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Full text of "Course of six lectures on the various forces of matter, and their relations to each other [microform]"

UNIVERSITY OF CALIFORNIA 

MEDICAL CENTER LIBRARY 

SAN FRANCISCO 





Ex Libris 
C. K. OGDEN 



Digitized by the Internet Archive 

in 2007 with funding from 

Microsoft Corporation 



http://www.archive.org/details/courseofsixlectuOOfararich 



COUKSE OF SIX LECTURES 



VAKIOUS FORCES OF MATTER 



THEIR RELATIONS TO EACH OTHER 



MICHAEL FARADAY, D.C.L. F.R.S. 

FULLERIAN PBOFESSOE OE CHEMISTRY, ROYAL INSTITUTION 



Delivered before a Juvenile Auditory at the Royal Institution 
of Great Britain during the Christmas Holidays 0/1859-60 



EDITED BY WILLIAM CROOKES, F.C.S. 

WITH NUMEROUS ILLUSTRATIONS 

LONDON AND GLASGOW 

RICHARD GRIFFIN AND COMPANY 

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PRINTED BY SPOTTISWOODE AND CO. 
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PREFACE. 



Which was first, Matter or Force ? If we think 
on this question we shall find that we are 
unable to conceive of matter without force, or 
force without matter. When God created the 
elements of which the earth is composed, He 
created certain wondrous forces, which are set 
free, and become evident when matter acts on 
matter. All these forces, with many differences, 
have much in common, and if one is set free 
it will immediately endeavour to free its com- 
panions. Thus heat will enable us to eliminate 
light, electricity, magnetism, and chemical 
action ; chemical action will educe light, elec- 
tricity, and heat ; in this way we find that all 
the forces in nature tend to form mutually 
dependent systems, and as the motion of one 
star affects another, so force in action liberates 
and renders evident forces previously tranquil. 
A 2 

143053 



IV PREFACE. 

We say tranquil, and yet the word is almost 
without meaning in the Cosmos; — where do 
we find tranquillity? The sea, the seat of 
animal, vegetable, and mineral changes, is at 
war with the earth, and the air lends itself to 
the strife. The globe, the scene of perpetual 
intestine change, is as a mass, acting on, and 
acted on, by the other planets of our system, 
and the very system itself is changing its place 
in space, under the influence of a known force 
springing from an unknown centre. 

For many years past the English public 
have had the privilege of listening to the dis- 
courses and speculations of Professor Faraday, 
at the Eoyal Institution, on Matter and Forces, 
and it is not too much to say that no lecturer 
on Physical Science since the time of Sir 
Humphry Davy has been listened to with 
more delight. The pleasure which all derive 
from the expositions of Faraday is of a some- 
what different kind to that produced by any 
other philosopher whose lectures we have ever 



PREFACE. V 

attended. It is partially derived from his ex- 
treme dexterity as an operator, — with him we 
have no chance of apologies for an unsuccessful 
experiment, no hanging fire in the midst of a 
series of brilliant demonstrations, producing 
that depressing tendency akin to the pain felt 
by an audience at a false note from a vocalist. 
All is a sparkling stream of eloquence and 
experimental illustration. We defy a chemist 
who loves his science, no matter how often he 
may himself have repeated an experiment, 
to feel uninterested when seeing it done by 
Faraday. 

The present publication presents one or two 
points of interest. In the first place, the 
Lectures were especially intended for young 
persons, and are therefore as free as possible 
from technicalities; and in the second place 
they are printed as they were spoken, verbatim 
et literatim. A careful and skilful reporter 
took them down, and the manuscript, as de- 
ciphered from his notes, was subsequently most 
carefully corrected by the Editor as regards 



VI PREFACE, 

any scientific points which were not clear to 
the short-hand writer ; hence all that is differ- 
ent arises solely from the impossibility, alas! 
of conveying the manner as well as the matter 
of the Lecturer. 

The interest which was felt in those num- 
bers of the Chemical News in which the 
lectures appeared was so great that the re- 
publication of them in a separate form was 
considered to be almost a duty to those young 
lovers of science to whom a purely chemical 
journal with its inevitable technicalities would 
be a sealed book. May the readers of these 
lectures derive one tenth of the pleasure and 
instruction from their perusal which they gave 
to those who had the happiness of hearing 
them ! 

W. C. 



CONTENTS. 






LECTURE I. 

PAGE 
THE FORCE OF GRAVITATION 1 

LECTURE II. 

GRAVITATION — COHESION 31 

LECTURE III. 

