercury in a tube. 
We can also find out that solids and gases expand also. 
Engineers always make allowances for the effects of 
winter and summer weather when building bridges ; in 
summer the bridge gets longer, and unless due provision 



14 HEAT. 

were made it would become strained and weakened. So 
there are compensating girders, and the structure remains 
safe. 

The effects of expansion by heat are very great and 
very destructive at times. Instances of boilers bursting 
will occur to every reader. It is very important to be 
able to ascertain the extent to which solid bodies will 
expand. Such calculations have been made, and are in 
daily use. 

We can crack a tumbler by pouring hot water into it, 
or by placing it on the "hob." A few minutes' con- 
sideration will assure us that the lower particles of the 
glass expanded before the rest, and cracked our tumbler. 
A gradual heating, particularly if the glass be thin, will 
ensure safety. Thick glass will crack sooner than thin. 

Again, many people at railway stations have asked us, 
"Why don't they join the rails together on this line.?" 
We reply that if every length of rail were tightly fixed 
against its neighbour, the whole railway would be dis- 
placed. The iron expands and joins up close in hot 
weather. In wet weather, also, the wooden pegs and 
the sleepers swell with moisture, and get' tightened up. 
Everyone knows how much more smoothly a train travels 
in warm, wet weather. This is due to the expansion of 
the iron and the swelling of the sleepers and pegs in the 
"chairs." A railway 400 miles long expands 338 yards 
in summer, — that is the difference in length between the 
laid railroad in summer and in winter. 

This can be proved. Iron expands 0001235 of its 
length for every 180° Fahr. Divided by 180 it gives us 
the expansion for 1°, which is 000000686, taking the 
difference of winter and summer at 70° Fahr. Multiply 
these together, and the result (o'Ooo48620 of its length) 
by the number of yards in 400 miles, and we find our 
answer 338 yards. Expansion acts in solids and most 



EXPANSION. 1 5 

liquids by the destruction of cohesion between the particles. 
Gases, however, having much less cohesion* amid the 
particles, will expand far more under a given heat than 
either solids or liquids, and liquids expand more than 
solids for the same reason, and more rapidly at a high 
temperature than at a low one. 

We have spoken of expansion. We may give an 
instance in which the subsequent contraction of heated 
metal is useful. Walls sometimes get out of the perpen- 
dicular, and require pulling together. No force which can 
be conveniently applied would accomplish this so well as 
the cooling force due to the potential energy of iron. 
Rods are passed through the walls and braced up by nuts. 
The rods are then heated, and as they cool they contract 
and pull the walls with them. 

When glass is suddenly cooled, the inner skin, as it 
were, presses with great force against the cooled surface, 
but as it is quite tight no explosion can follow. But 
break the tail, or scratch it with a diamond, and the strain 
is taken off. The glass drop crumbles with the effect 
of the explosion, as in the cases of Prince Rupert's drops, 
and the Bologna flasks ; the continuity is broken, and 
pulverization results. 

But a very curious exception to the general laws of 
expansion is noticed in the case of nearly freezing water. 
We know water expands by heat, at first gradually, and 
then to an enormous extent in steam. But when cooling, 
water,, instead of getting more and more contracted, only 
contracts down to 39-2° Fahr., it then begins to expand, 
and at the moment it freezes into ice it expands very much 

about one-twelfth of its volume, but according to 

Professor Huxley it weighs exactly the same, and the 
steam produced from that given quantity of water will 
v/eigh just exactly what the water and the ice produced 
by it weigh individually. At 39-2° Fahr. water is at its 



1 6 HEAT. 

maximum density, or in other words, a vessel of a certain 
size will hold more water when it is at 39° Fahr. than at 
any other time. Whether the water be heated or cooled 
at this temperature, it expands to the boiling or freezing 
point when it becomes steam or ice, as the case may be. 

Water, when heated, is lighter than cold water. You 
can prove this in filling a bath from two taps of hot and 
cold water at the same time. The cold falls to the bottom, 
and if you do not stir up the water when mixed you will 
have a hot surface and a cold foundation. The heat 
increases the volume of water, it becomes lighter, and 
comes uppermost. 

Steam and Water and Ice are all the same things under 
different conditions, although to the ej'e they are so 
different. They are alike inasmuch as a given weight of 
water will weigh as much when converted into ice or 
developed into steam. The half ounce of water will weigh 
half an ounce as ice or as steam, but the volume or bulk 
will vary greatly, as will be understood when we state that 
one cubic inch of water will produce 1,700 cubic inches 
of steam, and 1 1\ cubic inch of ice ; but at the same time 
each will yield, when decomposed, just the same amount 
of oxygen and hydrogen. 

Let us now consider the Effects of Heat upon Water. 
We have all seen the vapour that hangs above a locomotive 
engine. We call it " steam." It is not pure steam, for 
steam is really invisible. The visible vapour is steam on 
its way to become water again. On a very hot, dry day 
we cannot distinguish the vapour at all. 

The first effect of heat upon water is to expand it ; and 
as the heat is applied we know that the water continues 
to expand and bubble up ; and at last, when the tem- 
perature is as high as 2 1 2°, we say water " boils " — that 
is, at that heat it begins to pass away in vapour, and 
you will find that the temperature of the steam is the 



STEAM. 1 7 

same as the boiling water. While undergoing this trans- 
formation, the water increases in volume to 1,700 times 
its original bulk, although it will weigh the same as the 
water. So steam has 1,700 less specific gravity than 
water. 

It is perhaps scarcely necessary to remind our readers 
that water, when heated, assumes tremendous force. Air 
likewise expands with great violence, and the vessels con- 
taining either steam or air frequently burst with destructive 
effects. Solid bodies also expand when heated, and the 
most useful and accurate observations have been made, 
so that the temperatures at which solid bodies expand are 
now exactly known. Air also expands by heat. 

While speaking of Expansion by Heat, we may remark 
that a rapid movement is imparted to the air by Heat. 
In any ordinary room the air below is cool, while if we 
mount a ladder to hang up a picture, for instance, we shall 
find the air quite hot near the ceiling. This is quite in 
keeping with the effects of heat upon water. The hot 
particles rise to the top in a vessel, and thus a motion is 
conveyed to the water. So in our rooms. The heated 
air rushes up the chimney and causes a draught, and 
this produces motion, as may be seen by an experiment 
in which a cardboard spiral can be set in motion by heated 
air from a lamp chimney. A balloon will ascend, because 
.it is filled with heated air or gas ; and we all have seen 
the paper balloons which will ascend if a sponge containing 
spirits of wine be set on fire underneath them. 

Winds are also only currents of air produced by unequal 
temperature in different places. The heated air ascends, 
and the colder fluid rushes in sometimes with great velocity 
to fill the space. "Land" and "sea" breezes are constant; 
the cool air blows in from the sea during the day, and as 
the land cools more rapidly at night, the breeze passes out 
again. 



1 8 HEAT. 

We know that water can be made to boil by heat, but 
it is not perhaps generally known that it will apparently 
boil by cold, and the experiment may thus be made : — A 
flask half-full of water is maintained at ebullition for some 
minutes. It is removed from the source of heat, corked, 
inverted, and placed in one of the rings of a retort stand. 
If cold water is poured on the upturned bottom of the 
flask, the fluid will start into violent ebullition. The 
upper portion of the flask is filled with steam, which main- 
tains a certain pressure on the water. By cooling the 
upper portion of the flask some of this is condensed, and 
the pressure reduced. The temperature at which water 
boils varies with the pressure. When it is reduced, water 
boils at a lower heat. By pouring the cold water over the 
flask we condense the steam so that the water is hot enough 
to boil at the reduced pressure. To assert that water 
boils by the application of cold is a chemical sophism. 

Ebullition and Evaporatio7i may be now considered, and 
these are the two principal modes by which liquids assume 
the gaseous condition. The difference is, when water boils 
we term it ebullition (from the Latin ebullio, I boil) ; 
evaporation means vapour given out by water not boiling 
(from evaporo, I disperse in vapour). 

There are two operations based upon the properties 
which bodies possess of assuming the form of vapour under 
the influence of heat, which are called Distillation and 
Sublimation. These we will consider presently. 

Ebullition then irieans a bubbling up or boihng; and 
when water is heated in an open vessel two forces oppose 
its conversion into vapour ; viz., its own cohesive force and 
atmospheric pressure. At length, at 212° Fahr., the 
particles of water have gained by heat a force greater than 
the opposing forces ; bubbles of vapour rise up from the 
bottom and go off in vapour. This is ebullition, and at 
that point the tension of the vapour is equal to the pressure 



EBULLITION. 



19 



of the atmosphere, for if not, the bubbles would not form. 
All this time of boiling, notwithstanding any increase of 
heat, the thermometer will not rise above 2 1 2° (Fahr.), for 
all the heat is employed in turning the water to steam. 

We have said the ebullition takes place at 212° Fahr. 
(or 100° C), but that is only at a certain level. If we 
ascend 600 feet high we shall find that water will boil at 
a less temperature ; and on the top of a mountain (say 
Mont Blanc) water will boil at 185° Fahr.; so at an 
elevation of three miles water boils at a temperature less 
by 27° Fahr. An increase of pressure similarly will raise 
the boiling point of water. The heights of mountains are 
often ascertained by noticing the boiling point of water on 
their summits, the general rule being a fall of one degree 
for every 530 feet elevation at medium altitudes. We 
append a few instances taken at random : — 



Place. 


Height above level 
of the sea— Feet. 


Barometer mean 
height. 


Boiling point of 
water, Fahr. 


Quito 


9,541 
7,471 
6,808 
4,738 
1,221 
. 213 



20-7S 
22-52 

23-07 
24-96 
28-54 
2969 

30-00 


194-2 
1 98- 1 
199-2 
203-0 
209-5 
211-5 
2I2-0 


St. Gothard 

Garonne (Pyrenees) 

Geneva 

Paris (ist floor) 

Sea level 



[The difference for a degree depends upon the height, 
varying between 510 and 5 90 feet, according to the 
elevation reached. The approximate height of a mountain 
can be found by multiplying 530by the number of degrees 
between the boiling point and 2 1 2°. In some very elevated 
regions travellers have even failed to boil potatoes.] 

The boiling point of liquid may be altered by mixing 
some substance with it ; and although such a substance as 
sawdust would not alter the boiling point of water, yet if 
the foreign matter be dissolved in the liquid it will alter 



22 



HEAT. 



summer. The only inconvenience attending it is the 
employment of sulphuric acid, of which a considerable 
quantity is used to absorb the vapour from the water, as 




already referred to. If proper precaiitions are taken, 
however; there will be no danger in using the apparatus. 

The mode of proceeding' is as follows : — The bottle full 
of water is joined to t!ie air-pump by a tube, and after a 
few strokes the water is seen in ebullition. The vapour 



ARTIFICIAL ICE. 23 

thus disengaged traverses an intermediate reservoir filled 
with sulphuric acid, which absorbs it, and immediately 
condenses it, producing intense cold. In the centre of 
the liquid remaining in the carafe some needles of ice 
will be seen, which grow rapidly, and after a few more 
strokes of the pump the water will be found transformed 
into a mass of ice. This is very easy of accomplishment, 
and in less than a minute the carafe full of water will be 
found frozen. 

The problem for the truly economical formation of ice 
by artificial means is one of those which have occupied 
chemists for a long time, but hitherto, notwithstanding 
all their efforts, no satisfactory conclusion has been arrived 




Retort and Receiver. 



at. Nearly every arrangement possesses some drawback 
to its complete success, which greatly increases the cost of 
the ice, and causes inconvenience in its production. The 
usual mode in large towns is to collect the ice, in houses 
constructed for the purpose, during the winter, and this 
simple method is also the best, so far as at present has 
been ascertained. 

In connection with vaporization we may now mention 
two processes referred to just now — viz., sublimation and 
distillation. The former is the means whereby we change 
solid bodies into vapour and condense the vapour into 
proper vessels. The condensed substances tvhen deposited 
are called sublimates. The mode of proceeding is to place 
the substance in a glass tube, and apply heat to it. 



24 



HEAT. 



Vapour will be formed, and will condense at the cool end 
of the tube. The sublimate of sulphur is called "Flowers 
of Sulphur," and that of perchloride of mercury " Corrosive 
Sublimate." 

Distillation is a more useful process, or, at any rate, one 
more frequently employed, and is used to separate a 
volatile body from substances not volatile. A distilling 
apparatus [distillo, to drop) converts a liquid to vapour by 
means of heat, and then condenses it by cold in a separate 
vessel. 




Distilling apparatus. 



The distilling apparatus consists of three parts, — the 
vessel in which the liquid is heated (the still, or retort), the 
condenser, and the receiver. The simple retort and receiver 
are shown in previous page. But when very volatile 
vapours are dealt with, the arrangement shown above is 
used. Then the vapour passes into the tube encased in a 
larger one, the intervening space being filled with cold 
water from the tap above (c), the warm water dropping 
from g. The vapours are thug condensed, and drop into 
the bottle (or receiver), B. 

The apparatus for distilling spirits is shown (p. 25). The 
" still," A, is fitted into a furnace, and communicates with 



DISTILLATION. 



25 



a worm, O, in a metal cylinder filled with water, kept 
constantly renewed through the tube, TT. This spirit 
passes through the spiral, and being condensed, goes out 
into the receiver, c. 

There are even more simple apparatus for spirit distil- 
ling, but the diagram will show the principle of all 
" stills." In former days, in Ireland, whiskey was generally 
procured illegally by these means. 




Spirit Still. 



CHAPTER II. — HEAT [continued). 

SPECIFIC HEAT FUSION LATENT HEAT CONDUCTION 

AND CONVECTION OF HEAT CALORESCENCE. 

We have considered the effects of heat upon water, and 
touched upon one or two kindred experiments. But we 
have some other subjects to discuss, two in particular; viz., 
Specific Heat, and Latent Heat. 

The specific heat of any substance is " the numb. .• of 
units of heat required to raise on-e pound of such substanee 
one degree." We can explain this farther. When heat 
is communicated to a body it has two or three functions 
to perform. Some of it has to overcome the resistance of 
the air in expanding the body, more of it expands, and 
the remainder increases the temperature of the body. So 
some heat disappears as heat, and is turned into energy, 
— " molecular potential energy," — as it is called, and the 
rest remains. Of course in objects the molecules vary 
very much in weight and in their mutual attraction, and 
the heat requisite to raise equal weights of different sub- 
stances through the same number of degrees of temperature 
will vary. This is called capacity for heat, or specific heat. 
The capacity of different metals for heat can easily be 
shown. The specific heat of water is very high, because 
its capacity for heat is great. We can cool a hot iron in 
very little water, and it takes thirty times as much heat 
to raise a given weight of water a certain number of 
degrees, as it would, to raise the same weight of mercury 



LATENT HEAT. 27 

to the same temperature. Water has greater specific 
heat, generally speaking, than other bodies, and it is owing 
to this circumstance that the climate is so affected by- 
ocean currents. 

Nearly all substances can be melted by heat, if we go 
far enough, or frozen, if we could take the heat away. 
Solid can be made liquid, and these liquids can be made 
gases and fly off in vapour. Similarly, if we could 
get heat away sufficiently from the atoms of a sub- 
stance we could freeze it. We cannot freeze alcohol, nor 
make ice from air, nor can we liquify it, for we are unable 
to take away its heat sufficiently. But we can turn water 
into steam, and into ice ; or ice into water, and then into 
steam. But there is one body we cannot melt by heat ; 
that is carbon. In the hottest fire coal will not melt, it 
becomes soft. We call this melting fusion, and every body 
has its melting point, or fusing point, which is the same at 
all times if the air pressare be the same. 

It is a curious fact that when a body is melting it rises 
to a certain temperature (its fusing point), and then gets 
no hotter, no matter whether or not the fire be increased ; 
— all the extra heat goes to melt the remainder of the 
substance. The heat only produces changes of state. So 
this heat above fusing point disappears apparently, and is 
called Latent Heat. This can easily be proved by melting 
ice. Ice melts at 32° Fahr., or 0° Cent, and at that 
temperature it will remain so long as any ice is left ; but 
the water at 32°, into which the ice has melted, contains 
a great deal of latent heat, which it has absorbed in melting, 
and yet the thermometer does not- show it. It is just the 
same with boiling water. 

When substances are fused they expand as a rule, but 
ice contracts ; so does antimony. On the other hand, 
when water solidifies it does not contract as most things 
do. It expands, as many of us are aware, hy finding our 



28 HEAT. 

water pipes burst in the winter ; and the geologist will 
tell us hew the tiny trickling rills of water fall in between 
the cracks of rocks and there freeze. In freezing the drops 
expand and split the granite blocks. Type-metal expands 
also when it becomes solid, and leaves us a clear type ; 
but copper contracts, and won't do for moulding, so we 
have to stamp it when we want an impression on it. 

There is no doubt that chemical combinations produce 
heat, as we can see every day in house-building operations, 
when water is poured upon lime ; but there are also 
chemical combinations which produce cold. Fahrenheit 
produced his greatest cold by combining snow and salt, 
for in the act of combining, a great quantity of heat is 
swallowed up by reason of the heat becoming latent, as it 
will do when solid bodies become liquid. Such mixtures 
or combinations are used as Freezing Mixtures when it is 
necessaiy to produce intense cold artificially. Sulphate of 
sodium and hydrochloric acid will also produce great 
cold, and there are many other combinations equally or 
even more efficacious. 

Heat is communicated to surrounding objects in three 
well-known ways — by conduction, by radiation, and by 
convection. Conduction of heat is easily understood, and 
is the propagation of heat through any body, and it varies 
very much according to the substance through which it 
passes. Some substances are better conductors of heat 
than others. SUver has a far greater conductivity than 
gold, and copper is a better heat-conductor than tin. 
Flannel is a non-conductor, or rather a bad conductor, for 
no substance can be termed actually a non-conductor. 
Flannel, we know, will keep ice from melting, and a 
sheep's wool or a bird's feathers are also bad conductors 
of heat ; so Nature has provided these coverings to keep in 
the animal heat of the body. A good conductor of heat 
feel3 cold to the touch of our fingers, because it takes the 



CONDUCTION. 2q 

heat froiTl our hands. This can be tried by touching 
silver, lead, marble, wood, and wool. Each in turn Avill 
feel cold and less cold, because they respectively draw 
away, or conduct less and less heat from our bodies. So 
our clothes are made of bad-conducting substances. The 
bark of a tree is a bad conductor, and if you strip off this 
clothing the tree will die. 

Solids conduct heat the better the more compact they 
are. Air being a bad conductor it follows that the less 
tightly the molecules are packed the less Conductibility 
there will be ; and even a substance powdered will be a 
worse conductor than the same substance in solid form ; 
and also more readily in the direction of the fibres than 
crossways. 

Liquids do not possess great conductivity, but they, as 
well as gases, are influenced by convection, or the transport 
of heat from the bottom layers to the top {conveho, to 
carry up). We have already mentioned that the heated 
particles of water rise to the top because they expand, 
and so become lighter. This is convection of heat ; and 
by it liquids and gases, though actually bad conductors, 
may become heated throughout to a uniform temperature. 
Of course the more easily expansible the body is the more 
rapidly will convection take place — so gases are more 
readily affected than liquids. Solids are not affected, 
because convection of heat depends upon molecular move- 
ment or mobility, and it is obvious that the particles of 
.solid bodies are not mobile. Professor Balfour Stewart 
says with reference to this that " were there no gravity 
there would be no convection," for the displacement of 
the light warm particles by the heavier cold ones is due 
to gravity. The instances of convection of heat in 
nature are numerous, and on a gigantic scale. The 
ocean currents, trade winds, lake freezing, etc., while the 
chimney draught already referred to, is another example ; 



30 



HEAT. 



and in all these cases the particles of air or water are 
replaced by convection. In the case of the lake freezing 
the cold particles at the top sink, and the warmer ones 
ascend, until all the lake is at a temperature of 36'2°, or 
say 4° above freezing. At this temperature water assumes 
its maximum density, and then expands, as we have seen, 
instead of contracting. Ice is formed, and being thus 
lighter than water, floats ; and so unites to cover in the 
water underneath, which is never frozen solid, because the 
cold of the atmosphere cannot reach it through the ice in 
time to solidify the whole mass. 

Radiant heat is the motion of heat transmitted to the 
ether, and through it in the form of waves. The sun's 
heat is radiant heat, and radiation 
may be defined as "The communi- 
cation of the motion of heat from the 
■ articles of a heated substance to the 
ether." The fire gives out radiant 
heat, and so does heated metal, and 
it is transmitted by an unseen me- 
dium. It is quite certain that the 
heat of a suspended red-hot poker is 
not communicated to the air, because 
it will cool equally in a vacuum. Sir 
Humphrey Davy proved that radiant 
heat could traverse a vacuum, for by 
putting tin reflectors in an exhausted 
receiver he found that a hot substance 
,in the focus of one reflector caused an 
increase in the heat of the other. If 
we put a red-hot or a hot substance 
in one reflector, and tinder in the 
other, the latter will take fire. The velocity of heat rays 
is equal to that of light, 1 86,000 miles in a second, and 
indeed, radiant heat is identical with light. Heat is 




A 



iO 



y, 



Radiant heat. 



FRICTION. 3 1 

reflected as is light, and is refracted in the same way 
as sound. 

Some bodies allow the heat rays to pass through them, 
as air does, and as rock salt will do. White clothing is 
preferable in summer (and also in winter if we could only 
make people believe it). White garments radiate less heat 
in winter, and absorb less heat in summer. An old black 
kettle will boil water more quickly than a new bright one, 
but the latter will keep the water hotter for the longer time 
when not on the fire. 

Heat, then, is movement of particles. Energy can be 
changed into heat, as the savage finds when he rubs the 
bits of wood to produce heat and fire. Friction causes 
heat, and chemical combination produces heat ; and, if 
" visible energy can be turned into heat, heat- can be turned 
back into visible energy." For fire heats water, water 
expands into steam, and steam produces motion and energy 
in the steam-engine. 

If we heat water in Wollaston's bulb, — the opening of 
which is hermetically stopped by a piston, — the vapour 
will raise the piston. If we cool the bulb we condense 
the steam, and the piston falls. Here we have the prin- 
ciple of the steam-engine. 

Steam is the vapour of water educed by heat, and we 
may give a few particulars concerning it. Its mechanical 
properties are the same as those of other gases, and pure 
steam is colourless. and transparent — in fact, invisible. Its 
power when confined in boilers and subjected to pressure 
is enormous, for the volume of the steam is far greater than 
the water which gave rise to it. One cubic inch of water 
will produce 1,700 cubic inches of steam — in other words, 
a cubic inch of water produces a cubic foot of steam. 
When we obtain steam at 212", we do so under the 
pressure of one atmosphere ; but by increasing the pressure 
we can raise the boiling point, and thus water at the 



32 HEAT. 

pressure of sixteen atmospheres will not steam till it 
reaches 398°. It is thus we obtain pressure for locomo- 
tives and other engines, although a very small portion of 
the steam does work. Much the largest portion is 
expended in overcoming cohesion, and one way and 
another, taking into consideration defects in machinery, 
only about one-tenth of the heat is employed in doing the 
work. The force exercised by steam .under atmospheric 
pressure is sufficient to raise a ton weight one foot. 

To obtain very high temperatures we shall find the 
thermometer of no use, for mercury boils at 660°, so an 
instrument called a Pyrometer is used to ascertain the 
fusing points of metals. Mr. Wedgwood, the celebrated 
china manufacturer, invented an instrument made of small 
cylinders of clay moulded and backed, placed between two 
brass rods as gauges divided into inches and tenths. But 
this instrument has been long superseded by Professor 
Daniel's Pyrometer, which consists of a small bar of 
platina in an earthenware tube. The difference of expan- 
sion between the platina and the tube is measured on a 
scale on which one degree is equal to seven degrees of 
Fahrenheit. Thus the melting temperatures of metals are 
ascertained. 

The reflection and refraction of heat are ruled by the 
same laws as the reflection and refraction of light. A 
convex lens will bring the heat or light to a focus, and will 
act as a burning-glass if held in the sunlight. Gunpowder 
has been ignited by a lens of ice, and more than one house 
has been mysteriously set on fire at midday in summer by 
the sun's rays shining through a glass globe of water 
containing gold fish, and falling upon some inflammable 
substance. Professor Tyndall performed a series of experi- 
ments of a very interesting nature, described in his book, 
" Heat considered as a Mode of Motion," and showed the 
transmutation of invisible heat rays into visible rays, by 



HEAT SPECTRUM. 33 

passing a beam of electric light through an opaque 
solution, and concentrating it upon a lens. The dark heat 
rays were thus brought to a focus, all the light was cut off, 
and at the dark focus the heat was found to be intense 
enough to melt copper and explode gunpowder. This 
change of invisible heat into light is termed Calorescence. 
It wax Sir William Herschel who discQvered that there 
were heat rays beyond the red end of the spectrum. 
When light is split up into its component rays, or decom- 
posed. Sir William found that the heat increased as the 
thermometer passed from violet to indigo, and so on to blue, 
green, orange, and red, and the last were the hottest, 
while beyond the spectrum there was heat even greater. 
A Heat Spectrum was thus discovered, and by comparing, 
by means of the thermometer, the various degrees of heat 
within certain limits. Professor Tyndall found that the 
invisible Heat Spectrum is longer than the visible Light 
Spectrum. 





CHAPTER III.— LIGHT. 

SOURCES OF LIGHT — -WHAT IS LIGHT ? VELOCITY OF 

LIGHT— REFLECTION AND REFRACTION — RELATIVE 
VALUE OF LIGHTS. 

'he subject of Light and the science of Optics 
are so interesting to all of us that some short 
history of light is necessary before we can enter 
upon the scientific portion of the subject. The 
nature of the agent (as we may term light) upon which 
our sight depends has employed man's mind from a very 
early period. The ancients were of opinion that the light 
proceeded from the eye to the object looked at. But they 
discovered some of the properties of light. Ptolemy of 
Alexandria, who was born A.D. 70, made some attempts 
to discover the law of Refraction; and we are informed 
that Archimedes set the Roman fleet on fire with burning- 
glasses at Syracuse. The Arabian treatise of Alhagen, in 
1 100 A.D., contains a description of the eye and its several 
parts ; and the writer notices refraction and the effects of 
magnifying glasses (or spectacles.) Galen, the physician, 
practically discovered the principle of the stereoscope, for 
he laid down the law that our view of a solid body is made 
up of two pictures seen by each eye separately. 

Still the science of optics made little progress till the 
law determining the path of a ray of light was made known, 
and the laws of refraction discovered. Refraction means 
that a ray is deflected from its straight course by its 



LIGHT WAVES. 35 

passage from one transparent medium to another of 
different density. The old philosophers found out the 
theory of sound, and they applied themselves to light. 
Newton said light consisted of minute particles emanating 
from luminous bodies. Huyghens and Euler opposed 
Newton's theory of the emission of light ; and it was not 
till the celebrated Thomas Young, Professor at the Royal 
Institution, grappled with the question that the undulating 
or wave theory of light was found out. He based his in- 
vestigations upon the theory of sound waves ; and we 
know that heat, light, and sound are most wonderfully 
allied in their manner of motion by vibration. But he 
was ridiculed, and his work temporarily suppressed by 
Mr. Brougham. 

Light, then, is a vibratory motion (like sound and heat), a 
motion of the luminous atoms of an elastic body. But how 
is the motion transmitted ? Sound has its medium, air ; 
and in a vacuum sounds will be very indistinctly heard, if 
heard at all. But what is the medium of communication 
of light ? It is decided that light is transmitted through a 
medium called ether, a very elastic substance surrounding 
us. The vibrations, Professor Tyndall and other philo- 
sophers tell us, of the luminous atoms are communicated 
to this ether, or propagated through it in waves; these 
waves enter the pupil of the eye, and strike upon the 
retina. The motion is thus communicated by the optic 
nerve to the brain, and then arises the great primary 
faculty, Consciousness. We see light, the waves of which, 
or ether vibrations, are transversal ; air waves or sound 
vibrations are longitudinal. 

We have spoken of radiant heat. Light acts in the 
same way through the ether ; and when we consider 
Sound we shall learn that a certain number of vibrations 
of a string give a certain sound, and the quicker the 
vibration the shriller the tone. So in light. The more 



36 LIGHT. 

quickly the waves of luminosity travel to our eye, and the 
faster they strike it, the greater the difference in the colour, 
or virhat we call colour. Light as we see it is composed 
of different colours, as visible in the rainbow. There are 
seven primary colours in the sunlight, which is white. 
These can be divided or "dispersed," and the shortest rays 
of the spectrum are found to be red, the longest violet. 
It has been calculated that 39,000 red waves make an inch 
in length. Light travels at a rate of nearly 190,000 miles 
a second, so if we multiply the number of inches in that 
distance by the number of red waves, we shall have 
millions of millions of waves entering the eye in a single 
second of time. The other waves enter more rapidly still, 
and " the number of shocks corresponding to the impression 
of violet is seven hundred and eighty-nine millions of 
millions " per second ! Or taking the velocity of light 
at 186,000 miles in a second, it would be six hundred and 
seventy-eight millions of millions (Tyndall). There may 
be other colours which we cannot see because the impres- 
sions come too rapidly upon the retina ; but the violet 
impression has been thus accurately determined. 

We have seen that heat is a kind of motion of particles 
in a body — a vibratory motion which, instead of being 
apparent to the ear, is apparent to the eye in rays of light. 
Thus heat, sound, and light are all intimately connected in 
this way. We have also learnt that rays of light radiate 
and travel with tremendous speed to our eyes, but without 
any shock. There is nofeeling connected with the entrance 
of light to the eye any more than there is any sensation of 
sound when entering the ear, except when the light is 
vividly and very suddenly revealed, or when a very pierc- 
ing sound is heard. Then the nerves are excited, and a 
painful sensation is the result; but under ordinary circum- 
stances we are not physically conscious of the entrance of 
light or sound. 



SOURCES OF LIGHT. 37 

Heat and light are considered to be one and the same 
thing in different degrees of intensity. The sources of 
light are various. The sun and fixed stars, heat, electri- 
city, many animals, and some plants, as well as decaying 
animal matter, give out light. There are luminous and 
non-luminous bodies. The moon is non-luminous, as she 
derives, her light from the sun, as does the earth, etc. 

Light is distributed in rays. These rays are straight in 
all directions. The velocity of light is almost inconceiv- 
able. It travels at a rate of 186,500 miles a second. 
The latest computation with electric light has given a rate 
of 187,200 miles a second ; but the blue rays in the light 
experimented on probably account for the difference, for 
blue rays travel quicker by one per cent, than red rays. 
Romer first found out the velocity of light, which comes 
to us from the sun — ninety millions of miles — ^in eight 
minutes. Fizeau calculated the velocity by means of a 
wheel, which was set moving with tremendous speed, by 
making the light pass between the teeth of the Wheel and 
back again. 

When rays of light meet substances they are deflected, 
and the phenomena under these circumstances are some-, 
what similar to the phenomena of heat and sound. There 
are three particular conditions of rays of light : (i) they 
are absorbed ; (2) they are reflected ; (3) they are refracted. 
Firstly. Let us see what we mean by light being 
absorbed ; and this is not difficult to understand, for any 
" black " substance shows us at once that all the sunlight 
is taken in by the black object, and does not come out 
again. It does not take in the light and radiate it, as it 
might heat. The rose is red, because the rays of light 
pass through it, and certain of them are reflected from 
within. So colour may be stated to be rays- thrown out 
by the objects themselves — those they reject or reflect 
being the " colour " of the object. 



38 



LIGHT. 




Angle of reflection, etc. 



Secondly. Bodies which reflect light very perfectly are 
known as mirrors, and they are termed plane, concave, or 
convex mirrors, according to form. A 
plane mirror reflects so that the reflected 
ray, di, forms the same angle with the 
perpendicular as the incident ray, ri ; in 
other words, the angle of incidence is 
always equal to the angle of reflection, and these rays are 
perpendicular to the plane from which they are reflected 
The rays diverge, so that they appear to come from a 
point as far behind the mirror as the luminous point is in 
front, and the images reflected have the same appearance, 
but reversed. There is another law, which is that " the 
angular velocity of a beam reflected from a mirror is twice 
ttiat of the mirror." The Kaleidoscope, with which we 
are all familiar, is based upon the fact of the multipli- 
cation of images by two mirrors inclining towards each 
other. 

A concave mirror is seen in the accompanying diagram, 
and may be called the segment of a hollow sphere — V w. 

The point C is the geometrical' c 
centre, and o c the radius ; F 
is the focus ; the line passing 
through it is the optical axis ; 
o being the optical centre. 
All perpendicular rays pass 
through C. All rays falling 
in a direction parallel with the 
optical axis are reflected and 
collected at F. Magnified 
images will be produced, and 
if the object be placed between the mirror and the focus, 
the image will appear at the back ; while if the object be 
placed between the geometrical centre and the focus, the 
image will appear to be in front of the mirror. 




Concave mirror. 



MIRRORS. 39 

We can understand these phenomena by the accom- 
panying diagrams. Suppose a ray, A n, passes from one 
object, A B, at right angles, it will be reflected as n KC, the 
ray, A C, being reflected to F. These cannot meet in front 




Reflection ol mirrors (I). 



of the mirror, but they will if produced meet at a, and the 
point A will be reflected there ; similarly B will be reflected 
at b, and thus a magnified image will appear behind or at 
the back of the mirror's surface. In the next diagram the 




Reflection of mirrors (II). 



second supposed case will produce the image in the air at 
a b, and if a sheet of paper be held so that the rays are 
■ intercepted, the image will be visible on the sheet. In 
this case the perpendicular ray, An, is reflected in the 
same direction, and the ray, a c, parallel with the axis, is 



40 



LIGHT. 



reflected to the focus. These rays meet at a and corre- 
sponding rays at b, when the image will be reproduced ; 
viz., in front of the mirror. 

Tke concave mirror is used in the manufacture of 
telescopes, which, with other optical instruments, will be 
described in their proper places. We will now look at 
the Refraction of light. 

Bodies which permit rays of light to pass through them 
are termed transparent. Some possess this property more 
than others, and so long as the light passes through the 
same medium the direction will remain the same.; But if 
a ray fall upon a body of a different degree of density it 
cannot proceed in the same direction, and it will be broken 
or refracted^ the angle it makes being termed the angle of 
refraction. 

For instance, a straight stick when plunged into water 
appears to be broken at the point of immersion. This 

appearance is caused by the 

rays of light taking a different 

direction to our eyes. If in the 

diagram our eye were at o, and 

the vessel were empty, we should 

not see in; but when water is 

poured into the vessel the ob- 

Refraction in water. ject will appear higher up at n, 

and all objects under water appear higher than they 

really are. 

One may also place a piece of money at the bottom of 
a basin, and then stoop down gradually, until, the edge 
of the basin intervening, the coin is lost to view. If an 
operator then fills the basin with water, the piece of 
money appears as though the bottom had been raised. 
The glass lenses used by professors may be very well 
replaced by a round water-bottle full of water. A candle 
is lighted in the darkness, and on holding the bottle 




A LENS. 



41 



between the light and the wall which acts as a screen, we 
see the reflected light turned upside down by means of the 
convergent lens we have improvised. A balloon of glass 
constitutes an excellent microscope. It must be filled 
with perfectly clear, limpid water, and closed by means of 
a cork. A piece of wire is then rolled round its neck, and 
one end is raised, and turned up towards the focus ; viz., 




A water-bottle employed as a convergent lens 



to support the object we wish to examine, which is 
magnified several diameters. If a fly, for instance, is at 
the end of the wire, we find it is highly magnified when 
seen through the glass balloon. By examining the insect 
through the water in the balloon, we can distinguish every 
feature of its organism, thanks to this improvised magnifier. 
This .little apparatus may also serve to increase the in- 
tensity of a luminous focus of feeble power, such as a 



42 



LIGHT. 



lighted candle. It is often employed in this manner by 
watchmakers. If a bottle fiill of water is placed on a 
table, and exposed to the rays of the sun, the head of a 
lucifer match being placed in the brightest centre of light 
caused by the refracted rays, the match will not fail to 




A simpJe microscope foimed with a glass balloon full of water. 

ignite. We have succeeded in this experiment even 
under an October sun, and still more readily in warm 
weather. 

In the Conservatoire des Arts in Paris a visitor will 
always notice a number of people looking at the mirrors 
in the " optical " cabinets. These mirrors deform and 



DEFORMED IMAGES. 43 

distort objects in a very curious manner, and people find 
much amusement in gazing into them till they are " moved 
on " by the attendants. Such experiments create great 
interest, and a very excellent substitute for these may be 
found in a coffee-pot or even in a large spoon, and all the 
grotesque appearance will be seen in the polished surface. 
The least costly apparatus will sometimes produce the 
most marvellous effects. Look at a soap-bubble blown 
from the end of a straw. When the sphere has a very 
small diameter the pellicule is colourless and transparent ; 
but as the air enters by degrees, pressing upon all parts 
of the concave surface equally, the bubble gets bigger as 
tha thickness decreases, and then the colours appear, — ■ 
feeble at first, but stronger and stronger as the thickness 
diminishes. The study of soap-biibbles and of the effects 
of the light is very interesting. Newton made the soap- 
bubble the object of his studies and meditations, and it 
will ever hold its place amongst the curious phenomena 
of the Science of Optics. But before going into all the 
phases of Light we will proceed to explain the structure 
of the eye, as it is through that organ that we are enabled 
to appreciate light and its marvellous effects. 

It is often considered an embarrassing matter to fix 
precisely the value of two lights. Nothing, however, can 
be easier in reality, as we will show. In comparing 
different lights, it is necessary to bear in mind the amount 
of waste, the colour of the light, the luminous value of 
the source, and the steadiness of the flame. The luminous 
value of a lamp-burner is generally equalled by that of a 
wax candle, and we will take as an example one of those 
at six to the pound. Very precise appliances are used for 
this experiment when great exactness is required ; but it 
is easy to calculate in a simple manner the differences in 
ordinary lights. Supposing we desire to test the value of 
light given by a lamp and a wax candle, they must both 



44 



LIGHT. 



be placed on the table at an equal height, B and A, in 
front of some opaque body, A, and then a large sheet of 
paper must be fixed as vertically as possible to form a 
screen. When B and A are lighted, two shadows, E and 
F, are produced, to which it is easy to give exactly the 




Grotesque efTects of curved surfaces. 



same intensity, by advancing or withdrawing one of the 
two sources of light. The intensities of the two lights 
will then be inversely proportional to the squares of the 
measured distances, A B and AC. By a similar careful 
calculation it has been possible to draw up a table of the 
relative values of various ordinary lights. We have not 



PHOTOMETRY. 



45 




46 



LIGHT. 



included here the electric light, which has recently attracted 
so much attention, because this system of lighting can 
hardly be said to have yet penetrated the domain of 
domestic life ; but there is no' doubt that electricity is 
becoming more and more adapted to our daily life. 




The soap-bubble. 



The measurement of intensity of light is called Pho- 
tometry, and the instruments used are Photometers. Bun- 
sen's instrument consists of a screen of writing-paper, 
saturated in places with spermaceti to make' it trans- 
parent. A sperm candle is placed on one side, and the 
light to be compared on the other. The lights are pro- 



THE PHOtOMETER. 



47 



vided with graduated bars, and these lights are then 
removed farther and farther from the screen till the spots 
of grease are invisible. The relative intensities are as the 
squares of the distance from the screen. 

We append a table showing the comparative cost of 
light given by Dr. Frankland at the Royal Institution 
some few years ago. The standard of comparison was 
20 sperm candles burning for lo hours at the rate of 120 
grains an hour : — 



I. d. 




s. 


d. 


t. d. 


Wax ..72^ 


Spermaceti . 


. 6 


8 


Tallow ..28 


Sperm Oil. I 10 


Coal Gas . 


. 


# 


Cannel Gas . 3 


Paraffin . 3 10 


Paraffin Oil . 


. 


6 


Rock Oil. . 7| 



There are many other interesting experiments con- 
nected with Light, — Spectrum Analysis, etc., etc., — all of 
which we will defer for a time until we have examined 
the Eye and some effects produced upon it by Light, 
illustrated by numerous diagrams in the pages next 
following. 



Colour of the 
Spectrum. 

Extreme Red 

Red . . 

Intermediate 

Orange . 

Intermediate 

Yellow . 

Intermediate 

Green 

Intermediate 

Blue 

Intermediate 

Indigo . 

Intermediate 

Violet 

Extreme Violet 



VELOCITY OF LIGHT WAVES. 

According to Sir J. Herschel. 

No. of Undulations 
in a second. 
. 458,000,000,000,000 



No. of Undulations 
in an inch. 

■ 37,640 . 

. 39.i8o . 
. 40,720 . 
. 41,610 . 
. 42,510 . 
. 44,000 . 
. 45,600 . 

■ 47,460 . 
• 49,320 . 
. 51, no . 
. 52,910 . 

. 54,070 . 

. 55,240 . 

. 57,490 ., 

• 59,750 . 



477,000,000,000,000 
495,000,000,000,000 
506,000,000,000,000 
5 1 7,000,000,000,000 
535 ,000,000,000,000 
55 5,000,000,000,000 

5 77,000,000,000,000 
600,000,000,000,000 
622,000,000,000,000 
644,000,000,000,000 

6 5 8,000,000,000,000 
672,000,000,000,000 
699,000,000,000,000 
727,000,000,000,000 



CHAPTER IV.— VISION. 

VISION AND OPTICAL ILLUSIONS THE EYE DESCRIBED^ 

ACCOMMODATION OF THE EYE CHROMATIC ABERRA- 
TION — SPINNING TOPS. 




HE eye is an optical instrument that may be 
compared with those constructed by physicists 
themselves ; the media of which it is composed 
have surfaces like those which enter into the 
construction of optical instruments. It was Kepler who at 
the end of the eighteenth century discovered the passage of 
light into the eye. Soon after the discovery of the inner 
chamber he found that the eye realized the conditions 
that Porta had combined to obtain the reflection of 
external objects. 

We will now briefly state that the coats of this organ 
are constituted of a fibrous membrane, T, termed sclerotic, 

which is opaque, except 
in the anterior portion of 
the eye, where it forms 
the transparent cornea. 
The crystalline, C, en- 
shrined behind the cor- 
nea, is the convergent 
lens of the inner cham- 
ber ; it is covered with 
a transparent membrane, 
Structure of the eye. q^ capsuU, and is bathed 

in two fluids, the aqueous humour, bet^veen the crystalline 




TIIK EYE. 49 

humour and the cornea, and the vitreous body, a gelatinous 
humour lodged between the crystalline and the back of the 
eye. The image of exterior objects which is produced by 
the passage of light through these refracting surfaces, is 
received by a nervous membrane, the retina, B, formed by 
an expansion of the optic nerve, N. We must also 
mention the choroid, a membrane lined with a dark pig- 
ment, which absorbs the light, and prevents interior reflec- 
tions, and in front of the crystalline lens, a curtain with 
an opening, H, called the iris, which gives to the eyes 
their colour of blue, grey, or black. The opening in the 
centre of the iris is called the pupil. 

The penetration of light through the surfaces of the 
eye is easily demonstrated. An object throws divergent 
rays on the cornea, a part penetrates into the eye and falls 
upon the retina, forming a perfectly defined image of the 
object. Magendie has proved in the following mannar 
the truth of this mathematical deduction. The eye of a 
rabbit is very similar to an albino's ; that is to say, the 
choroid contains no black pigment, but a transparent 
matter, and when placed before a brilliant object, the 
image can be seen inverted on the retina. The experi- 
ment succeeds also with the eye of a sheep or a cow, if 
the sclerotic has been lessened. The optic centre of the 
eye is the point where the secondary axes cross ; the optic 
axis passes through the geometrical axis of the organ, and 
directs itself spontaneously towards the point that attracts 
the eye. 

We will now point out in what distinct vision consists. 
A screen placed behind a lens will only receive the image 
of a lighted object, A B, if placed in a position, rr'. If 
placed nearer at R"R", or further off at R'R', the light 
from the object is thrown on the screen, and the image is 
confused. To prove the imperfection of sight which is 
shown by the application of these theoretic rules, MM. 



50 



VISION. 



Boutan and d'Almeida * cite the following experinment : — 
If the head of a pin is placed from one to two inches 
from the eye, nothing will be perceived but a confused 
haziness of vague outline. The distance of distinct 
vision is that at which an object of small dimensions may 




Diagram of mode of vision. 

be placed to be plainly perceived. This distance, which 
averages fifteen inches, varies with different individuals. 
It can be determined for different sights by means of an 
apparatus constructed by Lepot. A white thread, a, is 
stretched horizontally on a dark board. We look at it 
by placi^ng our eye at one end, behind a little screen 




E\per!ment fur sight. 

pieiced with an aperture, O; it then appears much reduced 
in length, but either nearer or farther off it seems to 
enlarge and swell, having the appearance of a white 
surface, becoming larger and larger in proportion as we 
move away from the point at which it is seen most dis- 
tinctly. In this manner we can easily obtain a measure 
of the distance of distinct vision. One of the most 
remarkable properties oC the eye consists in the faculty 
* Traiie de Physique, Paris 1 874. 



ACCOMMODATION OF THE EYE. 



51 



which this organ possesses of seeing at different distances. 
If we consider it as a dark chamber, there is but one 
distance at which an object will be perfectly visible • 
nevertheless, a metal wire, for example, can be seen as 
well at a distance of seven, as ten, fifteen, or twenty inches 
by good sights. 

This faculty of accommodation in the eye is thus 
demonstrated : we place two pins, one in front of the 
other, one eye only being open ; we first look at the 
nearest pin, which appears confused if it is near the eye 




M Cramer's experiment. 

but by an effort of will the image becomes clear. If, 
while preserving the clearness of the image, we then carry 
OUT attention to the second pin, we find that it, too, 
presents a confused appearance. If we make an effort to 
distinguish the contour of the second pin, we at last 
succeed, and the first once more appears ill-defined. 
It is only since the experiments of M. Cramer and 
M. Helmholtz that the explanation of this phenomenon 
could have been given. M. Cramer has succeeded in 
determining on the living eye the curvature of the 
cornea, and of the two surfaces of the crystalline lens. 
In so doing he followed Samson's method, and observed 
the images thrown by a luminous object, whose rays strike 
the different refracting surfaces of the eye. A candle, L, 




52 VISION. 

is placed before the eye, O, and throws as in a convex 
mirror a straight image of the flame. The other portion 
of the light, which has penetrated the pupil, falls on the 
crystalline lens, and produces likewise a second straight 
image, B. Then the light refracted by the lens reaches 
the posterior surface ; a portion is reflected on a concave 
mirror, and gives the inverted image, c, very small and 
brilliant. M. Cramer observed it through a microscope, 
and studied the variations in the size of 
images when the eye passed from the ob- 
servation of adjacent to distarrt objects. He 
stated : — 
<^~ * I. That the image, A, formed on the surface 

Images in the ° . . . , , 

eye. of the cornea, remams the same size in both 

cases ; the form of the cornea therefore remains unaltered. 

2. That the image, B, formed on the upper surface of 
the lens, diminishes in proportion as the eye is nearer the 
object ; the surface therefore becoming more and more 
convex, as the focal distance diminishes — a result indi- 
cated by the theory that it is possible in the vision ot 
near objects to receive the image on the retina. 

3. That the third image, c, produced on the posterior 
surface of the lens, remains nearly invariable. 

We may confirm Cramer's statements by an easy 
experiment. We place ourselves in front of the eye of 
someone who looks in turn at two objects placed on the 
same black line at unequal distances from him, and are 
able to distinguish by the dimension of the images of the 
candle, which object it is that he is regarding. M. Helm- 
holtz has carried M. Cramer's methods to perfection, and 
has been able to formulate a complete theory of all the 
phenomena of accommodation. The laws of optics show 
that the rays emitted by a luminous point' may unite at 
another point by the action of the refracting surfaces of 
the eye. Nevertheless, a white light being composed of 



ABERRATION 53 

rays of diverse refrangibility, particular effects, known 
under the name of chromatic aberration, are produced 
through the decomposition of light, which we will proceed 
to study, under M. Helmholtz's auspices.* We make a 
narrow opening in a screen, and fix behind this opening a 
violet glass, penetrable only by red and violet rays. We 
then place a light, the red rays of which reach the eye of 
the observer after having passed through the glass and 
the opening in the screen. If the eye is adapted to the 
red rays, the violet rays will form a circle of diffusion, 
and a red point encircled with a violet aureola is seen. 
The eye may also be brought to a state of refraction, so 
that the point of convergence of the violet rays is in front, 
and that of the red rays behind the retina, the diameters 
of the red and violet circles of diffusion being equal. It 
is then only that the luminous point appears mono- 
chromatic. When the eye is in this state of refraction, 
the simple rays, whose refrangibility is maintained between 
the red and the violet rays, unite on the retina. 

There is another kind of aberration of luminous rays of 
one colour emitted through a hole, which generally only 
approach approximately to a mathematical focus, in con- 
sequence of the properties of ^ j 
refracting surfaces ; it is called 
aberration of sphericity. The phe-' 
nomena are as follows : — 

I. We take for our object a 
very small luminous point (t'he 
hole made by a pin in some black Aberration of sphericity, 
paper, through which the light ' passes), and having also 
placed before the eye a convex glass, if we are not near- 
sighted, we fix it a little beyond the point of accommoda- 
tion, so that it produces on the retina a little circle of 

* Traiie d'optique Physioloffiqite. French translation by MM. Javal 
and Klein 




54 



VISION 



diffusion. We then see, instead of the lunninous point, a 
figure representing from four to eight irregular rays, 
which generally differ with both eyes, and also with 
different people. We have given the result of M. Helm- 
holtz's observations {see cut over) ; a corresponds to 
the right eye, and b to the left. The outer edges of the 
luminous parts of an image, produced in this way by a 
white light, are bordered with blue ; the edges towards 
the centre are of a reddish yellow. The writer adds that 
the figure appears to him to have greater length than 
breadth. If the light is feeble, only the most briUiant 
parts of the figure can be seen, and several images of the 
luminous point are visible, of which one is generally more 
brilliant than the others. If, on the other hand, the light 
is very intense, — if, for example, the direct light of the 
sun passes through a small opening, — the rays mingle 
with each other, and are surrounded by aureola of rays, 
composed of numberless extremely fine lines, of all colours, 

possessing a much larger 
diameter, and which we dis- 
tinguish by the name of the 
aureola of capillary rays. 

The radiating form of stars, 
and the distant light of street- 
Radiating image. kmps bclong to thc pre- 

ceding phenomena. If the eye is accommodated to a 
greater distance than that of the luminous point, — and 
for this purpose, if the luminous point itself is distant, we 
place before the eye a slightly convex: lens, — we see 
another radiating image appear, which M. Hclmholtz 
represents thus : at c as it is presented to the right eye, 
and at d aS seen by the left. 

If the pupil is covered on one side, the side opposite to 
the image of diffusion disappears ; that is to say, that 
part of the retinal image situated on the same side as the 




DOUBLE IMAGES. 55 

covered half of the pupil. This figure, then, is formed by 
rays which have not yet crossed the axis of the eye. If 
we place the luminous point at a distance to which the 
eye can accommodate itself, we see. through a moderate 
light, a small, round, luminous spot, without any ir- 
regularities. If the light, on the contrary, is intense, the 
image is radiated in every position of accommodation, and 
we merely find that on approaching nearer, the figure 
which was elongated, answering to a distant accommoda- 
tion, gradually diminishes, grows rounder, and gives place 
to the vertically elongated figure, which belongs to the 
accommodation of a nearer point. When we examine a 
slender, luminous line, we behold images developed, which 
are easily foreseen, if for every point of the line we 
suppose radiating images of diffusion, which encroach on 
each other. The clearest portions of these images of 
dififusion mingle together and form distinct lines, which 
show multiplied images of the luminous line. Most 
persons will see two of these images : some, with the eyes 
in certain positions, will see five or six. 

To show clearly by experiment the connection existing ' 
between double images and radiated images from points, 
it is sufficient to make in a dark sheet of 
paper a small rectilinear slit, and at a 
little distance from one end, on a line 
with the slit, a small round hole, as shown 
at a. Looking at it from a distance we 
shall see that the double images of the 
line have exactly the same distance 
between them that the niost brilliant 
parts of the starred figure of diffusion 
have from the point, and that the latter 
are in a line with the first, as will be seen at b, where in 
the image of diffusion of the luminous point, we only see 
the clearest parts of star a of the figure. 




56 Vision. 

On lighted surfaces, to which the eye is not exactly 
accommodated, multiplied images are often remarked 
through the passage from light to darkness being made 
by two or three successive steps. 

A series of facts which have been collected under the 
title of irradiation, and which show that brightly-lighted 
surfaces appear larger than they are in reality, and that 
the dark surfaces which surround them appear diminished 
to a corresponding degree, explains this by the circum- 
stance that the luminous sensation is not proportional to 
the intensity of the objective light. These phenomena 
affect very various appearances, according to the form of 
respective figures ; they are generally seen with the 
greatest ease and intensity when the eye is not exactly 
accommodated to the object examined, either by the eye 
being too near or too far off, or by using a concave or 
convex lens, which prevents the object being seen clearly. 
Irradiation is not completely wanting, even when the 
accommodation is exact, and we notice it clearly in very 
luminous objects, above all when they are small; small 
circles of diffusion increase relatively the dimensions of 
small objects much more than of large ones, with regard 
to which, the dimensions of the small circles of diffusion 
which the eye furnishes, when properly accommodated, 
become insensible. 

I. Luminous surfaces appear larger. We can never 
judge exactly of the dimensions of a slit or small hole 
through which a bright light escapes ; it always appears 
to us larger than it really is, even with the most exact 
accommodation. Similarly, the fixed stars appear in the 
form of small luminous surfaces, even when we make use 
of a glass which allows of perfect accommodation. If a 
gridiron with narrow bars — the spaces intervening being 
exactly equal to the thickness of the bars — is held over a 
light surface, the spaces will always appear wider than the 



LUMINOUS SURFACES. 



57 



bars. With an inexact accommodation, these phenomena 
are still more remarkable. The illustration exhibits a 
white square on a « black foundation, and a black square 
on a white foundatioii. Although the two squares have 




Experiment r. 

exactly the same dimensions, the white appears larger 
than the black, unless with an intense light and an inexact 
accommodation. 

2. Two adjacent luminous sui faces mingle together. If 
we hold a fine metallic wire between the eye and the sun, 
or the light of a powerful lamp, 
we shall cease to see it : the 



lighted surfaces on all sides of 












the wire in the visual range pass 
one into the other, and become 
mingled. In objects composed 
of black and white squares, like 
those of a draught-board, the 
angles of the white squares join 
by irradiation, and separate the 
black squares. 

3. Straight lines appear interrupted. If a ruler is held 
between the eye and the light of a bright lamp or the sun, 
we perceive a very distinct hollow on the edge of the 
ruler in the part corresponding to the light. When one 



Experiment 2. 



58 



VISION. 




Disc which appears uniformly grey by 
reason of its rotation. 



point of the retina is affected by a light which undergoes 
periodical and regular variations, the duration of the period 

beingsufficientlyshort, there 
results a continuous impres- 
sion, like that which would 
be produced if thelightgiven 
during each period were dis- 
tributed in an equal manner 
throughout the whole dura- 
tion of the period. To verify 
the truth of this law, we will 
rhake use of somediscs,such 
as that represented. The 
innermost circleishalf white 
and half black ; the middle 
circle has two quarters, or 
half its periphery, white, and the outer circle has four 
eighths' white, the rest being black. If such a disc is 
turned round, its entire surface will appear grey ; only 
it is necessary to turn it with sufficient force to produce 
a continuous effect. The white may also be distributed 
in other ways, and provided only that on all the circles 
of the disc the proportion of the angles covered with 
white is the same, they will always exhibit the same 
grey colour. Instead of black and white we may make 
use of different colours, and obtain the same resultant 
colour from all the circles, when the proportion of the 
angles, occupied by each of the colours in the different 
circles is the same. 

If we paint on a disc a coloured star, which is detached 
from a foundation of another colour, during the rapid 
rotation of the disc the centre affects the colour of the 
star ; the outer circle assumes that of the background, 
and the intermediate parts of the disc present the con- 
tinuous series of the resultant colours. These results 




ROTATIVE DISCS. 59 

are in accordance with, the theory of the mixture of 
colours. 

Rotative discs, which are so much used in experiments 
in optical physiology, were employed for the first time by 
Miisschenbroeck ; the most 
simple is the top. M. Helm- 
holtz ordinarily uses a brass 
spinning-top, which the two 
cuts represent at a third of 
the natural sizes. The disc 
is set in motion by the hand, 
and its quickness may be in- 
creased or moderated at will ; 
but it cannot be made to spin 
quicker than six rounds in a 

second; this motion will be °=^= "=^:'/,„T;fPr^f,ToilV'"''- 
kept up for three or four 

minutes. Thus, with a feeble movement of rotation, a 
uniform luminous impression can only be obtained by 
dividing the disc into four or six sections, on each of 
which we repeat the same arrangement of colours, light, 
and shade. If the number of repetitions of the design is 
less, we obtain, with a bright light, a more or less shot- 
coloured disc. 

It is- easy to place designs on the disc, even when in 
motion, or to make any desired modification, by super- 
posing on the first disc another disc with sectors, of which 
we can vary the position b}' slightly touching it, or even 
blowing on it, thus producing during the rotation of the 
disc very varied modifications. If for instance, we place 
on a disc covered with blue and red sectors of equal size, 
a black disc, of which the sectors are alternately filled in 
or empty, the disc, as it turns round, will appear blue if 
the black sectors of the upper disc exactly cover the 
sectors of the lower disc ; and it appears red. '"*" -m the 



6o 



VISION. 



contrary, the blue sectors are covered with the black ■ 
while in the intermediate positions we obtain different 
mixtures of red and white, and during the rotation of the 
disc may vary the colour insensibly by a gentle touch. 
By dividing the different sectors with broken or curved 
lines, instead of straight ones, we can produce an arrange- 
ment of coloured rings of great variety and beauty. To 
give the top greater speed, we set it in motion by drawing 
a string twined round its stem. The simplest method 
consists in the employment of a handle similar to that of 
the German top. It is a hollow cylinder of wood set into 




M. Helmholt2*s top for studying the impression of light on the retina. 

a handle with two circular holes ; and at right angles with 
these is a groove for the passage of the string. The stem 
of the top is passed through the holes of the cylinder, one 
end of the string is fixed in the small hole in the stem, 
and is rolled round by turning the top in the hand. The 
part of the stem on which the string is twisted becomes 
sufficiently thick for the top to remain suspended to the 
handle ; then holding it a little above the table, and giving 
the string a powerful pull, we set the top in motion, and 
as the string unrolls it falls on the table, where it will 
continue its rotation for some time. The top represented 
IS constructed so that the discs may be firmly pressed by 
the stem, which is necessary in experiments for demon- 



SPINNING TOPS. 



6l 



strating Newton's theory of the minghng of colours. We 
make use for this purpose of a variety of discs, made of 
strong paper of different sizes, having an opening in the 
centre and a slit ; each of the discs is covered uniformly 




with a single colour ; and if two or more are superposed, 
with their slits placed one over the other, we obtain sectors, 
the size of which we may vary at will, so that we can 
modify in a continuous manner the proportions of the 
colours. The most perfect construction is that of Busold's 



62 



VISION. 



chromatic top, which should only be employed for very 
rapid rotations. The disc, which weighs 
5 lbs., is made of an alloy of zinc and lead, 
about an inch and a quarter in diameter. 
The brass axis terminates at its lower end 
with a blunt point of untempered steel ; the 
cylindrical part of the axis is roughened 
to encourage the adherence of the string ; the axis is 
placed between the clamps of a vice, and a plate is 





Top for experiments demonstrating Newton's tlieory of the mingling of colours. 

put underneath ; we then pull the string firmly with 
the right hand, and when the top is in motion it is 
separated from the clamps. By pulling the string very 
powerfully it is possible to obtain a speed of sixty turns 
in a second, and the movement will be kept up for three 
quarters of an hour. 

Besides tops, we may make use of different kinds of 
discs, with an axis rotating between two clamps ; they 



THE PHENAKISTOSCOPE. 6} 

are moved either by a kind of clock-work, or by the 
unrolling of a string, like the tops. Generally, however, 
these contrivances have this inconvenience, that the discs 
cannot be changed without stopping the instrument, and 
partly taking it to pieces. On the other hand, we have 
the advantage of being able to turn them on a vertical 
plane, so that we can conveniently carry on our experi- 
ments before a numerous auditory, which is a more diffi- 
cult matter with tops. Montigny contrived to obtain the 
mingling of colours by means of a turning, prism, which he 
caused to throw its shadow on a white screen. The 
Thaumatrope is a small rectangle of cardboard, which is 
made to rotate on an axis passing through the centres of 
the longest sides. We shall describe it at greater length 
when we come to consider a new apparatus known under 
the name of the Praxinoscope. 

More complicated contrivances have also been con- 
structed on the same principle, by which one may per- 
ceive the rotating disc through slits which turn at the 
same time. We will now describe the construction of 
some discs invented by Plateau under the name of the 
Phenakistoscope, page 8o. These discs are made of strong 
cardboard, from six to ten inches in diameter, on which a 
certain number of iigures (eight to twelve) are placed in 
circles at an equal distance from each other, presenting 
the successive phases of a periodical movement. This 
disc is placed on another opaque circle of rather larger 
diameter, which has on its niargin as many openings as 
the first disc has figures. The two discs are placed one 
on the other, and are fixed in the centre by means of a 
screw at the anterior extremity of a small iron axis, the 
other end being fitted into a handle. To make use of 
this contrivance we place ourselves in front of the glass 
towards which we turn the disc with the figures, placing 
the eye so as to see the figures through one of the holes 



64 



VISION. 



of the large disc. Directly the apparatus begins to turn 
round, the figures seen in the' glass appear to execute the 
particular movements which they represent in different 
positions. Let us designate by means of the figures 
I, 2, 3, the different openings through which the eye suc- 
cessively looks, and point out by the same numbers the 
figures in the radiuses thus numbered. If the experi- 
menter looks in the glass through opening i, he will see 
first figure i , which appears in the glass to pass before his 
eyes; then the rotation of the disc displacci opening i, and 




Busold's chromatic top, 

the cardboard intervenes, until opening 2 appears ; then 
figure 2 takes the place of figure i, until it in turn dis- 
appears, and opening 3 presents figure 3 to view. If 
these figures were all similar, the spectator would have 
but a series of visual impressions, separate but alike, 
which by a sufficiently rapid rotation mingle together 
in one durable impression like a perfectly immovable 
object. If, en the contrary, the figures differ slightly 
from each other, the luminous sensations will also mingle 
in a single object, which will however appear to be 
modified in a continuous manner, conformably with the 



dancer's top. 



65 



differences of successive images. With a difference of 
speed, we obtain a new series of phenomena. A most 
simple contrivance of this kind is a top of C. B. Dancer, 
of Manchester. It will be seen that the axis carries 
another disc, pierced with openings of different shapes, to 
the edge of which a thread Is attached. This second disc 




Rotating disc. 



is carried along by the friction of the axis, but its rotation 
is less rapid because of the great resistance offered by the 
air to the piece of thread which participates in the move^ 
ment. If the lower disc has several differently-coloured 
sectors, they produce a very motley appearance, which 
seetns to fnove sometimes by leaps, and sometimes by 
Continuous motion. We must distinguish between the 



66 



VISION. 



phenomena of successive contrast and simultaneous con- 
trast. 

Phenomena of successive contrast develop what are called 
accidental images. If we fix our eyes for a considerable 
time on a coloured object, and then suddenly direct them 
towards a uniform white surface, we experience the sen- 
sation of the object as it is, but it appears coloured with a 
complementary tint ; that is to say, it has the colour 
which, superposed on the genuine tint, we^ obtain from 
pure white. Thus a red object produces a consecutive 
green object The experiment can be tried by gazing at 




Mr. Dancer's top. 

the sun when it is setting, and then directing one's* eyes 
towards a white wall in the same direction. 

Phenomena of simultaneous contrast' arise from the 
influence exercised over each other by different shades and 
colours which we see simultaneously. That we may be 
certain that we have really obtained phenomena of this 
kind, the experiments must be arranged in such a manner 
that accidental images are not produced, and thaf the part 
of the retina affected by the sensation of colour does not 
receive, even momentarily, a passing image. 

The phenomena of simultaneous contrast appear with 
the greatest . clearness with slight differences of colour, 



CONTRAST dy 

and are therefore exactly the contrary of phenomena of 
successive contrast, which are favoured by strong opposi- 
tions of colour and light. We can, in general, characterize 
phenomena of simultaneous contrast as governed by this 
law, common to all perceptions of the senses : the differ- 
ences clearly perceived appear greater than the differences 
equal to them, but perceived with greater difficulty, either 
because they only affect the observation in an uncertain 
manner, or that the memory fails to judge of them. A 
man of middle height appears small beside a tall man, 
because at the moment it is forcibly impressed on us that 
there are taller men than he, and we lose sight of the 
fact that there are smaller. The same man of medium 
height appears tall beside a man of small stature. We 
can easily niake experiments on simultaneous contrast 
with a sheet of transparent paper. We fasten together a 
sheet of green and a sheet of rose-coloured paper, so as 
to obtain a sheet half red and half green. On the line of 
separation between the two colours we place a strip of 
grey paper, and cover the whole with a sheet of thin 
letter-paper of the same size. The grey strip will then 
appear at the edge touching the green, and green at the 
edge touching the red ; the centre presenting an inter- 
mediate shade. It presents a still more decided appear- 
ance if the grey strip is perpendicular with the line of 
separation of the two colours ; the piece of grey then 
stretching into the green will present as deep a red as the 
red foundation on the other side. If the line of grey 
colour exactly covers the line of separation between the 
two colours, the contrasting colour is more feeble ; the 
edges of the grey paper then present complementary 
strips of colour. Similar effects may be obtained by 
superposing, in gradually diminishing layers, strips of thin 
paper, so as to form successive bands of different thick- 
nesses. If it is then ht up from behind, the objective 



68 VISION. 

intensity is evidently constant through the extent of each 
layer ; nevertheless every strip appears darker at the 
edge touching a more transparent layer, and lighter at 
the edge in contact with a thicker layer. The dull tints 
of China ink, superposed in layers, will produce a similar 
effect. The phenomena are produced by means of rotative 
discs of most beautiful and delicate gradations of colour. 
Let us give the sectors of the disc the form represented, 
and make them black and white ; and when in rotation 
we shall see a series of concentric rings of a shade 




DisC; which exhibits, when in rotation, a series of concentric rings. 

that becomes darker and darker towards the centre. The 
angular surface of the dark portions is constant in each 
of these rings. The intensity, therefore, of each ring is 
uniform during rapid rotation ; it is only between one 
ring and another that the intensity varies. Each ring 
also appears lighter on its inner side when it borders on 
a darker ring, and darker on its outer side when in 
contact with a lighter ring. If the differences of intensity 
in the rings are very slight, one can scarcely judge some- 
times if the inner rings are darker than the outer ; the 
eye is only struck by the periodical alternations of light 



GRADATIONS OF COLOUR. 69 

and shade presented by the edges of the rings. If, 
instead of white and black we take two different colours, 
each ring will present two colours on its two edges, 
although the colour of the rest of the ring will be uniform. 
Each of the constituent colours presents itself with more 
intensity on ihe edge of that ring which borders on another 
ring containing a smaller quantity of the colour. Thus, 
if we mix blue and yellow, and the blue predominates in 
the exterior and the yellow in the interior, every ring 
will appear yellow at its outer, and blue at its inner edge ; 
and if the colours present together very slight differences, 
we may fall into the illusion which causes the differences 
really existing between the colours of the different rings 
to disappear, leaving instead, on a uniformly coloured 
background, the contrasting blue and yellow of the edges 
of the rings. It is very characteristic that in these cases 
we do not see the mixed colours, but seem to see the 
constituent colours separately, one beside the other, and 
one through the other. 

All the experiments we have described afford great 
interest to the student ; they can easily be performed by 
those of our readers who are particularly interested in 
these little-known subjects. Any one may construct the 
greater part of the appliances we have enumerated, and 
others can be obtained at an optician's. The discs in 
particular are extensively manufactured, and with great 
success. 




CHAPTER v.— OPTICAL ILLUSIONS. 




OCULAR ESTIMATION — ZOLLNER'S DESIGNS — THE THAU- 

MATROPE PHENAKISTOSCOPE — THE ZOOTROPE 

THE PRAXINOSCOPE THE DAZZLING TOP. 

[E shall now continue the subject by describing 
some illusions more curious still — those of 
oculay estimation. These illusions depend 
rather on the particular properties of the 
figures we examine, and the greater part of these pheno- 
mena may be placed in that category whose law we have 
just formulated : tJie differences dearly perceived appear 
rreater than the differences equal to thtm, but perceived with 

j^rcatcr difficulty. Thus a line when divided appears 

l^reater than when not divided ; the direct perception of 
llie parts makes us notice the number of the sub-divisions, 
the size of which is more perceptible than when the parts 
are net clearly marked off. Thus, in the cuts below, we 



Ocular estimation of length. 

imagine the length a b equals be, although ab\s'm reality 
longer than b c. In an experiment consi.sting of dividing 
a line into two equal parts, the right eye tends to increase 
the half on the right, and the left eye to enlarge that on 



Ocular EsxiMAxioisr. 



71 



1 




the left. To arrive at an exact estimate, we turn over 
the paper and find the exact centre. 

Illusions of this kind become more striking when the 
distances to be compared run in different directions. If 
we look at A and B (page 70), which are perfect squares, 
A appears greater in length than width, whilst B, on the 
contrary, appears to have greater width than length. 
The case is the same with angles. On looking at angles 
(in the margin) i, 2, 3, 4 are straight, and should appear 
so when examined. But i and 
2 appear pointed, and 3 and 4 
obtuse. The illusion is still greater 
if we look at the figure with the 
right- eye. If, on the contrary, we 
turn it, so that 2 and 3 are at 
the bottom, i and 2 will appear 
greatly pointed to the left eye. 
The divided angles always appear 
relatively greater than they would 
appear without divisions. illusion of angles. 

The same illusion is presented in a number of examples 
in the course of daily life. An empty room appears 
smaller than a furnished room, and a wall covered with 
paperhangings appears larger tnan a bare wall. It is a 
well-known source of amusemen*- to present someone in 
company with a hat, and request him to mark on the 
wall its supposed height from the ground. The height 
generally indicated will be a size and a half too large. 

We will relate an experience described by BraVais : 
" When at sea," he says, " at a certain distance from a 
coast which presents many inequalities, if we attempt to 
draw the coastline as it presents itself to the eye, we shall 
find on verification that the horizontal dimensions have 
been correctly sketched at a certain scale, while all the 
vertical angular objects have been represented on a scale 




72 OPTICAL ILLUSIONS. 

twice as large. This illusion, which is sure to occur in 
estimates of this kind, can be demonstrated by numerous 
observations." 

M. Helmholtz has also indicated several optical illu.sions. 

If we examine the diagrams below, the continuation 
of the line a does not appear to be d, — which it is in 
reality, — but f, which is a little lower. This illusion is 
still more striking when we make the figure on a smaller 
scale, as at B, where the two fine lines are in continuation 
with each other, but do not appear to be so, and at c, 




Experiment in optical illusion. 

where they appear so, but are not in reality. If we draw 
the figures as at A, leaving out the line d, and look at 
them from a gradually increasing distance, so that they 
appear to diminish, it will be found that the farther 'oft' 
the figure is placed, the more it seems necessary to lower 
the line /to make it appear a continuation of a. These 
effects are produced by irradiation ; they can also be 
produced by black lines on a white foundation. Near the 
point of the two acute angles, the circles of diffusion of 
the two black lines touch and mutually reinforce each 
other ; consequently the retinal image of the narrow line 



IRRADIATION. 



73 



presents its maximum of darkness nearest to the broad 
line, and appears to deviate on that side. In iigures of 
this kind, however, executed on a larger scale, irradiation 
can scarcely be the only cause of illusion. We will con- 
tinue our exposition as a means of finding an explanation. 
A and B present some examples pointed out by Hering ; 
the straight, parallel lines, a b, and c d, appear to bend 
outwards at A, and inwards at B. But the most striking 
example is that represented by the cut on page 74, 
published by Zollner. 





^dlll 



The horizontal lines, u, h, r, d, are strictly parallel ;_ their appearance of deviation i.s caused 
by the oblique lines. 

The vertical black strips of that figure are parallel with 
each other, but they appear convergent and divergent, 
and seem constantly turned out of a vertical position into 
a direction inverse to that of the oblique lines which 
divide them. The separate halves of the oblique lines 
are displaced respectively. If the figure is turned so that 
the broad vertical lines present an inclination of 45° to 
the horizon, the convergence appears even more remark- 
able, whilst we notice less the apparent deviation of the 
halves of the small lines, which are then horizontal and 



74 



OPTICAL ILLUSIONS. 



vertical. The direction of the vertical and horizontal 
lines is less modified than that of the oblique lines. We 
may look upon these latter illusions as fresh examples of 
the aforesaid rule, according to which acute angles clearly 
defined, but of small size, appear, as a rule, relatively 
larger when we compare with obtuse or right angles 
which are undivided ; but if the apparent enlargement of 
an acute angle shows itself in such a manner that the two 




The vertical strips are parallel ; they appear convergent or divergent 
under the influence of the oblique rays. 

sides appear to diverge, the experiments will result in 
illusions given. 

On page 73 the two halves of each of the two straight 
lines .seem to deviate through the entire length in such a 
manner that the acute angles which they form with the 
oblique lines appear enlarged. The same effect is shown 
by the vertical lines of above illustration. 

M. Helmholtz is of opinion that the law of contrast js 
insufficient to entirely explain the phenomena, and believes 



Experiments. 7e 

that the effect is also caused by the movements of the 
eye. In fact, the illusions almost entirely disappear, if 
we fix on a point of the object in order to develop an 
accidental image, and when we have obtained one very 
distinctly, which is quite possible with Zollner's design, 
this image will present not the slightest trace of illusion. 
The displacement of the gaze will exercise no very 
decided influence on the strengthening of the illusion ; on 
the contrary, it disappears when we turn our eyes on the 
narrow line, a d. On the other hand, the fixing of the 
eyes causes the illusion to disappear with relative facility, 
and with more difficulty in the designs. It will, however, 
disappear equally in the Is-tter design, if we fix it im- 
movably, and instead of considering it as composed of 
black lines on a white backgroupd, we compel ourselves 
to picture it as white lines on a black foundation ; then 
the illusion vanishes. But if we let our eyes wander over 
the illustration, the illusion will return in full force. We 
can indeed succeed in completely destroying the illusion 
produced by these designs by covering them with a sheet 
of opaque paper, on which we rest the point of a pin. 
Looking fixedly at the point, we suddenly draw away the 
paper, and can then j.ud,ge if the gaze has been fixed and 
steady according to the clearness of the accidental image 
which is formed as a result of the experiment. 

The light of an electric spark furnishes the surest and 
simplest means of counteracting the influence of move- 
ments of the eyes, as during the momentaiy duration of 
the spark the eye cannot execute any sensible movement. 
For this experim.ent the present writer has made use of a 
wooden box, A BCD, blackened on the inside. Two 
holes are made for the eyes on each side of the box, 
/ and g. The observer looks through the openings, /, and 
in front of openings, g, the objects are placed ; these are 
pierceci through with a pin, which can be fixed by the 



76 



OPTICAL ILLUSIONS. 



eyes in the absence of the electric spark, when the box is 
perfectly dark. The box is open, and rests on the table, 
BD, to allow of changing the object. The conducting 
wires of electricity are at h and i ; in the centre of the 
box is a strip of cardboard, white on the side facing the 
spark, the light of which it shelters from the eye of 
the observer and throws back again on the object. With 
the electric light the illusion was completely perceptible, 
while it disappeared altogether in some cases ; with some 




Observation of electric spark. 

it was not entirely absent, but when it showed itself, it 
was much more feeble and doubtful than usual, though 
the intensity of light was quite sufficient to allow of the 
form of the object being very distinctly examined. Thus 
two different phenomena have to be explained ; first, the 
feeble illusion which is produced without the intervention 
of movements of the eye ; and secondly, the strengthening 
of the illusion in consequence of these movements. The 
law of contrast sufficiently explains the first ; that which 
one perceives most distinctly with indirect vision is the 



EFFECT OF OBLIQUE LINES. T] 

concordance of directions with dimensions of the same 
kind. We perceive more distinctly the difference of 
direction presented at their intersection by the two sides 
of an acute or obtuse angle, than the deviation that exists 
between one of the sides and the perpendicular which we 
imagine placed on the other side, but which is not marked. 
By being distributed on both sides, the apparent enlarge- 
ment of the angles gives way to displacements, and 
changes of direction of the sides. It is difficult to correct 
the apparent displacement of the lines when they remain 
parallel to their true direction ; for this reason, the illusion 
of the figure is relatively more inflexible. Changes of 
direction, on the contrary, are recognised more easily if 
we examine the figure attentively, when these changes 
have the effect of causing the concordance of the lines 
(which accord in reality) to disappear ; it is probably 
because of the difference in aspect of the numerous 
oblique lines that the concordance of these lines escapes 
the observer's notice. As regards the influence exercised 
by the motion of the eyes in the apparent direction of 
the lines, M. Helmholtz, after discussing the matter very 
thoroughly, proves the strengthening of the illusion in 
Zollner's illustration to be caused by those motions. It 
is not now our intention to follow out the whole of this 
demonstration ; it will be sufficient to point out to the 
reader a fruitful .source of study, with but little known 
results. 

The Romans were well acquainted with the influence 
of oblique lines. At Pompeii, fresco paintings are to be 
found, in which the lines are not parallel, so that they 
satisfy the eye influenced by adjacent lines. Engravers 
in copper-plate have also studied the influence on etchings 
of the parallelism of straight lines, and they calculate the 
effect that they will produce on the engraving. In some 
ornamentations in which these results have not been calcu- 



78 



OPTICAL ILLUSIONS. 



lated, it sometimes happens that parallel lines do not appear 
parallel because of the influence of other oblique lines, and 
a disagreeable effect is produced. A similar result is to be 
seen at the railway station at Lyons, the roof of which is 
covered with inlaid work in point de Hongrie. The wide 
parallel lines of this ceiling appear to deviate, a result 
produced by a series of oblique lines formed by the planks 
of wood. 

Having given a long account of the result of M. Helm- 
holtz's labours, we will pass to the consideration of another 
kind of experiments, or rather appliances, based on the 
illusions of vision, and the persistence of impressions on 
the retina. 

The Thautnatrope, to which we have already referred, is a 




Two sides of a Th'aumatrope disc. 

plaything of very ancient origin, based on the principle we 
have rnentioned. It consists of a cardboard disc, which we 
put in motion by pulling two cords. On one side of the 
disc a cage, a, is portrayed, on the other a bird, b. When 
the little cpntrivance is turned round, the two designs are 
seen at the same time, and form but one image — that of 
a bird in its cage. It is of course hardly necessary to add 
that the designs may be varied. 

We have already referred to M. Plateau's rotating disc 
(the Phenakistoscope). Through the narrow slits we 
perceive in succession representations of different positions 
of a certain action. The persistence of the luminous 
impressions on the retina gives to the eye the sensation 
of a continuous image, which seems animated by the .same 
movenients as those portrayed in the different phases. 



THE ZOOTRQPE. 



79 



The Zootrope is a perfect specimen of this apparatus. 
It is composed of a cylinder of cardboard, turning on a 
central axis. The cylinder is pierced with vertical slits at 
regular intervals, through which the spectator can see 
the designs upon a band of paper adapted to the interior 
of the apparatus in rotation. The designs are so executed 
that they represent the different times of a movement 




Appearance of the Tha,umatrope in rotation. 

between two extremes ; and in consequence of the impres- 
sions upon the retina the successive phases are mingled, 
so the spectator believes he sees, without transition, the 
entire movement. We give (page 82) a few specimens 
of the pictures for the Zootrope. We have here an ape 
leaping over a hedge, a dancing " Punch," a gendarme 
pursuing a thief, a person holding the devil by the tail, a 
robber coming out of a box, and a sportsman firing at a 



8o 



OPTICAL ILLUSIONS. 



bird. The extremes of the movement are right and left ; 
the intermediary figures make the transitions, and they 
are usually equal in number to the slits in the Zootrope, 
It is not difficult to construct such an instrument, and 
better drawings could be made than the specimens taken 
at random from a model. The earth might be represented 
turning in space, or a fire-engine pumping water could be 




Plateau's Phenokistoscope {see page 63). 



given, and thus the Zootrope might be quite a vehicle of 
instruction as well as of amusement. This instrument is 
certainly one of the most curious in the range of optics, 
and never fails to excite interest. The ingenious con- 
trivances which have up to the present time, reproduced it, 
all consist in the employment of narrow slits, which besides 
reducing the light to a great extent, and consequently the 
light and clearness of the object, require the instrument to 



THE PRAXINOSCOPE. 8 1 

be set in rapid rotation, which greatly exaggerates the 
rapidity of the movements represented, and without which 
the intermissions of the spectacle could not unite in a 
continuous sensation. 

We present on page 83 an apparatus based on a very 
different optical arrangement. In ^e Praxinoscope * (a name 
given by the inventor, Mr. Reynaud, to this new apparatus), 




The Zootrope. 

the substitution of one object for another is accomplished 
without interruption in the vision, or solution of continuity, 
and consequently without a sensible reduction of light ; 
in a word, the eye beholds continuously an image which, 
nevertheless, is incessantly changing before it. The result 
was obtained in this manner. Having sought unsuccess- 
fully by mechanical means to substitute one object for 
another without interrupting the continuity of the spectacle, 
the inventor was seized with the idea of producing this 

* Yxova praxis, action, and skopein, to show 



82 



OPTICAL ILLUSIONS. 














^S^ 











5'^XiL- 

^ 

»*«>«_.. 












o 
N 






THE PRAXINOSCOPE. 



83 



substitution, not with the objects themselves, but with their 
virtual images. He then contrived the arrangement which 
we will now describe. A plane mirror, ab, is placed at a 
certam distance from an object, CD, and the virtual image 




M. Raynaud's Praxinoscope. 

will be seen at c'd'. If we then turn the plane mirror and 
object towards the point, o. letting BE and DF be their 
new positions, the image will be at c"d". Its axis, o, will 
not be displaced. In the positions, A B and c D, first occupied 
by the plane mirror and the object, we now place another 
mirror and object. Let us imagine the eye placed at M. 



84 OPTICAL ILLUSIONS. 

Half of the first object will be seen at Od", and half of the 
second at o c'. If we continue the rotation of the instrument, 
we shall soon have mirror No. 2 at tt', and object No. 2 
at SS'. At the same moment the image of object No. 2 
will be seen entirely at C"'d"'. Mirror No. 2 and its 
object will soon after be at BE and DF. If we then 
imagine another mirror and its corresponding object at 
AB and CD, the same succession of phenomena will be 
reproduced. This experiment therefore shows that a series 



M 



Detail of the Pi 



■axinoscope. 



of objects placed on the perimeter of a polygon will be 
seen successively at the centre, if the plane mirrors are 
placed on a concentric polygon, the '' apotheme " of which 
will be less by one-half, and which will be carried on by 
the same movement. In its practical form, M. Reynaud's 
apparatus consists of a polygonal or simply circular box 
(for the polygon may be replaced by a circle without the 
principle or result being changed), in the centre of which 
is placed a prism of exactly half a diameter less, the 
surface of which is covered with plane mirrors. A strip 



PRAXINOSCOPE THEATRE. 85 

of cardboard bearing a number of designs ot the same 
object, portrayed in different phases of action, is placed 
in the interior of the circular rim of the box, so that 
each position corresponds to a plate of the glass prism. 
A moderate movement of rotation given to the apparatus, 
which is raised on a central pivot, suffices to produce the 
subtitution of the figures, and the animated object is 
reflected on the centre of the glass prism with remark- 
able brightness, clearness, and delicacy of movement. 
Constructed in this manner, the Praxinoscope forms an 
optical toy both interesting and amusing. In the evening, 
a lamp placed on a support ad hoc, in the centre of the 
apparatus, suffices to light it up very clearly, and a 
number of persons may conveniently assemble round it, 
and witness the effects produced. 

Besides the attractions offered by the animated scenes 
of the Praxinoscope, the apparatus may also be made the 
object of useful applications in the study of optics. It 
permits an object, a drawing, or a colour, to be substituted 
instantaneously in experiments on secondary or subjective 
images, etc., on the contrast of colours or the persistence 
of impressions, etc. We can also make what is called a 
synthesis of movevients by placing before the prism a series 
of diagrams of natural objects by means of photography, 

M. Reynaud has already arranged an apparatus which 
exhibits in the largest dimensions the animated reflection 
of the Praxinoscope, and which lends itself to the demonstra- 
tion of curious effects before a numerous auditory. The 
ingenious inventor has recently contrived also a very curious 
improvement in the original apparatus In the Praxinoscope 
Theatre he has succeeded in producing truly ornamental 
tableaux, as on a small Lilliputian stage, in the centre of 
which the principal object moves with startling effect. 
To obtain this result, M. Reynaud commences by cutting 
out in black paper the different figures, the whole of which 

7 



66 



OPTICAL ILLUSIONS. 




M. reynaud's theatre. 87 

will form an object animated by the rotation given to the 
Praxinoscope. To supply the decorations, he arranges on 
the black foundation the image of an appropriate coloured 
design by means of a piece of glass. It is well known 
that transparent glass possesses the property of giving a 
reflection of the objects on the nearest side as well as on 
the farthest. ^We may recall the applications of this optical 
effect in theatres, and also in courses of physics, under the 
title of impalpable spectres. It is also by reflection on thin, 
transparent glass, that M. Reynaud produces the image of 
the ornamentations in the Praxinoscope Theatre. The 
decorations are really placed in the lid, which is held by 
a hook in a vertical positon, thus forming the front side of 
the apparatus. In this side a rectangular opening is made, 
through which the spectator (using both eyes) perceives at 
the same time the animated reflection of the Praxinoscope, 
and the immovable image of the decorations reflected in 
the transparent glass. The position of the latter and its 
distance from the coloured decorations are arranged so that 
the reflection is thrown behind the moving figure, which 
consequently appears in strong relief against the back- 
ground, the effect produced being very striking. It is 
evident that to change the decorations it is only necessary 
to place in succession on a slide the different chromos 
representing landscapes, buildings, the interior of a circus, 
etc. It is easy to choose an arrangement suitable for each 
of the moving figures placed in the Praxinoscope. By 
this clever and entirely novel optical combination, the 
mechanism of the contrivance is entirely lost sight of, 
leaving only the effect produced by the animated figures, 
which fulfil their different movements on the little stage. 
The Praxinoscope Theatre can also be used as well in the 
evening as in the daytime. By daylight it is sufficient to 
place it before a window, and in the evening the same 
effects may be produced, perhaps in even a more striking 



88 OPTICAL ILLUSIONS. 

manner, by simply placing a lamp on the stand, with a 
small plated reflector, and a lamp-shade. The illusion 
produced by this scentific plaything is very complete and 
curious, and M. Reynaud cannot be too much commended 




The Dazzling Top 

for so cleverly applying his knowledge of physics in the 
construction of an apparatus which is at the same time 
both an optical instrument and a charming source of 
amusement. 

Amongst the toys founded upon the persistency pf 
impressions upon the retina we may instance the " Dazzling 



TJte DAZZLING top. 89 

Top." This remarkable invention is quite worthy of a 
place in every cabinet, and is an ingenious specimen of a 
perfected Helmholtz top. It is a metallic toy put in 
motion by means of a cord wound round a groove. The 
axis is hollow, admits a metallic stem, and fits into a 
handle which is held in the hand. The top is placed 
upon a little cup in an upright portion, and it is then 
set spinning in the usual way with the cord. The stem 
and handle are then withdrawn, and as the top will 
continue to spin for a long time, discs and various out- 
line shapes can be fixed upon it, and various objects 
"will be shadowed thereon. Cups, bowls, candlesticks, and 
jugs can be seen plainly revolving as the top carries the 
wire representation in outline rapidly past the eyes. 
Coloured cardboard can be worked into various patterns, 
and much amusement will be created amongst children 
and young people. 





CHAPTER VL— OPTICAL ILLUSIONS. 
(Continued.) 

EXPERIMENTS THE TALKING HEAD GHOST 

ILLUSIONS. 

f---^—^ HE enumeration of optical illusions is so con- 
siderable that we have no intention of describing 
them all, and we merely cite a few other 
examples. The following facts have been 
communicated to us by M. Nachet : — 

When examining alg^ under the microscope, we notice 
the spaces which separate the streaks ornamenting the 
silicious covering of these curious organisms, and it is 
explained that they are formed by hexagons visible only 
when we examine the object with a powerful microscope. 
" For a long time," says M. Nachet, " I occupied myself 
with the examination of the hexagonal appearance of 
the points constituting the streaks. Why should these 
hexagons show themselves, and how could they be other 
than the visible base of small pyramids piled very closely 
one on the other ; and if this were the case, why were 
not the points of the little pyramids visible .? Or, was 
the structure before me analogous to that of the eyes of 
insects 1 Then the carapace would be but a surface of 
perforated polygonal openings. This latter hypothesis 
was attractive enough, and would have explained many 
things ; but some careful observations with very powerful 
object-classes, quite free from blemishes, had shown me 
that these hexagons had round points, contrary to the 



MICROGRAPHS. 9 1 

descriptions of micrographs. These observations, cor- 
roborated by the micrographic photographs of Lackerbauer, 
the much regretted designer, and by Colonels Woodward 




Hexagonal appearance formed by circles joined together. 

and Washington, left not the slightest doubt that it was 
necessary to discover why the eye persistently saw hexagons 
where there were circles. To elucidate this point, it was 




Another figure of the same kind. 

necessary to find some means of reproducing artificially 
what nature has accomplished with so much precision on 
the surfaces of algse. After many fruitless attempts, I 
decided on making a trial of a stereotype plate covered 
with dots arranged in quincunxes, very close together. 



92 OPTICAL ILLUSIONS. 

The result was more successful than I had hoped ; the 
effect produced is exactly that of the arrangement of the 
so-called hexagons of the most beautiful of the alga:, the 
Pleiirosigma angulata. If these stereotypes are examined 
with one eye only, we shall be immediately convinced that 
we have to do with hexagonal polygons." It is useless to 
give any long exposition of a figure so clearly explanatory; 
it is simply an effect of the contrast and opposition of the 
black and white in the sensation of the retina. This effect 
is particularly striking with the figure below, a negative 
photograph heliographically engraved according to the 




Third figure. 

previous one. In this the white points seem to destroy the 
black spaces, and to approach each other tangentially, and 
the irradiation is so intense that the white circles appear 
much larger than the black of the former one, although of 
the same diameter. There are in these facts many points 
which may interest not only students of micrography, but 
also artists. As to the algae, the origin of this investiga- 
tion, it remains to be discovered if these circles which 
cover their silicious carapace arc the projection of small 
hemispheres, or the section of openings made in the thick 
covering. Certain experiments, however, seem to prove 
that they are hemispheres, and the theory is also con- 



MR. THOMPSON'S APPARATUS. 