COHESION — CHEMICAL AFFINITY 58 

LECTURE IV. 

CHEMICAL AFFINITY — HEAT ...... til 

LECTURE V. 

MAGNETISM — ELECTRICITY 106 

LECTURE VI. 

THE CORRELATION OF THE PHYSICAL FORCES . .130 



LIGHTHOUSE ILLUMINATION — THE ELECTRIC LIGHT . 155 
NOTES 175 



LECTURES 



THE PHYSICAL FOKCES. 



LECTUEE I. 

THE FORCE OF GRAVITATION. 

It grieves me much to think that I may have 
been a cause of disturbance in your Christmas 
arrangements ( 2 ), for nothing is more satisfactory 
to my mind than to perform what I undertake ; 
but such things are not always left in our own 
power, and we must submit to circumstances as 
they are appointed. I will to-day do my best, 
and will ask you to bear with me if I am unable 
to give more thdfo a few words; and as a substi- 
tute I will endeavour to make the illustrations 
of the sense I try to express, as full as possible ; 



2 GRAVITATION. 

and if we find by the end of this lecture, that 
we may be justified in continuing them, think- 
ing that next week our power shall be greater, 
— why then, with submission to you, we will 
take such course as you may think fit, — either 
to go on or discontinue them : and although I 
now feel much weakened by the pressure of 
illness (a mere cold) upon me, both in facility 
of expression and clearness of thought, I shall 
here claim, as I always have done on these 
occasions, the right of addressing myself to the 
younger members of the audience, — and for 
this purpose, therefore, unfitted as it may seem 
for an elderly infirm man to do so, I will return 
to second childhood and become, as it were, 
young again amongst the young. 

Let us now consider, for a little while, how 
wonderfully we stand upon this world. Here 
it is we are born, bred, and live, and yet we 
view these things with an almost entire ab- 
sence of wonder to ourselves respecting the way 
in which all this happens. So small, indeed, is 
our wonder, that we are never taken by sur- 
prise ; and I do think, that, to*a young person 
of ten, fifteen, or twenty years of age, perhaps 
the first sight of a cataract or a mountain would 



VARIOUS POWERS OF MATTER. 3 

occasion him more surprise than he had ever 
felt concerning the means of his own existence ; 
how he came here; how he lives; by what 
means he stands upright; and through what 
means he moves about from place to place. 
Hence, we come into this world, we live, and 
depart from it, without our thoughts being 
called specifically to consider how all this takes 
place; and were it not for the exertions of 
some few inquiring minds, who have looked 
into these things and ascertained the very 
beautiful laws and conditions by which we do 
live and stand upon the earth, we should hardly 
be aware that there was anything wonderful in 
it. These inquiries, which have occupied phi- 
losophers from the earliest days, when they 
first began to find out the laws by which we 
grow, and exist, and enjoy ourselves, up to the 
present time, have shown us that all this was 
effected in consequence of the existence of cer- 
tain forces, or abilities to do things, or powers, 
that are so common that nothing can be more 
so : for nothing is commoner than the wonder- 
ful powers by which we are enabled to stand 
upright — they are essential to our existence 
every moment. 

B 2 



4 GKAVITATION. 

It is my purpose to-day to make you ac- 
quainted with some of these powers ; not the 
vital ones, but some of the more elementary, 
and, what we call, physical powers ; and, in the 
outset, what can I do to bring to your minds a 
notion of neither more nor less than that which 
I mean by the word poiver or force ? Suppose 
I take this sheet of paper, and place it upright 
on one edge, resting against a support before 
me (as the roughest possible illustration of 
something to be disturbed), and suppose I then 
pull this piece of string which is attached to it. 
I pull the paper over. I have therefore brought 
into use a power of doing so — the power of 
my hand carried on through this string in a 
way which is very remarkable when we come 
to analyse it; and it is by means of these powers 
conjointly (for there are several powers here 
employed) that I pull the paper over. Again, 
if I give it a push upon the other side, I bring 
into play a power, but a very different exertion 
of power from the former ; or, if I take now 
this bit of shell-lac [a stick of shell-lac about 
12 inches long and 1^ in diameter] and rub it 
with flannel, and hold it an inch or so in front 
of the upper part of this upright sheet, the 



WHAT IS FORCE.' 5 

paper is immediately moved towards the shell- 
lac, and by now drawing the latter away, the 
paper falls over without having been touched 
by anything. You see — in the first illustration 
I produced an effect than which nothing could 
be commoner — I pull it over now, not by 
means of that string or the pull of my hand, but 
by some action in this shell-lac. The shell-lac, 
therefore, has a power wherewith it acts upon 
the sheet of paper ; and as an illustration of 
the exercise of another kind of power, I might 
use gunpowder with which to throw it over. 