93 



firmed by a microscopic photograph from Lackerbauer's 
collection, magnified 3,000 diameters, in which a black 
central point is seen in the centre of each circle, a certain 
reflection of the luminous source reproduced in the focus 
of each of the small demi-spheres which constitute the 
ornament of the algse. The microscope, which has pro- 
gressively shown first the streaks, then the hexagons, and 
then the round points, will surely clear up the point some 
day or other. 




Mr. Thompson's optical illusion. Give a circular movement to these figures, and 
the circleswill appear to turn round. 



Mr. Silvanus P. Thompson, Professor of Physics at 
University College, Bristol, has recently presented the 
French Society of Physical Science with a curious example 
of optical illusion, the true cause of which is not clearly 
known, but which we may compare with other facts made 
known some time ago, of which no precise explanation 
has been given. Let us first consider in what the effect 
discovered by Mr. S. P. Thompson consists, according to 
the description that has been given of it by M. C. M. Gariel ; 
the illustrations here given will also allow of our verifying 
the truth of the statements. 



94 OPTICAL ILLUSIONS. 

The first illustration consists of a series of concentric 
circles of about the width of a millimetre, separated by 
white intervals of the same size. These dimensions are 
not absolute ; they vary with the distance, and may even 
be a few inches in width if it is desired to show the 
phenomenon to a rather numerous auditory. If we hold 
the design in the hand, and give it a twirl by a little 




Another figure of Mr. Thompson's. The different circles appear to turn round 
if we give the design a rotating movement. 

movement of the wrist, the circle appears to turn round 
its centre, and the rotation is in the same direction, and 
is equally swift ; that is to say, the circle appears to 
accomplish a complete turn, whilst the cardboard really 
accomplishes one in the same direction. For the second 
effect we draw a dark circle, in the interior of which are 
placed a number of indentations at regular intervals. 
Operating in the same manner as described above, this 
notched wheel appears to turn round its centre, but this 



RETINA IMPRESSIONS. 95 

time in a different direction from the real movement. 
In this, however, as in the other design, the effect is 
more satisfactory if we do not look directly at it ; the 
movements also are particularly striking in combinations 
such as that represented on page 94, in which the 
multiplicity of circles does not allow us to fix one specially. 
We may add that the same effects may be obtained with 
eccentric wheels, or even with other curves than circles. 
By means of a photograph on glass, Mr. Thompson has 
been able to reflect these designs on a screen where they 
were obtained on a large scale ; a circular movement 
was communicated to the photographic plate, so that the 
design moved in a circular manner on the screen, and in 
this case also there existed the illusion that every circle 
seemed turning round its centre. And what is the 
explanation of these curious effects ? Mr. Thompson 
does not believe (and we share his opinion) that the 
faculty possessed by the retina of preserving images 
during a certain time {persistence of impressions on the 
retina) can entirely explain these phenomena. Without 
desiring to formulate a decided theory, Mr. Thompson 
is of opinion that we may class these facts with others 
which have been known for some time, and that perhaps 
it is necessary to attribute to the eye some new faculty 
which may explain the whole at once. 

Brewster and Adams have described phenomena which 
are equally curious, the principal of which we will de- 
scribe, adding also some analogous investigations due to 
Mr. Thompson. The result seems to be that there exists 
in the eye a badly-defined purpose of nature, which in a 
certain way compe7isates (Brewster) for the real pheno- 
menon, because it has a contrary effect, which will con- 
tinue for some time after the cessation of the phenomena, 
and which gives by itself a sensation contrary to that 
which the real movement would have produced. Thus, 



96 



OPTICAL ILI,USIONS. 



after having fixed our eyes for two or three minutes on 
a rushing waterfall, if we suddenly turn our glance on the 
adjacent rocks, the latter appear to move from top to 
bottom. It is not a question here of the effect of the 
relative movement to be observed on regarding simul- 
taneously the falling water and the rocks ; if one can 
succeed in abstracting oneself to such an extent that the 
water appears motionless, the rocks appear to take a 
contrary movement. In the phenomenon we describe 




Experiment on complementary colours. 

there is no simultaneous comparison , the eyes are turned 
successively first on the water, and then on the rocks. 
In a rapid river, such as the Rhine above the fall at 
Schaffhausen, the stream is not equally swift in every 
part, and the current is noticeably more rapid in the 
middle of the river than near the banks. If we look 
fixedly at the centre of the stream, and then suddenly 
turn our eyes towards the banks, it will appear as though 
the river were flowing back towards its source. This 
kind of compensation does not only produce an apparent 



THE "DARK SPOT." 97 

displacement, but also changes in size. When travelling 
at great speed in a railway train, the objects of the 
surrounding country as one flies by them gradually appear 
smaller and smaller. If, when this occurs, we suddenly 
remove our eyes to the interior of the railway carriage, 
and fix them on immovable objects, such as the sides of 
the compartment, or the faces of our travelling com- 
panions, the images on the retina will really preserve the 
same size, and yet the objects will appear larger. Such 
are some of the interesting facts among those discovered 
by Mr. Thompson; and though we do not intend to push 
the inquiry further, we think it may not be without interest 



Design for experiment of the ptmchtin ctEciim. 



to describe here another illusion of that organ whose pro- 
perties are in every way so curious and remarkable. 

Another experiment to show the existence of impres- 
sions received by the retina can be made with the figure on 
page 96. If the gaze be fixed upon the dark spot in the 
centre of the white figure for about half a minute, and 
the eyes then directed to the ceiling, or a sheet of white 
paper, the white figure will be reproduced in black. This 
result is based upon the principle of complementary colours. 
A red design, for instance, will be reproduced in green. 

There is a dark spot in every human eye — ^that is, a 
spot which is insensible to light. The eye is generally 
regarded as a perfect instrument, but it is not yet so by 
any means. One of our great philosophers remarked that 



98 



OPTICAL ILLUSIONS. 



if an instrument were sent home to him so full of errors 
he would feel justified in returning it to the optician. But 
the eye has its dark place, the ptincUun cceciivi, and it can 
be discovered by covering the left eye with the hand, and 
holding the present page at arm's length with the other. 




An optical illusion. 

Then fix the gaze on the small cross in the picture, and 
bring the book close up. At a little distance the white 
ball will disappear from the page. 

The illustration shows us a very curious optical ilhision, 
and one very easy to practise. Roll up a sheet of paper, 
and look through it» as through a telescope, with the 



DIVIDED TELESCOPE. 



99 



right eye, keeping both eyes open. Then place the left hand 
open palm towards you against the roll of paper, you will 
then appear to be looking through a hole in your left 
hand-. Sometimes the effect is produced without holding 
up the other hand to the roll, as shown on page 98. 




Among optical illusions there are a great number that 
may be produced by means of mirrors. The divided 
telescope is an example. The apparatus, raised on a firm 
stand, allows of one apparently seeing an object through 
a stone or other opaque object, as shown in the cut above. 



lOO 



OPTICAL ILLUSIONS. 



The illustration shows the arrangement of the apparatus. 
The observer, looking through it, plainly perceives the 
object through the glass ; the image is reflected four 
times before reaching his eye, by means of small mirrors 
concealed in the instrument. 




Cylindrical Mirror and Anamorphosis. 



Convex or concave mirrors distort images in a singular 
manner, and produce very interesting effects. Anamorphoses 
constitute particular objects belonging specially to the class 
of experiments relating to cylindrical mirrors. They are 
images made according to determined rules, but so dis- 



ANAMORPHOUS DESIGNS. 



lOI 



torted that when regarding them fixedly we can only 
distinguish confused strokes. When they are seen reflected 
in the curved mirrors, they present, on the contrary, a 
perfectly regular appearance. The illustration exhibits an 
Anamorphosis made, by a cylindrical mirror. It will be 
seen that the confused image of the horizontal paper is 
reflected in the cylindrical mirror, producing the figure of 
a juggler. It is easy to contrive similar designs one's-self ; 




Anamorphous design for the ten of hearts. 

and conical mirrors may also be employed which produce 
particular effects of a no less interesting kind. The next 
illustration is of a set of figures which -in a cylindrical 
mirror look like the ten of hearts. 

One of the most remarkable applications of mirrors in 
amusing experiments is undoubtedly that of the severed 
and talking head. A few years back this trick obtained 
considerable success in Paris and a number of other towns. 
The spectators beheld a small space set apart, in which 



I02 



OPTICAL ILLUSIONS. 



/ 











THE TALKING HEAD. I03 

was placed a table on three legs ; on this table was a 
human head, placed in cloth on a dish. The head moved 

,its eyes and spoke ; it evidently belonged to a man whose 
body was completely hidden. The spectators thought 
they saw an empty space beneath the table, but the 
body of the individual who was really seated there was 
concealed by two glasses placed at an inclination of 45° 
to the walls on the right and left. The whole was 
arranged in such a manner that the reflection of the 
walls coincided with the visible part of the wall at the 
back of the room. The three walls were painted in one 
colour, and a' subdued light increased the illusion, the 
effect of which was remarkable. 

The spectres designed by Robin also attracted con- 
siderable public attention within recent times. They 
were Images formed by the medium of transparent glass. 
Glass panes often produce the phenomenon of spectres. 
In the evening, when it is dark out of doors, it is easy 
to prove that the reflection of objects in a lighted room 
can be reproduced behind the window panes by reason 
of the darkness outside.' If we approach the window 
pane, we see also the real objects outside, a balcony, 
tree, etc. These real objects mingle with the reflected 
image, and combine to produce very curious effects. In 

i this way Mr. Robin has contrived the effects of the 
theatre. He throws on the stage the reflection of a 
person dressed as a Zouave, and he himself, armed with 
a sabre, stabs the spectre through the body, A great 
number of other singular effects have been obtained in 
the same manner. Pepper's Ghost was managed in this 
way. 

Within recent times, images produced in a similar way 
have been utilized to facilitate the study of drawing. A 
piece of glass is fixed vertically on a black board. A 
model to copy from is placed on one side of the piece 



I04 



OPTICAL ILLUSIONS. 




DRAWING BY REFLECTION. I05 

of glass, and is arranged so fhnt- th^ ■ 1 

obliquely through the glass and wVn ^.''""'/^y P^^^^^ 
r *.u J ■ s'ass, and we perceive the reflecfinn 

of the design very clearly on the other side. It is tLn 
very eas.ly reproduced with a pencil on a sheet o white 
paper by tracing the outlines. ^^ 




Drawing by reflection. 




CHAPTER VII.— OPTICAL APPARATUS. 

THE EYE THE STEREOSCOPE SPECTRUM ANALYSIS — 

THE SPECTROSCOPE — THE TELESCOPE AND MICRO- 
SCOPE PHOTOGRAPHY DISSOLVING VIEWS 

LUMINOUS PAINT. 

;HE eye and vision are such important subjects 
to all of us that we may be excused for saying 
something more concerning phenomena con- 
nected with them, and the instruments we use 
for assisting 4:hem. We do not propose to write a treatise 
upon the physiology of vision, for we know the image in 
the eye is produced physically in the same manner as the 
image in a camera obscura. In the eye the sides of the 
box are represented by the sclerotic ; the dark inner surface 
has its parallel in the pigment of the choroid ; the opening 
in the box in the pupil of the eye ; the convex lens in 
the crystalline and the cornea ; and the retina receives 
the image. But why we see — beyond the fact that we 
do see — no one can explain. Science is dumb on the 
subject. Thought and consciousness elude our grasp ; 
and, as Professor Tyndall says on this subject, " we stand 
face to face with the incomprehensible." 

But there are many interesting facts connected with our 
vision which may be plainly described. Some people are 
obliged to carry an object (or a book) to within ten inches 
of the eye to see it distinctly; and a person who does not 
possess convergent power of the eye will have to move it 



THE RETINA OF THE EYE. I07 

farther off, or use convex glasses ; while a " near-sighted " 
person, whose eyes are too quickly convergent, will use 
concave glasses to bring the object near to the eye. 

There is but one small place in the retina of the eye 
which admits of perfect vision. This, the most sensitive 
portion, is called the " yellow spot," and vision becomes 
more and more indistinct from this point towards the 
circumference. This can be proved by any one ; for in 
reading we are obliged to carry our eyes from word to 
word, and backwards and forwards along the lines of 
print. Another very important element in our vision is 
the contraction and enlargement of the iris around the 
pupil. In cases where strong light would only dazzle us 
the iris expands, and the pupil is contracted to a sufficient 
size to accommodate our vision. At night, or in a darkened 
room, the pupil is enlarged. This change will account for 
our not being immediately able to see objects when we 
have passed from darkness to great light, or vice versd 
The iris must have time to accommodate itself to the light. 

Now, outside the small space of perfect vision above 
mentioned, there is a circle of considerable extent, called 
the "field of vision." In man this field, when the eyes 
are fixed, subtends an angle of about 180°, because beyond 
that the rays cannot enter the pupil of the eye. But 
in the lower animals, the fish and birds, — notably the 
ostrich, — the field of vision is much more extensive, 
because the pupils are more prominent, or the eyes are 
set more towards the sides of the head. The ostrich can 
see behind him, and fish can see in any direction without 
■ apparent limit. Man can only see indistinctly; and though 
he can move his eyes rapidly, he can see distinctly but a 
small portion of any object at a time, yet he sees with 
both eyes simultaneously a single object, because the two 
lines of vision unite at a single point, and as the two 
images cover each other we perceive only one image. 



Io8 OPTICAL APPARATUS. 

Beyond or within this point of meeting the vision is 
indistinct, but the angle of convergence is always varied 
according to the distance of the object. If we hold tip a 
penholder in front of us, and in a line with any other 
defined object, — say an ink-bottle, — we can see the pen- 
holder distinctly, and the ink-bottle indistinctly, as two 
images. If we then look at the ink-bottle we shall see it 
single, while the penholder will appear double, but with 
imperfect outlines. 

Again, if we look at a box both eyes will see it equally 




The Sterco-.cope. 

well, but the right eye will see a little more on its right 
side and the left eye on the left. It is on this principle 
that the Stereoscope is constructed. Sir Charles Wheat- 
stone was the inventor, and the instrument may be thus 
described : — Two pictures are taken by photography — 
one as the landscape is seen by the right eye, the other 
as it is viewed by the left ; the points of view thus 
differing slightly. When both eyes are simultaneously 
applied to the instrument the view is seen exactly as it 
would appear to the beholder at the actual place it repre- 
sents. The views are taken singly ; one side at one time, 
and another after, as in the camera. A is the first view; 



THE STEREOSCOPE. 



109 



B is kept dark ; c is the shutter for A. There are Reflect- 
ing and Refracting Stereoscopes. In the former a mirror 
reflects the image into each eye; in the latter the views 
are pasted on a card side by side, and looked at through 
prismatic lenses. The principles of Binocular Vision have 
been applied to the Microscope. 

In foregoing chapters we have given many examples 
v/ith diagrams of the temporary impressions made upon 
the retina of the eye. It is a fact that a wheel revolving 
at a great rate will appear to be standing still when 
suddenly illuminated by a flash of lightning, because the 





Mode of taking photograph for Stereoscope. 

eye has not time to take in the motion in the instant of 
time, for the spokes of the wheel are not moving fast 
enough to convey the impression of motion in that half 
second to the eye ; yet the perfect outline of the wheel 
is distinctly visible. 

Indeed, distinct vision can be exercised in a very small 
fraction of a second. It was calculated by Professor 
Rood, and proved by experiment, that forty billionths of 
a second is sufficient time for the eye to distinguish 
letters on a printed page. It this instance the illuminating 
power was an electric spark from a Leyden Jar. 

We have remarked upon the distinctness with which 



I lO OPTICAL APPARATUS. 

we can see an object when we direct our gaze upon it, 
and this appears a self-evident proposition ; but have 
any of our readers remarked the curious fact that when 
they want to see a faint and particular star in the sky it 
will at once disappear when they gaze at it ? The best 
way to see such very faint orbs as this is to look away 
from them, — a little to one side or the other, — and then 
the tiny point will become visible again to the eye. 
There is also a degree of phosphorescence in the eye, 
which any one who receives a blow upon that organ will 
readily admit. Even a simple pressure on the closed lid 
will show us a circle of light and " colours like a peacock's 
tail," as the great Newton expressed it. There are many 
occasions in which light is perceived in the eye — generally 
the result of muscular action ; and the Irish term to 
" knock fire out of my eye" is founded upon philosophical 
facts. 

We are many of us aware of " spots" on our eyes 
when our digestion is out of order, and the inability of 
the eye to see figures distinctly in a faint light — -within 
a proper seeing distance, too — has often given rise to the 
" ghost." These shadowy forms are nothing more than 
affections of the eye, and, as well remarked in Brewster's 
Letters on Natural Magic, "are always white because no 
other colour can be seen." The light is not sufficiently 
strong to enable the person to see distinctly; and as the 
eye passes from side to side, and strives to take in the 
figure, it naturally seems shadowy and indistinct, and 
appears to move as our eyes move. " When the eye 
dimly descries an inanimate object whose different parts 
reflect different degrees of light, its brighter parts may 
enable the spectator to keep up a continued view of it ; 
but the disappearance and reappearance of its fainter 
parts, and the change of shape which ensues, will neces- 
sarily give it the semblance of a living form ; and if it 



THE SOLAR SPECTRUM. 



I II 



occupies a position which is unapproachable, and where 
animate objects cannot find their way, the mind will soon 
transfer to it a supernatural existence. In like manner a 
human figure shadowed forth in a feeble twilight may 
undergo similar changes, and after being distinctly seen 
while it is in a situation favourable for receiving and 
reflecting light, it may suddenly disappear in a position 
before and within the reach of the observer's eye ; and if 
this evanescence takes place in a path or roadway where 
there is no sideway by which the figure could escape, it 
is not easy for an ordinary mind to efface the impression 




The Solar Spectrum, 



which it cannot fail to receive." This will account for 
many so-called " ghosts." 

Accidental colours, or ocular spectra, are, so to speak, 
illusions, and differently-coloured objects will, when our 
gaze is turned from them, give us different '■ spectra'' or 
images. For instance, a violet object will, when we turn 
to a sheet of white paper, give us a yellow " spectrum '' ; 
orange will be blue ; black and white will change respec- 
tively; red will become a blue-green-. From a very strong 
white light the accidental colours will vary. 

The Solar Spectrum is the name given to the coloured 
band formed by the decomposition of a beam of light 
into its elementary colours, of which there are seven. 
This is an easy experiment. A ray of light can be 



I I 2 OPTICAL APPARATUS. 

admitted into a darkened room through a. hole in the 
shutter, and thus admitted will produce a white spot on 
the screen opposite, as at £■ in the diagram. If we 
interpose a prism — a triangular piece of glass — the 
" drop " of a chandelier will do — we cause it to diverge 
from its direct line, and it will produce a longer streak 
of light lower down. This streak will exhibit the pris- 
matic colours, or the "colours of the rainbow"; viz., red 
(at the top), orange, yailow, green, blue, indigo (blue), and 
violet last. These are the colours of the Solar Spectrum. 
The white light is thus decomposed, and it is called 
mixed light, because of the seven rays of which it is 
composed. These rays can be again collected and re- 
turned to the white light by means of a convex lens. 

" White light," said Sir Isaac Newton, " is composed 
of rays differently refrangible," and as we can obtain the 
colours of the rainbow from white light, we can, by 
painting them on a circular plate and turning it rapidly 
round, make the plate appear white. Thus we can prove 
that the seven colours make "white" when intermingled 
But Newton (1675) did not arrive at the great importance 
of his experiment. He made a round hole in the shutter 
and found that the various colours overlapped each other. 
But, in 1802, Dr. WoUaston improved on this experiment, 
and by admitting the light through a tiny slit in the 
wood, procured an almost perfect spectrum of " simple " 
colours, each one perfectly distinct and divided by black 
lines. 

But twelve years later, Professor Fraunhofer made a 
chart of these lines, which are still known by his name. 
Only, instead of the 576 he discovered, there are now 
thousands known to us ! To Fraunhofer's telescope Mr 
Simms added a coUimating lens, and so the Spectroscope 
was begun ; and now we use a number of prisms and 
almost perfect instruments, dispersing the light through 



THE SPECTROSCOPE. I I 3 

each. We have here an illustration of a simple Spectro- 
scope, which is much used for chemical analysis. 

In the spectrum we have long and short waves of light, 
as we have long and short (high and low) waves in music, 
called notes. The long or low notes are as the red rays, 
the high notes as the blue waves of light. (Here we 
have another instance of the similarity between light and 
sound.) But suppose we shut out the daylight and sub- 



1 


[ 1 

1 

T 1 


1^^ J 



The Spectroscope. 



stitute an artificial light. If we use a lamp burning 
alcohol with salt (chloride of sodium), the spectrum 
will only consist of two yellow bands, all the other 
colours being absent. With lithium we obtain only two, 
one orange and one red. From this we deduce the fact 
that different substances when burning produce different 
spectra ; and although a solid may (and platinum will) 
give all seven colours in its spectrum, others, as we have 
seen, will only give us a few, the portion of the spectrum 



114 OPTICAL APPARATUS. 

between the colours being black. Others are continuous, 
and transversed by " lines " or narrow spaces devoid of 
light ; such is the spectrum of the sun, and by careful 
and attentive calculation and observation we can get an 
approximate idea of the matter surrounding the heavenly 
bodies. 

We have said there are lines crossing the spectrum 
transversely ; these are called Fraunhofer's lines, after 
the philosopher who studied them ; they were, however, 
discovered by WoUaston. These lines are caused by light 
from the lower portion of the sun passing through the 
metallic vapours surrounding the orb in a state of incan- 
descence, such as sodium, iron, etc. One of Fraunhofer's 
lines, a black double line known as D in the yellow 
portion of the spectrum, was known to occupy the same 
place as a certain luminous line produced by sodium 
compounds in the flame of a spirit lamp. This gave rise 
to much consideration, and at length Kirchkoff proved 
that the sodium vapour which gives out the yellow light 
can also absorb that light ; and this fact, viz., that every 
substance, which at a certain tetnperature emits light of a 
certain refran^ibility, possesses at that temperature the 
power to absorb that same light. So the black lines are 
now considered the reversal of luminous lines due to the 
incandescent vapours by which the sun is surrounded. 
Thus the presence of an element can be found from black 
or luminous lines, so the existence of terrestrial elements 
in celestial bodies has been discovered by means of pre- 
paring charts of the lines of the terrestrial elements, and 
comparing them with the lines of stella. spectra. 

We have supposed the beam of light to enter through 
a slit in the shutter, and fall upon a screen or sheet. 
The solar spectrum shown by the passage of the beam 
through a prism is roughly as below, 

Fraunhofer substituted a telescope for the lens and the 



THE SPECTROSCOPE. 



115 



screen, and called his instrument a Spectroscope. He 
then observed the lines, which are always in the same 
position in the solar spectrum. The principal of them 
he designated as A, u, C, D, E, F, G, H. The o 
first three are in the red part of the spec- 
trum ; one in the yellow, then one in the 
green ; F comes between green and blue, 
G in the indigo-blue, and H in the violet. 
But these by no means exhaust the lines 
now visible. Year by year the study of 
Spectrum Analysis has been perfected more 
and more, and now we are aware of more 
than three thousand " lines " existing in 
the solar spectrum. The spectra of the 
moon and planets contain similar dark 
lines as are seen in the solar spectrum, 
but the fixed stars show different lines. 
By spectrum analysis we know the various 
constituents of the sun's atmosphere, and 
we can fix the result of our observations 
made by means of the Spectroscope in 
the photographic camera. By the more 
recent discoveries great advances have been 
made in " solar chemistry." 

What can we do with the Spectroscope, 
or rather. What can we not do t By Spec- 
troscopy we can find out, and have already 
far advanced upon our path of discovery, 
" the measure of the sun's rotation, the 
speed and direction of the fierce tornados 
which sweep over its surface, and give rise 
to the ' maelstroms ' we term • sunspots,' and the mighty 
alps of glowing gas that shoot far beyond the visible orb, 
ever changing their form and size ; even the temperature 
and pressure of the several layers and their fluctuations 






"2 



Il6 OPTICAL APPARATUS. 

are in process of being defined and determined." This 
is what science is doing for us, and when we have actually 
succeeded in ascertaining the weather at various depths in 
the atmosphere of the sun, we shall be able to predict our 
own, which depends so much upon the sun. Recently 
(1880) Professor Adams, in his address to the British 
Association, showed that magnetic disturbances, identical 
in kind, took place at places widely apart simultaneously. 
He argues that the cause of these identical disturbances 
must be far removed from the earth. 

" If," he says, " we imagine the masses of iron, nickel, 
and magnesium in the sun to retain even in a slight 
degree their magnetic power in a gaseous state, we have 
a sufficient cause for all our magnetic changes. We know 
that masses of metal are ever boiling up from the lower 
and hotter levels of the sun's atmosphere to the cooler 
upper regions, where they must again form clouds to throw 
out their light and heat, and to absorb the light and heat 
coming from the hotter lower regions ; then they become 
condensed, and are drawn back again' towards the body 
of the sun, so forming those remarkable dark spaces or 
sunspots by their down rush to their former levels. In 
these vast changes we have abundant cause for those 
magnetic changes which we observe at the same instant 
at distant points on the surface of the earth." So we 
are indebted to the Spectroscope for many wonderful 
results — the constitution of the stars, whether they are 
solid or gaseous, and many other wonders. 

The manner in which we have arrived at these startling 
conclusions is not difficult to be understood, but some 
little explanation will be necessary. 

The existence of dark lines in the solar spectrum proves 
that certain rays of solar light are absent, or that there is 
less light. When we look through the prism we perceive 
the spaces or lines, and we can produce these ourselves 



SPECTRUM ANALYSIS. 117 

by interposing some substance between the slit in the 
shutter before mentioned and the prism. The vapour of 
sodium will answer our purpose, and we shall find a dark 
line in the spectrum, the bright lines being absorbed by 
the vapour. We can subject a substance to any tempera- 
ture we please, and into any condition — solid, liquid, or 
gaseous ; we can also send the light the substance may 
give out through certain media, and we can photograph 
the spectrum given out under all conditions. The distance 
rj the source cf the light makes no difference. So whether 
it be the sun, or a far-distant star, we can tell by the 
light sent to us what the physical condition of the star 
may be. It was discovered in 1864 that the same metallic 
body may give different spectra; for instance, the spec- 
trum might be a band of light,— like the rainbow, — or a 
few isolated colours ; or again, certain detached lines in 
groups. The brightness of the spectrum lines will change 
with the depth of the light-giving source, or matter which 
produces it. 

We have become aware by means of the Spectroscope 
that numerous metals known to us on earth are in com- 
bustion in the sun, and ne,w ones have thus been discovered. 
In the immense ocean of gas surrounding the sun there 
are twenty-two elements as given by Mr. Lockyer, including 
iron, sodium, nickel, barium, zinc, lead, calcium, cobalt, 
hydrogen, potassium, cadmium, uranium, strontium, etc. 
Not only is the visible spectrum capable of minute examina- 
tion, but, as in the case of the heat spectruin already men- 
tioned when speaking of Calorescence, the light spectrum 
has been traced and photographed far beyond the dark 
space after the blue and violet rays, seven times longer 
than the visible solar spectrum-^a spectrum of light 
invisible to our finite vision. Although a telescope has 
been invented for the examination of these "ultra violet" 
rays, no human eye can see them. But — and here science 



I 1 8 OPTICAL APPARATUS. 

comes in — when a photographic plate is put in place of 
the eye, the tiniest star can be seen and defined. Even 
the Spectroscope at length fails, because light at such 
limits has been held to be " too coarse-grained for our 
purposes " ! " Light," says a writer on this subject, " we 
can then no longer regard as made of smooth rays ; we 
have to take into account — and to our annoyance — the fact 
that its ' long levelled rules ' are rippled, and its texture, 
as it were, loose woven " ! 

Twenty years ago Professors Kirchkoff and Bunsen ap- 
plied Fraunhofer's method to the examination of coloured 
flames of various substances, and since then we have been 
continually investigating the subject ; yet much remains 
to be learnt of Spectrum Analysis, and Spectroscopy has 
still much to reveal. From Newton's time to the present 
our scientists have been slowly but surely examining with 
the Spectroscope the composition of spectra, and the Spec- 
troscope is now the greatest assistant we possess. 

" Spectrum Analysis, then, teaches us the great fact 
that solids and liquids give out continuous spectra, and 
vapours and gases give out discontinuous spectra instead 
of an unbroken light" (Lockyer). We have found out 
that the sunlight and moonlight are identical, that the 
moon gives a. spectrum like a reflection of the former, 
but has no atmosphere, and that comets are but gases or 
vapours. The most minute particles of a grain of any 
substance can be detected to the millionth fraction. The 
Twiy of a grain of blood can be very readily distinguished 
in a stain after years have passed. The very year of 
a certain vintage of wine has been told by means of 
"absorption," or the action of different bodies on light 
in the spectrum. It is now easy, " by means of the 
absorption of different vapours and different substances 
held in solution, to determine not only what the absorbers 
really are, but also to detect a minute quantity." The 



SPECTRUM ANALYSIS. I 19 

application of this theory is due to Dr. Gladstone, who 
used hollow prisms filled with certain substances, and so 
thickened the "absorption lines." By these lines, or bands, 
with the aid of the Spectrum Microscope, most wonderful 
discoveries have been made, and will continue to be made. 
We will close this portion of the subject with a brief 
description of the Spectroscope in principle. 

The instrument consists of two telescopes arranged 
with two object-glasses on a stand. A narrow slit is put 
in place of the eye-piece of one, the arrangement admitting 
of the slit being made smaller or larger by means of 
screws. The glass to which the slit is attached is called 
the collimating lens. The light, at the end of the slit seen 
from the other telescope, being separated by the prisms 
Ibetween the. two telescopes, will produce the spectrum. 
The Spectroscope is enclosed, so that no exterior light 
■shall interfere with the spectra the student wishes to 
■observe. This merely indicates the principle, not the 
details, of the Spectroscope, which vary in different 
instruments. 

We tnay now pass from the Spectroscope to the 
Telescope and the Microscope, instruments to which we 
are most largely indebted for our knowledge of our 
•surroundings in earth, air, and water. 

The word Telescope is derived from the Greek tele, 
■far, and skopein, to see ; and the instrument is based upon 
the property possessed by a convex lens or concave mirror, 
■of converging to a focus the rays of light falling on it 
•from any object, and at that point or focus forming an 
image of the object. The following diagram will illustrate 
this. Let vw be a lens, and AB an object between the 
glass, and F the focus. The ray, he, is so refracted as 
to appear to come from a. The ray from b likewise 
appears in a similar way, and a magnified image, ab, is 
the result. 



I20 OPTICAL APPARATUS. 

The ordinary Telescope consists of an object-glass and 
an eye-lens, with two intermediates to bring the object 
into an erect position. A lens brings it near to us, and 
a magnifier enlarges it for inspection. We will now give 
a short history of the Telescope and its, improved con- 
struction. 

Roger Bacon was supposed to have had some knowledge 
of the Telescope, for in 1 5 5 i it was written : " Great 
talke there is of a glass he made at Oxford, in which men 
see things that were don." But a little later, Baptista 




Converging rays to a focus. 

Porta found out the power of the convex lens to bring 
objects " nearer." It was, however, according to the old 
tale, quite by an accident that the Telescope was discovered 
about the year 1608. 

In Middleburg, in Holland, lived a spectacle-maker 
named Zachary Jansen, and his sons, when playing with 
the lenses in the shop, happened to fix two of them at 
the proper distance, and then to look through both. To 
the astonishment of the boys, they perceived an inverted 
image of the church weathercock much nearer and much 
larger than usual. They at once told their father what 
they had seen. He fixed the glasses in a tube, and 



THE TELESCOPE. 121 

having satisfied himself that his sons were correct, thought 
httle more about the matter. This is the story as told, 
but there is little doubt that for the first Telescope the 
world was indebted either to Hans Lippersheim or Joseph 
Adriansz, the former a spectacle-maker of Middleburg ; 
and in October 1608, Lippersheim presented to the 
Government three instruments, with which he "could see 
things at a distance." Jansen came after this. The 




The Microscope. 

report of the invention soon spread, and Galileo, - who 
was then in Venice, eagerly seized upon the idea, and 
returning to Padua with some lenses, he managed to 
construct a telescope, and began to study the. heavens. 
This was in i6og. Galileo's Tube became celebrated, 
and all the first telescopes were made with the concave 
eye-lens. Rheita, a monk, made a binocular telescope, as 
now used in our opera and field-glasses approximately. 

But the prismatic colours which showed themselves in 
the early telescopes were not got rid of, nor was it till 



122 OPTICAL APPARATUS. 

1729 that Hall, by studying the mechanism of the eye, 
managed a combination of lenses free from colour. Ten 
years before (in 171 8) Hadley had established the Reflector 
Telescope ; Herschel made his celebrated forty-foot " re- 
flector" in 1789. 

However, to resume. In 1747, Euler declared that it 
was quite possible to construct an arrangement of lenses so 
as to obtain a colourless image, but he was at first chal- 
lenged by John Dollond. The latter, however, was afterwards 
induced to make experiments with prisms of crown and 
flint glass. He then tried lenses, and with a concave lens 




Image on the Retina, 



of iflint, and a convex lens of crown, he corrected the colours. 
The question of proper curvature was finally settled, and 
the "Achromatic" Telescope became an accomplished fact 

There are two classes of Telescopes — the reflecting and 
refracting. Lord Rosse's is an instance of the former. 
Mr. Grubb's immense instrument is a refractor. 

The Microscope has been also attributed to Zacharias 
Jansen, and Drebbel, in 16 19, possessed, the instrument 
in London, but it was of little or no use. The lens 
invented by Hall, as already mentioned, gave an impetus 
to the Microscope. In the simple Microscope the objects 
are seen directly through the lens or lenses acting as one. 
The compound instrument is composed of two lenses (or 



THE MICROSCOPE. 



123 



a number formed to do duty as two), an eye-lens, and an 
object-lens. Between these is a " stop" to restrain all 
light, except what is necessary to view the object distinctly. 
The large glass near the object bends the rays on to the 
eyeglass, and a perfect magnified image is perceived. We 
annex diagrams, from which, the construction will be readily 
understood. 

We have in the previous chapter 
mentioned the effect of light upon the 
eye and its direction, and when an 
object is placed very near the eye we 
know it cannot be distinctly seen ; a 
magnified image is thrown upon the 





The Microscope lenses. 



Concave lens. 

retina, and the divergency of the rays 
prevents a clear image being perceived. 
But if a small lens of a short " focal 
length " be placed in front of the eye, 
having PQ for its focus, the rays of 
light will be parallel, or very nearly 
so, and will as such produce " distinct vision," and the 
image will be magnified at pq. In the Compound Refract- 
ing Microscope, BAB is the convex lens, near which an 
object, PQ, is placed a little beyond its focal length. An 
inverted image, pq, will then be formed. This image is 
produced in the convex lens, bab', and when the rays are 



124 



OPTICAL APPARATUS. 



reflected out they are parallel, and are distinctly seen. 
So the eye of the observer at the point E will see a 
magnified image of the object at PQ brought up to pq. 




I. Focus of parallel rays. 2. Focus of divergent rays. 
3. Focus of divergent rays brought forward by more convex lens. 

Sir Isaac Newton suggested the Reflecting Microscope, 
and Dr. WoUaston and Sir David Brewster improved the 
instrument called the " Periacopic Microscope," in which 
two hemispherical lenses were cemented together by the 
plane surfaces, and having a "stop" between them to limit 



Diverging rays. 

the aperture. Then the " Achromatic " instrument came 
into use, and since then the Microscope has gradually 
attained perfection. 

We have so frequently mentioned lenses that it may 
be as well to say something about them. Lenses may 
be spherical, double-convex, plane-convex, plane-concave, 



LENSES. I 2 5 

double-concave, and concave- convex. Convex lenses bring 
the parallel lines which strike them to a focus, as we see 
in the "burning-glass." The concave or hollow lens appears 
as in first cut, page 123. The rays that follow it parallel 
to its axis are refracted, and as if they came from a point 




Hypermetropia (long sight). 



F in the diagram. But converging rays falling on it 
emerge in a parallel direction as on page 123, or diverge 
as in the second illustration on page 124. 

The use of spectacles to long or short-sighted people 
is a necessity, and the lenses used vary. The eye has 




Myopia (short sight). 

usually the capacity of suiting itself to viewing objects — 
its accommodation, as it is termed — near or far. But 
when the forepart of the eye is curved, and cannot adapt 
itself to distant objects, the person is said to be short- 
sighted. In long sight the axis of the eyeball is too 
short, and the focus falls beyond the retina ; in short 
sight it is too long. In the diagrams herewith (see above) 



126 



OPTICAL APPARATUS, 



the first shows by the dotted lines the position of the 
retina in long sight, and in the second in short sight, 
the clear lines showing in each case the perfectly-formed 
eye. For long sight and old sight the double-convex 
glass is used, for short sight the double-concave. We 
know the burning-glass gives us a small image of 




Concave and convex lenses. 

the sun as it converges the rays to. its focus. But lenses 
will do more than this, and in the Photographic Camera 
we find great interest and amusement. 

Photography (or writing by light) depends upon the 
property which certain preparations possess of being 
blackened by exposure to light while in contact with 




TxTises :or Jong and short sight. 



matter. By an achromatic arrangement of lenses the 
camera gives us a representation of the desired object 
The cut on page 127 shows the image on the plate, and 
the lower illustration gives the arrangement of lenses. 

To Porta, the Neapolitan physician, whose name we 
have already mentioned more than once, is due the first 
idea of the Photographic Camera He found that if light 
was admitted through a small aperture, objects from which 



THE CAMERA. 



127 



rays reached the hole would be reflected on the wall like 
a picture. To this fact, we are indebted for the Camera 
Obscura, which receives the picture upon a plane surface 
by an arrangement of lenses. In fact, Porta nearly arrived 



=□=_>. 




The Camera. 

at the Daguerreotype process. He thought he could teach 
people to draw by following the focussed picture with a 
crayon, but he could not conquer the aerial perspective. 

So the camera languished till 1820, when Wedgwood 
and Sir Humphrey Davy attempted to obtain some views 




Arrangement of lenses. 

with nitrate of silver, but they became obliterated when 
exposed to the daylJght. 

As early as 18 14, however, M. Niepce had made a 
series of experiments in photography, and subsequently 
having heard that M. Daguerre was turning hi,s attention 
to the same subject, he commuincated with him. In 



128 OPTICAL APPARATUS. 

1827 a paper was read before the Royal Society, and 
in 1829 a partnership deed was drawn up between 
Daguerre and Niepce for " copying engravings by photo- 
graphy." Daguerre worked hard, and at length succeeded 
in obtaining a picture by a long process, to which, perhaps, 
some of our readers are indebted for their likenesses forty 
years ago. By means of iodine evaporated on a metal 
plate covered with " gold-yellow," and exposing the plate 
then in a second box to mercurial vapour, he marked the 
image in the camera, and then he immersed the plate in 
hyposulphate of soda, and was able to expose the image 
obtained to daylight. 

But the mode now in use is the " collodion " process. 
We have all seen the photographer pouring the iodized 
collodion on the plate, and letting the superfluous liquid 
drain from a corner of the glass. When it is dry the 
glass-plate is dipped into a solution of nitrate of silver, 
and then in a few minutes the glass is ready. The focus 
is then arranged, and the prepared plate conveyed in a 
special slide — to keep it from the light — to the camera. 
When the " patient " is ready, the covering of the lens is 
removed, and the light works the image into the sensitive 
plate. The impression is then " brought up," and when 
developed is washed in water, and after by a solution 
which dissolves all the silver from the parts not darkened 
by the light. Thus the negative is obtained and printed 
from in the usual manner. 

Instantaneous photography is now practised with great 
success. An express train, or the movements of a horse 
at full speed, can thus be taken in a second or less. 
These results are obtained by using prepared plates, and 
the "emulsion process," as it is called, succeeds admirably. 
The mode of preparation is given in a late work upon 
the subject, and the photographic plates may also be 
obtained ready for use. Gelatine and water, mixed with 



PHOTOGRAPHY. 1 29 

bromide of ammonium, nitrate of silver, and carbonate of 
ammonium, mixed with certain proportions of water, form 
the "emulsion." We need not go into all the details 
here. Information can easily be obtained from published 
works, and as the plates can be purchased by amateurs, 
they will find that the best way. 

Aside from the art interest in the new plates there is 
another, that springs from the fact that it is now possible 
to take pictures of men, animals, and machinery in rapid 
motion, thus enabling us to view them in a way that 
would be impossible with the unaided eye. The first 
experiments in this direction were applied to the move- 
ments of a horse moving at full speed. The pictures, 
taken in series, showed that he performed muscular actions 
that were not before comprehended or even imagined. 
These pictures at the time attracted great attention, and 
instantaneous pictures have been since taken of dancers 
in a ball-room, of vessels and steam-boats in rapid move- 
ment, of all kinds of animals in motion, and of machinery 
in operation. As the pictures represent the movements 
at one instant of time, they give, as it were, a fixed view 
of a motion, precisely as if it were suddenly alrrested in 
full action. In the case of animals, the motions of the 
nostrils are represented in the most singular manner, and 
the spokes of a steam -boat's paddle-wheel are shown 
apparently perfectly still while the spray and waves 
appear in active motion, or, rather, as they would look if 
they could be instantly frozen. It is clear the new process 
and pictures will open a wide and instructive field in art 
and in the study of mechanical action. 

While on the subject of Photography we may mention 
a very ingenious little apparatus called a SCENOGRAPH, 
the invention of Dr. Candize. It is really a pocket-camera, 
and is so easily manipulated that it will be found a most 
pleasant and useful holiday companion. Any one may 



130 CHEMlSTRV. 

age ! Soap is quite soluble in spirits, but in ordinary 
water it is not so greatly soluble, and produces a lather, 
owing to the lime in the water being present in more or 
less quantity, to make the water more or less " hard." 

Sodium is not unlike potassium, not only in appear- 
ance, but in its attributes ; it can be obtained from the 
carbonate, as potassium is obtained from its carbonate. 
Soda is the oxide of sodium, but the most common and 
useful compound of sodium is the chloride, or common salt, 
which is found in mines in England, Poland, and elsewhere. 
Salt may also be obtained by the evaporation of sea water. 

Rock salt is got at Salz- 
burg, and the German salt 
mines and works produce 
a large quantity. The 
Carbonate of Soda is 
manufactured from the 
chloride of sodium, al- 
though it can be procured 
from the salsoda plants by 
burning. The chloride of 
Machine for cutting soap in bars. sodium is Converted into 

sulphate, and then ignited with carbonate of lime and 
charcoal. The soluble carbonate is extracted in warm 
water, and sold in crystals as soda, or (anhydrous) " soda 
ash." The large quantity of hydrochloric acid produced 
in the first part of the process is used in the process of 
making chloride of lime. A few years back, soda was 
got from Hungary and various other countries where it 
exists as a natural efflorescence on the shores of some 
lakes, also by burning sea-weeds, especially the common 
bladder wrack {Fucus vesiculosus), the ashes of which were 
melted into masses, and came to market in various states 
of purity. The bi-carbonate of soda is obtained by pass- 




LITIilUM. 131 

ing carbonic acid gas over the carbonate crystals. Soda 
does not attract moisture from the air. It is used in wash- 
ingi Jn glass manufactories, in dyeing, soap-making, etc. 

Sulphate of Soda is "Glauber's Salt"; it is also employed 
in glass-making. Mixed with sulphuric acid and water, 
it forms a freezing mixture. Glass, as we have seen, is 
made with silicic acid (sand), soda, potassa, oxide of lead, 
and lime, and is an artificial silicate of soda. 

Lithium is the lightest of metals, and forms the link 




Soap-boiling house. 

between alkaline and the alkaline earth metals. The salts 
are found in many places in solution. The chloride when 
decomposed by electricity yields the metal. 

CESIUM and Rubidium require no detailed notice 
from us. They were first found in the solar spectrum, 
and resemble potassium. 

Ammonium is only a conjectural metal. Ammonia, of 



132 OPTICAL APPARATUS. 

The illustration shows a small apparatus by which on thin 
plates small photographs can be taken and fixed till it is 
found desirable to enlarge them. 

The Photophone, one of the most recent contributions 
to science, is an instrument which, in combination v/ith 
the telephone principle, makes it possible to convey 
sounds by means of a ray of light, and by means of a 
" quivering beam " to produce articulate speech at a dis- 
tance. The success of the Photophone depends upon a 
rare element, selenium, which has its "electrical resistance" 
affected by light. Professor Adams demonstrated that 
the resistance of selenium was reduced just in proportion 
as the intensity of the light which was acting upon it. 
Here was the key to the Photophone as thought out by 
Professor Belli He fancied that he might by means of 
his telephone produce sound if he could vary the intensity 
of the beam of light upon the selenium, which he con- 
nected with his telephone and battery. 

The Photophone consists of a transmitter for receiving 
the voice and conveying it along the beam of light, and 
a receiver for taking the light and converting it into 
sound — the receiver being the telephone. There is a 
small mirror (silvered mica has been used) suspended 
freely for vibration. A lens is used to transmit to this 
the beam of light, and this beam is again reflected by 
another lens to the receiver, which consists of a reflector 
which has a cell of selenium in its focus, connected, as 
already stated, with the telephone and battery. The speaker 
stands behind the mirror, and the sound of his voice against 
the reverse side makes it vibrate in unison with the sounds 
uttered. The movements cause a quivering in the reflected 
beam, and this in its changing intensity acts on the sele- 
nium, which changes its resistance accordingly, and through 
the telephone gives forth a sound ! 

This is the apparently complicated but really simple. 



POLARIZATION. I 3 3 

and at the same time wonderful, invention of Professor 
Bell. By the Photophone not only sounds but movements 
can be converted into sound ; even the burning of a candle 
can be heard! The Photophone is still capable of im- 
provement, and has not as yet arrived at its full develop- 
ment, for it is stated it can be made quite independent 
of a battery or telephone. 

There are many phenomena connected with the Polari- 
zation of Light. This requires some notice at our hands. 
We know that a ray of ordinary light is supposed to be 
caused by vibrations of the highly attenuated medium, 
aether. These vibrations occur across the direction of the 
ray; but when they occur only in one plane the light is 
said to be " polarized." Polarization means possessing 
poles (like a magnet) ; the polarized rays have " sides," as 
Newton said, or, as explained by Dr. Whewell, " opposite 
properties in opposite directions, so exactly equal as to 
be capable of accurately neutralizing each other." There 
are some crystals which possess the property of " double 
refraction," and thus a ray of common light passing through 
such a crystal is divided into two polarized rays, taking 
different directions. One is refracted according to the 
usual laws of refraction ; the other is not, and the planes 
of polarization are at right angles. It is difficult within 
the limits of this chapter to explain the whole theory of 
Polarization. In order to account for certain phenomena 
in optics, philosophers have assumed that rays possess 
polarity ; and polarized h'ght is light which has had the 
property of Polarization conferred upon it by reflection,' 
refraction, or absorption. Common light has been com- 
pared to a round ruler, and polarized light to a fiat ribbon. 
Huygens found out, when engaged upon the investigation 
of double refraction, that the rays of light, divided by 
passing through a crystal (a rhomb) of Iceland spar, 
possessed certain qualities. When he passed them through 

10 



134 OPTICAL APPARATUS. 

a second rhomb, he found that the brightness, relatively, 
of the rays depended upon the position of the second 
prism, and in some positions one ray disappeared entirely. 
The light had been reduced to vibrations in one plane. 
In I 808, Malus, happening to direct a double refracting 
prism to the windows then reflecting the sunset, found 
that as he turned the prism round, the ordinary image of 
the window nearly disappeared in two opposite positions ; 
and in tv'-i other positions, at right angles, the " extra- 
ordinary '■ image nearly vanished. So he found that 
polarization was produced by reilection as well as by 
transmission. The differences between common and 
polarized light have been summed up by Mr. Goddard 
as follows : — 

Common Light Polarized Light 
" Is capable of reflection at ob- " Is capable of reflection at ob- 
lique angles of incidence in lique angles only in certain 
every position of the reflector. positions of the reflector. 
" Will pass through a bundle of " Will only pass through such 
plates of glass in any position glasses when they are in cer- 
vix which they may be placed. tain positions. 
"Will pass through a plate of "Will only pass in certain posi- 
tourmaline, cut parallel to the tions, and in others will not 
axis of the crystal, in every pass at all." 
position of the plate." 

The bundle of glass plates or the tourmaline plate is 
thus the test for polarized light, and is termed an analyzer. 

The arrangement called a " Nichol's prism," made by 
cutting a prism of Iceland spar and uniting the halves 
with a cement, so that only one polarized ray can pass 
through it, is termed a Polarizer. It only permits one of 
the two rays produced by " double refraction " to pass, 
and the ray (as said above) will contain none but transverse 
vibrations. Polarized light will produce beautiful colours. 
The whole subject is very interesting to the scientist, but 
rather a difficult one for the general reader to understand. 



LACTOSCOPE. 135 

Amongst the uses to which light has been put is that 
of a milk-tester. The LACTOSCOPE will show the quantity 
of butter contained in a certain quantity of milk, by diluting 
it till it displays a certain degree of transparency. There 
is another method, by the transmission of light. 

The first test is obtained by means of a glass tube 
about nine inches long, closed at one end, and containing 
a small porcelain rod marked with black lines. A small 
quantity of milk is measured and placed in the tube. The 
black lines cannot at first be seen through the tube, but 
by adding water the milk is rendered transparent, and the 
black lines become visible. The surface of milk in the 
tube, by a graduated scale upon it, shows the percentage 
of butter. 

The second method is not so simple. A short tube of 
tin, blackened on the inside, and supported upright, has 
an opening on one side, and opposite this, inside the tube, 
is a mirror placed at an angle of 45°. "By placing a 
lighted candle at a known distance opposite the opening, 
its light is reflected in the mirror and thrown upward 
through the tube. On top of the tube is placed a round 
vessel of glass or metal, closed at the bottom by a sheet 
of clear glass. The vessel is closed at the top by a cover 
having an opening in the centre, in which slides up and 
down a small tube closed at the bottom with glass, and 
having an eye-piece at the top. The milk to be tested is 
placed in this vessel on the top of the tin tube, so that 
the light of the candle reflected from the mirror passes 
upward through the milk. Then, by looking through the 
sliding tube and moving it up and down, a point may be 
found where the image of the candle in the mirror can be 
seen through the milk. This device depends, as will be 
seen, on observing the light transmitted through a film of 
milk, and the thickness of- the film is the measure of the 
value of the milk. The movable tube contains a graduated 



136 



OPTICAL APPARATUS. 



scale, and by comparison of this with a printed table, the 
percentage of butter in the milk may be ascertained." 

In concluding this chapter we give a few hints for some 
pleasant relaxation for young people, which has many a 

time created amusement. 
The experiment consists 
in cutting out in paper 
or cardboard certain por- 
tions of a face or figure, 
as per the illustration 
herewith 

No. I gives the card as 
cut with the scissors, and 
the two subsequent faces 
are the result of the same 
held at a less or greater 
I distance from a screen 
I The illustrations shown 
S herewith will assist those 
3 who wish to amuse chil- 
dren by making rabbits, 
etc., on the wall, The 
shadows will be seen 
perfectly thrown if the 
hands be carefully fixed 
near a good light. 

We are all so familiar 
with the " Magic Lan- 
tern," and the apparatus 
for dissolving views by an 
arrangement of lenses and manipulation of slides, that we 
need do no more than refer to them. 

The various ghost illusions, etc., produced by indirect 
mirrors, have already been referred to, the ghost being 
merely the reflection of an individual seen through a sheet 




HAND SHADOWS. 



137 




138 OPTICAL APPARATUS. 

of glass between the spectators and the stage. The strong 
light throws a reflection from a parallel mirror lower down, 
and this reflected image can he made to appear amongst 
the real actors who are behind the plate-glass in full view 
of the audience, who are, however, ignorant of the existence 
of the glass screen. 

For the winter evenings one may easily procure an 
apparatus for dissolving views by the oxy-hydrogen light. 
One, as shown in the illustration herewith (see opposite 
page), will answer every purpose, and by this double arrange- 
ment phantasmagoria may be produced, or a fairy tale may 
be illustrated. The effect of gradually-approaching night 
may be given to the picture by means of a special glass 
in the lower lanthorn. The apparatus is exhibited by 
means of a Drummond light, and is very simple, although 
a certain supply of gas is necessary for the performance. 
But this can be easily procured by an indiarubber tube, 
or in a bag supplied for the purpose. Almost any objects 
can be used, photographs, etc., etc., and many very comical 
arrangements can be made. 

We have -lately ^een reading a curious method of 
■obtaining light from oyster-shells in a Trans-Atlantic 
magazine. We give an extract wherewith to close this 
chapter. The compound is " luminous paint." 

" It has been known that certain compounds of lime 
and sulphur had the property of absorbing light, and giving 
it out again when placed in the dark. A simple way to 
do this is to expose clean oyster-shells to a red heat for 
half an hour. When cold, the best pieces are picked out 
and packed with alernate layers of sulphur in a crucible, 
and exposed to a red heat for an hour. When cold, the 
mass is broken up, and the whitest pieces are placed in 
a clean glass bottle. On exposing the bottle to bright 
sunshine during the day, it is found that at night its 
contents will give out a pale light in the dark. Such a 



GHOST ILLUSION. 



139 




140 OPTICAL APPARATUS. 

bottle filled more than a hundred years ago still gives out 
light when exposed to the sun, proving the persistency 
of the property of reproducing light. Very many experi- 
ments have been more recently made in this direction, 
and the light-giving property greatly enhanced. The 
chemicals, ground to a flour, may now be mixed with 
oils or water for paints, may be powdered on hot glass, 
and glass covered with a film of clear glass, or mixed 
with celluloid, papier-mache, or other plastic materials. 
As a paint, it may be applied to a diver's dress, to cards, 
clock dials, signboards, and other surfaces exposed to 
sunlight during the day ; the paint gives out a pale violet 
light at night sufficient to enable the objects to be readily 
seen in the dark. If the object covered with the prepared 
paint is not exposed to the sun, or if the light fades in 
the dark, a short piece of magnesium wire burned before 
it serves to restore the light-giving property." 





CHAPTER VIII.— SPECTRAL ILLUSIONS. 

A SPECTRE VISIBLE CURIOUS ILLUSIONS GHOSTS. 

E have already given numerous examples of the 
effects produced by impressions on the retina 
by mechanical appliances. We can now in a 
short chapter speak of the cause of many 
spectral illusions, commonly supposed to be " ghosts " or 
" spirits." That there are many " well-authenticated 
' ghost stories ' " no one can doubt who has read the 
literature of the day ; and we ourselves do not in any 
way desire to throw any doubt upon the existence of 
certain so-called " ghosts." That appearances of some 
kind or another are seen by people we know. We our- 
selves hava seen such, but we cannot say we believe in 
the popular ghost. 

In ancient times mirrors were much employed by the 
so-called magicians, and in our day many wonderful ghost 
effects have been shown at the (late) Polytechnic Institu- 
tion. Some people are believers in table-turning and 
spiritualism, and mesmerists still attract large audiences, 
and appear to possess extraordinary power over some 
individuals. But apparitions have been seen by people 
eminently worthy of credit. The experience of the learned 
Doctor, which appeared some time ago in the Athencemn, 
is a case in point. This narrative is concise and clear. 
The spectre was there. How did it get there .? Was 



142 SPECTRAL ILLUSIONS. 

the " appearance " objective or subjective ? Let us give 
an extract from the Reverend Doctor's narrative, and 
comment upon it afterwards. We may premise that Dr 
Jessopp had gone over to Lord Orford's (Mannington 
Hall), and at eleven o'clock was busy writing in the library, 
and was " the only person downstairs." We will give this 
ghost story in the Doctor's own words. After taking up 
a certain volume — time about i a.m. : — 

" I had been engaged on it about half an hour, and 
was beginning to think my work was drawing to a close, 
when, as I was actually writing, I saw a large white 
hand within a foot of my elbow. Turning my head, there 
sat a figure of a somewhat large man with his back to 
the fire, bending slightly over the table, and apparently 
examining the pile of books that I had been at work 
upon." . . . After describing the appearance of the noc- 
turnal visitor. Dr. Jessopp proceeds : — • 

" There he sat, and I was fascinated ; afraid not of his 
staying, but lest he should go. Stopping in my writing 
I lifted my left hand from the paper, stretched it out to 
the pile of books, an-d moved the top one — my arm passed 
in front of the figure, and it vanished." ^ . . Shortly 
after the figure appeared again, and " I was penning a 
sentence to address to him, when I discovered I did not 
dare to speak. I was afraid of the sound of my own 
voice ! There he sat, and there sat I. I turned my 
head and finished writing. Having finished my task, I 
shut the book, and threw it on the table; it made a 
slight noise as it fell ; — the figure vanished." 

Now here we have a perfectly plain narrative, cleai" and 
full, A ghost appeared ; he is described distinctly. How 
can we account for the apparition ? In the first place, 
someone might have played a trick, but that idea was 
put aside by Dr. Wilks, who attempted to explain the 
appearances. He went fully into the question, and as it 



GHOSTS. 143 

bears upon our explanation of the reality of Spectral 
Illusions, we may condense his evidence. It will of course 
be conceded that all the usual objects seen by people are 
material, and the image of what we look at is formed 
upon the retina in the manner already explained. But 
a// images upon the retina are not immediately observed; 
the impression may, to a certain extent, remain. Words 
are often impressed upon the brain, — words which we in 
our sober senses would never think of repeating, — and 
yet when we are delirious we give vent to these expres- 
sions, of whose very nature and meaning we are perfectly 
unconscious. It is, according to our reference (Dr. Wilks), 
"quite possible for the perceptive part of the brain to be 
thrown into an active condition quite independent of the 
normal stimulus conducted to it from the retina." If, 
under these circumstances, an object be viewed indepen- 
dently, and, as it were, unconsciously, it is merely, we 
believe, a parallel to the impression of words before 
noted. Sound and light are governed by the same laws. 
In fevers we fancy we see all kinds of things which 
have no existence. In dreams we hear noises ; and 
many a time people dreaming have been awakened by 
the report of a gun, or the ringing of a bell which had 
no material origin, — the nerves were excited, the "per- 
ceptive centre" of the brain was moved. 

But if sight and hearing thus have their origin from 
the brain and not from without, there must have been 
some predisposing cause, some excitement to induce such 
a condition of things. "The impressions become abnormal 
and subjective, — the normal condition being objective, — 
the impression is received from without, and impressed 
upon the eye. 

Now, let us consider the " ghost " ! Lately there have 
been many instances brought forward of "spiritual" appear- 
ances, but we" think nobody has ever seen a "material" 



144 SPECTRAL ILLUSIONS. 

ghost ; yet on the other hand none of us have any know- 
ledge of anything in the likeness of a ghost, or that has 
not a material basis which can bring forward an image on 
the retina ! Therefore we are brought to the conclusion 
that apparitions are spectres emanating from within the 
brain, not from any outward manifestation, because it is 
within the experience of everybody that in bad health, or 
disordered digestive functions, images are produced in the 
brain and nerves of the eye. 

These remarks have perhaps been made before in one 
form or other, but as much popular interest is always 
awakened by the supernatural, or what is supposed to be 
supernatural, we may go a little farther, and inquire how 
it was that the ghost seen by Dr. Jessopp disappeared 
when he raised his arm. Would any ghost be afraid of 
the Doctor extending his hand .' The fact no doubt 
occurred as related. The explanation is that the narrator 
had been much impressed by a certain picture, which a 
correspondent soon identified as a portrait of " Parsons, 
the Jesuit Father." The description given is that of the 
priest who was described by the Doctor in one of his 
books. The association of ideas in the library of a 
Norfolk house connected with the Walpoles, with whom 
Parsons had been a leader, gave rise, during a period of 
" forty winks " at midnight, to the spectre. 

In the interesting letters written upon "Natural Magic" 
by Sir David Brewster, the subject of Spectral Illusions 
is treated at some length, and with undoubted authority. 
Sir David thought the subject worth discussing with 
reference to the illusions or spectres mentioned by Dr. 
Hibbert. Sir David Brewster gives his own experiences 
which occurred while he was staying at the house of a 
lady in the country. 

The illusions appear to have affected her ear as well as 
the eye. We shall see in the next chapter how intimately 



GHOSTS. 145 

sound and light are connected, and how the eyes and ears 
are equally impressed, though in a different way, by the 
vibration of particles. The lady referred to was about to 
go upstairs to dress for dinner one afternoon, when she 
heard her husband's voice calling to her by name. She 
opened the door, and nobody was outside ; and when she 
returned for a moment to the fire she heard the voice 
again calling, "Come to me; come, come away," in a 
somewhat impatient tone. She immediately went in search 
of her husband, but he did not come in till half an hour 
afterwards, and of course said he had not called, and told 
her where he had been at the time — some distance away. 
This happened on the 26th December, 1830, but a more 
alarming occurrence took place four days after. 

About the same time in the afternoon of the 30th 
December, the lady came into the drawing-room, and to 
her great astonishment she perceived her husband standing 
with his back to the fireplace. She had seen him go out 
walking a short time previously, and was naturally sur- 
prised to find he had returned so soon. He looked at 
her very thoughtfully, and made no answer. She sat 
down close beside him at the fire, and as he still gazed 
upon her she said, " Why don't you say something ! " 
The figure immediately moved away towards the window 
at the farther end of the room, still gazing at her, " and 
it passed so close that she was struck by the circumstance 
of hearing no step nor sound, nor feeling her dress brushed 
against, nor even any agitation of the air." Although 
convinced this was not her husband, the lady never fancied 
there was anything supernatural in the appearance of the 
figure. Subsequently she was convinced that it was a 
spectral illusion, although she could not see through the 
figure which appeared as substantial as the reality. 

Were it advisable, we could multiply instances. In the 
Edinburgh Journal of Science these, and many more in- 



146 SPECTRAL ILLUSIONS. 

stances of spectral illusions were narrated by the husband 
of the lady. She frequently beheld deceased relatives or 
absent friends, and described their dress and general 
appearance very minutely. On one occasion she perceived 
a coach full of skeletons drive up to the door, and noticed 
spectral dogs and cats (her own pets' likenesses) in the 
room, There can be no doubt upon these points ; the 
appearances were manifest and distinct. They were seen 
in the presence of other people, in solitude, and in the 
society of her husband. The lady was in delicate health, 
and very sensitive. The spectres appeared in daylight as 
well as in the dark, or by candle-light. 

Let us now, guided by what we have already written, 
and by Sir David Brewster's experience, endeavour to 
give a rational explanation of these illusions. "The 
mind's eye is really the body's eye, and the retina is the 
common tablet upon which both classes of impressions 
are painted, and by means of which they receive their 
visual existence according to the same optical laws." 

" In the healthy state of mind and body the relative 
intensity of the two classes of impressions on the retina 
are nicely adjusted — the bodily and mental are balanced. 
The latter are feeble and transient, and in ordinary 
temperaments are never capable of disturbing or effacing 
the direct images of visible objects. . . . The mind cannot 
perform two different functions at the same instant, and 
the direction of its attention to one of the two classes 
of impressions necessarily produces the extinction of the 
other; but so rapid is the exercise of mental power, that 
the alternate appearance and disappearance of the two 
contending impressions is no more recognized than the 
successive observations of external objects during the 
twinkling of the eyelids." 

We have before illustrated, by means of the pen and 
the ink-bottle, how one object is lost sight of when the 



SPECTRES. 147 

other is attentively regarded, and a material picture or 
scene may be equally lost sight of, and a mental picture 
take its place in the eye, when we recall places or people 
we have seen or remembered. 

We have all heard numerous anecdotes of what is 
termed "absent-mindedness." Some people are quite 
absorbed in study, and can see or hear no one in the 
room when deeply occupied. We may be satisfied then 
that "pictures of the mind and spectral illusions are 
equally impressions upon the retina, and only differ in 
the degree of vividness with which they are teen." If 
we press our eyes the phosphorescence becomes apparent, 
and we can make a picture of the sun or a lamp visible 
for a long time to our closed eyes if we stare at either 
object for a few seconds, and shut our lids. So by in- 
creasing the sensibility of the retina we can obtain the 
image, and alter its colour by pressure on the eye. 

It is well known that poisons will affect sight, and 
belladonna applied to the eyes will so affect them as to 
render the sight nil, by enlargement of the "pupil." If 
one is out of health there is practically a poisoning of 
the system, and when we have a " bilious headache " we 
see colours and stars because there is a pressure upon the 
blood-vessels of the eye. The effects of a disordered 
stomach, induced by drinking too much, are well known ; 
objects are seen double, and most ghosts may be traced 
to a disordered state of health of mind or body, brought 
on by excitement or fatigue. We could relate a series 
of ghost stories, — some in our own experience, for we 
have seen a ghost equally with our neighbours, — but this 
is not the place for them. Although many apparently 
incontrovertible assertions are made, and many spectres 
have been produced to adorn a tale, we must put on 
record our own opinion, that every one could be traced 
to mental impression or bodily affection had we only 



148 SPECTRAL ILLUSIONS. 

the key to the life and circumstances of the ghost-seer. 
Many celebrated conjurers will convince us almost against 
our reason that our pocket-handkerchief is in the orange 
just cut up. They will bring live rabbits from our coat- 
pockets or vests, and pigeons from our opera-hats. These 
are equally illusions. We know what ean be done with 
mirrors. We have seen ghosts at the Polytechnic, but we 
must put down all apparitions as the result of mental or 
bodily, even unconscious impressions upon the retina of 
the eye. There are numerous illusions, such as the Fata 
Morgana, the Spectre of the Brocken, etc., which are due 
to a peculiar state of the atmosphere, and to the unequal 
reflection and refraction of light. Those, and many other 
optical phenomena, will, with phenomena of heat and 
sound, be treated under METEOROLOGY, when we will 
consider the rainbow and the aurora, with many other 
atmospheric effects. 





CHAPTER IX.— ACOUSTICS. 



THE EAR, AND HEARING PHYSIOLOGY OF HEARING AND 

SOUND SOUND AS COMPARED WITH LIGHT WHAT 

IS SOUND ? — VELOCITY OF SOUND — CONDUCTIVITY 
— THE HARMONOGRAPH. 

^EFORE entering upon the science of ACOUSTICS, 
a short description of the ear, and the mode in 
which sound is conveyed to our brain, will be 
no doubt acceptable to our readers. The study 
of the organs of hearing is not an easy one; although 
we can see the. exterior portion, the interior and delicate 
membranes are hidden from us in the very hardest bone 
of the body — the petrous bone, the temporal and rock-like 
bone of the head. 

The ear (external) is composed of the auricle, the 
visible ear, the auditory canal, and the drum-head, or 
membrana tympani. The tympanum, or " drum," is situated 
between the external and the internal portions of the ear. 
This part is the " middle ear," and is an air cavity, and 
through it pass two nerves, one to the face and the other 
to the tongue. The internal ear is called the " labyrinth," 
from its intricate structure. We give an illustration of the 
auditory apparatus of man. 

The auricle, or exterior ear, is also represented, but we 
need not go into any minute description of the parts. We 
will just name them. 

Sound is the motion imparted to tV..* auditory nerve, 



I50 



SOUND. 



and we shall see in a moment how sound is produced. 
The undulations enter the auditory canal, having been 
taken up by the auricle ; the waves or vibrations move at 
the rate of i,ioo feet a second, and reach the drum-head, 
which has motion imparted to it. This motion or oscilla- 
tion is imparted to other portions, and through the liquid 




I . Temple bone. 2. Outer surface of temple. 3. Upper wall of bony part 
of hearing canal. 4. Ligature holding " hammer" bone to roof of drum 
cavity. 5. Roof to drum cavity. 6. Semi-circular canals. 7. Anvil 
bone. 8. Hammer bone. 9. Stirrup bone. 10. Cochlea. 11. Drum- 
head cut across. 12. Isthmus of Eustachian tube. 13. Mouth of tube 
in the throat. 14. Auditor^' canal. 15. Lower wall of canal. 16. Lower 
wall of cartilaginous part of canal. 17. Wax glands. 18. Lobule. 
19. Upper wall of cartilaginous portion of canal. 20. Mouth of auditory 
canal. 21. Anti-tragus. 

in the labyrinth. The impressions of the sound wave are 
conveyed to the nerve, and this perception of the move- 
ment in the water of the labyrinth by the nerve threads 
and the brain causes what we term "hearing." 

Let us now endeavour to explain what sound is, and 
how it arises. There are some curious parallels between 
sound and light. When speaking of light we mentioned 



MUSIC AND NOISE. 15 I 

some of the analogies between sound and light, and as 
we proceed to consider sound, we will not lose sight o( 
the light we have just passed by. 

Sound is the influence of air in motion upon the hearing 
or auditory nerves. Light, as we have seen, is the ether 
in motion, the vibrations striking the nerves of the eye. 

There are musical and unmusical sounds. The former 
are audible when the vibrations of the air reach our 
nerves at regular intervals. Unmusical sounds, or irregular 




L. Pit of anti-helix, a, 6, lo. Curved edge of the auricle, 3. Mouth of auditory 
canal. 4. Tragus. 5. Lobe. 7. Anti-helix. 8. Concha. 9. Anti-tragus. 

vibrations, create noise. Now, musical tones bear the same 
relation to the ear as colours do to the eye. We must 
have a certain number of vibrations of ether to give us a 
certain colour (vide page 47). " About four hundred and 
fifty billion impulses in a second " give red light. The 
violet rays require nearly double. So we obtain colours 
by the different rate of the impingement of impulses on 
the retina. The eyes, as we have already learned, cannot 
receive any more rapidly-recurring impressions than those 
producing violet, although as proved, the spectrum is by 



I $2 SOUND. 

no means exhausted, even if they are invisible. In the 
consideration of Calorescence we pointed this out. These 
invisible rays work great chemical changes when they get 
beyond violet, and are shown to be heat. So the rays 
which do not reach the velocity of red rays are also heat, 
which is the effect of motion. 

Thus we have HEAT, Light, and Sound, all the 
ascertained results of vibratory motions. The stillness of 
the ether around us is known as " Darkness " ; the stillness 
of the air is " Silence " ; the comparative absence of heat, 
or molecular motion of bodies is " Cold"! 

In the first part we showed how coins impart motion 
to each other. When an impulse was given the motion 
was carried from coin to coin, and at length the last one 
in the row flew out. This is the case with sound. The 
air molecules strike one upon another, and the wave of 
" sound" reaches the tympanum, and thus the impression 
is conveyed to the brain. We say we hear — but why 
we hear, in what manner the movement of certain particles 
effects our consciousness, we cannot determine. 

That the air is absolutely necessary to enable us to hear 
can readily be proved. The experiment has frequently 
been made ; place a bell under the receiver of an air- 
pump, and we can hear it ring. But if we exhaust the 
air the sound will get fainter and fainter. Similarly, as 
many of us have experienced upon high mountains, sounds 
are less marked. Sound diminishes in its intensity, just 
as heat and light do. Sound is reflected and refracted, 
as are light and radiant heat. We have already shown 
the effect of reflectors upon heat. Sound is caught and 
reflected in the same way as light from mirrors, or as the 
heat waves in the reflectors. We have what we term 
" sounding boards " in pulpits, and speaking tubes will 
carry sound for us without loss of power. Echoes are 
merely reflected sounds. 



Velocity o¥ sound. ts3 

The velocity of sound is accepted as 1,100 feet in a 
second, which is far inferior to the velocity of light. 
Fogs will retard sound, while water will carry it. Those 
who have ever rowed upon a lake will remember how 
easily the sound of their voices reached from boat to boat, 
and Dr. Hutton says that at Chelsea, on the Thames, he 
heard a person reading from a distance of a hundred and 
forty feet. Some extraordinary instances could be deduced 
of the enormous distances sound is said to have travelled. 
Guns have been heard at eighty miles distant, and the 
noise of a battle between the English and Dutch, in 1672, 
was heard even in Wales, a distance of two hundred miles 
from the scene of action. 

Sound always travels with uniform velocity in the air 
in the same temperature. But sound ! What is the cause 
of it .' How does it arise ? These questions can now be 
fully answered with reference to the foregoing observations. 
Phenomena of vibration render themselves visible by light, 
heat, and sound, and to arrive at some definite ideas of 
sound vibrations we may compare them to waves, such as 
may be produced by throwing a stone into a pond. 

There are, so to speak, " standing " waves and " pro- 
gressive" waves. The former can be produced (for 
instance) by thrumming a fiddle-string, and when the 
equilibrium of the cord is disturbed, the position of the 
equilibrium is passed simultaneously by the string-waves. 
In water the waves or vibrating points pass the position 
of equilibrium in succession. 

Waves consist of elevations and depressions alternately, 
and when we obtain two " systems " of waves by throwing 
two stones into water, we can observe some curious effects. 
It can be seen how one series of depressions will come 
in contact with the other series of depressions, and the 
elevations will likewise unite with the result of longer 
depressions and elevations resnprf-i^oi" • or it may very 



154 SOUND. 

well be that elevation will meet depression, and then the 
so-called " interference " of waves will produce points of 
repose. These points are termed nodes. The waves of 
the string proceed in the plane of its axis ; water waves 
extend in circles which increase in circumference. 

The progression or propagation of sound may be said 
to begin when some tiny globule of matter expands in 
the air. The air particles strike one against the other, 
and so the motion is communicated to the air waves, 
which in time reach the ear. But the velocity of the 
sound is not equal in all substances. Air will convey 
it around our earth at the rate of 765 miles an hour, or 
1,090 feet in a second. That is, we may accept such 
rate as correct at a temperature of 32° Fahr., and at a 
pressure of thirty inches, and the velocity increases almost 
exactly one foot per second for each degree of tempera- 
ture above 32°. Therefore on an average, and speaking 
in "round numbers," the estimate of 1,100 feet in a 
second may be accepted as correct. In hydrogen gas the 
rate is much higher. Through water again it is different, 
and still faster through iron, glass, and wood, as will be 
seen in the following table : — 



TAKING AIR AS I 

Whalebone .... 6f 

Tin 7i 

Silver 9 

Walnut lof 

Brass lof 

Oak lof 

Earthen pipes ....11 

Copper 12 



I'ear-wood \2\ 

Ebony \^\ 

Cherry 15 

Willow 16 

Glass i6| 

Iron or Steel .... i6f 

Deal 18 



So there is a considerable difference in the velocities of 
sound through the solid substances quoted, but these figures 
cannot be taken as exact, as different samples may give 
different results. In wires and bells the bodies themselves 



VIBRATION, 155 

produce the sounds we hear. In wind instruments and the 
voice the air is the cause of the sound. 

The very deepest notes are produced by the fewest 
vibrations. Fourteen or fifteen vibrations will give us a 
very low note, if not the very lowest. The pipe of sixteen 
feet, closed at its upper end, will produce sound waves of 
thirty-two feet. High notes can be formed from vibrations 
up to 48,000 in a second. Beyond these limits the ear 
cannot accept a musical sound. 

We will explain the phenomenon of the vibration of 
strings by means of the illustration. In the cut we find 
a string or wire, which can be lengthened or shortened 




The vibration. 

at pleasure by a movable bridge, and stretched by weights 
attached to the end. 

We can now easily perceive that the shorter and thinner 
the string is, and the tighter it is the number of vibrations 
will be greater and greater. The density of it is also to 
be considered, and when these conditions are in the 
smallest proportion then the tone will be highest. The 
depth will naturally increase with the thickness, density, 
and length, and with a decreasing tension. But we have 
strings of same thickness stretched to different degrees of 
tension, and thus producing different notes. Some strings 
are covered with wire to iricrease their gravity, and thus 
to produce low notes. 

When a number of separate sound?; succeed each other 



156 SOUND. 

in very rapid course they produce a sound, but to appear 
as one sound to the ear they must amount to fifteen or 
sixteen vibrations every second. The particles of matter 
in the air form a connected system, and till they are 
disturbed they remain in equilibrium; but the moment 
they are in any way thown out of this state they vibrate 
as the pendulum vibrates. The particles thus strike each 
other, and impart a motion to the elastic medium ether, so 
a sound comes to us. 

The intensity of sounds gets less the farther it goes 
from us, or the loudness of sound is less the greater its 
distance. The law is, that in an unvarying medium the 
loudness varies inversely as the square of the distance. 
But Poisson has shown that when air-strata, differing in 
density, are existing between the ear and the source of 
the sound, the intensity or loudness with which it is heard 
depends only on the density of the air at the place the 
sound originated. This fact has been substantiated by 
balloonists who heard a railway whistle quite distinctly 
when they were nearly 20,000 feet above the ground. 
It therefore follows that sound can be heard in a balloon 
equally well as on the earth at certain given distances. 
But as the density of the air diminishes the sound becomes 
fainter, as has been proved by the bell rung in the receiver 
of an air-pump. The velocity of sound, to a certain 
extent, depends upon its intensity, as Earnshaw sought 
to prove ; for he instanced a fact that in the Arctic regions, 
where sound can be heard for an immense distance, in 
consequence of the still and homogeneous air, the report 
of a cannon two miles and a half away was heard before 
the loud command to " fire," which must have preceded 
the discharge. Another instance showing the difference 
in hearing through mixed and homogeneous media may 
be referred to. In the war with America, when the English 
and their foes were on opposite sides of a stream, an 



ECHOES. 157 

American was seen to beat his drum, but no sound came 
across. " A coating of soft snow and a thick atmosphere 
absorbed the noise." Glazed, or hard snow, would have 
a contrary effect. Reynault also experimentally verified 
his theory, that sound when passing through a space of 
nearly 8,ooo feet lost velocity as its intensity diminished, 
and in that distance between its arrival at 4,000 feet 
and at 7,5oo"feet, the sound velocity diminished by 2'2 
feet per second. He also tried to demonstrate that sound 
velocity depended upon its pitch, and that lower notes 
travelled with the greater speed. 

The reflection and refraction of sound follows the same 
fundamental laws as the reflection and refraction of light. 
The reflection of sound is termed an Echo, which is familiar 
to all tourists in Switzerland and Ireland particularly. 
There are several very remarkable echoes in the world : 
at Woodstock, and at the Sicilian cathedral of Gergenti, 
where the confessions poured forth near the door to 
priestly ears were heard by a man concealed behind the 
high altar at the opposite end. It is curious that such 
a spot should have been accidentally chosen for the Con- 
fessional. The whispering gallery in St. Paul's is another 
instance of the echo. 

Echoes are produced by the reflection of sound waves 
from a plane or even surface. A wall, or even a cloud, 
will produce echoes. Thunder is echoed from the clouds. 
(The celebrated echo of " Paddy Blake," at Killarney, 
which, when you say "How do you do," is reported to 
reply, "Very well, thank you," can scarcely be quoted as 
a scientific illustration.) And the hills of Killarney con- 
tain an echo, and the bugle sounds are beautifully repeated. 
In the cases of ordinary echo, when the speaker waits for 
the answer, he must place himself opposite the rock. If he 
stand at the side the echo will reply to another person 
in a corresponding place on the farther side, for the voice 



158 SOUND. 

then strikes the rock at an angle, and the angle of reflec- 
tion is the same, as in the case of light. 

But if it should happen that there are a number of 
reflecting surfaces the echo will be repeated over and over 
again, as at the Lakes of KiUarney. The Woodstock 
Echo, already referred to, and mentioned by several 
writers, repeats seventeen syllables by day, and twenty 
by night. In Shipley there is even a greater repetition. 
Of course the echo is fainter, because the waves are 
weaker if the reflecting surface be flat. But, as in the 
case of the mirrors reflecting light, a circular or concave 
surface will increase the intensity. A watch placed in 
one mirror will be heard ticking in the other focus. 
Whispering galleries carry sound by means of the curved 
surface. Sir John Herschel mentions an echo in the 
Menai Suspension Bridge. The blow of a hammer on 
one of the main piers will produce the sound from each 
of the crossbeams supporting the roadway, and from the 
opposite pier 576 feet distant, as well as many other 
repetitions. 

Refraction of sound is caused by a wave of sound 
meeting another medium of different density, just as a 
beam of light is refracted from water. One sound wave 
imparts its motion to the new medium, and the new 
wave travels in a different direction. This change is 
refraction. The sound waves are refracted in different 
directions, according to the velocity they can acquire in the 
medium. If a sound pass from water into air it will be 
bent towards the perpendicular, because sound can travel 
faster in water than in air. If it pass from air into water 
its force will cause it to assume a less perpendicular 
•direction, there being greater velocity in water. The 
velocity in air is only 1,100 feet in a second in our 
atmosphere. In water sound travels 4,700 feet in the 
sane time. When the wave of sound falls upon a 



VIBRATORY CURVES. 159 

medium parallel to the refracting surface there is, however, 
no refraction — only a change of velocity, not direction. 

When sound waves are prevented from dispersing the 
voice can be carried a great distance. Speaking tubes 
and trumpets, as well as ear trumpets, are examples of 
this principle, and of the reflection of sound. 

There are many very interesting experiments in con- 
nection with Acoustics, some of which we will now impart 
to our readers. We shall then find many ingenious inven- 
tions to examine, — the Audiphone, Telephone, Megaphone, 
and Phonograph, which will occupy a separate chapter. 
We now resume. 

Amongst the experiments usually included in the course 
of professors arid lecturers, who have a complete apparatus 
at their command, and which at first appear very compli- 
cated and difficult, there are some which can be performed 
with every-day articles at hand. There is no experiment 
in acoustics more interesting than that of M. Lissajons, 
which consists, as is well known to our scientists, of 
projecting upon a table or other surface, with the aid of 
oxy-hydrogen light, the vibratory curves traced by one 
of the prongs of a tuning-fork. We can perform without 
difficulty a very similar experiment with the humble 
assistance of the common knitting-needle. 

Fix the flexible steel needle firmly in a cork, which 
will give it sufficient support ; fasten then at the upper 
extremity a small ball of sealing wax, or a piece of paper 
about the size of a large pea. - If the cork in which the 
needle is fixed be held firmly in one hand, and you cause 
the needle to vibrate by striking it, and then letting it 
sway of itself, or with a pretty strong blow with a piece 
of wood, you will perceive the little pellet of wax or paper 
describe an ellipse more or less elongated, or even a circle 
will be described if the vibrations be frequent. The effect 
is much enhanced if the experiment be performed beneath 



i6o 



SOUND. 



a lamp, so that plenty of light may fall upon the vibrating 
needle. In this case, the persistence of impressions upon 
the retina admits of one seeing the vibrating circle in 
successive positions, and we may almost fancy when the 
needle is struck with sufficient force, that an elongated 




Experiment showing vibration of sound waves. 

conical glass, like the old form of champagne glass, is 
rising from the cork, as shown in the illustration annexed. 
Acoustics may be studied in the same way as other 
branches of physical science. We will describe an in- 
teresting experiment, which gives a very good idea of the 
transmission of sounds through solid bodies. A silver 



CONDUCTION. 



i6i 



spoon is fastened to a thread, the ends of which are 
thrust into both ears, as shown in the illustration ; 
we then slightly swing the spoon until we make it touch 
the edge of the table ; the transmission of sound is in 
consequence so intense that we are ready to believe we 




Conduction of sound by solid bodies. 

are listening to the double diapason of an organ. This 
experiment explains perfectly the transmission of spoken 
words by means of the string of a telephone, another 
feontrivance which any one may make for himself without 
any trouble whatever. Two round pieces of cardboard are 
fitted to two cylinders of tin-plate, as large round as a 



1 62 



SOUND. 



lamp-glass, and four-and-a-half inches in length. If the 
two rounds of cardboard are connected by a long string 
of sixteen to eighteen yards, we can transmit sounds from 
one end to the other of this long cord ; the speaker 




pronouncing the words into the first cylinder, and the 
listener placing his ear against the other. It is easy to 
demonstrate that sound takes a certain time to pass from 
one point to another. When one sees in tne distance a 
carpenter driving in a stake, we find that the sound pro- 



HARMONOGRAPH. 163 

duced by the blow of the hammer against the wood only 
reaches the ear a few seconds af^er the contact of the 
two objects. We see the flash at the firing of a gun, 
before hearing the sound of the report — of course on the 
condition that we are at a fairly considerable distance, as 
already remarked upon. 

We can show the production of the Gamut by cutting 
little pieces of wood of different sizes, which one throws 
on to a table; the sounds produced vary according to the 
size of the different pieces. The same effect may be 
obtained much better by means of goblets more or less 
filled with water ; they are struck with a short rod, and 
emit a sound which can be modified by pouring in a 
greater or less quantity of water ; if the performer is 
gifted with a musical ear, he can obtain, by a little 
arrangement, a perfect Gamut by means of seven glasses 
which each give a note. {See illustration.) A piece of 
music may be fairly rendered in this manner, for the 
musical glasses frequently produce a very pure silvery 
sound. We will complete the elementary principles of 
acoustics by describing a very curious apparatus invented 
by M. Tisley, the HARMONOGRAPH. This instrument, 
which we can easily describe, is a most interesting object 
of study. The Harmonograph belongs to mechanics in 
principle, and to the science of acoustics in application. 
We will first examine the apparatus itself. It is composed 
of two pendulums, A and B {see page 164), fixed to 
suspensions. Pendulum B supports a circular plate, P, on 
which we may place a small sheet of paper, as shown in 
the illustration. This paper is fixed by means of small 
brass clips. Pendulum A supports a horizontal bar, at 
the extremity of which is a glass tube, T, terminating at 
its lower extremity with a capillary opening ; this tube 
is filled with aniline ink, and just rests on the sheet of 
paper; the support and the tube are balanced by a 



164 



SOUND. 



counterpoise on the right. The two pendulums, A and B, 
are weighted with round pieces of lead, which can be 
moved at pleasure, so that various oscillations may be 
obtained. The ratio between the oscillations of the two 
pendulums may be exactly regulated by means of pen- 




M. Tiblcy s Harmonograpli. 

dulum A carrying a small additional weight, the height 
small wmdiass. If we give to pendulum A a slight move- 
iTne on ^r" "°"' *' P°'"^ '"' ^"t.^ ^ traces a straight 

B the n P^" P''-^^^ '■" ^ ■' ^"t ^f -- -°ve pendulum 
B, the paper also is displaced, and the point of tube T w^ 
trace curves, the shape of which varies with the nature of 



CURVES. 



t6s 



the movement of pendulum B, the relation between the 
oscillations of the two pendulums, etc. If the pendulums 
oscillate without any friction the curve will be clear, and 
the point will pass indefinitely over the same track, but 
when the oscillations diminish, the curve also diminishes 
in size, still preserving its form, and tending to a point 
corresponding with the position of repose of the two 
pendulums. The result is therefore that the curves traced 





Ratio 1 : 2. 



Ratio 2 ; 3. 



by the apparatus, of which we produce three specimens 

■(see cuts above, and page i66), are traced in a continuous 

^stroke, commencing with the part of the greatest amplitude. 

' By changing the relation and phases of the oscillations 

we obtain curves of infinitely varied aspect. M. Tisley 
-has a collection of more than three thousand curves, which 

we have had occasion to glance over, in which we failed 
• to meet with two corresponding figures. The ratio between 

these curves corresponds with some special class, of which 

the analyst may define the general characters, but which 



12 



1 66 



SOUND. 



is outside our present subject. By giving the plate P a 
rotatory movement, we obtain spiral curves of a very 
curious effect, but the apparatus is more complicated. 
Considered from this point of view it constitutes an in- 




Ratio 1 : 2 and a fraction. 



teresting mechanical apparatus, showing the combination 
of oscillations, and resolving certain questions of pure 
mechanics. From the point of view of acoustics it consti- 
tutes a less curious object of study. The experiments of 



j: 



if 



^ 1 




=J 

1 „,. 




•.■ M 




«M 




.-. Hi, 







Construction of the Harmonograph. 

M. Lissajons have proved that the vibrations of diapasons 
are oscillations similar to, though much more rapid than 
those of the pendulum. We can therefore with this 
apparatus reproduce all the experiments of M. Lissajons, 
with this difference, that the movements being slower are 
easier to study. When the ratio between the number bf 



THE HARMONOGRAPH. 



1^7 



vibrations — we purposely use the term vibration instead 
of the term oscillation — is a whole number, we obtain 
ratios 1:2, and 2:3 {see page 165). If the ratio is 
not exact, we obtain figures on page 166, which is rather 
irregular in appearance, corresponding to the distortions 
noticeable in M. Lissajon's experiments. The first illus- 
tration has been traced in . the exact ratio 1:2; the 
second cut in the ratio 2:3; and the third corresponds 
to the ratio 1:2 and a small fraction, which causes the 
irregularity of the figure. 




^ 



n 



^TL 





Method of constructing an Harmonograph. 

In considering the harmony of the two first figures, — 
the first of which corresponds to the octave, the second 
to the fifth, whilst the third figure corresponds to the 
disagreeable interval of the ninth, — one is almost tempted 
to put a certain faith in the fundamental law of simple 
ratios as the basis of harmony. At first sight this appea-rs 
beyond doubt, but perhaps musicians would be hardly 
content with the explanation. M. Tisley's Harmonograph, - 
it will be seen, is a rather complicated apparatus ; and I 
will now explain how it may be constructed by means of 
a ie:'W pieces of wood. I endeavoured to construct as 
simple an apparatus as possible, and with the commonest 



1 68 



SOUND. 



materials, feeling that it is the best means of showing how 
it is possible for everybody to reproduce these charming 
curves of musical intervals. Also I completely excluded 
the employment of metals, and I constructed my apparatus 
entirely with pieces of wooden rulers, and old cigar boxes. 
I set to work in the following manner : on the two con- 
secutive sides of a drawing board I fixed four small pieces 
of wood {see cut, page 167), side by side in twos, having 
at the end a small piece of tin-plate forming a groove 




The apparatus completed. 

as in the cut above. In these grooves nails- are placod 
which support the pendulums. The piece of wood is 
placed on the corner of the table, so that the pendulums 
which oscillate in two planes at right angles, are in two 
planes that are sensibly parallel to the sides of the table. 
The pendulums are made of a thin lath, with two small 
pieces of wood fixed to them containing some very pointed 
nails, on which the pendulum oscillates. 

Page 167 gives us an illustration. The pendulums havea 
pin fixed in vertically, which passes through a piece of wood, 
and by means of a hinge connects the upper ends of the 



DETAILS OF HARMONOGRAPH. 



169 



two pendulums. This contrivance of the pin is very 
useful, and if care is taken to make the hole through the 
hinge in the form of a double cone, as shown in illustration 
on page 167, at c, it makes a perfect joint, which allows 
the piece of wood to be freely moved. 