Now, I want you to endeavour to comprehend 
that when I am speaking of a power or force, 
I am speaking of that which I used just now to 
pull over this piece of paper. I will not embar- 
rass you at present with the name of that power, 
but it is clear there was a something in the 
shell-lac which acted by attraction, and pulled 
the paper over; this, then, is one of those things 
which we call power, or force; and you will 
now be able to recognise it as such in whatever 
form I show it to you. We are not to suppose 
that there are so very many different powers ; 
on the contrary, it is wonderful to think how 
few are the powers by which all the phenomena 
b 3 



6 GRAVITATION. 

of nature are governed. There is an illustration 
of another kind of power in that lamp ; there is 
a power of heat — a power of doing something, 
but not the same power as that which pulled 
the paper over: and so, by degrees, we find 
that there are certain other powers (not many) 
in the various bodies around us; and thus, 
beginning with the simplest experiments of 
pushing and pulling, I shall gradually proceed 
to distinguish these powers one from the other, 
and compare the way in which they combine 
together. This world upon which we stand 
(and we have not much need to travel out of 
the world for illustrations of our subject; but 
the mind of man is not confined like the 
matter of his body, and thus he may and does 
travel outwards, for wherever his sight can 
pierce, there his observations can penetrate) is 
pretty nearly a round globe, having its surface 
disposed in a manner of which this terrestrial 
globe by my side is a rough model ; so much is 
land and so much is water, and by looking at it 
here we see in a sort of map or picture how the 
world is formed upon its surface. Then, when 
we come to examine further, I refer you to this 
sectional diagram of the geological strata of the 



WHAT IS MATTER? 7 

«arth, in which there is a more elaborate view 
of what is beneath the surface of our globe. 
And, when we come to dig into or examine it 
(as man does for his own instruction and ad- 
vantage, in a variety of ways), we see that it is 
made up of different kinds of matter, subject to 
a very few powers; and all disposed in this 
{strange and wonderful way, which gives to man 
a history — and such a history — as to what 
there is in those veins, in those rocks, the ores, 
the water springs, the atmosphere around, and 
all varieties of material substances, held toge- 
ther by means of forces in one great mass, 
8000 miles in diameter, that the mind is over- 
whelmed in contemplation of the wonderful 
history related by these strata (some of which 
are fine and thin like sheets of paper), — all 
formed in succession by the forces of which I 
have spoken. 

I now shall try to help your attention to what 
I may say by directing, to-day, our thoughts to 
one kind of power. You see what I mean by 
the term matter — any of these things that I 
can lay hold of with the hand, or in a bag (for 
I may take hold of the air by enclosing it in a 
bag) _they are all portions of matter with 

B 4 



8 GRAVITATION. 

which we have to deal at present, generally or 
particularly, as I may require to illustrate my 
subject. Here is the sort of matter which we 
call water — it is there ice [pointing to a block 
of ice upon the table], there water — [pointing 
to the water boiling in a flask] — here vapour 
— you see it issuing out from the top [of the 
flask]. Do not suppose that that ice and that 
water are two entirely different things, or that 
the steam rising in bubbles and ascending in 
vapour there is absolutely different from the 
fluid water — it may be different in some par- 
ticulars, having reference to the amounts of 
power which it contains ; but it is the same, 
nevertheless, as the great ocean of water around 
our globe, and I employ it here for the sake of 
illustration, because if we look into it we shall 
find that it supplies us with examples of all the 
powers to which I shall have to refer. For in- 
stance, here is water — it is heavy; but let us 
examine it with regard to the amount of its 
heaviness, or its gravity. I have before me a 
little glass vessel and scales [nearly equipoised 
scales, one of which contained a half-pint glass 
vessel], and the glass vessel is at present the 
lighter of the two; but if I now take some 