To complete the apparatus, the heads of the two 




Details of mechanism. 



pendulums are united by the hinge, at the bend of which 
a slender glass tube is fixed, which traces the curves. 
The hinge is given in the illustration above, and to its 
two extremities are adjusted the two pins of the pen- 
dulum as in cut, page 168. The pendulums are encircled 
with round pieces of lead, which can be fixed at any 
height by means of a screw. 





CHAPTER X.— ACOUSTICS. 

(Continued!) 

THE TOPOPHONE THE MEGAPHONE THE AUTOPHONE 

THE AUDIPHONE — THE TELEPHONE THE PHO- 

NOTrRAPH THE MICROPHONE. 

E propose in this chapter to give as shortly as 
possible a description of the various instruments 
lately come into use, by means of which, and 
electricity, sounds can be carried from place to 
place, and their locality identified. It is only within the 
last few years that these wonderful inventions have come 
into use, and in a measure superseded the at one time 
invincible electric telegraph. The Telephone is now in 
daily use in London and other places, and its novelty, if 
not all its capability, has been discounted. The Phono- 
graph has also been frequently seen. So we will on this 
occasion commence with the ToPOPHONE, a rather novel 
instrument. 

As the name indicates, the ToPOPHONE is an apparatus 
for discovering the position of a sound, from the Greek 
words signifying a " place '' and " sound." The sources 
of sound can be found by it, and indeed this is its actual 
and practical use. It is claimed for this new apparatus 
that it stands in the same relation to the sailor as his old 
and trusty friends, the compass and sextant. These in 
navigation inform the steersman as to his course, and tells 
him his position by observation. The Topophone will 
tell him whence a sound arises, its origin wherever it 



THE TOPOPHONE. I71 

may be ; and this in a fog is no mean advantage. Suppose 
a ship to be approaching a dangerous coast in a fog. Wc 
are all aware how deceptive sounds are when heard through 
such a medium. We cannot tell from what precise direc- 
tion the horn, whistle, or bell is sounding. The Topophone 
will give us the exact spot, and we can then, from our 
general knowledge of the locality, work our vessel up the 
river, or into the harbour, in safety. 

The Topophone was invented in 1880, by Professor 
Alfred Mayer, an American, and is based upon the well- 
known theory of sound waves. These, as we have already 
explained, exist in the air; and if the theory of sound 
waves has perfected the Topophone, we can fairly say 
that it has confirmed the supposed form of the sound 
waves. " Sound," says the inventor of the apparatus, "is 
supposed to be a particle continually expanding in the 
air, composed of a wave produced by compression, and 
followed by rarefaction. A continuous sound is a series 
of these particles or globules spreading and expanding as 
the water-rings in a pond." This much will be at once 
perceived. 

Now, suppose a person up to his shoulders in a pond 
of water; and someone throws a stone into it. If that 
person extend his arms and hands at right angles facing 
the sound, each hand would touch the edge of a ripple 
as it came towards him across the pond. He would then 
be facing the source of the ripples or waves, and look 
along a radius of the circle formed by the waves. But 
if he please, he can move his body so that both hands 
shall touch the same wave at the same time, or he might 
turn away from the source, and only one hand would 
touch the wave. But when both hands are actually 
washed by the same circular ripple he must be facing the 
source of it. Any position in which his fingers did not 
touch the ripple almost at the same instant, would not be 



172 SOUND. 

facing the source of the wave ripples. So by turning 
and extending his hands, he could with his eyes shut 
find out whether he was or was not facing the original 
source of the waves. 

This applied to sound waves in the air is the whole 
theory of the Topophone, which, however, depends for 
its usefulness upon the same note being sounded by all 
horns and whistles. One note must be better than all 
the others, and that note, probably C (treble), caused by 
about two hundred and sixty vibrations per second, has 
been found most applicable. If all whistles and horns 
can by law be compelled to adjust themselves to this 
note, then the Topophone will be a real and lasting 
benefit. 

Let us now look at the apparatus itself. 

It being conceded that the resonators are in the same 
key as the Foghorn, — and this is necessary, — they are 
placed upon the deck of the vessel. An ear-tube of 
indiarubber is carried from each of these " resonators " 
into the cabin. These tubes unite and again separate, 
ending in small pieces ready to be fitted to the ears. 
The apparatus is fixed on deck, and the arrangement 
which supports it passes into the cabin, and can be turned 
about in any direction. Of course in this case a dial 
point is necessary to indicate the direction in which the 
instrument is turned. If the machine be worn on the 
shoulders of the officer of the watch he can move as he 
pleases, and wants no indicator. 

The Topophone when used is so constructed, that when 
a horn is heard, and when the listener is facing the sound, 
he can liear nothing ! When not facing the origin of the 
sound he can hear the horn very well, but the moment 
the resonators receive the sound together as they face the 
source, a very low murmur is heard, or perhaps no sound 
at all— Why .? 



"PITCH." 173 

A certain pitch of tone is composed of vibrations or 
waves of equal length. In all waves there is a hollow 
and a crest. One neutralizes the other. The hollow of a 
sound, wave meeting the crest-of another wave "interferes" 
to produce silence, stillness, a dead level. So in " light " ; 
two rays will produce darkness. We will endeavour to 
explain this. 

If we have two equal strings, each performing an equal 
number of vibrations in a second, they will produce equal 
sound waves, and the sound produced by both together 
will be uninterrupted, and twice as loud as one of them. 
But if one string vibrate, say one hundred times, and the 
other one _hundred and one times in a second, they will 
not be in unison, and one will gain upon the other string, 
till after it has got to fifty vibrations it will be half a 
vibration ahead. At that moment they will neutralize 
each other, and silence will ensue for an appreciable time. 

In the case of light suppose a red ray strikes the eye, 
and another red ray to come upon it from somewhere 
else. If the difference between its distance and the other 
point from the spot in the retina on which the first ray 
fell, is the -j^o^q^o P^'^^ °f ^"^ inch, or exactly twice, thrice, 
four times as much, etc., that distance, the light will be 
seen twice as strong. Butif the difference in the distances 
between the points whence the light comes be only one- 
half the 1^0%^ P'^'''^ ^f ^^ ^'^'^^' °'' "i' 2^' si. or 4j times 
that distance, one light will extinguish the other, and 
dar'kness will be the result. Now this is precisely what 
happens in the case of the Topophone. To return to 
our simile of water waves. If two stones be cast into a 
pond, and two equal and similar waves produced, and if 
they reach at certain place at the same moment, they 
will make one large wave. But if one followed the other 
a little, so that the hollow of one coincided with the crest 
of the other, and vice versa, the waves would obliterate 



174 SOUND. 

each other, and a dead level would result. One tube of 
the Topophone is half a wave length longer than the 
other, and when the resonators are in a line and receive 
the wave at the same time, one ear hears the elevation 
of the sound wave, and the other the depression,— the 
sound is neutralized, and comparative, if not actual, silence 
results. The sailor knows in what direction the land lies, 
and can calculate his distance, or anchor if he please. 

If amongst our readers there be any who wish to make 
for themselves an acoustic signalling apparatus there is 
physically nothing to prevent them from constructing 
such an instrument as that shown in the annexed woodcut. 
It is founded upon the speaking-trumpet principle, which 
is supposed to have been originated hy Samuel Markland, 
in 1670. 

Kircher, in his "Ars magna et umbra" and in his 
"Pkonurgia,'' mentions a kind of speaking-trumpet, or 
parte voix, of gigantic dimensions, and called the " Horn 
of Alexander." According to Kircher, the instrument 
was used by Alexander the Great to summon his soldiers 
from a distance of ten miles. The diameter of the circum- 
ference was about eight feet, and Kircher conjectured that 
the instrument was mounted upon three supports. 

During the last century, a German professor, named 
Huth, made a model of the horn, and found it answered 
every purpose of a speaking-trumpet with most powerful 
results, but we beg leave to doubt whether the instrument 
really carried the voice to any very great distance. 

The Acoustic Cornet, which is the counterpart of the 
speaking-trumpet, has been made in many different forms 
during the last two centuries, but none of them to the 
present time consist of anything more intricate than a 
simple tube with a mouthpiece and bell-shaped orifice. 

Professor Edison, however, in his researches regarding 
the conveyance of sounds, has made numerous and interest- 



THE MEGAPHONE. 



^75 



ing experiments. On one occasion, with his Megaphone 
he carried on a conversation at a distance of nearly two 
miles, without any other assistance from instruments 
except a few little cornets of cardboard. These constitute 




The Megaphone. 

the Megaphone, which may be regarded as a curiosity, 
considering the effects produced by such simple means. 
The illustration represents the instrument which is (or 
was lately) fixed upon the balcony of Mr. Edison's house. 
At a mile-and-a-half distant from the house, at a spot 



176 



SOUND. 



indicated by the two birds in the picture, another instru- 
ment was fixed, and conversation was carried on with ease. 
Perhaps the present opportunity will be the most con- 
venient to speak of the AUTOPHONE, although it is more 
a musical than an acoustic instrument. Until lately 
Barbary organs and piano organs have been the only 
means by which poor people have been able to hear any 




The Autophone. 

music, and that not of a very elevated class. ' Besides, 
there is a good deal of expense connected with the 
possession of an organ. But the Americans, with a 
view to popularize music, have invented the AuTOPHONE, 
which is simply a mechanical accordeon, manufactured by 
the Autophone Company, of Ithaca, New York. 

The principle of the instrument is represented in 
the illustration, and is extremely simple. An upright 



THE AUTOPHONE. 



177 



frame carries within it on one side a bellows, and on the 
other a flexible air chamber, which serves as a reservoir. 

The upper portion contains a set of stops like an 
accordeon, but the escape of the air throiagh the small 
vibrating plates can only take place by the upper surface 
of the frame work, upon which slides a thin plate of 
Bristol board pierced with holes at convenient distances, 
and set in motion by the mechanism shown in the annexed 
diagram. 

The figure represents an axle furnished with a series 




Detail of the Autophone. 

of " washers," which, acting upon the plate, cause it lo 
move round. It is the bellows movement that turns the 
axle by the aid of two '" catches," B and C, which work 
upon a toothed wheel fixed upon it. 

The " catch " B moves the paper on which the tune is 
" perforated," when the bellows is empty, the other catch 
when it is distended; but a counter catch, D, represented 
by the dotted lines in the illustration, is so arranged that 
the paper cannot pass on except the tooth of the catch 
D is opposite a hole pierced upon the plate above. In 
the contrary case there is no movement of the paper 



178 SOUND. 

during the dilatation of the bellows. The effect of this 
very ingenious arrangement is to give to the "musical" 
band of "board" -an irregular movement, but it economises 
it in the case of sustained notes. The whole action of 
the instrument depends upon the correct working of the 
bellows. 

The effect, from an artistic point of view, certainly 
leaves something to be desired, but the instrument is 
cheap, and not cumbersome, and the slips of paper upon 
which the music is " cut out " can be made by machinery, 
and consequently are not dear. So far, the Autophone 
is fitted for popular favour and use, and may supersede 
the barrel organ. 

The AUDIPHONE is an instrument to conduct sound 
to the ear, to supplement it when temporary or partial 
deafness has occurred. Very likely many of our readers 
have observed ladies carrying large black fans on occasions, 
— at church, or lecture, or theatre, — and wondered why, 
perhaps. Those " fans " are Audiphones. The instrument 
is made of vulcanized rubber, and consists of a long flexible 
disc supported by a handle. To the upper edge of the 
" fan " are attached cords, which pass through a clip on 
the handle. If the person who wishes to hear by means 
of the Audiphone will hold the fan against the upper 
teeth, — the convex side of the fan outward, — he or she 
will hear distinctly, for the vibrations of sound are collected 
and strike upon the teeth and bones and act upon the 
auditory nerves from within, precisely as the vibrations 
act from without through the auricle. We need hardly 
add that if the ear be injured the Audiphone will be of 
no use. A writer says: "From personal observation with 
the Audiphone it appears to convey, the sonorous vibrations 
to the ear through the teeth, just as a long wooden rod 
held in the teeth will convey the vibrations of the sounding- 
board of a piano, though the piano is in another room 



THE AUDIPHONE. 



179 



and out of hearing by the ear. In using the Audiphone 
during conversation there is no movement or vibration felt 
by the teeth ; in Hstening to a piano there is a very faint 
sensation as if the Audiphone vibrated slightly, while with 
the handle of the Audiphone resting on the sounding-board 
of the piano the vibrations are so violent as to be painful 
to the teeth. By closing the ears a person with even acute 
hearing can observe the admirable manner in which the 
instrument conveys spoken words to the ear. The Audi- 
phone will prove to be of great value to deaf mutes, as it 




The Telephone, 

enables them to hear their own voices, and thus to train 
them to express words, while, before, they could only 
make inarticulate sounds." 

We have a variation of this instrument which has been 
introduced employing a diaphragm held in a telephone 
mouthpiece, and free to vibrate under the influence of 
sounds. This is connected by a string to a bit of wood 
that may be held in the teeth. . In use the hearer places 
the wood between his teeth, the string is drawn tight, and 
the speaker speaks through the telephone mouthpiece, the 
vibrations of the diaphragm being then conveyed to the 
teeth through the stretched string. This apparatus works 



l8o SOUND, 

very successfully, and ladies use it, but it is not so con- 
venient for general use as the Audiphone. 

The Telephone is now in daily use in London, and is 
by no means strange to the majority of our countrymen,, 
still some description of it will probably be acceptable, 
and a glance at its history may prove interesting. 

In speaking of the Telephone, we must not lose sight 
of the facts before mentioned, as regards our sense of 
hearing, and the manner in which the ear acts by the 
series of bones termed the hammer, the anvil, and stirrup. 
In the process of reproduction of tone in the magnetic 
instruments, the mechanism of the human ear was, to a 




The " receiving " apparatus. 



certain extent, imitated, and a diaphragm, by vibration«, 
generates and controls an electric current. 

Professor Wheatstone was the first person to employ the 
electric wire for the transmission of sounds, but Professor 
Ph.hp Reiss, of Friedrichsdorf, was the first to make the 
experiment of producing musical sounds at a distance. 
His first instrument was of a most primitive nature : 
subsequently he produced an instrument of which the 
first cut is the Telephone, the illustration above the 
receiver. ' 

In the first cut, it will be seen that there is an aper-^ 
ture on the top and one at the side; the latter is the 
mouthpiece. The top aperture is covered with a mem- 



THE TELEPHONE. l8l 

brane which is stretcked very tightly. When a person 
speaks or sings into the mouthpiece his voice is at once 
concentrated upon the tight membrane, which it causes tc 
vibrate in a manner corresponding with the vibrations of 
the voice. There are two binding screws, one at each 
side. To the centre of the tight membrane a piece of 
platinum is fixed, and this is connected with the binding 
screw on one side, in which a wire from the battery is 
fixed. On the membrane is a tripod, the feet of which 
(two) rest in metal cups, one of them being in a mercury 
cup connected with the binding screw at the opposite side 
to that already mentioned. The third " foot " — a platinum 
point — is on the platinum in the centre of the membrane 
or top, and moves with it. Every time the membrane is 
stretched by a vibration the platinum point is touched, 
and the closed circuit is broken by the return of each 
vibration. 

The receiving instrument {see page 1 80) consists of a 
coil enclosing an iron rod, and fixed upon a hollow 
sounding box. It is founded upon a fact discovered by 
Professor Henry, that iron bars when magnetized by an 
electric current become a little longer, and at the interrup- 
tion of the current resume their former length. Thus in 
the receiver - the iron will become alternately longer and 
shorter in accordance with the vibrations of the membrane 
in the box far away, and so the longitudinal vibrations 
of the bar of iron will be communicated to the sounding 
box, and become perfectly audible. This instrument, 
however, could only produce the "pitch" of sound, "not 
different degrees of intensity, or other qualities of tones." 
It merely sang with its own little trumpet whatever was 
sung into it; for all the waves were produced by an 
electric current of a certain and uniform strength, and 
therefore the sound waves were of the same size. 

But in 1874, Mr. Elisha Gray, of Chicago, improved 

13 



l83 



SOUND. 



Reiss' instrument, and discovered a method by which the 
intensity or loudness of tones, as well as their " pitch," 
were transmitted and reproduced. In this method he 




S2 

V O 






^ s 



T3 

. S 

*' bo 
1 g 



o a 



n 2 



M E 
a o 






employed electrical vibrations ot varying strength and 
rapidity, and so was enabled to reproduce a tune. Sub- 
sequently he conceived the notion of controlling the 
vibrations by means of a diaphragm, which responded to 



PROFESSOR -BELL. 



183 



every 'known sound, and by this he managed to transmit 
speech in an articulate manner. 

In 1876, Professor Graham Bell sent a Telephone to 
the Centennial' Exhibition at Philadelphia. Mr. Eell, 
according to the report, managed to produce a variation 
of strength of current in exact proportion to the particle 
of air moved by the sound. A piece of iron attached to 
a membrane, and moved to and fro in proximity to an 
electro magnet, proved successful. The battery and wire 




Bell's Telephone (Receiver). 

of the electro magnet are in circuit with the telegraph 
wire, and the wire of another electro magnet at the 
receiving station. This second magnet has a solid bar 
of iron for core, which is connected at one end, by a 
thick disc of iron, to an iron tube surrounding the coil 
and bar. The free circular end of the tube constitutes 
one pole of the electro magnet, and the adjacent free 
end of the bar core the other. A thin circular iron disc 
held (pressed against the end of the tube by the electro- 
magnetic attraction, and free to vibrate through a very 



r84 



SOUND. 



small space without touching the central pole, constitutes 
the sounder by which the electric effect is reconverted 




External appearance of Bell 
Telephone. 




a Bobbin ofcoil wire round magnet, i. Dia- 
phragm, c. Mouthpiece, d. Permanent 
™gn«'. f. Wires to binding screws. 
f. Both wires as one for convenience, 
.r- Adjusting screw-holding magnet. 



into sound. The accompanying illustrations {see page 1 82) 
show Mr. Bell's Telephone as described. 

The Telephone, subsequently simplified by Professor 
Bell, is shown in the two following illustrations. The 



MR. EDTSON. 1 85 

voice strikes against the diaphragm, and it begins to 
vibrate. The sound is not conveyed by the wire; the 
motion is communicated, and the vibrations becoine sound 
waves again. The Telephone consists of a cyhndrical 
magnet encircled at one end by a bobbin, on which is 
wound a quantity of fine insulated copper wire. The 
magnet and coil are contained in a wooden case, the 
ends of the coil being soldered to thick copper wire, 
which traverse the " wooden envelope," and terminate in 




Mode of using the Telephone. 



the binding screws. In front of the magnet is a thin 
circular iron plate, in which is the mouthpiece. The 
drawings will explain the instrument. 

Mr. Edison also invented a Telephone like Gray's, and 
made the discovery, that when properly prepared, carbon 
■would change its resistance with pressure, and that the 
ratio of these changes corresponded with the pressure. 
This solved the problem of the production of speech. 
The carbon is placed between two plates of platinum 
connected in the circuit and near the diaphragm, and 



1 86 



SOUND. 



the carbon receives the pressure from it by means of the 
mouthpiece. 







Q 



Wheii we come to MAGNETISM and Electricity we 
may have something more to say respecting the mysteries 
of the Teliiphone and its later developments. At present 



THE PHONOGRAPH. 187 

we are only concerned with it as a sound conveyer, and it 
answers its purpose admirably, although somewhat liable to 
attract other sounds or vibrations from neighbouring wires. 

The Phonograph, a mechanical invention of Mr. Edison, 
does not make use of electricity, although the vibratory 
motion of the diaphragm is utilized. It, in a simple form, 
consists of a diaphragm so arranged as to operate upon a 
small stylus placed just opposite and below the centre, 
and a brass cylinder, six or eight inches long, by three 
or four in diameter, mounted upon a horizontal axis, 
extending each way beyond its ends for a distance about 
its own length. 

"A spiral groove is cut in the circumference of the 
cylinder, from one end to the other, each spiral of the 
groove being separated from its neighbour by about one- 
tenth of an inch. The shaft or axis is also cut by a 
screw thread corresponding to the spiral groove of the 
cylinder, and works in screw bearings ; consequently 
when the cylinder is caused to revolve, by means of a 
crank that is fitted to the axis for this purpose, it receives 
a forward or backward movement of about one-tenth of 
an inch for every turn of the same, the direction, of 
course, depending upon the way the crank is turned. 
The diaphragm is firmly supported by an upright casting 
capable of adjustment, and so arranged that it may be 
removed altogether when necessary. When in use, how- 
ever, it is clamped in a fixed position above or in front 
of the cylinder, thus bringing the stylus always opposite 
the groove as the cylinder is turned. A small, flat spring 
attached to the casting extends underneath the diaphragm 
as far as its centre and carries the stylus, and between 
the diaphragm and spring a small piece of indiarubber 
is placed to modify the action, it having been found that 
better results are obtained by this means than when the 
stylus is rigidly attached to the diaphragm itself. 



l88 SOUND. 

"The action of the apparatus will now be readily 
understood from what follows. The cylinder is first very 
smoothly covered with tin-foil, and the diaphragm securely 
fastened in place by clamping its support to the base of 
the instrument. When this has been properly done, the 
stylus should lightly press against that part of the foil 
over the groove. The crank is now turned, while, at the 
same time, someone speaks into the mouthpiece of the 
instrument, which will cause the diaphragm to vibrate, 
and as the vibrations of the latter correspond with the 
movements of the air producing them, the soft and yielding 
foil will become marked along the line of the groove by 
a series of indentations of different depths, varying with 
the amplitude of the vibrations of the diaphragm ; or in 
other words, with the inflections or modulations of the 
speaker's voice. These inflections may therefore be looked 
upon as a sort of visible speech, which, in fact, they really 
are. If now the diaphragm is removed, by loosening the 
clamp, and the cylinder then turned back to the starting 
point, we have only to replace the diaphragm and turn in 
the same direction as at first, to hear repeated all that 
has been spoken into the mouthpiece of the apparatus ; 
the stylus, by this means, being caused to traverse its 
former path, and consequently, rising and falling with the 
depressions in the foil, its motion is communicated to 
the diaphragm, and thence through the intervening air to 
the ear, where the sensation of sound is produced. 

"As the faithful reproduction of a sound is in reality 
nothing ii»ore than a reproduction of similar acoustic 
vibrations in a given time, it at once becomes evident 
that the cylinder should be made to revolve with absolute 
uniformity at all times, otherwise a difference more or less 
marked between the original sound and the reproduction 
will become manifest. To secure this uniformity of motion, 
and produce a practically working machine for automatically 



THE PHONOGRAPH. I 89 

recording speeches, vocal and instrumental music, and 
perfectly reproducing the same, the inventor devised an 
apparatus in which a plate replaces the cylinder. This 
plate, which is ten inches in diameter, has a volute spiral 
groove cut in its surface on both sides from its centre to 
within one inch of its outer edge ; an arm guided by the 
spiral upon the under side of the plate carries a diaphragm 
and mouthpiece at its extreme end. If the arm be placed 
near the centre of the plate and the latter rotated, the 
motion will cause the arm to follow the spiral outward 
to the edge. A spring and train of wheel-work regulated 
by a friction governor serves to give uniform motion to 
the plate. The sheet upon which the record is made is 
of tin-foil. This is fastened to a paper frame, made by 
cutting a nine-inch disc from a square piece of paper of 
the same dimensions as the plate. Four pins upon the 
plate pass through corresponding eyelet-holes punched in 
the four corners of the paper, when the latter is laid upon 
it, and thus secure accurate registration, while a clamping- 
frame hinged to the plate fastens the foil and its paper 
frame securely to the latter. The mechanism is so arranged 
that the plate may be started and stopped instantly, or 
its motion reversed at will, thus giving the greatest con- 
venience to both speaker and copyist. 

" The articulation and quality of the Phonograph, 
although not yet perfect, is full as good as the Telephone 
was. The instrument, when perfected and moved by 
clock-work, will undoubtedly reproduce every condition 
of the human voice, including the whole world of expres- 
sion in speech and song, and will be used universally. 

"The sheet of tin-foil or other plastic material receiving 
the impressions of sound, will be stereotyped or electro- 
typed so as to be multiplied and made durable ; or the 
cylinder will be made of a material plastic when used, 
and hardening afterward. Thin sheets of papier mache. 



rgo SOUND. 

or of various substances which soften by heat, would be 
of this character. Having provided thus for the durability 
of the Phonograph plate, it will be very easy to make it 
separable from the cylinder producing it, and attachable 
to a corresponding cylinder anywhere and at any time. 
There -will doubtless be a standard of diameter and pitch 
of screw for Phonograph cylinders. Friends at a distance 
will then send to each other Phonograph letters, which 
will talk at any time in the friend's voice when put upon 
the instrument."* 

The Microphone (an outcome of the Telephone) was 
discovered by Professor Hughes, of London. It is an 
instrument which in its main features consists of a carbon 
" pencil," so suspended that one end rests upon a carbon 
" die." The instrument being connected with a Telephone 
by the circuit wires, will reproduce faint sounds very 
distinctly. Once a Microphone was put into a preacher's 
pulpit, and joined to a private telegraph wire which led 
to a gentleman's house. The owner was thus enabled to 
hear the sermon. So long as it is thus connected every 
minute sound, even h fly's footstep, will be faithfully 
reproduced. 




* Scribner's Magazine, 




CHAPTER XI.— ACOUSTICS, 
{Continued^ 

THE TUNING-FORK THE SYREN — SOUND FIGURES — 

SINGING FLAMES 

■ E cannot close the subject of Sound without some 
mention of -the -Musical Pitch, and various in- 
struments and experiments which have from 
time to time been made to discov:er the pitch, 
sound', and vibrations, and even to see Sound. To under- 
stand' the vibrations or " pitch "of a musical note we 
may study the illustration, which shows us a tuning-fork 
ite vibration. 

You will perceive that each prong of the tuning-fork 
beats the air in an opposite direction at the sam« time, 
say from- « to ^ ^ee next page). The prong strikes the 
air, and the wave thus created strikes again outward, and 
the condensation thus created travels along the back beat, 
rarefying the air, and both these, the rarefaction and the 
condensation, move with the same rapidity one behind 
the other. 

The tuning-fork of course vibrates a very great many 
times in a second, every vibration generating a wave. 
" Pitch," in a general sense, is the number of vibrations 
per second which constitute a note. For instance, the 
note A, the standard pitch consists of four hundred and 
thirty-five complete vibrations per second. Concert pitch 
is slightly higher, for there are a few more vibrations in 
the second. The lowest sound pitch is forty vibrations. 



193 



SOUND. 



the highest forty thousand. "Pitch" may be determined 
by an instrument termed the "Syren," or by a tooth-wheeled 
apparatus. 

The Syren was invented by Cagniard de Latour. It 
consists of a metal cylinder, a tube passes through the 
bottom, and through the tube air is blown into the cylinder. 
On the top a number of holes are drilled, while just over 
the cylinder top, almost in contact with it, is a metallic 
disc, which rotates upon a vertical axis. The disc is 





Vibrations of tuning fork. 



perforated with holes equal in number to those in the 
cylinder top, but the holes are not perpendicular, they 
slope in opposite directions. So when the air is forced 
through the holes in the top of the cylinder it impinges 
upon one side of the holes in the rotating disc, and blows 
it round. 

The disc in one revolution will therefore open and shut 
as many holes as there are in the disc and cylinder, and 
the air blown in will escape in so many puffs — the number 
of puffs in a given time depending upon the rapidity of 
rotation. There is an arrangement to show the number 



SOUND FIGURES. 



193 



of turns. By these rotations a sound is produced which 
rises in pitch as the revolutions are increased in number. 

To determine the pitch of a certain sound we must 
find the number of times the plate revolves in that time, 
then we- shall have the number of vibrations per second 
required to produce the note we desire. The arrangement 
working in a notched wheel tells us the number of rotations 
of the disc. Successive, and rapidly-successive puffs or 
beats are lieard as the rotation increases, and at length 
the two sounds will disappear, and merge into one, which 
is perhaps that of the tuning-fgrk, whose note you require 





Sound Figures. 

to find the "pitch" of By maintaining this rate for a 
minute or less, and setting the gear to tell the revolutions, 
the number will be found marked on the dial of the 
apparatus. So by multiplying the number of revolutions 
of the disc by the number of the holes, and dividing the 
product by the number of seconds during which the disc 
was in connection with the recording gear, we shall have 
the number of vibrations per second necessary to produce 
the pitch corresponding to the given sound. The above 
is the description of one form of Syren ; there are others, 
which, however, we need not detail. 

We have seen that there are certain nodal points, or 



194 



SOUND. 



res'^ing-places, in vibrations, and this can easily be shown 
upon a fiddle-string-, from which paper discs will fall off 
except on the nodal point, showing that there is no 
vibration there. The same experiment may be made by 
means of plates, which will give us what are termed 
Chladni's figures. Suppose we strew a glass-plate with 
fine sand, and stroke the edge with a fiddle-bow. The 
vibrations of the plates will make certain patterns, and 
cast the sand upon those points of repose to form nodal 
lines in various directions. The plates must, of course, 
be held or fastened, and a variety of souitd figures may 
be produced. {See page 193). 

The relation between the number of segments on the 
plate and the pitch of the note, can be ascertained .by 
using a circular plate clamped in the centre. " if -tht 
finger on the plate and the fiddle-bow are one-eighth of 
the circumference apart, the fundamental note will "be 
produced. If one-sixteenth apart, the higher octave will 
be heard." 

Sensitive flames will detect air vibrations, and flames can 
also be made to sing. Sensitive flames were discovered 
by Mr. Barrett, who noticed the effect a shrill note had 
upon a gas flame from a tapering jet. The flame was 
a very long one (fourteen inches), and when the sound 
was produced it shortened at once, while the upper part 
expanded like a fan ; the same effects, in a less marked 
degree, were observable when the shrill sound was 
prolonged from a distance of forty feet. Professor 
Tyndall was immediately interested in this discovery, 
and in January 1867 he lectured upon it at the Royal 
Institution. 

If any one wish to try the experiment, a piece of 
glass tubing should be obtained, and let the mouth be 
tapered down to a small orifice one-sixteenth of an inch 
in diameter. Then when the highest pressure is on for 



SINGING FLAMES. I95 

the evening, light the gas and sound a shrill whistle. The 
flame will sink down and spread out. The illuminating 
power may thus be increased, and many experiments may 
be made. For instance, if a person be in the room and 
try to read, he will probably not be able to do so at a 
little distance; but if his friend whistle to the gas it will 
so expand itself as to enable him to read, so long as the 
whistle lasts. 

A very ingenious burglar-detector was made upon the 
principle of the sensitive flame, which expands at a noise 
and heats a welded plate of gold, silver, and platinum. 
The plate swerves aside, the metals being unequally 
affected by heat, and as it is connected with a battery, 
rings a bell by electricity. A small high flame has been 
made sensitive to the chinking of coin, or even to the 
ticking of a watch. We will now give some explanation, 
derived partly from Professor Tyndall, of the cause of 
sensitive flames. 

A sensitive flame is one just on the point of " roaring," 
and about to change its aspect. "It stands," says Tyndall, 
" on the edge of a precipice. The proper sound pushes 
it over . . . We bring it to the verge of falling, and the 
sonorous pulses precipitate what was already imminent." 
The flame is in a state of vibration, so sounds being 
vibrations, practically increase the pressure; and the flame 
acknowledges the pressure thus invisibly applied by air 
waves. 

Singing Flames are produced by burning hydrogen 
in a tube ; a musical note is , thus produced in the same 
way as the air calises a note in an organ pipe. Faraday 
attributed the sound to rapid vibration caused by successive 
explosions of the burning gas. The Gas Harmonicon has 
been made on this principle. The air, being heated in 
the glass tube, ascends, and the flame is thus permitted 
fo come up more forcibly in the tube; so violent agitation 



196 



SOUND. 



results when the air tries to get into the opening above. 
The size of the flame and its position in the tube will 
give a certain note which will be the same note as the 
air would emit if in a pipe, for the vibrations give the 
sound. 

Sir Charles Wheatstone has shown by experiment how 
sound can be transmitted by placing a rod on a musical- 
box, and carrying the rod through the ceiling. When a 
guitar or violin was placed upon the rod, the sounds of 
the musical-box were distinctly heard in the upper room. 
A Phantom Band can be made by connecting certain 
instruments with others being played on under the stage. 
Every one will then appear to play by itself. 




MARVELS OF EARTH, AIR, 
AND WATER. 



INTRODUCTION. 




:HERE are some people who go through life 
practically blind. Indeed, for many purposes 
they might just as well be blind. Of them 
it might with truth be said, that " seeing, they 
see not.'' To their eyes and perceptions the sun is just 
a hot, bright body, that warms us too much sometimes ; 
sunset is simply the signal for lighting candles or gas, 
or for sitting idly, or groping awkwardly under the 
pretence of " blind man's holiday ; " a thunderstorm is 
a terrible nuisance, especially if, dressed for a visit, they 
happen to be caught in one; the star-spangled heavens 
afford a very pretty excuse for a walk, during which they 
never so much as lift their eyes to the splendid vision ; and 
life's pageant is but a round of duties or parties, which 
certainly do not lift their thoughts heavenward. 

How extraordinary and forceful is the contrast between 
this state of mind and that person's who possesses the 
seeing eye, the hearing ear. To such, among whom 
we venture to claim a place, the sun is a glorious orb 
of fire, emitting light and heat which are essential to 
the life of a world ; sometimes dazzling us with its full 
radiance, often warming us and cheering our hearts after 
a winter's cold, ripening the harvest and embrowning the 
complexion ; the leader, for us, of that continuous pro- 
cession of brightness across our sky ; now bold and ruddy 
at the beginning and close of his daily round, now pure 



VI 1NTRODUCTIO.N. 

and white as he is seen higher in the sky ; and anon 
showing, in the glories of sunset, the extraordinary effects 
which may be produced by simple light and cloud, with 
the varying distribution of vapour in the air. How can 
people be insensible to the charms of twilight, whether 
long drawn out or suddenly precipitated, the stillness of 
the air as the sun glides down, or the shrill whistle of the 
wind as the night storm rises, the graceful oscillation 
of the branches of trees, too often and too early shedding 
their leaves as they move ? Even the dull leaden sky, 
the gentle, steady downpour of rain, have their own points 
of interest, which the lover of nature is not slow to find 
out; while the consequences of rain in the general 
refreshment of plants, the cleansing of the air and of 
the ground, the washing of houses, the filling of streams 
and rivers, are among the most delightful of natural 
phenomena. Only at one atmospheric effect, in produc- 
ing which, however, man is a participator, do we not 
rejoice — namely, at the various kinds of fogs, laden with 
sooty particles from manufactories and locomotives, and 
all kinds of effluvia and germs of disease ; and we look 
upon it as a pretty sharp lesson, with its attendant colds 
and rheumatisms and accidents, to sluggish mankind to 
mend his ways and consume his own smoke, — a lesson 
which will probably become more severe each year till 
we learn it. 

But the thunderstorm, — how grand an event, how 
striking a study ! The lightning flash in all its varieties, 
sheet and forked, near and far, blinding or merely glow- 
ing in the distance ; the thunderclap, now sudden and 
sharp as a hammer blow, now slow and soft in sound, 
and gradually waxing to a climax of rattling peals, 
and dying away in the distance, and again seeming to 
shake houses to their foundations, and even to affect 
the solid earth with its violence ; and the rain, so often 



INTRODUCTION. Vll 

following with desperate energy, and keeping on with 
wonderful persistence, as if it would exhaust the foun- 
tains of heaven by its copious discharges ; and finally 
the stillness, freshness, and cleanliness succeeding the 
storm, — all these are rich treasures of delight to the 
instructed mind, which sees in these wonders but a faint 
expression of the surpassing glories and powers which 
belong to the supreme Worker of all. 

True it is that " the heavens declare the glory of God, 
and the firmament showeth His handiwork." The con- 
tinual procession of spots of beauty, each differing in 
magnitude and brightness, is a constant reminder to us 
to look to things above. The thought that each of these 
bright stars is a sun, essentially similar to our own sun, 
and supplying light to a number of non-luminous planets 
circling round it, is overwhelming when we consider 
the vast multiplicity of suns and planets that must exist 
in the universe. And the stately moon moves with 
soft grace through the sky, fulfilling its appointed task 
with as much regularity as the enormously greater and 
brighter sun. Can the dull soul of man, woman, or child 
remain blind to these glories after once having the 
attention vividly awakened, or forget them in a base 
surrender to evil jealousies and struggles ? How attrac- 
tive to the thoughtful mind it should be to penetrate, 
if but a little way, into the mystery of the forces which 
thus surround us and influence our being 1 

But some will say, " Oh, but we can appreciate the 
beauties of nature without studying them in a book. 
It is so dry, what is said in books, compared to enjoying 
things." We are prepared to assert that what is found 
in books about nature need not be dry, and very often 
is not, and that some of the most entertaining of these 
accounts may be found in the following pages. Even 
should there be a little close attention demanded, in order 



vili INTRODUCTION. 

to understand some explanations, yet we maintain that 
this will be amply compensated by the great gain to our 
appreciation of nature which follows a closer acquaint- 
ance with the details. Does not a knowledge of the 
solar system, and the mode in which the planets revolve 
round the sun, — of the fact of the stars being so many 
suns at very great distances, — of the changes of day and 
night being produced by the revolution of the earth upon 
its axis, and the other wonders of astronomy, greatly 
enlarge the pleasure to be derived from their contempla- 
tion ? Does not the reference of everything to its course, 
and the realisation of the orderliness of the complex 
arrangements of the universe, both increase our enjoy- 
ment of the results and raise our minds to the wonderful 
powers of the great First Cause of all ? 

The basis of a satisfactory examination of the powers 
of nature must be the understanding of the simple pro- 
perties of the matter or substance of which they are 
composed. There arc certain properties which are found 
to be common to all matter, of whatever composition ; and 
when they are clearly grasped, we shall be equipped for 
a consideration of the differences between the properties 
of different kinds of matter. The familiar questions and 
answers, ''What is matter? Never mind. What is 
mind > Never matter," contain a great deal of truth, 
although some people have asserted that mind is a pro- 
duct of matter, a sort of fruit produced by its workings. 
But they have made this rather as an assertion than 
as a subject of proof. Because our thinking is done in 
connection with the brain, they have suggested that 
no thinking can be done anywhere without a brain. It 
is really idle to waste time on such conjectures, when 
there is so much to be done in studying what wc can 
understand. 

Others have suggested that matter is a delusion of the 



INTRODUCTION. ix 

senses, and that we only imagine we see or feel different 
objects. They say that matter has no real existence, and 
that the only real thing is our brain receiving certain 
impressions. But they will never persuade the mass of 
humanity to regard the world as anything but a very 
real thing. Try to make a man who has just hit his 
head against a wall, or fallen downstairs, believe that he 
has not really been struck, and that it is only a delusion 
of his senses, and he will either feel inclined to strike 
the persuasive person who makes the remark or to 
reply that it is quite as real to him whichever way it 
is ; and he knows, too, that the doctor's charge will really 
affect his pocket in the way of making his purse lighter. 
So the reality of matter is firmly fixed in the mind of 
mankind; and not even a surgical operation can make 
him believe that it is all a joke or a sport of nature. 

Having implanted in our minds the chief properties 
of matter, we shall then proceed to exemplify the various 
studies of nature that can be satisfactorily pursued in 
the open air without expensive apparatus. The variety 
of charming creatures that can be found on our field 
excursions is much greater than is ordinarily realised. 
Stones, mud, slime, pond water, insects, nests, flowers, 
leaves, fungi, seaweeds, all furnish subjects for many 
a day's examination. Air and water in their different 
conditions afford material for profoundly interesting 
observations which any one may make. Gradually we 
acquire a perception of different forces of nature which 
may be separately understood and followed out through 
a variety of purposes. Attraction and cohesion will lead 
us through very interesting phenomena. We shall 
gradually acquire a notion of what is meant by a 
centre of gravity, and how from this follows the prin- 
ciple of the balance, — a principle which in all its variations 
is well worth studying ; for the balance is used in an 



X Introduction. 

infinite number of operations in life, and many are the 
occasions on whicii it would be extremely useful to us to 
be able to say positively whether a balance is correct 
or not. The question of equilibrium, too, is of a most 
practical nature; for we continually have to arrange our 
own loads so as to balance, or to place things on tables 
or shelves so that they shall not fall down. The know- 
ledge of how to tell the relative weight of liquids is of 
great importance to us in estimating the purity of milk, 
oils, etc. The pressure of the air is of interest to every 
one, though it is so equally adjusted that we never feel 
it except when strong winds attack us ; but it produces 
many of the variations of the weather, and none of us 
can be really indifferent to it. The barometer, the air- 
pump, the diving-bell, the pendulum, ballooning, the 
syphon, the Bramah press, capillarity, and buoyancy, — 
these are a few of the many subjects upon which wc shall 
touch, each of which is calculated to reward the patient 
student, to enlarge the capacity of his mind, to give him 
new powers of appreciation of nature, and to make him 
in manifold ways a wiser and more capable being. 



CONTENTS. 



CHAPTER I.— THE STUDY OF NATURE. 

THE BOOK OF NATURE — THE SENSES NATURAL HISTORY 

NATURAL PHILOSOPHY — MATTER OBJECTS — -PROPERTIES OF 

MATTER I 



CHAPTER n.— SCIENCE IN THE OPEN AIR. 

APHIDES — EVAPORATION BY LEAVES — AN AQUARIUM — THE CATA- 
LEPTIC FOWL — NEEDLE POINTS AND THORNS — MICROSCOPIC 
AQUARIUM — CAPE GRISNEZ — CRYSTALS — ICE ON THE GAS 
LAMPS 8 



CHAPTER III.— SIMPLE PHYSICS. 

THE MEANING OF PHYSICS — FORCES OF NATURE— GRAVITY CO- 
HESION — CHEMICAL ATTRACTION — CENTRE OF GRAVITY 

EXPERIMENTS — AUTOMATON TUMBLERS 3! 



CHAPTER IV.— SOLID BODIES. 

SOME PROPERTIES OF SOLID BODIES — INERTIA — MOTION — FRICTION 

— THE PENDULUM — EQUILIBRIUM 50 



CHAPTER v.— GASES AND LIQUIDS. 

PRESSURE OF THE AIR — EXPERIMENTS — THE MADGEBURG HEMI- 
SPHERES—AIR-PUMPS — THE BAROMETER — THE PUMP . . 63 



Xll CONTENTS. 

CHAPTER VI.— AERONAUTICS. 

PAGE 

PRESSURE OF AIR IN BODIES — EARLY ATTEMPTS TO FLY IN THE 

AIR -^DISCOVERY OF HYDROGEN THE MONTGOLFIER BAL- 
LOONS — FIRST EXPERIMENTS IN PARIS — NOTED ASCENTS . 86 



CHAPTER VII.— WATER. 

ABOUT WATER — HYDROSTATICS AND HYDRAULICS LAW OF 

ARCHIMEDES — THE BRAMAH PRESS — THE SYPHON — SPECIFIC 
GRAVITY. ilO 




CHAPTER I.— THE STUDY OF NATURE. 

THE BOOK OF NATURE THE SENSES NATURAL HIS- 
TORY — NATURAL PHILOSOPHY MATTER — OBJECTS 

PROPERTIES OF MATTER. 

ERNARD PALISSY used to say that he 
wished " no other book than the earth and 
the sky," and that " it was given to all to read 
this wonderful book." 
It is indeed by the study of the material world that 
discoveries are accomplished. Let an attentive observer 
watch a ray of light passing from the air into water, and 
he will see it deviate from the straight line by refraction ; 
let him seek the origin of a sound, and he will discover 
that it results from a shock or a vibration. This is 
physical science in its infancy. It is said that Newton 
was led to discover the laws of universal gravitation by 
beholding an apple fall to the ground, and that Mont- 
golfier first dreamt of air-balloons while watching fogs 
floating in the atmosphere. The idea of the inner 
chamber of the eye may, in like manner, be developed in 
the mind of any observer, who, seated beneath the shade 
of a tree, looks fixedly at the round form of the sun 
through the openings in the leaves. 



THE STUDY OF NATURE. 



''ii'''<i|iii'ii',i"i'i;'i 



„. m' 'I 

II.JI I I I 



I I ,ll I 



Ml I 



I I 



4 jii 






THE BOOK OF NATURE. 3 

Every one, of course, may not possess the ambition to 
make such discoveries, but there is no one who cannot 
compel himself to learn to enjoy the pleasure that can be 
derived from the observation of Nature. 

It must not be imagined that in order to cultivate 
science it is absolutely necessary to have laboratories and 
scientific work-rooms. The book of which Palissy spoke 
is ever present ; its pages are always open, wherever we 
turn our eyes or direct our steps. So we may hope to 
introduce all our friends to a pleasant and lasting acquaint- 
ance with Dame Nature. 

" But what is Nature .' " We are fond of admiring 
Nature, and the effects of certain causes in the world, and 
we want to know why things are so. Very well — so you 
shall ; and as to the question, "What is Nature.'" we will 
endeavour to answer you at once. 

Nature is the united totality of all that the various 
Senses can perceive. In fact, all that cannot be made by 
man is termed " Nature " ; i.e., God's creation. 

From the earliest ages man has sought to read the open 
leaves of the Book of Nature, and even now, with all our 
attainments, we cannot grasp all, or nearly all. One 
discovery only leads up to another. Cause and Effect are 
followed up step by step till we lose ourselves in the 
search. Every effect must have a cause. One thing 
depends upon another in the world, and it does not need 
Divine revelation to tell us that. Nothing happens by 
" mere chance." " Chance ! " said a Professor to us at the 
University, " Chance ! — Remember, there is no such thing 
in the world as chance." 

Between our minds or consciousness and Nature are 
our Senses. We feel, we see, we hear, we taste, we smell, 

. so it is only through the Senses that we can come to 

any knowledge of the outer world. These attributes, or 
Senses, act directly upon a certain '• primary faculty " 



4 THE STUDY OF NATURE. 

called Consciousness, and thus we are enabled to under- 
stand what is going on around us. The more this great 
existing faculty is educated and trained, the more useful 
it will become. So if we accustom our minds to observa- 
tion of Nature, we shall find out certain causes and effects, 
and discover Objects. Now an Object is a thing per- 
ceptible both to feeling and sight, and an Object occupies 
space. Therefore there are objects Artificial as well as 
Natural. The former are created by man from one or 
more Natural products. Natural Objects are those such 
as trees, rocks, plants, and animals. We may also class 
the heavenly bodies, etc., as Objects, though we cannot 
touch them, but we can feel their effects, and see them. 
The Phenomena of Nature include those results which 
are perceptible by only one sense, as thunder ; light and 
sound may also be classed as Phenomena. 

Take a familiar instance. A stone is a Natural Object. 
We take it up, open our fingers, and it falls. The motion 
of that object is a Phenomenon. We know it falls, because 
we see it fall, and it possesses what we term weight ; but 
we cannot tell why it possesses weight. 

[Professor Huxley says : " Stones do not fall to the 
ground in consequence of a law of nature," for a law is 
not a cause. " A law of nature merely tells us what we 
may expect natural objects will do under certain circum- 
stances."] 

A cause of a Phenomenon being independent of human 
will is called a Force, and the stones fall by the force 
of Gravitation, or that natural law which compels every 
material object to approach every other material object. 

A single Force may produce a great number of Phe- 
nomena. 

Nature being revealed to us by Objects, and by means 
of Phenomena, we have got already two Branches of 
Science extending from such Roots ; viz., Natural 



Natural 
Philosophy 



WHAT IS MATTER? 5 

History, the Science of Objects ; and Natural Philo- 
sophy, the Science of Phenomena. 

Both of these branches have been subdivided thus : 
f Zoology, referring to Animals ) „. . 

Natural j Botany, referring to Plants ) '° °^^' 

History ) Mineralogy 1 . . n,,r. , 

/ ^ , } referring to Mmerals, etc. 

(^ Geology j ^ 

Physics. Phenomena without essential 

change of the Objects. 
Chemistry. Phenomena with change of 

the Objects. 
Physiology. Phenomena of animated Ob- 
jects. 

These two great divisions comprehend, in their ex- 
tended senses, all that is known respecting the material 
world. 

We have spoken of Objects. Objects occupy Space. 
What is Space ? — -Space is magnitude which can be con- 
ceived as extending in three directions — Length, Breadth, 
and Depth. Matter occupies portions of Space, which 
is infinite. Matter, when finite, is termed a body or 
object. The general properties of Matter are Magnitude, 
Form, Impenetrability , Inertia, Divisibility, Porosity, Elas- 
ticity, Compressibility, Expansibility. 

Matter is present in Nature in three conditions. We 
find it as a Solid, a Liquid, and a Gas. We shall 
explain the various properties of Solids, Liquids, and 
Gases in their proper places (in Physics). To test the 
actual existence of Matter in one or other of these forms 
our Senses help us. We can touch a Solid, or -taste it and 
see it. But touch is the test. We have said that Matter 
possesses certain properties. We will examine these 
briefly. The two which belong to all material bodies 
are Impenetrability and Magnitude. You cannot, strictly 
speaking, penetrate Matter. You can find the form of an 



6 THE STUDY OF NATURE. 

object by touch or sight, but you cannot penetrate it 
You will think you can drive a nail or a screw into a 
board, but you cannot ; you only displace the fibres of 
the wood by the screw. Take water as a very common 
instance. Water is Matter, for it occupies a certain space. 
Water is impenetrable, for if you put your hand or foot into 
a basin full of it, it will overflow, thus proving that you 
displace, and do not penetrate it. It is almost impossible 
to compress water. 

Divisibility is another quality of Matter ; and when we 
attempt to show how far Matter can be divided, the brain 
refuses to grasp the infinity. A pin's head is a small 
object, but it is gigantic compared to some animals, of 
which millions would occupy a space no larger than the 
head of a pin. These tiny animals must contain organs 
and veins, etc., and those veins are full of blood globules. 
Professor Tyndall informs us that a drop of blood contains 
three millions of red globules. So these infinitesimally 
small animals must have millions of globules in their blood 
also. Thus we see to what an extent, far beyond our 
Senses' power to grasp. Matter can be divided. 

But there is something even more astonishing than 
this. It is stated that there are more germs in the milt 
of a single codfish than there are men in the world ; and 
that one grain of sand is larger than four millions of these 
germs ! each of which must be possessed of life germs 
of an equal amount, which would grow up as it grew to 
maturity. This carries us back again, and 

" Imagination's utmost stretch 
In wonder dies away." 

Or take other interesting facts. One hundred threads 
of the silkworm must be placed side by side to make up 
the thickness of a line ( — ) about -^\!n. of an inch ; and 
metals can be drawn out to such exceeding fineness that 
twelve hundred of the fine wires will occupy only the 



ATTRIBUTES OF MATTER. 7 

space of one hundred silkworms' threads, or one milli- 
vietrc. 

Porosity is another attribute of Matter, for in all Matter 
there are pores, or spaces, between the particles. Some- 
times such openings are plainly visible ; in very " solid " 
bodies, they are, to a great extent, indistinguishable. But 
we know that the spaces exist, because we can compress 
the particles together. 

Inertia is also a general property of Matter, and the 
meaning of the term is "inactivity," or passiveness — a 
want of power in an object to move, or when moving, to 
stop of itself. It will come to rest apparently by itself, 
but the resistance of the air and the friction of the ground, 
or the attraction of the earth, will really occasion the 
stoppage of the object. We will speak more fully of 
Inertia presently. Elasticity and Expansibility are evi-' 
dent in fluids and gases. 

We have thus introduced our readers to some of the 
most evident facts connected with Matter. The various 
Forces and Phenomena of attraction will be fully con- 
sidered farther on ; at present we are about to show our 
readers how they may first profitably study Science in 
the open air for themselves, and we will give them our 
experience of the Book of Nature. 





CHAPTER II.— SCIENCE IN THE OPEN AIR. 

APHIDES — EVAPORATION BY LEAVES AN AQUARIUM 

THE CATALEPTIC FOWL NEEDLE POINTS AND 

THORNS — MICROSCOPIC AQUARIUM — CAPE GRISNEZ 
CRYSTALS ICE ON THE GAS LAMPS. 

lOME years ago we were staying in Normandy, 

not far from the town of C , enjoying, in 

the midst of most cordial hospitality, the peace- 
fulness of country life; and my kind hosts, 
with me, took great pleasure in having what we called " a 
course of science in the open air." The recollections of 
that time are some of the pleasantest in the whole course 
of my life, because all our leisure was intelligently occu- 
pied. Each of us set himself to provide the subject of 
some curious observation or instructive experiment ; one 
made a collection of insects, another studied botany. In 
the daytime we might have been seen examining, under a 
magnifying glass, the branch of a rose-tree, from which the 
ants were endeavouring to extract the aphides.* At night 
we admired through the telescope the stars and planets 
that were visible ; or if the sky was not clear, we examined 
under a strong magnifier grains of pollen from flowers, or 
the infttsoria in a drop of stagnant water. Frequently 
some very insignificant object became the occasion for 

* It is well known that ants, by touehing the skin of aphides, extract 
therefrom a secretion of viscous matter, which nourishes them. They 
will frequently carry off the aphides to their habitations, and keep them 
here ; thus one may say they keep a cow in their stable. 



PRACTICAL PHYSICS. 



9 



some scientific discussion, which terminated with an ex- 
perimental verification. 

I recollect that one day one of us remarked that after 
a week of dry weather a stream of water had nearly dried 








Ants engaged in extracting aphides from a rose-tree (highly magnified). 



up, although sheltered by thick trees, which necessarily 
impeded the calorific action of the sun ; and he expressed 
surprise at the rapid evaporation. An agriculturist among 
the company, however, drew his attention to the fact that 
the roots of the trees were buried in the course of the 



lO 



OPfiN-AIK SCIENCE. 




Experiment sliowing evaporatitn of water 
by leaves. 



Stream, and that, far from 
preventing the evaporation 
of the water, the leaves had 
contributed to accelerate it. 
As the first speaker was not 
convinced, the agriculturist, 
on our return to- the house, 
prepared an experiment 
represented in margin. He 
placed the branch of a tree 
covered with foliage in a 
U-shaped tube, the two 
branches of unequal diame- 
ter, and filled with water. 
He placed the vegetable 
stem in the water, and 
secured it to the tube by 
means of a cork covered 
with a piece of india-rubber, 
and tied tightly to make it 
hermetically closed. 

At the commencement of 
the experiment the water 
was level with A in the 
larger branch of the tube, 
and level with B in the 
smaller, rising to a slightly 
higher point in the more 
slender of the two by capil- 
larity. The evaporation of 
the water caused by the 
leaves was so active that in 
a very short time we beheld 
the water sink to the points 
C and C. 



PRESERVATION OF INSECTS. ' 1 1 

Thus did the excellent method of seeking the cause of 
phenomena by experiments often lead us to interesting 
results. We had among us many children and young 
people who had reached the age of ardent curiosity. We 
took pleasure in pointing out to them the means of study- 
ing natural science ; and we were not long before feeling 
convinced that our lessons out in the fields had much 
greater success than those given between the four walls of 
a class-room. Insects were collected, and preserved by 
being carefully placed in a small bottle, into which was 
let fail a drop of sulphuret of carbon ; * the insect was 
immediately asphyxiated, and we thus avoided the cruelty 
of passing a pin through a living body. Having chased 
butterflies and insects, we next desired to study the 
aquatic creatures which swarmed in the pools of the 
neighbourhood. For this purpose I constructed a fishing- 
net fitted to an iron ring, and firmly secured to a wooden 
handle. When this was plunged under the water and 
drawn quickly out again, it came back full of slime. In the 
midst of this muddy substance one generally succeeded in 
finding the hydrophilus, tadpoles, coleeptera, many curious 
kinds of caddis-worms, tritons, and sometimes frogs, com- 
pletely astounded by the rapidity of their capture. All 
these creatures were transported in a bottle to the house, 
and I then constructed, at small expense, a glass aquarium, 
by means of the bell of a melon-glass turned upside down, 

* The preservation of insects, and their preparation for collections, 
necessitates some precaution. Entomologists are in the habit of 
spreading them out on a small board, and arranging the legs and 
aiitennce by means of large pins. The wings should be dried by 
placing them on strips of paper, which preserves them. These pre- 
cautions are indispensable if it is wished that the insects in a collection 
should retain their distinctive characters. Worms and caterpillars can 
be raised in pots filled with earth, if carefully covered over with mushn 
or wire gauze with very fine meshes. The process of hatching may 
give rise to many interesting observations. 



12 



OPEN-AIR SCIENCE, 



thus forming a transparent receptacle of considerable size. 
Four wooden stakes were then f^xed in the ground, and a 
plank with a circular hole nailed on the top, in which the 




■i 



5 






> 
\ 



'^ '■ 



I 







Aquarium foi-med by ineanB of a melon-glass. 

glass bell was placed. I next scattered seme large pebbles 
and shells at the bottom of the vase to form a stony bed, 
poured in some water, placed a few reeds and water plants 
among the pebbles, and then threw a handful of water 



THE insects' palace, I 3 

lentils on the surface ; thus a comfortable home was con- 
trived for all the captured animals* The aquarium, when 
placed under the shade of a fine tree in a rustic spot 
abounding with field flowers, became a favourite rendez- 
vous, and we often took pleasure in watching the antics 
of the little inmates. Sometimes we beheld very san- 
guinary scenes ; the voracious hydrophilus would seize a 
poor defenceless tadpole, and rend him in pieces for a 
meal without any compunction. The more robust tritons 
defended themselves better, but sometimes they also suc- 
cumbed in the struggle. 

The success of the aquarium was so complete that one 
of us resolved to continue this museum in miniature, and 
one day provided himself with an insects' palace, which 
nearly made us forget the tadpoles and tritons. It was 
a charming little cage, having the form of a house, covered 
with a roof; wires placed at equal distances forming the 
sides. In it was a large cricket beside a leaf of lettuce, 
which served as his food. The little creature moved up 
and down his prison, which was suspended from the 
branch of a tree, and when one approached him very 
closely gave vent to his lively chirps. 

The menagerie was soon further augmented by a 
hitherto unthought-of object ; namely, a frogs' ladder. 
It was made with much skill. A large bottle served for 
the base of the structure. The ladder which was fixed 
in it was composed of the twigs of very small branches, 
recently cut from a tree, and undivested of their bark, 
which gave to the little edifice a more picturesque and 
rustic appearance. The pieces of wood, cleverly fixed 
into two posts, conducted the green frogs (tree-frogs) on 
to a platform, whence they ascended the steps of a 

* It frequently happens that in a small aquarium, constructed after 
this fashion, the animals escape. This is avoided by covering the vase 
with a net. 



14 



OPEN-AIR SCIENCE. 



genuine ladder. There they could disport themselves at 
pleasure, or climb up further to a branch of birch-tree 
placed upright in the centre of the bottle. A net with 




Cage for j 



fine meshes prevented the little animals from escaping. 
We gave the tree-frogs flies for their food, and sometimes 
they caught them with remarkable dexterity. I have 
often seen a frog when at liberty watching a fly, on which 



AN AQUARIUM. 



IS 



It pounces as a cat does on a bird. The observations 
that we made on the animals of our menagerie led us to 
undertake others of a very different nature ; I recollect 




Small aqnnrinm, with frogs' ladder. 



particularly a case of catalepsy produced in a code. I 
will describe this remarkable experiment, certainly one of 
the most curious we ever performed. 

We place a cock on a table of dark colour, rest its 



i6 



OPEN-AIR SCIENCE. 



beak on the surface, where it is firmly held, and with a 
piece of chalk slowly draw a white line in continuation 
from the beak, as shown in our engraving. If the crest 
is thick, it is necessary to draw it back, so that the animal 




Frog lying in wait for a fly. 



may follow with his eyes the tracing of the line. When 
the line has reached a length of two feet the cock has 
become cataleptic. He is absolutely motionless, his eyes 
are fixed, and he will remain from thirty to sixty seconds 
in the same posture in which he had at first only been 
head remains resting on the table in 



held by force. His 



THE CATALEPTIC COCIC 



U 




iS OPEN-AIR SCIENCE. 

the position shown. This experiment, which we have 
successfully performed on different animals, can also be 
accomplished by drawing a straight line with a piece of 
chalk on a slate. M. Azam declares that the same result 
is also produced by drawing a black line on a table of 
white wood. According to M. Balbiani, German students 
had formerly a great predilection for this experiment, 
which they always performed with marked success. Hens 
do not, when operated on, fall into a cataleptic condition 
so easily as cocks ; but they may often be rendered 
motionless by holding their heads fixed in the same 
position for several minutes. The facts" we have just 
cited come properly under the little studied phenomena, 
designated by M. Braid in 1843 by the title of Hypnotism. 
MM. Littri^ and Ch. Robin have given a description of 
the hypnotic condition in their Dictionnaire de MMecine. 

If any shining object, such as a lancet, or a disc of 
silver-paper gummed to a plate, is placed at about the 
distance of a foot from the eyes of a person, slightly 
above the head, and the patient regards this object fixedly, 
and without interruption for twenty or thirty minutes, he 
will become gradually motionless, and in a great number 
of cases will fall into a condition of torpor and genuine 
sleep. Dr. Braid affirms that under such circumstances 
he has been able to perfcrm surgical operations without 
the patient having any consciousness of pain. Later also, 
M. Azam has proved the complete insensibility to pricking 
on the part of individuals whom he has rendered cataleptic 
by the fixing of a brilliant object. The experiment of 
the cataleptic cock was first described under the name of 
Experimentum Mirahile, by P. Kircher, in his Ars Magna, 
published at Rome in 1646. It evidently belongs to the 
class of experiments which were performed at the Sal- 
pdtriere asylum at Paris, by M. Charcot, on patients 
suffering from special disorders. It must now be evident 



THORNS AND STINGS. 



19 



to our readers that our scientific occupations were suffi- 
ciently varied, and that we easily found around us many 
objects of study. When the weather was wet and cloudy 
we remained indoors, and devoted ourselves to micro- 
scopical examinations. Everything that came under our 
hands, insects, vegetables, etc., were worthy of observation. 
One day, while engaged over a microscopical preparation. 




Ordinary pin and needle, teen through a microscope (magnified 500 dianielers). 



I was making use of one of those steel points generally 
employed in such purposes, when Jiappening to pass it 
accidentally beneath the microscope, I was astonished to see 
how rough and uneven it appeared when highly magnified. 
The idea then occurred to me to have recourse to some- 
thing still more pointed, and I was thus led to make 
comparisons between the different objects represented. 
It will here be seen how very coarse is the product of 
our industry when compared with the product of Nature. 



20 



OPEN-AIR SCIENCE. 



No. I represents the point of a pin that has already been 
used, magnified 500 diameters. The point is evidently 
slightly blunted and flattened. The malleable metal has 
yielded a little under the pressure necessary to make it 
pass through a material. No. 2 is a little more pointed ; 
it is a needle. This, too, will be seen to be defective 
when regarded by the aid of the microscope. On the 




Thorn of a ros", and wasp's sting through a microscope ^magnified 500 diameters). 

other hand, what fineness and delicacy do the rose thorn 
and wasp's sting present when examined under the same 
magnifier ! See the two points in illustration. 

An examination of this exact drawing has led me to 
make a calculation which leads to rather curious results : 
at a half millimetre from the point, the diameters of the 
four objects represented are in thousandths of a milli- 
metre respectively, 3*4 ; 2'2 ; i"i ; 0'38. The corre- 
sponding sections in millionths of a square millimetre are : 



INFUSORIA. 2 1 

907'92 ; 380-13; 95'03 ; ii'34; or, in round numbers, 
908 ; 380 ; 95 ; II. 

If one bears in min"d, which is much below the truth, 
that the pressure exercised on the point must be propor- 
tional to the section, and admitting that a pressure of 1 1 
centigrams suffices to thrust in the sting of a wasp half 
a millimetre, it will require more than 9 grams of 
pressure to thrust in a needle to the same extent. In 
fact, this latter figure is much too small, for we have 
not taken into acco.unt the advantage resulting from the 
elongated shape of the rose thorn, which renders it more 
favourable for penetration than a needle through a drop 
of tallow. 

It would be easy to extend observations of this kind to 
a number of other objects, and the remarks I have just 
made on natural and artificial points will apply incon- 
testably to textures for example. There is no doubt that 
the thread of a spider's web would far surpass the thread 
of the finest lace, and that art will always find itself 
completely distanced by nature. 

We amused ourselves frequently by examining the 
infusoria which are so easily procured by taking from 
some stagnant water the mucilage adhering to the 
vegetation on the banks, or attached to the lower part of 
water lentils. In this way we easily captured infusoria, 
which, when placed under a strong magnifier, presented 
the most remarkable spectacle that one can imagine. 
They are animalcules, having the form of transparent 
tulips attached to a long stem. They form bunches 
which expand and lengthen ; then, suddenly, they are 
seen to contract with such considerable rapidity that the 
eye can scarcely follow the movement, and all the stems 
and flower-bells are folded up into the form of a ball. 
Then, in another moment, the stems lengthen, and the 
tulip-bells open once more. One can easily encourage 



22 



OPEN-AIR SCIENCE. 



the production of infusoria by constructing a small micro- 
scopic aquarium, in which one arranges the centre in a 
manner favourable to the development of the lowest 




Arrangeinent of a m;croscop:c aqunnum for examining infusoria. 



organisms. It suffices to put a few leaves (a piece of 
parsley answers the purpose perfectly)* in a small vase 

The infusion of parsley has the advantage of not sensibl) obscuring 
the water. 



BUTTERFLIES. 2 3 

containing water, over which a glass cover is placed, and 
it is then exposed to the rays of the sun. In two or 
three days' time, a drop of this water seen under the 
microscope will exhibit infitsoria. After a certain time, 
too, the different species will begin to show themselves. 
Microscopical observations can be made on a number of 
different objects. Expose to the air some flour moistened 
by water, and before long a mouldiness will form on it ; 
it is the penicillium glancum, and when examined under a 
magnifier of 200 to 300 diameters, cells are distinguish- 
able, branching out from an organism remarkable for its 
simplicity. We often amused ourselves by examining, 
almost at hazard, everything that came within our reach, 
and sometimes we were led to make very instructive 
investigations. When the sky was clear, and the weather 
favourable to walking, we encouraged our young people 
to run about in the fields and chase butterflies. The 
capture of butterflies is accomplished, as every one knows, 
by means of a gauze net, with which we provided the 
children, and the operation of chasing afforded them some 
very salutary exercise. It sometimes happens that butter- 
flies abound in such numbers that it is comparatively 
easy to capture them. During the month of June 1879, 
a large part of Western Europe was thronged with swarms 
of Vanessa algina butterflies, in such numbers that their 
appearance was regarded' as an important event, and 
attracted the lively attention of all entomologists. This 
passage of butterflies provided the occasion for many 
interesting studies on the part of naturalists. 

We cannot point out too strongly to our readers that the 
essential condition for the student of natural science, is 
the possession of that sacred fire which imparts the energy 
and perseverance necessary for acquiring and enlarging 
collections. It is also necessary that the investigator 
should furnish himself with certain indispensable tools. 



OPEN-AIR SCIENCE. 




STUDY OF STRATA. 25 

For collecting plants the botanist should be armed with a 
good hoe set in a thoroughly strong handle, a trowel, of 
which there is a variety of shapes, and a knife with a 
sharp blade. A botanical case must also be included, for 
carrying the plants. The geologist, or mineralogist, needs 
no more elaborate instruments ; a hammer, a chisel, and 
a pickaxe with a sharp point for breaking the rocks, and 
a bag for carrying the specimens, will complete his outfit. 
We amused ourselves by having these instruments made 
by the blacksmith, sometimes even by manufacturing 
them ourselves ; they were simple, but solid, and ad- 
mirably adapted to the requirements of research. Often 
we directed our walks to the seashore, where we liked to 
collect shells on the sandy beach, or fossils among^ the 
cliffs and rocks. I recollect, in a walk I had taken some 
years previously along the foot of the cliffs of Cape 
Blanc-Nez, near Calais, having found an impression of an 
ammonite of remarkable size, which has often excited the 
admiration of amateurs ; this ammonite measured no less 
than twelve inches in diameter. The rocks of Cape 
Grisnez, not far from Boulogne, also afford the geologian 
the opportunity of a number of curious investigations. 
In the Ardennes and the Alps I have frequently procured 
some fine mineral specimens ; in the first locality-crystal- 
lized pyrites, in the-second fine fragments of rock crystal. 
I did not fail to recount these successful expeditions to 
the young people who accompanied me, and their ardour 
was thereby inflamed by the hope that they also should 
find something valuable. It often happened when the 
sun was powerful, and the air extremely calm, that my 
young companions and I remarked some very beautiful 
effects of mirage on the beach, due to the heating of the 
lower strata of the atmosphere. The trees and houses 
appeared to be raised above a sheet of silver, in which 
their reflectiong wer? visible as in a sheet of tranquil 



26 



OPEN-AIR SCIENCE. 



water. It can hardly be believed how frequently the 
atmosphere affords interesting spectacles which pass un- 
perceived before the eyes of those who know not how to 
observe. I recollect having once beheld at Jersey a 
magnificent phenomenon of this nature, on the 24th June, 
1877, at eight o'clock in the evening : it was a column 




Gioup uf ruck crjsial. 



of light which rose above the sinking sun like a sheaf of 
fire. I was walking on the St. Helier pier, where there 
were also many promenaders, but there were not more 
than two or three who regarded with me this mighty 
spectacle. Columns and crosses of light are much more 
frequent than is commonly supposed, but they often 
pass unperceived before indifferent spectators. We will 



A SdUN cross. 27 

describe an example of this phenomenon observed at 
Havre on the 7th May, 1877. The sun formed the 
centre of the cross, which was of a yellow golden colour. 
This cross had four branches. The upper branch was 
much mere brilliant than the others ; its height was about 
15°. The lower branch was smaller, as seen in the 
sketch on page 2, taken from nature by Monsieur Albert 
Tissandier. The two horizontal branches were at times 
scarcely visible, and merged in a streak of reddish-yellow 
colour, which covered a large part of the horizon. A 
mass of cloud, which the setting sun tinged with a deep 
violet colour, formed the foreground of the picture. The 
atmosphere over the sea was very foggy. The pheno- 
menon did not last more than a quarter of an hour, but 
the conclusion of the spectacle was signalized by an 
interesting circumstance. The two horizontal branches, 
and the lower branch of the luminous cross, completely 
disappeared, whilst the upper branch remained alone for 
some minutes longer. It had now the appearance of 
a vertical column rising from the sun, like that which 
Cassini studied on the 21st May, 1672, and that which 
M. Renon* and M. A. Guillemin observed on the 12th July, 
i876.t Vertical columns, which, it is well known, are 
extremely rare phenomena, may therefore indicate the 
existence of a luminous cross, which certain atmospheric 
conditions have rendered but partially visible. 

How often one sees along the road, little whirlwinds of 
dust raised by the wind accomplishing a rotatory movement, 
thus producing the imitation of a waterspout ! How 
often halos encompass with a circle of fire the sun or 

* Detailed accounts \n Vol. Ixxxiii , pp. 243 and 292 of "La Nature." 

+ .See "La Nature," 4th year, 1876, 2nd half-year, p. 167. M. A. 

Guillemin mentions, in connection with the phenomenon of July 12th, 

1876, the presence of light masses of cloud of a greyish-blue colour, 

similar to those perceived in the phenomena just described. 



2 8 OPEN-AIR SCIENCE. 

the stars ! How often we see the rainbow develop its 
iridescent beauties in the midst of a body of air traversed 
by bright raindrops ! And there is not one of these 
great natural manifestations which may not give rise to 
instructive observations, and become the object of study 
and research. Thus, in walks and travels alike, the 
study of Science may always be exercised ; and this 
method of study and instruction in the open air con- 
tributes both to health of body and of mind. As we 
consider the spectacles which Nature spreads before us, — 
from the insect crawling on the blade of grass, to the 
celestial bodies moving in the dome of the heavens, — we 
feel a vivifying and salutary influence awaken in the 
mind. The habit of observation, too, may be everywhere 
exercised — even in towns, where Nature still asserts her- 
self ; as, for example, in displays of meteorological pheno- 
mena. We will give an example of such. 

The extraordinary abundance of snow which fell in 
Paris for more than ten consecutive hours, commencing 
on the afternoon of Wednesday, January 22nd, 1880, 
will always be looked upon as memorable among the 
meteorological events of the city of Paris. It was stated 
that in the centre of Paris, the thickness of the snow that 
had fallen at different times exceeded fourteen inches. 
The snow had been preceded by a fall of small transparent 
icicles, of rather more than a millimetre in diameter, some 
having crystalline facets. They formed on the surface of 
the ground a very slippery glazed frost. On the evening 
of the 22nd January, flakes of snow began to hover in the 
atmosphere like voluminous masses of wool. The greater 
part of the gas-lamps were ornamented by frozen stalac- 
tites, which continually attracted the attention of passers- 
by. The formation of these stalactites, of which we give 
a specimen, is easy of explanation. The snow falling on 
the glass of the lamp became heated by the flame of gas, 



ICICLES ON THE LAMP. 29 

melted, and trickled down, freezing anew into the shape 
of a stalactite below the lamp, at a temperature of 0° 
centigrade. Not only can meteorology be studied in 
towns, but certain other branches of natural science — 
entomology, for example. We will quote what a young 




Icicles on gas lamp. 

student in science, M. A. Dubois, says on this very 
subject : " Coleoptera," he declares, " are to be met with 
everywhere, and I think it may be useful to notice this 
fact, supporting it by examples. I desire to prove that 
there are in the midst of our large towns spots that 
remain unexplored, where some fine captures are to be 



30 



OPEN-AIR SCIENCE. 



made. Let us visit, at certain times, the approaches to 
the quays, even at low tide, and we shall be surprised 
to find there species which we have searched for far and 
near." This opinion is confirmed by the enumeration 
of several interesting captures. 

Was not the great Bacon right when he said, " For the 
keen observer, nothing in Nature is mute " ? 




The clifts of Cape Grisnex. 




CHAPTER III.— SIMPLE PHYSICS. 

THE MEANING OF n-IYSICS FORCES OF NATURE — 

GRAVITY COHESION CHEMICAL ATTRACTION — 

CENTRE OF GRAVITY EXPERIMENTS AUTOMATON 

TUMBLERS. 

[AVING now introduced our readers to Science 
^ which they can find for themselves in the open 
^ air, and the pursuit of which will both instruct 
and amuse, we will proceed to investigate the 
Branch of Science called PHYSICS. 

Physics may be briefly described as the Branch of 
Natural Science which treats of such phenomena as are 
unaccompanied by any important changes in the objects 
wherein such phenomena are observed. 

For instance, the sounding of a bell or the falling of a 
stone are physical phenomena, for the objects which cause 
the sound, or the fall, undergo no change. Heat is set 
free when coal burns. This disengagement of heat is a 
physical phenomenon ; but the change during combustion 
which coal undergoes is a chemical phenomenon. So the 
objects may be the same, but the circumstances in which 
they are placed, and the forces which act upon them, may 
change their appearance or position. 

This brings us at once to the Forces of Nature, which 
are three in number ; viz.. Gravity, Cohesion, and Affinity, 
or Chemical Attraction. The phenomena connected with 
the last-named forms the Science of Chemistry. We give 
these three Forces these names. But first we must see 



32 SIMPLE PHYSICS. 

what is Force, for this is very important. Force is a 
CAUSE — the cause of Motion or of Rest. This may 
appear paradoxical, but a Httle reflection will prove it. 
It requires force to set any object in motion, and this 
body would never stop unless some other force or forces 
prevented its movement beyond a certain point. Force is 
therefore the cause of a change of " state " in matter. 

We have said there are three forces in nature. The 
first is Gravity, or the attraction of particles at a distance 
from each other. We may say that Gravity, or Gravita- 
tion, is the mutual attraction between different portions 
of matter acting at all distances, — the force of attraction 
being, of course, in proportion to the mass of the bodies 
respectively. The greatest body is the Earth, so far as 
our purposes are concerned. So the attraction of the 
Earth is Gravity, or what we call Weight. 

We can easily prove this. We know if we jump from 
a chair we shall come to the floor ; and if there were 
nothing between us and the actual ground sufficient to 
sustain the force of the attracting power of the earth, we 
should fall to the earth's surface. In a teacup the spoon 
will attract air bubbles, and large air bubbles will attract 
small ones, till we find a small mass of bubbles formed in 
the centre of the cup of tea. Divide this bubble, and the 
component parts will rush to the sides of the cup. This 
form of attraction is illustrated by the accompanying 
diagrams. 

Suppose two balls of equal magnitude, A and B. These 
being of equal magnitude, attract each other with equal 
force, and will meet, if not opposed, at a point (m) half- 
way between the two. Jkit they do not meet, because 
the attraction of the earth is greater than the attraction 
they relatively and collectively exercise towards each 
other. But if the size of the balls be different, the attrac- 
tion of the greater will be morq evident, as shown opposite 



GRAVITY. 33 

where the points of meeting are indicated respectively. 
These experiments will illustrate the phenomena of 
falling bodies. Gravity is the cause of this, because 
every object on the surface of the earth is very much 
smaller than the earth itself, and therefore all bodies 
fall towards the centre of the earth. A certain time is 



-1 



Attraction of gravitation (i\ 

thus occupied, and we can find the velocity or rapidity of 
a falling body very easily. On the earth a body, if let 
fall, will pass through a space sixteen feet in the first 
second ; and as the attraction of the earth still continues 
and is exercised upon a body already in rapid motion, 
this rate of progress must be proportionately increased. 
Just as when steam is kept up in an engine running down 







Attraction of gravitation (2), 

hill, the velocity of the train will rapidly increase as it 
descends the gradient. 

A body falling, then, descends sixteen feet in the first 
second, and for every succeeding second it assumes a 
greater velocity. The distance the body travels has been 
calculated, and the space it passes through has been found 
to increase in proportion to the square of the time it takes 
to fall. For instance, suppose you drop a stone from the 
top of a cliff to the beach, and it occupies two seconds in 



34 SIMPLE PHYSICS. 

falling, if you multiply 2X2, and the result by sixteen, 
you will find how high the cliff is : in this (supposed) case 
it is (omitting decimals) sixty-four feet high. The depth 
of a well can also be ascertained in the same way, leaving 
out the effect of air resistance. 

But if we go up into the air, the force of gravity will 
be diminished. The attraction will be less, because we 
are more distant from the centre of the earth. This 
decrease is scarcely, if at all, perceptible, even on very 
high mountains, because their size is not great in com- 
parison with the mass of the earth's surface. The rule 
for this is that gravity decreases in proportion to the square 
of the distance. So that if at a certain distance from the 
earth's surface the force of attraction be i, if the distance 
be doubled the attraction will be only o?ie quarter as much 
as before — not one-half. 

Gravity has exactly the same influence upon all bodies, 
and the force of the attraction is in proportion to the mass. 
All bodies of equal mass will fall in the same time in a 
given distance. Two coins (or a coin and a feather in 
vacuo) will fall together. But in the air the feather will 
remain far behind the coin, because nearly all the atoms 
of the former are resisted by the air, while in the coin 
only some particles are exposed to the resistance, the 
density of the latter preventing the air from reaching more 
than a few atoms, comparatively speaking. The theory 
of weight and gravitation, and experiments relating to the 
falling of bodies, may be easily demonstrated with ordinary 
objects that we have at hand. I take a halfpenny and a 
piece of paper, which I cut in the shape of the coin, and 
holding them side by side, I drop them simultaneously ; 
the halfpenny reaches the ground some time before the 
p^per, a result quite in accordance with the laws of 
gravitation, as one must bear in mind the presence of air, 
and the different resistance it offers to two bodies differing 



COHESION. 3S 

in density. I next place the paper disc on the upper 
surface of the piece of money, and then drop them simul- 
taneously. The two objects now reach the ground at the 
same time, the paper, in contact with the halfpenny, being 
preserved from the action of the air. This experiment is 
so well known that we need not further discuss it ; but it 
must be plainly evident that it is capable of development 
in experiments on phenomena relating to falling bodies.* 
When a body influenced by the action of a force acts, in 
its turn, upon another, the latter reacts in an opposite 
manner upon the first, and with the same intensity. 

TJie attraction of Cohesion is the attraction of particles 
of bodies to each other at very small distances apart. 
Cohesion has received various names in order to expresu 
its various degrees. For instance, we say a body is tough 
or brittle, or soft or hard, according" to the degrees of co- 
hesion the particles exercise. We know if we break a 
glass we destroy the cohesion ; the particles cannot be 
reunited. Most liquid particles can be united, but not 
all. Oil will not mix with water. 

* M. A. G. has written us an interesting letter on the subject of 
similar experiments, which we here transcribe : — 

"When a siphon of seltzer water has been opened some little time, 
and the equihbrium of tension is nearly established between the escaped 
gas and the dissolved gas, a vertical stream of bubbles is seen to rise 
from the bottom of the apparatus, which present a very clear example 
of the law of ascension of bubbles ; that is to say (putting out of the 
question the expansion of the bubbles in their passage upwards), it is 
an inverse representation of the law of gravity affecting falling bodies. 
The bubbles, in fact, detach themselves from their starting point with 
perfect regularity; and as the interval varies in one file from another, 
we have before us a multiplied representation of that terrible law which 
Attwood's machine made such a bugbear to the commercial worid. I 
believe it is possible, by counting the number of bubbles that detach 
themselves in a second, in each file, and the number which the whole 
stream contains at a given instant, to carry the verification further ; 
but I must confess that I have not done so myself." 



36 SIMPLE PHYSICS. 

The force of cohesion depends upon heat. Heat 
expands everything, and the cohesion diminishes as 
temperature increases. 

There are some objects or substances upon the earth 
the particles of which adhere much more closely than 
others, and can only, with very great difficulty, be separated. 
These are termed Solids. There are other substances 
whose particles can easily be divided, or their position 
altered. These are called Fluids. A third class seem to 
have little or no cohesion at all. These are termed Gases. 

Adhesion is also a form of attraction, and is cohesion 
existing on the surfaces of two bodies. When a fluid 
adheres to a solid we say the solid is wet. We turn this 
natural adhesion to our own purposes in many ways, — we 
whitewash our walls, and paint our houses ; we paste our 
papers together, etc. 

On the other hand, many fluids will not adhere. Oil 
and water have already been instanced. Mercury will not 
stick to a glass tube, nor will the oiled glass tube retain 
any water. We can show the attraction and repulsion in 
the following manner : — Let one glass tube be dipped into 
water and another into mercury, you will see that the 
water will ascend slightly at the side, owing to the attrac- 
tion of the glass, while the mercury will be higher in the 
centre, for .it possesses no attraction for the glass. If 
small, or what are termed capillary (or hair) tubes, be used, 
the water will rise up in the one tube, while in the other 
the mercury will remain lower than the mercury outside 
the tube. (See Capillarity}) 

Chemical attraction is the force by which two different 
bodies unite to form a new and different body from 
either. 

It is needless for us to dwell upon the uses of these 
Forces of Nature. Gravity and Cohesion being left out of 
our world, we can imagine the result. The earth and sun 



CENTRE OF GRAVITY. 



37 



and planets would wander aimlessly about ; we should 
float away into space, and everything would fall to pieces, 
while our bodies would dissolve into their component 
parts. 

The Balance and Centre of Gravity. — We have spoken 
at some length about Gravity, and now we must say some- 
thing respecting tliat point called the Centre of Gravity, 
and the Balance, and upon the latter we have a few 
remarks to make first, for a well-adjusted balance is a 
most useful thing, and we will show you how to make one, 
and then proceed to our illustrations of the Centre of 
Gravity, and explain it. 

All those who cultivate experimental science are aware 





Capillarity, 

that it is useful to unite with theoretical ideas that manual 
dexterity which is acquired by the student accustoming 
himself to practical operations. One cannot too strongly 
urge both chemist and physicist to exercise themselves in 
the construction of the appliances they require, and also 
to modify those already existing, which may be adapted 
to their wants. In a large number of cases it is possible 
to manufacture, at small expense, delicate instruments, 
capable of rendering the same service as the most elaborate 
apparatus. Important scientific labours have often been 
undertaken by men whose laboratories were most simple, 
who, by means of skill and perseverance, knew how to do 
great things with small resources. A delicate balance, 
for instance, indispensable alike to chemist and physicist, 
can be manufactured at little cost in different ways. A 
thin platinum wire and a piSce df Wood is all thit ia 

4 



38 



SIMPLE PHYSICS. 



needed to make a balance capable of weighing a milligram; 
and to make a very sensitive hydrostatic balance, little is 
required besides a glass balloon. The cut represents a 
small torsion balance of extreme simplicity. A thin 
platinum wire is stretched horizontally through two staples, 
from the wooden supports, AB, which are fixed in a deal 
board. A very thin, delicate lever, CD, cut in wood, or 
made with a wisp of straw, is fixed in the centre of the 
platinum wire by means of a small clip, which secures it 
firmly. This lever is placed in such a manner that it is 
raised perceptibly out of the horizontal line. At D is fixed 




Torsion balance, which can ea<;ily be constructed, capable of weighing a milligram 
one-tenth of full size 

a paper scale, on which is put the weight of a centigram. 
The lever is lowered to a certain point, slightly twisting 
the platinum wire. Near the end of the lever a piece of 
wood, F, is fixed, on which is marked the extreme point 
of its movements. Ten equi-distant divisions are marked 
between these two points, which represent the distance 
traversed by the lever under the weight of the milligram. 
If a smaller weight than a centigram is placed on the 
paper scale the lever falls, and balances itself after a few 
oscillations. If it falls four divisions, it is evident that the 
substance weighs four milligrams. Taking a rather thicker 
platinum wire, to which a shorter lever must be adapted, 



THE BALANCE. 



39 



one can weigh the decigram, and so on. It would be an 
^asy matter, also, to make, on the same model, balances 

3r weighing considerable weights. The platinum wire 
iihould be replaced by iron wires of larger diameter, firmly 

tretched, and the lever should be made of a piece of very 

■sistmg wood. One can also, by adaptation, find the exact 

alue of the most trifling 

eights. By lengthening 

very fine platinum wire 

svcral yards, and adapt- 
ing a long, slender lever, 
it will not be impossible 
to ascertain the tenth 
of a milligram. In this 
latter case the balance 
can be set when it is 
wanted. 

The next cut represents 
Nicholson's Areometer, 
which any one may con- 
struct for himself, and 
which, as it is here 
represented, constitutes 
another kind of balance. 
A glass balloon, filled 
with air, is hermetically 
closed with a cork, 

through which is passed a cylinder of wood, surmounted 
by a wooden disc, D. The apparatus is terminated at its 
lower end by a small tray, C, on which one can put pieces 
of lead in variable quantities. It is then plunged into a 
3-lass filled with water. The pieces of lead on the tray, c, 
ire added by degrees, until the stem of the areometer rises 
ilmost entirely above the level of the water ; it is next 
passed th.rpugb a ring, which keeps it in position, and 




Nicholson's Areometer, contrived to serve as 
a balance. 



40 SIMPLE PHYSICS. 

which is fastened to the upper part of the glass by means 
of four iron wires in the shape of a cross. The stem is 
divided in such a way that the space comprised in each 
division represents the volume of a cubic centimetre. 
Thus arranged, the apparatus constitutes a balance. The 
object to be weighed is placed on the disc, D, and the 
areometer sinks in the water, oscillates, and then remains 
in equilibrium. If the stem sinks five divisions, it is 
evident that the weight of the object corresponds to that 
of five cubic centimetres of displaced water, or five grams. 

It is obvious, therefore, from the preceding examples, 
that it is not impossible to construct a weighing apparatus 
with ordmary and very inexpensive objects. We can, in 
the same way, show that it is possible to perform instruc- 
tive experiments with no appliances at all, or, at any rate, 
with common things, such as eveiyone has at hand. The 
lamented Balard, whose loss science has had recently to 
deplore, excelled in chemical experiments without a labora- 
tory; fragments of broken glass or earthenware were used 
by him for improvising retorts, bottles and vases for form- 
ing precipitates, and carrying on many important opera- 
tions. 

Scheele also operated in like manner ; he knew how 
to make great discoveries with the humblest appliances 
and most slender resources. One cannot too earnestly 
endeavour to imitate such leaders, both in teaching others 
and instructing oneself 

The laws relating to the weight of bodies, the centre of 
gravity, and stable or unstable equilibrium, may be easily 
taught and demonstrated by means of a number of very 
familiar objects. By putting into the hands of a child a 
box of soldiers cut in elder-wood, the end of each fixed 
into half a bullet, we provide him with the means of 
making some easy experiments on the centre of gravity; 
According to some authorities on equilibrium, it is Hot 



EQUILIBRIUM. 



41 



impossible, with a little patience and delicacy of manipu- 
lation, to keep an egg balanced on one of its ends. This 
experiment should be performed on a perfectly horizontal 
surface, a marble chimney-piece, for example. If one 
can succeed in keeping the egg up, it is, according to the 
most elementary principles of physics, because the vertical 
line of the centre of gravity passes through the point of 








Experiment on '* centre of gravity." 



contact between the end of the egg and the surface on 
which it rests. 

Here is a curious experiment in equilibrium, which is 
performed with great facility. Two forks are stuck into a 
cork, and the cork is placed on the brim of the neck of a 
bottle. The forks and the cork form a whole, of which the 
centre of gravity is fixed over the point of support. We 
can bend the bottle, empty it even, if it contains fluid, with- 
out the little construction over its mouth being in the least 



42 



SIMPLE PHYSICS. 



disturbed from its balance. The vertical line of the centre 
of gravity passes through the point of support, and the 
forks oscillate with the cork, which serves as their support, 
thus forming a movable structure, but much more stable 
than one is inclined to suppose. This curious experiment 




Another experiment on the same sulject. 



is often perfoimed by conjurors, who inform their audience 
that they will undertake to empty the bottle without 
disturbing the cork. If a woodcock has been served for 
dinner, or any other bird with a long beak, take off the 
head at the extreme end of the neck ; then split a cork so 
that you can insert into it the neck of the bird, which 
must be tightly clipped to keep it in place ; two forks are 



AUlUMAiA. 



43 



then fixed into the cork, exactly as in the preceding 
example, and into the bottom of the cork a pin is inserted. 
This little contrivance is next placed on a piece of money, 
which has been put on the opening of the neck of the 
bottle, and when it is fr.irly balanced, we give it a rotatory 




Automatic puppets, 

movement, by pushing one of the forks as rapidly as we 
please, but as much as possible without any jerk. We 
then see the two forks, and the cork surmounted by the 
woodcock's head, turning on the slender pivot of a pin. 
Nothing can be more comical than to witness the long 
beak of the bird turning round and round, successively 
facing all the company assembled round the -table, some- 



44 



SIMPLE PHYSICS. 



times with a little oscillation, which gives it an almost life- 
like appearance. This rotatory movement will last some 
time, and wagers are often laid as to which of the company 
the beak will point at when it stops. In laboratories, 
wooden cylinders are often to be seen which will ascend 
an inclined plane without any impulsion. This appears 
very surprising at first, but astonishment ceases when we 
perceive that the centre of gravity is close to the end of 
the cylinder, because of a piece of lead, which has been 
fixed' in it. 




First posilion of the puppets. 



Above is a very exact representation oF a plaything 
which was sold extensively on the Boulevards at Paris. 
This little contrivance, which has been known for some 
time, is one of the most charming applications of the prin- 
ciples relating to the centre of gravity. With a little skill, 
any one may construct it for himself. It consists of two 
little puppets, which turn round axles adapted to two 
parallel tubes containing mercury. When we place the 
little toy in the position as above, the mercury being at a, the 
two dolls remain motionless, but if we lower the doll s, so 
that it stands on the second step (No. 2) of the flight, as 
indicated in the second cut, the mercury descends to b at the 



THE PUPPETS. 



45 



Other end of the tube ; the centre of gravity is suddenly 
displaced ; the doll R then accomplishes a rotatory move- 
ment, as shown by the arrow in the third cut, and finally 
ahghts on step No. 3. The same movement is also 
effected by the doll S, and so on, as many times as there 
are steps. The dolls may be replaced by a hollow 
cylinder of cartridge paper closed at both ends, and con- 
taming a marble ; the cylinder, when placed vertically on 
an mclined plane, descends in the same way as the 
puppets. The laws of equilibrium and displacement of 




Second positiun of the puppets. 

the centre of gravity, are rigorously observed by jugglers, 
who achieve many wonderful feats, generally facilitated 
by the rotatory motion given to the bodies on which they 
operate, which brings into play the centrifugal force. The 
juggler who balances on his forehead a slender rod, on 
the end of which a plate turns round, would never succeed 
in the experiment if the plate did not turn on its axis 
with great rapidity. But by quick rotation the centre of 
gravity is kept near the point of support. We need 
hardly remark, too, that it is the motion of a top that 
tends to keep it in a vertical position. 

Many experiments in mechanical physics may occur 



46 



SIMPLE PHYSICS. 



to one's mind. To conclude the enumeration of those 
we have collected on the subject, I will describe the 
method of lifting a glass bottle full of water by means of 
a simple wisp of straw. The straw is bent before being 
passed into the bottle of water, so that, when it is lifted, the 





Lifting a bottle witll a singie straw. 

centre of gravity is displaced, and brought directly under 
tlic point of suspension. It is \\ell to lia\e at hand 
several pieces of straw perfectly intact, and free from 
cracks, in case the experiment does not succeed with the 
first attempt. 

Having now seen how this point we call the centre of 
gravity acts, we may briefly explain it. 



CENTRE OF GRAVITY. 



47 



The centre of gravity of a body is that point in which 
the sum of the forces of gravity, acting upon all the 
particles, may be said to be united. We know the 
attraction of the earth causes bodies to have a property 
we call Weight This property of weight presses upon 
■■liliiiiiii«iaiiiBii<...ii.m I .— Ti-^- iifM- f , , 




Balancing a v.^.^..! .^.i » uail and key. 



every particle of the body, and acts upon them as parallel 
forces. For if a stone be broken all the portions will 
equal the weight of the stone ; and if some of them be 
suspended, it will be seen that they hang parallel to each 
other, so we may call these weights parallel forces united 
in the whole stone, and equal to a single resultant. Now 
to find the centre of gravity, we must suspend the body, 



48 SIMPLE PHYSICS. 

and it will hang in a certain direction. Draw a line from 
the point of suspension, and suspend the body again : a 
line drawn from that point of suspension will pass 
through the same place as the former line did, and so on. 
That point is the centre of gravity of that suspended 
body. If the form of it be regular, like a ball or 
cylinder, the centre of gravity is the same as the mathe- 
matically central point. In such forms as pyramids it will 
be found near the largest mass ; viz., at the bases, about 
one-fourth of the distance between the apex and the centre 
of gravity of the base. 

When the centre of gravity of any body is supported, 
that body cannot fall. So the well-known leaning towers 



Anotlier experiment. 

are perfectly safe, because their lines of direction fall 
within the bases. The centre of gravity is in the rentre 
of the leaning figure. The line of direction drawn 
vertically from that point falls within the base ; but if the 
tower were built up higher, so that the centre of gravity 
were higher, then the structure would fall, because the 
line of direction would fall without the base. 

We see that animals (and men) are continually altering 
the position of the centre of gravity; for if a man bears 
a load he will lean forward, and if he takes up a can of 
water in one hand he will extend the other to preserve 
his balance or equilibrium. 

The experiment shown in the foregoing illustration 
is apparently very difficult, but it will be found easy 



THE KEY BALANCED. 



49 



enough in practice if the hand be steady. Take a key, 
and by means of a crooked nail or " holdfast,'' attach it 
to a bar of wood by a string tied tightly round the bar, 
as in the picture. To the other extremity of the bar 
attach a weight, and then drive a large-headed nail into 
the table. It will be found that the key will balance, and 
even move upon the head of the nail, without falling. 
The weight, is under the table, and the centre of gravity 
is exactly beneath the point of suspension. 

Another simple experiment may prove amusing. Into 
a piece of wood insert the points of two knives, and at 
the centre of the end of the bar insert a needle between 
the knife handles. The wood . and the knives may then 
be balanced on another needle fixed in a cork at A. 

We may conclude this chapter by summing up in a 
few words what the Centre of Gravity is. We can define 
it as " that point in a body upon which the body, acted 
on solely by the force of gravity, will balance itself in all 
positions." Such a point exists in every body, and 
equally in a number of bodies fastened tightly together. 
The Centre of Gravity has by some writers been denomi- 
nated the Centre of Parallel Forces, or the Centre of Mag- 
nitude, but the Centre of Gravity is the most usual and 
best understood term. 





CHAPTER IV.— SOLID BODIES. 

SOME PROPERTIES OF SOLID BODIES INERTIA MOTION 

FRICTION— THE PENDULUM EQUILIBRIUM. 

HOSE who have followed us through the pre- 
ceding pages have now, we hope, some ideas 
upon Gravity and the Forces of Nature. In 
speaking of Forces we said "Force was a cause 
of Motion." Let us now consider Inertia, and Motion 
with its accompanying opponent, Friction. 

Inertia is the passiveness of Matter. This perfect 
indifference to either rest or m,otion makes the great 
distinction between living and lifeless matter. Inertia, or 
Vis Inertia, is this passiveness. Now, to overcome this 
indifference we must use force, and when we have applied 
force to matter we set it in motion ; that is, we move it. 
When we move it we find a certain resistance wtiich is 
always proportionate to the force applied. In mechanics 
this is termed Action, and Reaction, which are always 
equal forces acting in opposite directions. This is 
Newton's law, and may be explained by a "weight" on a 
table, which presses against the table with the same force 
with which the table presses against the "weight"; or 
v/hen j'ou strike a ball, it strikes the hand with the same 
force. 

We can communicate motion by elasticity. For in- 
stance, if we place a number of coins upon a table touching 
each other and in a straight line, . and strike the last coin 
of the line by pushing another sharply against it. the piece 



PROPERTIES OF BODIES. 5 I 

at the opposite extremity will slip out of its place from the 
effect of the shock transmitted by the coin at the other 
end. 

When two forces act upon a body at the same time it 
takes a direction intermediate. This is known as the 
re.sultant. The enormous forces.exercised by the heavenly 
bodies will be treated of later. We will first consider 
Inertia. 




Shoclc communicated by elasticity. 



There are several experiments relating to the subject of 
Inertia which may be performed. I once witnessed one 
quite accidentally when taking a walk. 

I was one day passing the Observatory at Paris, when 
I noticed a number of people collected round a professor, 
who after executing several juggling tricks, proceeded to 
perform the curious experiment I am about to describe. 
He took a broomstick and placed it horizontally, passing 
the ends through two paper rings. He then asked two 



52 



SOLID BODIES. 




A SIMPLE EXPERIMENT. 



53 



children to hold the paper rings by nieans of two razors, 
so that the rings rested on the blade. This done, the 
operator took a stout stick, and, with all his strength, 
struck the broomstick in the centre; it was broken into 
shivers, but the paper rings were not torn in the least, or 




Another experiment on the same subject. 

even cut by the razors ! One of my friends, M. M , 

a painter, showed me how to perform this experiment as 
represented in the illustration. A needle is fixed at each 
end of the broomstick, and these needles are made to rest 
on two glasses, placed on chairs ; the needles alone must 
be in contact with the glasses. If the broomstick is then 
struck violently with another stout stick, the former will be 



54 SOLID BODIES. 

broken, but the glasses will remain intact. The experi- 
ment answers all the better the more energetic the action. 
It is explained by the resistance of inertia in the broom- 
stick. The shock suddenly given, the impulse has not 
time to pass on from the particles directly affected to the 
adjacent particles ; the former separate before the move- 
ment can, be transmitted to the glasses serving as 
supports.* 

The experiment next represented is of the same nature. 
A wooden ball is suspended from the ceiling by a rather 
slender thread, and a similar thread is attached to the 
lower end of the ball. If the lower thread is pulled 
forcibly it will break, as shown in the illustration; the 
movement communicated to it has not time to pass into 
the ball ; if, on the contrary, it is pulled very gradually and 
without any shock, the upper thread instead will break, 
because jn this case it supports the weight of the ball. 
Motion is not imparted simultaneously to all parts of a 
body, but only to the particles first exposed to a blow, for 
instance. One might multiply examples of this. If a 

* The experiment we have just described is a very old one. M. V. 
Sircoulon has told us that it was described at length in the works 
of Rabelais. The following remarks are in " Pantagruel," book II., 
chap. xvii. 

" Panuras then took two glasses of the same size, filled them with 
water, and put one on one stool, and the other on another, about five 
feel apart, and placed the staff of a javelin about five-and-a-half feet 
long across, so that the ends of the staff just touched the brim of the 
glasses. That done, he took a stout piece of wood, and said to the 
others : ' Gentlemen, this is how we shall conquer our enemies ; for 
in the same way that I shall break this staff between these two glasses, 
without the glasses being broken or injured, or spilling a single drop 
of water, so shall we break the head of our Dipsodes, without any injury 
to ourselves, and without getting wounded. But that you may not 
think there is magic in it, you, Eusthenes, strike with this stick as hard 
as yoa can in the centre.' This Eusthenes did, and the staff broke in 
two pieces, without a drop of water being spilt." 



INERTIA. 



55 



bullet be shot from a gun, it will make a round hole in a 
piece of wood or glass, whilst if thrown by the hand, — 
that is to say, with much less force, — it will shiver the 
wood or the pane of glass to pieces. When the celerity 
of the motive force is very great, the particles directly 
affected are disturbed so quickly that they separate from 
the adjacent particles before there is time for the move- 
ment to be communicated to the latter. 




Extracting a *' man " from a pile of draughts without overturning the pile. 



It is possible, for the same reason, to extract from a 
pile of money a piece placed in the middle of the pile 
without overturning the others. It suffices to move them 
forcibly and quickly with a flat wooden ruler. The 
experiment succeeds very well also if performed with 
draughtsmen piled up on the draught-board. 

Another experiment which belongs to the laws of 
resisting force is herewith shown. A sixpence is placed 



= 6 



SOLID BODIES. 



on a table covered with a cloth or napkin. It is covered 
with a glass, turned over so that its brim rests on two 
penny pieces. The problem to be solved is how to 
extract the sixpence from underneath the glass without 
touching it, or slipping anything beneath it To do this 




Call ng out a sixpence from the glass. 



it is necessary to scratch the cloth with the nail of the 
forefinger ; the elasticity of the material communicates 
the movement to the sixpence, which slowly moves in the 
direction of the finger, until it finally comes out completely 
from beneath the glass. 

Wc may give another experiment concerning Inertia. 
Take a strip of paper, and upon it place a coin, on a 



EXPERIMENT OF ELASTICITY. 



57 



marble chimney-piece, as in the illustration. If, holding 
the paper in the left hand, you strike it rapidly and 
forcibly, you will be enabled to draw away the paper 
without causing the coin (say a five-shilling-piece) to fall 
down. 




Drawing a slip of paper from beneath a coin. 



It is not impossible to draw away a napkin laid as a 
tablecloth for one person's dinner, without disturbing the 
various articles laid upon it. A quick motion is all that 
is necessary, keeping the napkin tightly extended by the 
hands at the same time. This latter experiment, however, 
is not recommended to boys home for the holidays, as they 



-8 SOLID BODIES. 

may unwillingly practise a feat analogous to that executed 
by Humpty-Dumpty, and find equal difficulty to match 
the pieces. 

We will now examine the term Motion. A body is 
said to be in motion when it changes its position in 
relation to surrounding objects. To perceive motion the 
surrounding objects must be relatively at rest, for if they 
all hurried along at the same rate no motion would be 
perceptible. This is evident, for when we stand still trees 
and houses appear stationary, as do we ourselves, but we 
know we all are rushing round with the earth, though our 
relative positions are unchanged. Hence there is no 
absolute rest. 

What are the causes of motion i" — Gravity is one. The 
influence of heat, which is itself caused by the motion of 
atoms, the eflects of electricity, etc., and finally, the power 
of force in men or animals — any of these causes will pro- 
duce motion. But a body at rest cannot put itself in 
motion, nor can a body in motion stop itself, or change 
its condition of motion. 

But you may say a body will stop itself. Your ball 
on the ground, or even upon ice, will eventually come to 
a stop. Wc fire a bullet, and it will stop in time. We 
reply it docs not stop of itself. The resistance of the Air 
and Friction tend to bring the body in motion to a state 
of rest. In the case of a bullet gravity brings it down. 

There is no need .to insist upon the resistance offered 
by the air even when it is not rushing violently past to 
fill up a vacuum beyond us, and called a breeze, or high 
v/ind. But we may say something of Friction. 

Friction is derived from the Latin frico, to rub, and 
expresses th.e resistance to motion which arises from 
uneven surfaces. It is a passive resistance, and depends 
upon the force which keeps the bodies together. Thus a 
train running upon a smooth iron rail would never be able 



FRICTION. 59 

to proceed but for friction, which gives the necessary 
purchase or grip to the wheel and rail in contact. 

No surface is perfectly smooth, for we must push a 
body upon the smoothest surface we possess. Friction 
tends to resist motion always, and is the cause of a great 
loss of power in mechanics, though it is employed to stop 
motion by certain appliances, such as " breaks " and 
" drags," for sliding friction is greater than rolling friction. 
But without friction most structures would fall to pieces, 
and all forward motion would cease. So though it is an in- 
convenient force to overcome, we could not do without it. 

If a body is set in motion, we see that the tendency of 
it is to go on for ever. Such, indeed, is the case with the 
stars ; but so long as we are within the influence of the 
earth's attraction, we cannot expect such a result. We 
know now what motion is ; we must also, to understand 
it perfectly, consider its direction and its velocity. 

The line which indicates the way from the starting 
point to the end is the direction of the object in motion, 
and the rate it rrttves at its velocity. The latter is calcu- 
lated at so many miles an hour, as a train ; or so many 
feet in a second if the object be a shot, or other very 
rapidly- moving body. In equal velocity the same distance 
is traversed in the same time ; and so if a train run a mile 
in a minute, we know it will travel sixty miles in an hour, 
and is therefore during that minute going at the rate of 
sixty miles an hour. We have already spoken of the 
velocity of a stone, falling from a cliff as sixteen feet in a 
second, and a stone thrown into the air to rise sixteen 
feet will be a second in going up, and a second in descend- 
ing. But the velocity will be accelerated in the descent 
after the first second of time, and retarded in the upward 
cast by gravity. So we have two terms — accelerated and 
retarded velocity — used to express an increased or de- 
creased force of attraction. 



/ 



6o SOLID BODIES. 

Perpetual motion has often been sought, but never 
discovered, nor will it ever be till the elixir of life has 
been found. It is quite impossible to construct any 
machine that will work without friction ; if any work be 
done energy will be expended and transformed into other 
energy, so the total must be diminished by so much as 
was employed to transform the remainder. No body can 
give unlimited work, therefore the perpetual motion theory 
is untenable and impossible. 

The pendulum is considered the nearest approach to 

perpetual motion. This is so well known that no descrip- 

.f.?v_ tion is needed, but we may 

/ I \ say a few words concerning it. 

/ i \ By the diagram, we see that 

\ if we lift the ball to b, and 

I '\ let it fall, it will descend to /, 

/ j \ and pass it to a opposite, 

nearly as far from / as i^ is 

from it. So the oscillations 

will continue, each beat being 

_„ less and less, till rest is reached 

The pendulum. 

by the action of gravity. Were 
it not for friction and the pressure of the air, the oscilla- 
tions would continue for ever ; as it is, it declines by 
shorter swings till it remains in equilibrium. 

The seconds' pendulum oscillates sixty times an hour, 
and must be of a certain length in certain places. In 
London it is 39"I393 inches, and furnishes a certain 
standard of length, and by an Act of Parliament the yard 
is divided into 36 parts, and 39" 1393 such parts make 
the seconds' pendulum in the latitude of London (in 
vacuo) in a temperature of 62°. 

But the same pendulum will not perform the same 
number of oscillations in one minute in all parts of the 
globe. At the equator they will be less, and at the pole 




CENTRIFUGAL FORCE. 



6l 



more. Thus it was discovered that, as the movements of 
the pendulum are dependent upon the force of gravity, 
and as this force decreases the farther we get from the 
centre of the earth, the equator must be farther from the 
earth's centre than the poles, and therefore the poles must 








Centrifugal force. 

be depressed. The decline of the pendulum at the equator 
is also, in a measure, due to Centrifugal Force. 

Centrifugal Force, which means " flying from the centre," 
is the force which causes an object to describe a circle 
with uniform velocity, and fly away from the centre ; the 
force that counteracts it is called the centripetal force. A 
very simple experiment will illustrate it. 



62 



SOLID BODIES. 



To represent its action we shall have recourse to an 
ordinary glass tumbler placed on a round piece of cardboard, 
held firmly in place by cords. Some water is poured 
in the glass, and we then show that it can be swung to 




Another Hlustrfition of centrifugal force. 



and fro and round without the water being spilt, even 
when the glass is upside down. 

Another experiment on the same subject is as shown 
in the above illustration, by which a napkin ring can be 
kept in revolution around the forefinger, and by a con- 
tinued force the ring may be even held suspended at the 
tip of the finger, apparently in the air, without support. 




CHAPTER v.— GASES AND LIQUIDS. 

PRESSURE OF THE AIR EXPERIMENTS THE MAGDE- 
BURG HEMISPHERES AIR-PUMPS THE BAROMETER 

— THE PUMP. 

I E have more than once referred to the pressure 
of the air which exerts a great influence upon 
bodies in motion, but a few experiments will 
make this more obvious, and clearly demon- 
strate the fact. We have also told you some of the 
properties of Solids, such as Weight, Inertia, Friction, 
and Resistance, or Strength. Solids also, as we have 
seen, occupy space, and cannot be readily compressed, 
nor bent to other shapes. Now the subject of the 
Pressure of the Air leads us to the other forms of 
Matter ; namely. Gases and Liquids, which it will be 
found very interesting to study. 

The force of air can very soon be shown as acting with 
considerable pressure upon an egg in a glass. By blowing 
in a claret glass containing a hard-boiled egg, it is possible 
to cause the egg to jump out of the glass ; and with 
practice and strength of lungs it is not impossible to 
make it pass from one glass to ancther, as per illustration. 
The force of heated air ascending can also be ascer- 
tained by cutting up a card into a spiral, and holding it 
above the flame of a lamp. The spiral, if lightly poised, 
will turn round rapidly. 

Now let us turn to a few experiments with the air, 
which is composed in two gases. Oxygen and Nitrogen, 
Qf which we shall bear more when we learn Chemistry, 



64 



GASES AND LIQUIDS. 



It is not intended here to prosecute researches, but 
rather to sketch a programme for instruction, based on 
amusing experiments in Physics, performed without 
apparatus. The greater part of these experiments are 
probably well known, and we desire to say that we 







Blowing an egg iVom one glass to another, 

merely claim to have collected and arranged them for 
our descriptions. We must also add that we have 
performed and verified these experiments ; the reader, 
therefore, can attempt them with every certainty of 
success. We will suppose that we are addressing a 
young auditory, and continue our course of Physics 



AIR PRESSURE. 



65 



with some facts relating to the pressure of air. A wine- 
glass, a plate, and water, will serve for our first experi- 
ments. Pour some water on the plate, light a piece 
of paper resting on a cork, and cover the flame with 
the glass which I turn upside down. What follows ? — 



^r\ ^ 



cc 








Movement of heated air 



The water rises in the glass. Why .'— Because the burn- 
ing of the paper having absorbed a part of the oxygen, 
and the volume of confined gas being diminished, the 
pressure of the outer air has driven back the fluid. I 
next fill a goblet with water up to the brim, and cover it 
with a sheet of paper which touches both the edge of the 
glass and the surface of the water. I turn the glass 



66 



GASES AND LIQUIDS. 



upside down, and the sheet of paper prevents the water 
running out, because it is held in place by atmospheric 
pressure. It sometimes happens that this experiment 
does not succeed till after a few attempts on the part of 
the operator ; thus it is prudent to turn the glass over a 




Pressure of the air. 



basin, so that, in case of failure, the water is not spilt. 
Having obtained a vase and a bottle, both quite full of 
water, take the bottle, holding it round the neck so that 
the thumb can be used as a stopper, then turn it upside 
down, and pass the neck into the water in the vase. 
Remove your thumb, or stopper, keeping the bottle in 



AN EXPERIMENT. 



67 



a vertical position, and you will see that the water it 
contains does not escape, but remains in suspension. It 
is atmospheric pressure which produces this phenomenon. 
If, instead of water, we put milk in the bottle, or some 
other fluid denser than water, we shall see that the milk 




- .essure of the air. 



also remains suspended in the bottle, only there is a 
movement of the fluid in the neck of the bottle, and on 
careful examination we perceive very plainly that the 
milk descends to the bottom of the vase, and the water 
rises into the bottle. Here, again, it is atmospheric 
pressure which maintains the fluid in the bottle, but the 



68 



GASES AND LIQUIDS. 



milk descends, because fluids are superposed according to 
their order of density, and the densest Hquid falls to the 
bottom. 

This can be verified by means of the phial of ttie fotcf 
elements, which is a plain, long, and narrow bottle, contain- 




w'o adhering by pressure of air. 



ing equal volumes of metallic mercury, salt water, alcohol, 
and oil. These four liquids will lie one on the top of the 
other without ever mixing, even if shaken. 

Another experiment as to the pressure of the air may 
be made. Take a penny and press it against some oaken 
bookcase or press, rub the coin against the wood for a few 
seconds, then press it, and withdraw the fingers. The 



THE EGG EXPERIMENT. 



69 



coin will continue to adhere to the wood. The reason of 
this is, because by the rubbing and the pressure you have 
dispersed the film of air which was between the penny and 
the wood, and under those conditions the pressure of 
the atmospheric air was sufficient to keep the penny in its 
place. 




Hard-boiled egg. divested of its sliell, pnssing through the tiecTc ofa glass bottle, under 
the influence of atmospheric pressure. 

Or, again, let us now add a water-bottle and a hard- 
boiled Qgg to our appliances ; we will make use of the air- 
pump, and easily perform another experiment. I light a 
piece of paper, and let it burn, plunging it into a water- 
bottle full of air. When the paper has been burning a 
few seconds I close the opening of the water-bottle by 

6 



•JO GASES AND LIQUIDS. 

means of a hard-boiled egg, which I have previously 
divested of its shell, so that it forms a hermetic stopper 
The burning of the paper has now caused a vacuum of air 
in the bottle, and the egg is gradually thrust in by the 
atmospheric pressure outside. We see it slowly lengthening 
and stretching out as it passes through the aperture ; then 
it is suddenly thrust completely into the bottle with a little 
explosive sound, like that produced by striking a paper 
bag expanded with air. This is atmospheric pressure 
demonstrated in the clearest manner, and at little cost. 

If it is desired to pursue a little further the experi- 
ments relating to atmospheric pressure, it will be easy 
enough to add to the before-mentioned appliances a 
closed glass-tube and some mercury, and one will then 
have the necessary elements for performing Torricelli's 
and Pascal's experiments, and explaining the theory of 
the barometer. 

An amusing toy, well-known to schoolboys, called the 
"sucker," may also be made the object' of many disserta- 
tions on the vacuum and the pressure of air. It is com- 
posed of a round piece of soft leather, to the centre of 
which is attached a small cord. This leather is placed on 
the ground and pressed under foot, and when the cord 
is pulled it forms a cupping-glass, and is only separated 
with difficulty from the pavement. 

Atmospheric air, in common with other gases, has a 
tendency to fill any space into which it may enter. The 
mutual attraction of particles of air is nil : on the contrary, 
they appear to have a tendency to fly away from each 
other ; this property is called " repulsion." Air also 
possesses an expansive property — a tendency to. press 
against all the sides of any vessel in which it may be 
enclosed. Of course the larger the vessel containing a 
given quantity of air, the less actual pressure it will exert 
un the sides of the vessel, The felasticity of air therefore 



WEIGHT OF AIR. 7 1 

decreases with increasing expansion, but it gains in 
elasticity or force when compressed. 

There is a law in Physics which expresses the relation 
between expansion and elasticity of gases, which may be 
said to be as follows : — 

The elasticity (of a gas) is in inverse ratio to the space 
it occupies, and therefore by compressing air into a small 
space we can obtain a great force, as in the air-gun and 
the pop-gun of our youthful days. 

In the cut below we can illustrate the principle of the 
pop-gun. The chamber full of air is closed by a cork 
and by an air-tight piston (s) at / and p. When the 
piston is pushed into the chamber the air is compressed 
between it and the stopper, which at length flies out 
forcibly with a loud report. 




The principle of the pop-gun. 

We have said that the tendency of air particles is to 
fly away from each other, and were it not for the earth's 
attraction the air might be dispersed. The height of the 
atmosphere has been variousl}' estimated from a height of 
45 miles to 212 miles in an attenuated form ; but perhaps 
100 miles high would be a fair estimate of the height to 
which our atmosphere extends. 

The pressure of such an enormous body of gas is very 
great. It has been estimated that this pressure on the 
average human body amounts to fourteen tons, but being 
balanced by elastic fluids in the body, the inconvenience is 
not felt. The Weight of Air can easily be ascertained, 
though till the middle of the seventeenth century the air 
was believed to be without weight. The following ex» 
periment will ptovie the weight of air. Takfe an GH-dittary 



72 



GASES AND LIQUIDS. 



balance, and suspend to one side a glass globe fitted with 
a stop-cock. From this globe extract the air by means of 
the air-pump, and weigh it. When the exact weight is 




Weighing the air. 

ascertained turn the stop-cock, the air will rush in, and the 
globe will then pull down the balance, thus proving that air 
possesses weight. The experiments of Torricelli and Otto 
Von Guerike, however, demonstrated that the air has weight 



THE AIR-PUMP. 



73 




Magdeburg Hemispheres. 



and great pressure. Torricelli practically invented the 

barometer, but Otto Von Guerike, by the cups known as 

Magdeburg Hemispheres, proved 'the pressure of the 

outward air. This apparatus is 

well known, and consists of two 

hollow copper hemispheres which 

fit very closely. By means of the 

air-pump which he invented in 1 6 5 o, 

Otto Von Guerike exhausted the 

air from the closed hemispheres. 

So long as air remained in them, 

there was no great difficulty in 

separating them ; but when it had 

been iinally exhausted, the pressure 

of the surrounding atmosphere was 

so great that the hollow spheres 

could not be dragged asunder even 

by horses harnessed to rings which had been inserted in 

the globes. 

The Air-Ptimp is a very useful machine, and we will 
now briefly explain its action. The inventor was, as 
remarked above, Otto von Guerike, of Magdeburg. The 
pump consists of a cylinder and piston and rod, with two 
valves opening upwards — one valve being in the bottom 
of the cylinder, the other in the piston. This pump is 
attached by a tube to a plate with a hole in it, one ex- 
tremity of the tube being fixed in the centre of the plate, 
and the other at the valve at the bottom of the cylinder. 
A glass shade, called the receiver, is placed on the top of 
the plate, and of course this shade will be full of air. 

When the receiver is in position we begin to work the 
pump. We have said there are two valves. So when the 
piston is drawn up, the cylinder would be quite empty did 
not the valve at the bottom, opening upwards, admit some 
air from the glass shade through the tube to enter the 



74 



GASES AND LIQUIDS. 



'^ 



9 



] 



The air-pump. 



cylinder. Now the lower part of the cylinder is full of 
air drawn from the glass shade. When we press the piston 
down again, we press against the air in it, which, being 
„ compressed, tries to escape. It cannot 

go back, because the valve at the bottom 
of the cylinder won't open, so it escapes 
by the valve in the piston, and goes 
away. Thus a certain amount of air is 
got rid of at each stroke of the piston. 
Two cylinders and pistons can be used, 
and so by means of cog-wheels, etc., the 
air may be rapidly exhausted from the receiver. Many 
experiments are made with the assistance of the air-pump 
and receiver, though the air is never entirely exhausted 
from the glass. 

The " Sprengel " air-pump is used to create an almost 
perfect vacuum, by putting a vessel to be exhausted in 
connection with the vacuum at the top of a tube of 
mercury thirty inches high. Some air will bubble out, 
and the mercury will fall. By filling up again and repeat- 
ing the process, the air vessel will in time be completely 
exhausted. This is done by Mr. Sprengel'.s pump, and a 
practically perfect vacuum is obtained, like the Torricellian 
vacuum. 

The " Torricellian vacuum" is the empty space above 
the column of mercury in the 
i^° \^ barometer which we will proceed 
to describe. Air has a certain 
weight or pressure which is suf- 
ficient to raise a column of mercury 
thirty inches. We will prove this 
by illustration. Take a bent tube 
and fill it with mercury ; the liquid 
Air pressure. ^^.j^ ^^^^^ equally high in both 

arms, in consequence of the ratio of equilibrium in 




THE BAROMETER, 



75 



fluids, of which we shall read more when we come to 
consider Water. So the two columns of mercury are in 
equilibrium. (See A.) Now stop the arm a with a cork, 
and take out half the mercury. It will remain in one 
arm only. Remove the cork, and the fluid will fall in both 




TKe Barometer. 



arms, and remain in equilibrium. If a long bent glass tube 
be used, the arms being thirty-six inches high, the mercury 
will fall to a point, c, which measures 29-9 inches from the 
bottom. If the tube be a square inch in bore, we have 
29-9 cubic inches of mercury, weighing I4|lbs., balancing 
a column of air one square inch thick and as high as the 
atmosphere. So the mercury and the column of air must 



76 



gaSes and liquids. 



weigh the same. Thus every square inch on the earth 
supports a weight of (nearly) i 5 lbs. 

The barometer invented by Pascal, working on the 
investigations of Torricelli, is a very simple and useful 
instrument. Fill a tube with mercury from which all 
moisture has been expelled, and turn it over in a dish of 
mercury : the mercury will rise to a certain height (30 
inches), and no higher in vacuo. When the pressure of 
the air increases the mercury rises a little, and falls when 
the pressure is removed. Air charged with aqueous vapour 
is lighter than dry air, so a fall in the mercury indicates a 
certain amount of water-vapour in the air, which may. 
condense and become rain. The action of mercury is^ 
therefore used as a weather-glass, by which an index-point 
shows the movements of the fluid, by means of a wheel 
over which a thread passes, sustaining a float and a 
counterpoise. When the mercury rises the float goes up, 
and the weight falls, and turns the wheel by means of the 
thread. The wheel having a pointer on the dial tells us 
how the mercury moves. This weather-glass is the usual 
syphon barometer with the float on the surface 
and a weight. 

The Syphon Barometer is a bent tube like 
the one already shown, with one limb much 
shorter than the other. 

The Aneroid Barometer, so called because it 
is "without moisture," is now in common use. 
In these instruments the atmospheric pressure 
is held in equilibrium by an elastic metal spring 
or tube. A metal box, or tube, is freed from 
air, and then hermetically sealed. This box 
has a flexible side, the elasticity of which, and 
the pressure of the air on it, keep each other in 
equilibrium. Upon this elastic side the short arm of a 
lever is pressed, while the longer arm works an index- 




byphon 
baromeler. 



WATER BAROMETER. 



77 



When pressure 



point, as in the circular barometer, 
increases the elastic 
box " gives " ; when 
pressure diminishes it 
reti;rns to its former 
place, and the index 
moves in the opposite 
direction. It is neces- 
sary to compare and 
" set" the aneroid with 
the mercurial barome- 
ter to ensure correct- 
ness. A curved tube 
is sometimes used, 
which coils and un- 
coils like a spring, 
according to the pres- 
sure on it. 

There are other 
barometers, such as 
the Water Barometer, 
which can be fixed 
against the side of a 
house, and if the water 
be coloured, it will 
prove a useful indi- 
cator. As the name 
indicates, water is used 
instead of mercury, but 
as the latter is thirteen- 
and-a-half times heavier 
than water, a much 
longer tube is neces- 
sary ; viz., one about thirty-five feet in length. The con- 
struction is easy enough. A leaden pipe can be fixed 




The Water Barometer. 



78 Gases and liquids. 

against the house ; on the top is a funnel furnished with 
a stop cock, and placed in a vase of water. The lower 
part of the tube is bent, and a glass cylinder attached, 
with another stop-cock — the glass being about three feet 
long, and graduated. Fill the tube with water, shut the 
upper stop-cock, and open the lower one. The vacuum 
will be formed in the top of the tube, and the barometer 
will act on a larger scale than the mercury. 

The Glycerine Barometer, invented by Mr. Jordan, and 
in use at the Times oiifice, registers as more than one inch 
movements which on the mercurial thermometer are only 
one-tenth of an inch, and so are very distinctly visible. 
The specific gravity of pure glycerine is less than one-tenth 
that of mercury, so the mean height of the glycerine 
column is twenty-seven feet at sea level. The glycerine 
has, however, a tendency to absorb moisture from the air, 
but Mr. Jordan, by putting some petroleum oil upon the 
glycerine, neutralized that tendency, and the atmospheric 
pressure remains the same. A full description of this 
instrument was given in the Times of 25th October, 
1880. 

The uses of the barometer are various. It is employed 
to calculate the heights of mountains ; for if a barometer 
at sea level stand at 30° it will be lower on a mountain 
top, because the amount of air at an elevation of ten 
thousand feet is less than at the level of the sea, and 
consequently exercises less pressure, and the mercury 
descends. [The pressure is on the bulb of mercury at the 
bottom, not on the top, remember.] 

The pressure of the air at the tops of mountains some- 
times decreases very much, and it is not sufficiently 
dense for perfect respiration, as many people find. Some 
climbers suffer from bleeding at the nose, etc., at great 
altitudes. This is occasioned by the action of the heart, 
which pumps with great force, and the outward pressure 



DIVING-BELL. 



79 



upon the little veins being so much less than usual, they 
give way. 

Many important instruments depend upon atmospheric 
pressure. The most important of these is the pump, 
which will carry us to the consideration of water and 




The principle of the diving-bell. 



Fluids generally. The fire-engine is another example, 
but we will now proceed to explain the diving-bell already 
referred to. 

The experiment of the diving-bell, which is so simple, is 
explained farther on. It belongs to the same category of 
experiments as those relating to the pressure of air and 



8o 



GASES AND LIQUIDS, 



compression of gas. Two or three flies have been intro- 
duced into the glass, and they prove by their buzzing 




Diver under water. 



about that they are quite at their ease in the rather 
confined space. 

The Diving-Bell in a crude form appears to have 



THE PUMP. 8 1 

been used as early as 1538. It was used by two Greeks 
in the presence of the Emperor Charles V., and numerous 
spectators. In the year 1720 Doctor Halley improved 
the diving-bell, which was a wooden box or chamber open 
at the bottom. Air casks were used to keep the inmate 
supplied with air. The modern diving-bell was used by 
Smeaton in 1788, and was made of cast iron. It sinks 
by its own weight. The pressure of the air inside is 
sufficient to keep the water out. Air being easily com- 
pressed, it is always pumped in to keep the hollow iron 
" bell " full, and to supply the workmen. There are 
inventions now in use by which the diver carries a supply 
of air with him on his back, and by turning a tap can 
supply himself for a long time at a distance from the 
place of descent, and thus is able to dispense with the 
air-tube from the boat at the surface. This apparatus 
was exhibited at the Crystal Palace some years ago. 

The Pump. 

We have seen in the case of the Water Barometer that 
the pressure of the air will sustain a column of water 
about thirty feet high. So the distance between the 
lower valve and the reservoir or cistern must not be more 
than thirty-two feet, practically the distance is about 
twenty-five feet in pumps. 

We can see by the illustration that the working is 
much the same as in the air-pump. The suction pipe, B, 
is closed by the valve, C, the cylinder, D, and spout, E, are 
above, the piston rod, F, lifts the air-tight piston in which 
is a valve, H. When the piston is raised the valve, c, 
opens and admits the water into the cylinder. When the 
piston is depressed the valve, C, is closed, the water already 
in forces H open, and passing through the piston, reaches 
the cylinder and the spout. 



82 



GASES AND LIQUIDS. 



The hand fire-engine depends upon the action of com- 
pressed air, which is so compressed by pumping water 
into the air chamber, a. The tube is closed at g, and the 
pumps, e e, drive water into the air chamber. At length 
the tap is opened, and the air drives the water out as it 
is continually supplied. 

Compressed air was also used for driving the boring 
machines in the Mount Cenis tunnel. In this case also 




The Hand Fire-Engine 

the air was compressed by water, and then let loose, like 
steam, to drive a machine furnished with boring instru- 
ments. 

A pretty little toy may be made, and at the same time 
exemplify an interesting fact in Physics. It is called the 
ludion, and it " lies in a nut shell " in every sense. When 
the kernel has been extracted from the shell, fasten the 
portions together with sealing wax, so that no water can 
enter. At one endj Oj as in the illustration) leave a small 



PROPERTIES OF AIR. 83 

hole about as large as a pin's head ; fasten two threads 

to the sealing wax, and to the threads a wooden doll. 

Let a weight be attached to his waist. 

When the figure is in equilibrium, and 

will float, put it into a jar of water, 

and tie a piece of bladder over the 

top. If this covering be pressed with 

the finger, the doll will descend and 

remount when the finger is removed. 

By quick successive pressure, the 

figure may be made to execute a pas 

seiil. The reason of the movement is 

because the ^ight cushion of air in 

the upper part of the vase is com- 
pressed, and the little water thus caused 
to enter the nut shell makes it heavier, 
and it descends with the figure. 

We have now seen that air is a 
gas, that it exercises pressure, that it 
possesses weight. We know it can be 
applied to many useful purposes, and 
that the air machines and inventions — 
such as the air-pump and the "Pneu- 
matic Despatch " — are in daily use Ivt - 
our laboratories, our steam engines, our condensed milk 
manufactories, and in many other industries, and for our 
social benefit. Compressed air is a powerful motor for 
boring machinery in tunnels where steam cannot be used, 
even if water could be supplied, for smoke or fire would 
suffocate the workers. To air we owe our life and our 
happiness on earth. 

Pneumatics, then, deals with the mechanical properties 
of elastic fluids represented by air. A gas is an elastic 
fluid, and diflfers very considerably from water ; for a gas 
win fill d lat-ge dr Small space with equal ieonveniencej like 




The Pump, 



84 



GASES AND LIQUIDS. 



the genii which came out of the bottle and obligingly 
retired into it again to please the fisherman. We have 
seen that the pressure of the air is 14* lbs. per square inch 
at a temperature of 3 2°. It is not so easy to determine 




The Lud.on. 



the pressure of air at various times as that of water. We 
can always tell the pressure of a column of water when 
we find the height of the column, as it is the weight of so 
many cubic inches of the liquid. But the pressure of the 
atmosphere per square inch at any point is equal to the 
weight of a vertical column of air one inch square, reach- 
ing from that point to the limit of the atmosphere above 
it. Still the density is not the same at all points, so we 



DENSITY OF AIR. 



8S 



have to calculate. The average pressure at sea level is 
147 per square inch, and sustains a column of mercury 
I square inch in thickness, 29-92, or say 30 inches high. 
These are the data upon which the barometer is based. 




Diving-bell. 




CHAPTER VI.— AERONAUTICS. 

PRESSURE OF AIR IN BODIES EARLY ATTEMPTS TO 

FLY IN THE AIR DISCOVERY OF HYDROGEN THE 

MONTGOLFIER BALLOONS FIRST EXPERIMENTS IN 

PARIS NOTED ASCENTS. 

E have now examined into the circumstances of 
air pressure ; and in " Marvels of the Elements " 
we shall be told about the atmosphere and its 
constituents. We know that the air around 
us is composed principally of two gases, oxygen and 
nitrogen, with aqueous vapour and some carbonic acid. 
An enormous quantity of carbonic acid is produced every 
day, and were it not for the action of vegetation the 
amount produced would speedily set all animal life at 
rest. But our friends, the plants, decompose the carbonic 
acid by assimilating the carbon and setting free the 
oxygen which animals consume. Thus our atmosphere 
keeps its balance, so to speak. Nothing is lost in nature. 
We have illustrated the pressure of the atmosphere 
by the Magdeburg hemispheres, and we know that the 
higher we ascend the pressure is lessened. The weight 
of the atmosphere is 15 lbs. to the square inch at sea 
level. This we have seen in the barometer. Now 
pressure is equal. Any body immersed in a liquid 
suffers pressure, and we remember Archimedes and the 
crown. It displaced a certain amount of water when 



EARLY ATTEMPTS TO FLY. 87 

immersed. A body in air displaces it just the same. 
Therefore when any body is heavier than the air, it will 
fall just as a stone will fall in water. If it be of equal 
weight, it will remain balanced in the air, if lighter it 
will rise, till it attains a height where the weight of the 
atmosphere and its own are equal ; there it will remain 
till the conditions are altered. Now we will readily 
understand why balloons float in the air, and why clouds 
ascend and descend in the atmosphere. 

In this chapter we propose to consider the question of 
ballooning, and later the possibility of flying. We all have 
been anxious concerning the unfortunate balloonist who 
was lost in the Channel some years ago, so some details 
concerning the science generally, with the experiences of 
skilled aeronauts, will guide us in our selection of material. 
We will first give a history of the efforts made by the 
ancients to fly, and this ambition to soar above the earth 
has not yet died out. 

From a very early period man appears to have been 
desirous to study the art of flying. The old myths of 
Daedalus and Icarus show us this, and it is not to be 
wondered at. When the graceful flight of birds is noticed, 
we feel envious almost that we cannot rise from the earth 
and sail away at our pleasure over land and sea. Any 
one who has watched the flight of the storks around and 
above Strasburg will feel desirous to emulate that long, 
swift-sailing flight without apparent motion of wing, and 
envy the accuracy with which the bird hits the point 
aimed at on the chimney, however small. It is Httle 
wonder that some heathens of old time looked upon birds 
as deities. 

The earliest flying machine that we can trace is that 
invented by Archytas, of Tarentum, B.C. 400. The 
historian of the " Brazen Age " tells us how the geo- 
metrician, Archytas, made a wooden pigeon which was 



88 AERONAUTICS. 

able to sustain itself in the air for a few minutes, but it 
came down to the ground after a short time, notwith- 
standing the mysterious " aura spirit " with which it was 
supposed to be endowed. The capability of flying has 
for centuries been regarded as supernatural. Putting 
angels aside, demons are depicted with wings like bats' 
wings, while witches, etc., possessed the faculty of flying 
up chimneys upon broomsticks. We even read in childish 
lore of an old woman who " went up in a basket " 
(perhaps a balloon-car), and attained a most astonishing 
altitude — an elevation no less than " seventy times as 
high as the moon ! " 

But to descend to history. It is undoubtedly true that 
in the time of Nero Simon Magus attempted to fly from 
one house to another by means of some mechanical con- 
trivance, and failing, killed himself. Roger Bacon, the 
" admirable doctor," to whom the invention of gunpowder 
is generally attributed, had distinct notions of flying by 
means of machines, and "hollow globes," and "liquid fire." 
But he did not succeed, nor did many successive attempts 
succeed any better in subsequent years. Bishop Wilkins 
treated of the art of flying, but most, if not all who dis- 
cussed the subject appear to have been indebted to Roger 
Bacon for the idea. 

When the nature and pressure of the atmosphere by 
Torricelli's experiments became better known, Father Lana, 
a Jesuit priest, constructed a flying machine or balloon of 
curious shape. He proposed to fix four copper globes, 
very thin, and about twenty feet in diameter, and to 
these he fastened a boat or car, looking very much like 
a basin. His idea was to empty his great copper globes, 
and that their buoyancy would then bear the weight of 
the traveller. But he overlooked or was ignorant of the 
effect of the atmospheric pressure, which would have 
speedily crushed the thin copper globes when , empty. 



MONTGOLFIER. 8g 

Lana's suggestion was made in 1670, the ba-rometer had 
been discovered in 1643. 

There were some fairly successful experiments made 
in flying in 1678 and in 1709. The former attempt 
was made by Besmir, a locksmith of Sable, who raised 
himself by mean3 of wings up to the top of a house by 
leaps, and then succeeded in passing from one house to 
another lower down by supporting himself in the air for 
a time. He started from an elevated position, and came 
down by degrees. Dante, a mathematician, also tried to 
fly, but without great success. He broke his thigh on 
one occasion. Laurence de Gusman claimed an invention 
for flying in 1709, and petitioned for a "patent," which 
was granted by the king's letter. The machine appears 
to have borne some resemblance to a bird. 

It was not till 1782, however, that the true art of aerial 
navigation was discovered. The knowledge of hydrogen 
gas possessed by Cavendish in 1766 no doubt led up to 
it, and in the year following its discovery Professor Black, 
lecturing in Edinburgh, stated that it was much lighter 
than the atmosphere, and that any vessel filled with the 
gas would rise in the air. We now come to the invention 
of the Balloon (so called from its shape being similar 
to a vessel used in the laboratory) by the Brothers 
Montgolfier. 

Stephen and James Montgolfier were paper-makers, and 
carried on their business at Annonay, near Lyons, but it 
was partly by accident that the great discovery was made. 
They had no knowledge of the buoyancy of hydrogen 
gas. They took their idea of the balloon (inflated) from 
noticing an ascending column of smoke. It occurred to 
Stephen that if a paper bag were filled with smoke it 
would ascend into the air. A large bag was made and 
some paper burnt beneath it in a room.. When the 
smoke had filled the bag it was released, and immediately 



90 AERONAUTICS. 

ascended to the ceiling. Here was the germ of the 
Montgolfier or heated air balloon. The experiment was 
repeated in the open air with even greater success, and 
a trial upon a larger scale was immediately determined 
upon. A story is related of Montgolfier when prosecuting 



I 






*%* 



r 

^ ^ 



(1 n H p 




Montgolfier balloon. 

his researches, that a widow whose husband had belonged 
to the printing firm with whom Montgolfier was then 
connected in business, saw the smoke issuing from the 
room in which the little balloon was being filled. She 
entered, and was astonished to see the difficulty ex- 
perienced by the experimenter in filling the balloon. It 
swerved aside, and increased the trouble he had to keep 



THE FIRST BALLOON. 91 

it above the chafing dish. Montgolfier was greatly 
troubled, and seeing his disappointment, the widow said, 
" Why don't you fasten the balloon to the chafing dish.''" 
This had not occurred to the experimenter, and the idea 
was a valuable one. That was the secret of success. 

The Montgolfier Brothers determined to exhibit their 
successful experiment, and accordingly on the 5th of June, 
1783, a great concourse assembled to see the wonderful 
sight. A large canvas or linen balloon was made and 
suspended over a fire of chopped straw. The heated air 
quickly filled the balloon, which rose high in the air, and 
descended more than a mile away. This balloon con- 
tained 22,000 cubic feet of heated air, which is lighter 
than cold air, and of course rising carried the globe with 
it. As soon as the air began to cool the balloon ceased 
to rise, and as it got colder descended. 

Here was the actual discovery of the science of Aero- 
statics. The intelligence of the success achieved soon 
spread from France to other countries. Paris, however, 
was in advance, and the Brothers Robert applied, hydrogen 
gas to a balloon which was sent up from the Champ de 
Mars in August 1783. There was some trouble ex- 
perienced in filling it, but when the balloon was at length 
released it realized all expectations by remaining in the 
air nearly an hour. When at length it fell it met with 
a worse fate than it deserved, for the ignorant and 
superstitious peasantry at once destroyed it. After this 
Montgolfier exhibited his experiment this time at Versailles 
in the presence of the Court. The first aerial travellers 
appeared on this occasion — viz., a sheep, a cock, and a 
duck, which were secured in the car. They all descended 
in safety, and this success encouraged M. Pilatre de Rozier 
to make an attempt in a " fire balloon." He went up 
first in a captive balloon, and at length he and a friend, 
the Marquis d'Arlandes, ascended from the Bois de 



92 



AERONAUTICS. 



Boulogne. The trip was a decided success, and the 
possibility of navigating the air was fully demonstrated. 

Soon after this, — viz., in December 1783, — an Italian 
Count, named Zambeccari, made an ascent in London, 
and came down safely at Pet worth. MM. Charles and 
Robert ascended from Paris in December, and in February 




MM. Charles' and Roberts' balloon. 



a balloon crossed the English Channel. We must pass 
over some time and come to the ascents of Lunardi, 
which caused great excitement in London. His balloon 
was a very large one, and was inflated, or rather partially 
so, at the Artillery ground. Some delay occun-cd, and 
fearing a riot, M. Lunardi proposed to go up alone with 
the partially-filled balloon. A Mr. Biggin who had in- 



LUNARDI S ASCENT. 



93 



tended to ascend was left behind, The Prince of Wales 
was present, and thousands of spectators. Lunardi cast 
off and ascended rapidly, causing great admiration from 
the whole metropolis. Judge and jury, sovereign and 
ministers, all turned out to gaze at the balloon ; a guilty 
prisoner was acquitted hurriedly, so that no time was lost 




Blanchard's balloon. 

in discussion, and one lady died of excitement. Lunardi 
was regarded as a hero, and made many other ascents. 
He died in 1806. 

In those earlier days one or two fatal accidents happened. 
Count Zambeccari and a companion were in a balloon 
which caught fire, and both occupants of the car leaped 
from it as they were descending. The Count was killed 



94 



AERONAUTICS. 



on the spot, and his companion was much injured. 
Pilatre de Rozier made an attempt to cross the channel 
to England in 1785 ; he had reached three thousand feet 
when the balloon caught fire, and the unfortunate traveller 



♦5* 



• - w 4 



.».' 










The Nassau balloon. 



was precipitated to the ground. His associate only sur- 
vived him a few minutes. It is to the celebrated English 
aeronaut, Mr. Green, that the substitution of carburetted 
hydrogen or street gas for hydrogen is due, and since his 
ascent in 1821 no other means of inflation have been 
used. A great many quite successful and a few un- 



MR. GREEN. 



95 



successful ascents have been made for pleasure or profit. 
Mr. Green, in the Nassau balloon, passed over to Nassau, 
a distance of five hundred miles, in eighteen hours. This 
exploit was the cause of the name being bestowed upon 




The " Giant" balloon of M. Nadar- 



the balloon. The Giant of M. Nadar was exhibited in 
England, and it was an enormoUs one, being an hundred 
feet high, and nearly as wide in the widest part. But even 
this machine was outdone by the Godard " Montgolfier '' 
balloon, which was one hundred and seventeen feet high, 



gb AERONAUTICS. 

and carried a stove. We give illustrations of these 
celebrated balloons, and will now pass on to the more 
scientific portion of the subject and the ascents of Mr. 
Glaisher and other aeronauts for the purpose of making 
meteorological observations, and the use of balloons for 
purposes of observation in war. 

It appears that the first ascent for scientific investiga- 
tion was made in the year 1803. The aeronauts were 
Messrs. Robertson and Lhoest. They ascended from 
Hamburg and came down at Hanover, and made mean- 
time several experiments with reference to the electrical 
condition of the atmosphere, its influence upon a magnetic 
needle, and some experiments with regard to acoustics 
and heat. The report was presented to the St. Petersburg 
Academy, and contains the result of their interesting obser- 
vations.^ The travellers ascertained that at the elevation 
to which they attained,- — viz., 25,500 feet, — the tempera- 
ture was on that July day fifty degrees colder, falling to 
I9'6°, while on the earth the thermometer had shown 68^. 
They ascertained that glass and wax did not become 
electric when rubbed, that the Voltaic battery lost much 
of its power, that the oscillation of a "dipping needle" 
increased as they mounted into the air, while sound was 
certainly less easily transmitted at that elevation, and 
struck them as less powerful in tone. The heat experi- 
ment was not a success, owing to the breaking of the 
thermometer. They wished to find the temperature of 
boiling water at that elevation, but when the experiment 
was about to be made Robertson accidentally plunged 
the instrument into the fire instead of into the water. So 
the question was not settled. 

The effect upon the aeronauts was a sensation of 
sleepiness, and two birds died. The muscular powers of 
the voyagers also appear to have been much affected, 
and similar sensations may be experienced by travellers 



GAY-LUSSAC. 97 

On high mountains who find their breath very short and 
a disinclination to exertion oppress them. 

MM. Biot and Gay-Lussac made a very interesting 
ascent in 1804. We will detail their experiences at 
some length, for the coolness displayed and the value of 
the observations made are remarkable in the history of 
scientific ballooning. They started at 10 o'clock a.m. on 
the 23rd of August, and when the balloon had carried 
them up to an altitude of 8,600 feet they commenced 
their experiments. They had some animals in the car 
with them, a bee amongst the number, and the insect 
was let go first. It flew away swiftly, not at all in- 
convenienced apparently. The sun was very hot at 
56° Fahr. Their pulses were beating very fast, but no 
inconvenience was felt. 

When 1 1,000 feet had been reached a linnet was 
permitted to go at large, but after a little time the bird 
returned to the balloon. It remained perched for a few 
minutes, and then dashed downwards at a tremendous 
pace. A pigeon was then liberated. It also appeared 
very uncertain, and wheeled around in circles for a time. 
At last it gained confidence and descended, and dis- 
appeared in the clouds beneath. They made ether 
experiments, but descended without having obtained as 
accurate results as had been anticipated. 

On the next occasion, however, every care was taken, 
and on the 15th of September the important ascent was 
made by Gay-Lussac alone. He fixed hanging ropes to 
the balloon with the view to check the rotating move- 
ments, and having provided himself with all necessary 
apparatus and two vacuum flasks to bring down some of 
the upper air, the young man started. The barometer 
marked 30"66°, the thermometer 82° (Fahr.). At an 
elevation of 12,680 feet Lussac perceived that the varia- 
tion of the compass was the same as on land. Two 



98 AERONAUTICS. 

hundred feet higher up he ascertained that a key held 
in the magnetic direction repelled with the lower, and 
attracted with its upper extremity the north pole of a 
needle. This experiment was repeated with the same 
result at an elevation of 20,000 feet, which shows how 
the earth exercises its magnetic influence. The tempera- 
ture of the air was found to decrease in proportion as the 
ascent up to 12,000 feet, where the reading was 47'3°. 
It then increased up to 14,000 feet by 6°, and then 
regularly diminished again as the balloon rose, till at 
the greatest elevation reached, 23,000 feet, there was a 
difterence of 6"]° in the temperature on the earth, for at 
the maximum height attained the thermometer stood 
at I4'9°. 

But the most important fact ascertained, and one which 
set many theories at rest, was the composition of the 
atmosphere in those high altitudes. We mentioned that 
Gay-Lussac took up two empty flasks from which the air 
had been taken. The vacuum was almost perfect. When 
the aeronaut had reached 21,460 feet he opened one flask, 
and it was quickly filled ; he secured it carefully ; and 
when at his highest point, — four miles and a half above 
the sea-level, — he opened the other flask. The barometer 
stood at 1 2 '9 5 inches, and the cold was very great. 
The voyager felt benumbed, and experienced difficulty of 
breathing; his throat was parched and dry. So Lussac 
determined to return, he could go no higher. He dropped 
gently near Rouen, and soon reached Paris. As soon as 
possible the air in the flasks was submitted to very delicate 
tests, and to the satisfaction of the scientists engaged it 
was found to be in exactly the same proportions as that 
collected near the earth — two hundred and fifteen parts 
of oxygen to every thousand of atmospheric air. 

Messrs. Banal and Bixio, in 1850, also made some 
observations, and found the temperature very variable. 



M, FLAMMARION. 99 

At 23,000 teet they found the thermometer at minus 
38'2° Fahr., which was much below the cold experienced 
by Gay-Lussac. We may still conclude that the various 
currents of the atmosphere cause considerable variation, 
and that it is impossible to lay down any law respecting 
the degrees of heat and cold hkely to be found at certain 
elevations. We quote Arago's observations upon this 
ascent : — 

" This discovery " (the ice particles found in the air) 
" explains how these minute crystals may become the 
nucleus of large hailstones, for they may condense round 
them the aqueous vapour contained in the portion of the 
atmosphere where they exist. They go far to prove the 
truth of Mariotte's theory, according to which these crystals 
of ice suspended in the air are the cause of parahelia — or 
mock-suns and mock-moons. Moreover, the great extent 
of so cold a cloud explains very satisfactorily the sudden 
changes of temperature which occur in our climates." 

M. Flammarion gives in his " Voyages " some very 
interesting and amusing particulars, as well as many 
valuable scientific observations. During one ascent he 
remarked that the shadow of the balloon was white, '^u^ 
at another time dark. When white the surface upon 
which it fell looked more luminous than any other part 
of the country ! The phenomenon was an anthelion. The 
absolute silence impressed the voyager very much. He 
adds, "The silence was so oppressive that we cannot help 
asking ourselves are we still alive ! We appear to apper- 
tain no longer to the world below." M. Flammarion's 
observations on the colour of what we term the sky are 
worth quoting — not because they are novel, but because 
they put so very clearly before us the appearance we call 
the " blue vault." He says,- — speaking of the non-existence 
of the " celestial vault," — " The air reflects the blue rays 
of the solar spectrum from every side. The white light of 



100 



AERONAUTICS. 



the sun contains every colour, and the air allows all tints 
to pass through it except the blue. This causes us to 
suppose the atmosphere is blue. But the air has no such 
colour, and the tint in question is merely owing to the 
reflection of light. Planetary space is absolutely black ; 





The " Eagle'' of M. Godard. 



the higher we rise the thinner the layer of atmosphere 
that separates us from it, and the darker the sky appears." 
Some beautiful effects may be witnessed at night from 
a balloon, and considering the few accidents there have 
been in proportion to the number of ascents, we do not 
wonder at balloon voyages being undertaken for mere 
pleasure. When science has to be advanced there can be 



SOUND IN UPPER AIR. !01 

no objection flnade, for then experience goes hand-in-nand 
with caution. It is only tlie ignorant who are rasli ; the 
student of Nature learns to respect her, and to attend to 
her admonitions and warnings in time. The details of 
the ascents of famous aeronauts give us a great deal of 
pleasant and profitable reading. The phenomena of the 
sky and clouds, and of the heavens, are all studied with 
great advantage from a balloon, or " aerostat," as it is the 
fashion to call it. The grand phenomena of " Ulloa's 
circles," or anthelia, which represent the balloon in air, 
and surrounded by a kind of glory, or aureola, like those 
represented behind saintly heads, appear, as the name 
denotes, opposite to the sun. 

The various experiments made to ascertain the intensity 
of sounds have resulted in the conclusion that they can 
be heard at great distances. For instance, the steam 
whistle is distinctly audible 10,000 feet up in the air, 
and human voices are heard at an altitude of 5,000 
feet. A man's voice alone will penetrate more than 
3,000 feet into the air ; and at that elevation the croak- 
ing of frogs is quite distinguishable. This shows that 
sound ascends with ease, but it meets with great resist- 
ance in its downward course, for the aeronaut cannot 
make himself audible to a listener on the earth at a 
greater distance than 300 or 400 feet, though the latter 
can be distinctly heard at an elevation of 1,600 feet. 
The diminution of temperature noted by M. Flammarion 
is stated to be 1° Fahr. for "every 345 feet on a fine day. 
On a cloudy day the mean decrease was 1° for every 
354 feet of altitude. The temperature of clouds is higher 
than the air surrounding them, and the decrease is more 
rapid near the surface, less rapid as the balloon ascends. 
We may add that at high elevations the cork from a 
"water-bottle will pop out as if from a champagne flask. 

We have hitherto referred more to M. Flammarion and 

8 



102 AERONAUTICS. 

Other French aeronauts, but we must not be considered in 
Any way oblivious of our countrymen, iVIessrs. Glaisher, 
Green, and Coxwell, nor of the American, — one of the 
most experienced of aerial voyagers, — Mr. Wise. The 
scientific observations made by the French voyagers con- 
firmed generally Mr. Glaisher's experiments. This noted 
air-traveller made twenty-eight ascents in the cause of 
science, and his experiences related in " Travels in the 
Air," and in the "Reports" of the British Association, are 
both useful and entertaining. For " Sensational ballooti- 
ing" one wishes to go no farther than his account df 
his experience with Mr. Coxwell, when (on the 5 th of 
September, 1862J he attained the greatest elevation ever 
reached — viz., seven miles, or thirty-seven thousand feet. 

We condense this exciting narrative for the benefit of 
those who have not seen it already. 

The ascent was made from Wolverhampton. At 
1.39 p.m., the balloon was four miles high, the temperature 
was 8°, and by the time the fifth mile had been reached 
the mercury was below zero, and up to this time obser- 
vations had been made without discomfort, though Mr. 
Coxwell, having exerted himself as aeronaut, found SQme 
difficulty in breathing. About 2 o'clock, the balloon still 
ascending, Mr. Glaisher could not see the mercury in the 
thermometer, and Mr. Coxwell had just then ascended 
into the ring above the car to release the valve line 
which had become twisted. Mr. Glaisher was able to 
note the barometer, however, and found it marked 10 
inches, and was rapidly decreasing. It fell to pf inches, 
and this indicated an elevation of 29,000 feet! But the 
idea was to ascend as high as possible, so the upward 
direction was maintainisd. " Shortly afterwards," writes 
Mr. Glaisher, " I laid my arm upon the table possessed 
of its full vigour, and on being desirous of using it I 
found it powerless, — it must have lost power momentarily. 



A SENSATIONAL ASCENT. 



103 



I tried to move the other arm, and found it powerless 
also. I then tried to shake myself, and succeeded in 
shaking my body. I seemed to have no limbs. I then 




A descending balloon. 

looked at the barometer, and whilst doing so my head 
fell on my left shoulder." 

Mr. Glaisher subsequently quite lost consciousness, and 
" black darkness " came. While powerless he heard 
Mr. Coxwell speaking, and then the words, " Do try, now 



I04 AERONAUTICS. 

do." Then sight slowly returned, and rousing himself, 
Mr. Glaisher said, " I have been insensible." Mr. Coxwell 
replied, " You have, and I, too, very nearly." Mr. Cox- 
well's hands were black, and his companion had to pour 
brandy upon them. Mr. Coxwell's situation was a perilous 
one. He had lost the use of his hands, which were frozen, 
and had to hang by his arms to the ring and drop into 
the car. He then perceived his friend was insensible, 
and found insensibility coming on himself. There was 
only one course to pursue — to pull the valve line and 
let the gas escape, so as to descend. But his hands were 
powerless 1 As a last resource he gripped the line with 
his teeth, and bending down his head, after many attempts 
succeeded in opening the valve and letting the gas escape, 
The descent was easily made, and accomplished in safety. 

Some pigeons were taken up on this occasion, and were 
set free at different altitudes. The first, at three miles, 
" dropped as a piece of paper " ; the second, at four miles, 
" flew vigorously round and round, apparently taking a dip 
each time"; a third, a little later, " fell like a stone." On 
descending a fourth was thrown out at four miles, and 
after flying in a circle, " alighted on the top of the balloon." 
Of the remaining pair one was dead when the ground was 
gained, and the other recovered. 

The observations noted are too numerous to be included 
here. Some, we have seen, were confirmed by subsequent 
aeronauts, and as we have mentioned them in former 
pages we need not repeat them. The results differed very 
much under different conditions, and it is almost impossible 
to decide upon any law. The direction of the wind in 
the higher and lower regions sometimes differed, sometimes 
was the same, and so on. The " Reports " of the British 
Association (i 862-1 866) will furnish full particulars of all 
Mr. Glaisher's experiments. 

We have scarcely space left to mention the parachutes 



PARACHUTES. 105 

or umbrella-like balloons which have occasionally been 
used. Its invention is traced to very early times ; but 
Gamerin was the first who descended in a parachute, in 
1 797i '^nd continued to do so in safety on many subsequent 
occasions. The parachute was suspended to a balloon, 
and at a certain elevation the voyager let go and came 
down in safety. He ascended once from London, and let 
go when 8,000 feet up. The parachute did not expand 
as usual, and fell at a tremendous rate. At length it 
opened out, and the occupier of the car came down 
forcibly, it is true, but safely. The form of the parachute 
is not unlike an umbrella opened, with cords attaching 
the car to the extremities of the " ribs," the top of the 
basket car being fastened to the " stick " of the umbrella. 

Mr. Robert Cocking invented a novel kind of parachute, 
but when he attempted to descend by it from Mr. Green's 
balloon it collapsed, and the unfortunate voyager was 
dashed to pieces. His remains were found near Lee, in 
Kent. Mr. Hampton did better on Garneron's principle, 
and made several descents in safety and without injury. 

The problem of flying in the air has attracted the 
notice of the Aeronautical Society, established in 1873, 
but so far without leading to practical results, though 
many daring and ingenious suggestions have been put 
forth in the " Reports." 

It is not within our province to do more than refer to 
the uses of the balloon for scientific purposes, but we 
may mention the services it was employed upon during 
the French war, 1870-71. The investment of Paris by 
the German army necessitated aerial communication, for 
no other means were available. Balloon manufactories 
were established, and a great number were made, and 
carried millions of letters to the provinces. Carrier pigeons 
were used to carry the return messages to the city, and 
photography was applied to bring the correspondence into 



io6 



AERONAUTICS. 



the smallest legible compass. The many adventures of 
the aeronauts are within the recollection of all. A few 
of the balloons never reappeared ; some were carried into 
Norway, and beyond the French frontier in other directions. 












Filling a balloon. 

The average capacity of these balloons was 70,006 
cubic feet. 

Of course it will be understood how balloons are enabled 
to navigate the air. The envelope being partly filled with 
coal-gas-heated air and hydrogen is much lighter than the 



BALLOONING. I07 

surrounding atmosphere, and rises to a height according 
as the density of the air strata diminishes. The density- 
is less as we ascend, and the buoyant force also is lessened 
in proportion. So when the weight of the balloon and 
its occupants is the same as the power of buoyancy, it 
will come to a stand, and go no higher. It can also be 
understood that as the pressure of the outside becomes 
less, the expansive force of the gas within becomes greater. 
We know that gas is very compressible, and yet a little 
gas will fill a large space. Therefore, as the balloon rises, 
it retains its rounded form, and appears full even at great 
altitudes ; but if the upper part were quite filled before it 
left the ground, the balloon would inevitably burst at a 
certain elevation when the external pressure of the air 
would be removed, unless an escape were provided. This 
escape is arranged for by a valve at the top of the 
balloon, and the lower part above the car is also left open 
very often, so that the gas can escape of itself When 
a rapid descent is necessary, the top valve is opened by 
means of a rope, and the balloon sinks by its own weight. 
Mr. Glaisher advises for great ascensions a balloon of a 
capacity of 90,000 cubic feet, and only filled one-third of 
that capacity with gas. Six hundred pounds of ballast 
should be taken. 

A very small quantity of ballast thrown away will make 
a great difference ; a handful will raise the balloon many 
feet, and a chicken bone cast out occasions a rise of thirty 
yards. The ballast is carried in small bags, and consists 
of dry sand, which speedily dissipates in the air as it 
falls. By throwing out ballast the aeronaut can ascend 
to a great height — in fact, as high as he can go, the limit 
apparently for human existence being about seven miles, 
when cold and rarefied air will speedily put an end to 
human life. 

It is a curious fact, that however rapidly the balloon 



I08 AERONAUTICS. 

may he travelling through the air, the occupants are not 
sensible of the motion. This, in part, arises from the 
impossibility of comparing it with other objects. We 
pass nothing stationary which would indicate the pace at 
which we travel. But the absence of oscillation is also 
remarkable ; even a glass of water may be filled brim-full, 
and to such a level that the water is above the rim of 
the glass, and yet not a drop will fall. This experiment 
was made by M. Flammarion. When the aeronaut has 
ascended some distance the earth loses its flat appearance, 
and appears as concave as the firmament above. Guide 
ropes are usually attached to balloons, and as they rest 
upon the ground they relieve the balloon of the amount 
of weight the length trailing would cause. They thus 
act as a kind of substitute for ballast as the balloon is 
descending. Most of the danger of aerial travelling lies 
in the descent ; and though in fine weather the aeronaut 
can calculate to a nicety where he will .descend on a 
windy day, he must cast a grapnel, which' catches with an 
ugly jerk, and the balloon bounds and strains at her 
moorings. 

Although many attempts have been made to guide 
balloons through the air, no successful apparatus has ever 
been completed for use. Paddles, sails, fans, and screws 
have all been tried, but have failed to achieve the desired 
end. Whether man will ever be able to fly we cannot of 
course say. In the present advancing state of science it 
may not be impossible ere long to supply human beings 
with an apparatus worked by electricity, perhaps, which 
will enable them to mount into the air and sustain them- 
selves. But even the bird cannot always fly without 
previous ^momentum. A rook will run before it rises, and 
many other birds have to " get up steam," as it were, 
before they can soar in the atmosphere. Eagles and 
such heavy birds find it very difficult to rise from the 



FLYING IN THE AIR. 



log 



ground. We know that vultures when gorged cannot 
move at all, or certainly cannot fly away ; and eagles 
take up their positions on high rocks, so that they may 
launch down on their prey, and avoid the difficulty of 
rising from the ground. They swoop down with tremen- 
dous rhomentum and carry off their booty, but often lose 
their lives from the initial difficulty of soaring immediately. 
We fear man's weight will militate against his ever 
becoming a flying animal. When we obtain a knowledge 
of the atmospheric currents we shall no doubt be able to 
navigate our balloons ; but until then — and the informa- 
tion is as yet very limited, and the currents themselves 
very variable — we must be content to rise and fall in the 
air, and travel at the will of tlic wind in the upper regions 
of the atmosphere. 

We shall have more to say upon this subject in a 
subsequent book about some novel modes of locomo- 
tion in water and air. We will now glance at water 
and its uses. 




I'he Resistance of the Aii 




CHAPTER VII.— WATER. 



ABOUT WATER — HYDROSTATICS AND HYDRAULICS — 

LAW OF ARCHIMEDES THE BRAMAH PRESS^THE 

SYniON SPECIFIC GRAVITY. 



T present we will pass from Air to Water, from 
Pneumatics to Hydrostatics and Hydraulics. 
We must remember that Hydrostatics and Hy- 
draulics are very different. The former treats 
of the weight and pressure of liquids when they are at 
rest, the latter treats of them in motion. We will now 
speak of the properties of Liquids, of which Water may 
be taken as the most familiar example. 

We have already seen that Matter exists in the form 
of Solids, Liquids, and Gases, and of course Water is one 
form of Matter. It occupies a certain space, is slightly 
compressible ; it possesses weight, and exercises force 
when in motion. It is a fluid, but also a liquid. There 
are fluids not liquid, such as air or steam, to take equally 
familiar examples. These are elastic fluids and compres- 
sible, while water is inelastic, and termed incompressible. 

We may state that water is composed of oxygen and 
hydrogen, and proportions of eight of the former to one 
of the latter by weight ; in volume the hydrogen is as 
two to one. 

From these facts, as regards water, we learn that 
volume and weight are very different things, — that equal 
volumes of various things may have different weights, and 



VOLUME AND WEIGHT. Ill 

that volume (or bulk) by no means indicates weight. 
Equal volumes of feathers and sand will weigh very 
differently. 

[The old " catch " question of the " difference in weight between a 
pound of lead and a pound of feathers " here comes to the mind. The 
answer generally given is that "feathers make the heavier 'pound,' 
because they are weighed by avoirdupois, and lead by troy weight." 
This is an error. They are both weighed in the same way, and pound 
for pound, are the same weight, though different in volume. 

Fluids in equilibrium have all their particles at the 
same distance from the centre of the earth, and although 
within small distances liquids appear perfectly level (in a 
direct line), they must, as the sea does, conform to the 
shape of the earth, though in small levels the space is too 
limited to admit of any deviation from the plane at right 
angle to the direction of gravity. 

Liquids always fall to a perfectly level surface, and 
water will seek to find its original level, whether it be in 
one side of a bent tube, in a watering pot and its spout, 
or as a fountain. The surface of the water will be on the 
same level in the arms of a bent tube, and the fountain 
will rise to a height corresponding with the elevation of 
the parent spring whence it issues. The waterworks com- 
panies first pump the water to a high reservoir, and then 
it rises equally high in our high-level cisterns. 

As an example of the force of water, a pretty little 
experiment may be easily tried, and, as many of our 
readers have seen in a shop in the Strand in London, it 
always is attractive. A good-sized glass shade should be 
procured and placed over a water tap and basin, as per 
the illustration over-leaf. Within the glass put a number 
of balls of cork or other light material. Let a stop-cock, 
with a small aperture, be fixed upon the tube leading into 
the glass. Another tube to carry away the water should, 
of course, be provided, but it may be used over again. 



1 12 



WATER. 



When the tap is properly fixed, if the pressure of the 
water be sufficient, it will rush out with some force, and 
catching the balls as they fall to the bottom of the glass 
shade bear them up as a juggler would throw oranges 
from hand to hand. If coloured balls be used the effect 




b and balls. 



may be enhanced, and much variety imparted to the 
experiment, which is very easy to make. 

Water exercises an enormous pressure, but the pressure 
does not depend upon the amount of v/ater in the vessel. 
It depends upon the vessel's height, and the dimensions 
of the base. This has been proved by filling vessels 



PRESSURE OF WATER. 



113 



whose bases and heights are equal, but whose shapes are 
different, each holding a different quantity of water. The 
pressure at the bottom of each vessel is the same, and de- 
pends upon the depth of the water. If we subject a portion 
of the liquid surface to certain force, this pressure will be 
dispersed equally in all directions, and from an acquaint- 






Pressure of water. 



?J 



ance with this fact the Hydraulic Press was brought into 
notice. If a vessel with a horizontal bottom be filled with 
water to a depth of one foot, every square foot will sustain 
a pressure of 62-37 ^hs., and each square inch of 0^43 3 lbs. 
We will now explain the principle of this Water 
Press. In the small diagram, the letters AB represent 
the bottom of a cylinder which has a 
piston fitted in it (p). Into the op- 
posite side a pipe is let in, which 
leads from a force-pump, D, which is 
fitted with a valve, E, opening upwards. 
When the piston in D is pulled up 
water enters through the valve; " ^^^^^^^^^^ 
when the piston is forced down the 
valve shuts, and the water rushes into the chamber, AB. 
The pressure pushes up the large piston with a force 
multiplied as many times as the area of the small piston 
is contained in the large one. So if the large one be ten 
times as great as the small one, and the latter be forced 
down with a 10 lb. pressure, the pressure on the large 
one will be 100 lbs., and so on. 



14 



WATER. 



The accompanying illustration shows the form of the 
rlydraulic or Bramah Press. A B C D is a strong frame, 
!■ the force-pump worked by means of a lever fixed at G, 
ind H is the. counterpoise. E is the stop-cock to admit 
he water. 

The principles of hydrostatics will be easily explained. 




Eramah Press. 

fhe Lectures of M. Aim6 Schuster, Professor and 
-librarian at Metz, have taught us in a very simple 
nanner the principle of Archimedes, in which it is laid 
lown that " a body immersed in a liquid loses a portion 
)f its weight equal to the weight of the liquid displaced 
)y it." We take a body of as irregular form as we 
jlease ; a stone, for example. A thread is attached to 
he stone, and it is then placed in a glass of water full up 



UPWARD PRESSURE OF LIQUIDS. I I 5 

to the briin. The water overflows ; a volume of the 
liquid equal to that of the stone runs over. The glass 
thus partially emptied is then dried, and placed on the 
scale of a balance, beneath which we suspend the stone ; 
equilibrium is established by placing some pieces of lead 
in the other scale. We then take a vase full of water, 
into which we plunge the stone suspended from the scale, 
supporting the vase by means of bricks. The equilibrium 
is now broken ; to re-establish it, it is necessary to fill up 
with water the glass placed on the scale ; that is to say, 
we put back in the glass the weight of a volume of water 
precisely equal to that of the stone. 

If it is desired to investigate the principles relating to 
connected vessels, springs of water, artesian wells, etc., two 
funnels, connected by means of an india-rubber tube of 
certain length, will serve for the demonstration ; and by 
placing the first funnel at a higher level, and pouring in 
water abundantly, we shall see that it overflows from the 
second. 

A disc of cardboard and a lamp-glass will be all that 
is required to show the upward pressure of liquids. I 
apply to the opening of the lamp-glass a round piece of 
cardboard, which I hold in place by means of a string ; 
the tube thus closed I plunge into a vessel filled with 
water. The piece of cardboard is held by the pressure of 
the water upwards. To separate it from the opening it 
suffices to pour some water into the tube up to the level 
of the water outside. The outer pressure exercised on the 
disc, as well as the pressure beneath, is now equal to the 
weight of a body of water having for its base the surface 
of the opening of the tube, its depth being the distance 
from the cardboard to the level of the water. 

Syringes, pumps, etc., are the effects of atmospheric 
pressure. Balloons rise in the air by means of the pressure 
of gas ; a balloon being a body plunged in gas, is con- 



Ii6 



WATER. 



sequently submitted to the same laws as a body pluflged 
in water. 

Boats float because of the pressure of liquid, and water 
spurts from a fountain for the same reason, I recollect 




Demonstration of the upward pressure of liquids. 

having read a very useful application of the principles of 
fluid pressure. 

A horse was laden with two tubs for carrying a supply 
of water, and in the bottom of the tubs a valve was fixed.. 
When the horse entered the stream the tubs were partly 
immersed ; the water then exercised its upward pressure,, 
the valve opened, and the tubs slowly filled. When they 



WATER LEVEL. 



117 



were nearly full the horse turned round and came out of 
the water ; the pressure had ceased. 

Thus the action of the water first opened the valve, and 
then closed it. 

The particular phenomena observable in the water level 




Experiment on the convexity of a meniscus, 

in narrow spaces, as of a fine glass tube, or the level of two 
adjoining waves, capillary phenomena, etc., do not need 
any special appHance for demonstration, and it is the same 
with the convexity or concavity of meniscuses.* 

*> The curved surface of a column of liquid is termed a " meniscus," 
from the Greek word meniskos, meaning " a little' lens.'' 

y 



ii8 



WATER. 



The foregoing cut represents a pretty experiment in con ■ 
nection with these phenomena. 1 take a glass, which I fill 
up to the brim, taking care that the meniscus be concave, 
and near it I place a pile of pennies. I then ask my 
young friends how many pennies can be thrown into the 
glass without the water overflowing. Everyone who is 
not familiar with the experiment will answer that it will 
only be possible to put in one or two, whereas it is possi- 
ble to put in a considerable number, even ten or twelve. 
As the pennies are carefully and slowly dropped in, the 

surface of the liquid will be seen 
to become more and more convex, 
and one is surprised to what an 
extent this convexity increases 
before the water overflows. 

The common syphon may be 
mentioned here. It consists of a 
bent tube with limbs of unequal 
length. We give an illustration 
of the syphon. The shorter leg 
being put into the mixture, the air 
is exhausted from the tube at o, 
the aperture at g being closed with the finger. When the 
finger is removed the liquid will run out. If the water 
were equally high in both legs the pressure of the atmo- 
sphere would hold the fluid in equilibrium, but one leg being 
longer, the column of water in it preponderates, and as it 
falls, the pressure on the water in the vessel keeps up the 
supply. 

Apropos of the syphon, we may mention a very simple 
application of the principle. Cut off a strip of cloth, and 
arrange it so that one end shall remain in a glass of water 
while the other hangs down, as in the illustration. In a 
short time the water from the upper glass will have passed 
through the cloth-fibres to the lower one. 




The Syphon 



CAPILLAKITY. 



119 



This attribute of porous substances is called capillarity, 
and shows itself by capillary attraction in very fine pores or 
tubes. The same phenomenon is exhibited in blotting 
paper, sugar, wood, sand, and lamp-wicks, all of which give 
familiar instances of capillarity. The cook makes use of 




An Improvised syphon. 

this property by using thin paper to absorb grease from 
the surface of soups. 

Capillarity (already referred to) is the term used to 
define capillary force, and is derived from the word capillits, 
a hair ; and so very small bore tubes are called capillary 
tubes. We know that when we plunge a glass tube into 



I20 



WATER. 



water the liquid will rise up in it, and the narrower the tube 
the higher the water will go ; moreover, the water inside 
will be higher than at the outside. This is in accordance 
with a well-known law of adhesion, which induces concave 
or convex surfaces in the liquids in the tubes, according 




Molecular attraction. 



as the tube is wetted with the liquid or not. For instance, 
water, as we have said, will be higher in the tube and 
concave in form ; but mercury will be depressed below the 
outside level, and convex, because mercury will not adhere 
to glass. When the force of cohesion to the sides of the 
tube is more than twice as great as the adhesion of the 



Molecular attraction. 



121 



particles of the liquid, it will rise up the sides, and if the 
forces be reversed, the rounded appearance will follow. 
This accounts for the convex appearance, or " meniscus," 
in the column of mercury in a barometer. 

Amongst the complicated experiments to demonstrate 







4 










Vase of Tantalus. 



molecular attraction, the following is very simple and very 
pretty : — Take two small balls of cork, and having placed 
them in a basin half-filled with water, let them come close 
to each other. When they have approached within a certain 
distance they will rush together. If you fix one of them 
on the blade of your pen-knife, it will attract the other as 
a magnet, so that you can lead it round the basin. But 



122 



WATER. 



if the balls of cork are covered with grease they will repel 
each other, which fact is accounted for by the form of the 
menisques, which are convex or concave, according as they 




iJecepiiou jugs of old pattern. 



are moistened, op preserved from action of the water by 
the grease. 

This attribute is of great use in the animal and vegetable 
kingdoms. The rising of the sap is one instance of the latter. 



VASE OF TANTALUS. 



123 



Experience in hydrostatics can be easily applied to 
amusing little experiments. For instance, as regards the 
syphon, we may make an image of Tantalics as per illus- 
tration. A wooden figure may be cut in a stooping 
posture, and placed in the centre of a wide vase, as if about 
to drink. If water be poured slowly into the vase it will 
never rise to the mouth of the figure, and the unhappy 
Tantalus will remain in expectancy. This result is ob- 
tained by the aid of a syphon hidden in the figure, the 
shorter limb of which is in the chest. The longer limb 
descends through a hole in the table, and carries off the 
water. These vases are called vases of Tantalus. 

The principle of the syphon may also be adapted to our 
domestic filters. Charcoal, as we know, makes an excellent 
filter, and if we have a block of charcoal in one of those 
filters, — now so common, — we can fix a tube into it, and 
^.^ar any water we may 
require. It sometimes (in 
the country) happens that 
drinking-water may be- 
come turgid, and in such a 
case the syphon filter will 
be found useful. 

The old " deception " 
jugs have often puzzled 
people. We, give an illus- 
tration of one, and also a 
sketch of the "deceptive" 
portion. This deception is 
very well managed, and 
will create much amuse- 
ment if a jug can be pro- 
cured ; they were fashionable in the eighteenth century 
and previously. A cursory inspection of these curious 
utensils will lead one to vote them utterly useless. They 




Section of jug. 



124 WATER. 

are, however, very quaint, and if not exactly useful are 
ornamental. They are so constructed, that if an in- 
experienced person wish to pour out the wine or water 
contained in them, the liquid will run out through the 
holes cut in the jug. 

To use them with safety it is necessary to put the spout, 
A, in one's mouth, and close the opening, B, with the finger, 
and then by drawing in the breath, cause the water to 
mount to the lips by the tube which runs around the jug. 
The specimens herein delineated have been copied from 
some now existent in the museum of the Sevres china 
manufactory. 

The Buoyancy of Water is a very interesting subject, and 
a great deal may be written respecting it. The swimmer 
will tell us that it is easier to float in salt water than in 
fresh. He knows by experience how difficult it is to sink 
in the sea ; and yet hundreds of people are drowned in the 
water, which, if they permitted it to exercise its power of 
buoyancy, would help to save life. 

The sea-water holds a considerable quantity of salt in 
solution, and this adds to its resistance, or floating power. 
It is heavier than fresh water, and the Dead Sea is so salt 
that a man cannot possibly sink in it. This means that 
the man's body, bulk for bulk, is much lighter than the 
water of the Dead Sea. A man will sink in fresh, or 
ordinary salt water if the air in his lungs be exhausted, 
because without the air he is much heavier than water, bulk 
for bulk. So if anything is weighed in water, it apparently 
loses in weight exactly equal to its oWn bulk of water. 

Water is the means by which Specific Gravity of liquids 
or solids is found, and by it we can determine the relative 
densities of matter in proportion. Air is the standard for 
gases and vapours. Let us examine this, and see what is 
meant by SPECIFIC Gravity. 

We have already mentioned the difference existing 



SPECIFIC GRAVITY. 



between two equal volumes of different substances, and their 
weight, which proves that they may contain a different 
number of atoms in the same space. We also know, from 
the principle of Archimedes, that if a body be immersed in 
a fluid, a portion of its weight will be sustained by the fluid 
equal to the weight of the fluid displaced. 

[This theorem is easily proved by filling a bucket with 
water, and moving it about in water, when it will be easy 
to lift ; and likewise the hum.an body may be easily 
sustained in water by a finger under the chin.j 




Vveij^lung metal in water. 

The manner in which Archimedes discovered the dis- 
placement of liquids is well known, but is always interesting. 
King Hiero, of Syracuse, ordered a crown of gold to be 
made, and when it had been completed and delivered to His 
Majesty, he had his doubts about the honesty of the gold- 
smith, and called to Archimedes to tell him whether or 
not the crown was of gold, pure and simple. Archimedes 
was puzzled, and went home deep in thought. Still 
considering the problem he went to the bath, and ... his 
abstraction filled it to the brim. Stepping in he spilt a 
considerable quantity of water, and at once the idea struck 
him that any body put into water would displace its own 
bulk of the liquid. He did not wait to dress, but ran 
half-naked to the palace, crying out, "Eureka, Eureka ! I 



126 WATER. 

have found it, I have found it ! " What had he found ? — 
He had solved the problem. 

Fie got a lump of gold the same weight as the crown, 
and immersed it in water. He found it weighed nineteen 
times as much as its own bulk of water. But when he 
immersed the king's crown he found it displaced more 
water than the pure gold had done, and consequently it 
had been adulterated by a lighter metal. He assumed 
that the alloy was silver, and by immersing lumps of silver 
and gold of equal weight with the crown, and weighing 
the water that overflowed from each dip, he was able to 
tell the king how far he had been cheated by the 
goldsmith. 

It is by this method now that we can ascertain 
the specific gravity of bodies. One cubic inch 
of water weighs about half an ounce (or to be 
exact, 252^ grains). Take a piece of lead and 
weigh it in air ; it weighs, say, eleven ounces. 
Then weigh it in a vase of water, and it will be 
only ten ounces in weight. So lead is eleven 
times heavier than water, or eleven ounces of 
lead occupy the same space as one ounce of 
water. 

[The heavier a fluid is, or the greater its 
density, the greater will be the weight it will 
support. Therefore we can ascertain the purity 
or otherwise of certain liquids by using hy- 
drometers, etc., which will float higher or lower 
in different liquids, and being gauged at the 
standard of purity, we can ascertain (for instance) 
how much water is in the milk when supplied 
from the dairy.] 

Hydrometer. g^^ ^q rctum tO SPECIFIC GRAVITY, wllich 

means the "Comparative density of any substance relatively 
to water," or as Professor Huxley says, " The weight of a 




SPECIFIC GRAVITY. 



127 



volume of any liquid or solid in proportion to the weight 
of the same volume of water, at a known temperature and 
pressure." 

Water, therefore, is taken as the unit ; so anything whose 
equal volume under the same circumstances is twice as 
heavy as the water, is declared to have its specific gravity 
2; if three-and-a-half times it, is 3*5, and so on. We 
append a few examples ; so we see that things which 
possess a higher specific gravity than water sink, which 
comes to the same thing as saying they are heavier than 
water, and vice versd. 

To find the specific gravity of any solid body proceed 
as above, in the experiment of the lead. By weighing the 
substance in and out of water we find the weight of the 
water displaced ; that is, the first weight less the second. 
Divide the weight in air by the remainder, and we shall 
find the specific gravity of the substance. 

The following is a table of specific gravities of some very 
different substances, taking water as the unit. 



Substance. 


Specific 
Gravity. 


1 Substance. 


Speciric 
Gravity. 


Substance. 


Specific . 
Gravity.. 


Platinum . 


21-5 


Iron . 


779 


Water 


I'OOO 


Gold . 


19-5 


Tin . 


7-29 


Sea Water . 


1-026 


Mercury 


i3'59 


j Granite 


2-62 


Rain Water 


I -00 1 


Ltad . 


11-45 


1 Oak Wood. 


077 


Ice . 


•916 


Silver.. 


io'5o 


; Cork . 


0-24 


Ether . 


0-723 


Copper 


8-96 


Milk . 


I 032 


Alcohol 


0-793 



But we have by no means exhausted the uses of water. 
Hydrodynamics, which is the alternative term for hydraulics, 
includes the consideration of many forms of water-wheels, 
most of which, as mill-wheels, are under-shot, or over-shot 
accordingly as the water passes horizontally over the floats, 
or acts beneath them. These wheels are used in relation 
to the fall of water. If there is plenty of water and a 
slight fall, the under-shot wheel is used. If there is a good 



128 



WATER. 



fall less water will suffice, as the weight and momentum 
of the falling liquid upon the paddles will turn the wheel. 
Here is the Persian water-wheel, used for irrigation. The 




Archimedian Screw, called after its inventor, was one of 
the earliest modes of raising water. It consists of a cylinder 
somewhat inclined, and a tube bent like a screw within it. 



WATER-MIT,!,. 



129 



By turning the handle of the screw the water is drawn up 
and flows out from the top. 

The Water Ram is a machine used for raising water to 
a great height by means of the momentum of falling water. 




^^f?Sis#i' 



Over-shot wheel of mill. 



The Hydraulic Lift is familiar to us all, as it acts in our 
hotels, and we need only mention these appliances here ; 
full descriptions will be found in Cyclopaedias.