ATTRACTION OF THE EARTH. 9 

water and pour it in, you see that that side of 
the scales immediately goes down ; that shows 
you (using common language, which I will not 
suppose for the present you have hitherto ap- 
plied very strictly) that it is heavy, and if I put 
this additional weight into the opposite scale, I 
should not wonder if this vessel would hold 
water enough to w T eigh it down. [The Lecturer 
poured more water into the jar, which again 
weut down.] "Why do I hold the bottle above 
the vessel to pour the water into it ? You will 
say, because experience has taught me that it is 
necessary. I do it for a better reason — because 
it is a law of nature that the water should fall 
towards the earth, and therefore the very means 
which I use to cause the water to enter the 
vessel are those which will carry the whole body 
of water down. That power is what we call 
gravity, and you see there [pointing to the 
scales] a good deal of water gravitating towards 
the earth. Now here [exhibiting a small piece of 
platinum ( 2 )] is another thing which gravitates 
towards the earth as much as the whole of that 
water. See what a little there is of it — that 
little thing is heavier than so much water 
[placing the metal in opposite scales to the 



10 GRAVITATION. 

water]. What a wonderful thing it is to see 
that it requires so much water as that [a half- 
pint vessel full] to fall towards the earth, com- 
pared with the little mass of substance I have 
here ! And again, if I take this metal [a bar of 
aluminium ( 3 ) about eight times the bulk of the 
platinum] we find the water will balance that as 
well as it did the platinum ; so that we get even 
in the very outset, an example of what we want 
to understand by the words forces or powers. 

I have spoken of water, and first of all of its 
property of falling downwards : — you know very 
well how the oceans surround the globe — how 
they fall round the surface, giving roundness to 
it, clothing it like a garment ; but, besides that, 
there are other properties of water. Here, 
for instance, is some quicklime, and if I add 
some water to it, you will find another power or 
property in the water. ( 4 ) It is now very hot, 
it is steaming up, and I could perhaps light 
phosphorus or a lucifer-match with it. Now, 
that could not happen without a force in the 
water to produce the result ; but that force is 
entirely distinct from its power of falling to the 
earth. Again, here is another substance [some 
anhydrous sulphate of copper ( 5 )] which will il- 



EVOLUTION OF HEAT FROM WATEK. 11 

lustrate another kind of power. [The Lecturer 
here poured some water over the white sulphate 
of copper, which - immediately became blue, 
evolving considerable heat at the same time.] 
Here is the same water with a substance which 
heats nearly as much as the lime does, but see 
how differently. So great indeed is this heat 
in the case of lime, that it is sufficient some- 
times (as you see here) to set wood on fire ; and 
this explains what we have sometimes heard, 
of barges laden with quicklime taking fire in 
the middle of the river, in consequence of this 
power of heat brought into play by a leakage 
of the water into the barge. You see how 
strangely different subjects for our considera- 
tion arise, when we come to think over these 
various matters — the power of heat evolved by 
acting upon lime with water, and the power 
which water has of turning this salt of copper 
from white to blue. 

I want you now to understand the nature of 
the most simple exertion of this power of mat- 
ter called weight or gravity. Bodies are heavy ; 
— you saw that in the case of water when I 
placed it in the balance. Here I have what we 
call a weight [an iron half cwt.] — a thing called 



12 GRAVITATION. 

a weight, because in it the exercise of that 
power of pressing downwards is especially used 
for the purposes of weighing ; and I have also 
one of these littie inflated india-rubber bladders, 
which are very beautiful although very common 
(most beautiful things are common), and I am 
going to put the weight upon it, to give you a 
sort of illustration of the downward pressure of 
the iron, and of the power which the air pos- 
sesses of resisting that pressure ; — it may burst, 
but we must try to avoid that. [During the 
last few observations the Lecturer had suc- 
ceeded in placing the half cwt. in a state of 
quiescence upon the inflated india-rubber ball, 
which consequently assumed a shape very much 
resembling a flat cheese with round edges.] 
There you see a bubble of air bearing half a 
hundred weight, and you must conceive for 
yourselves what a wonderful power there must 
be to pull this weight downwards, to sink it 
thus in the ball of air. 

Let me now give you another illustration of 
this power. You know what a pendulum is. 
I have one here (fig.\\ and if I set it swinging, 
it will continue to swing to and fro. Now, I 
wonder whether you can tell me why that body 



THE PENDULUM. 



13 



oscillates to and fro — that pendulum bob as it 
is sometimes called. Observe, if I hold the 
straight stick horizontally, as high as the posi- 
tion of the balls at the two ends of its journey, 
you see that the ball is in a higher position at 
the two extremities than it is when in the 
middle. Starting from one end of the stick, 
the ball falls towards the centre, and then 
rising again to the opposite end, it constantly 
tries to fall to the lowest point, swinging and 
vibrating most beautifully, and with wonderful 
properties in other respects — the time of its 
vibration and so on — but concerning which we 
will not now trouble ourselves. 

Fig. l. 




If a gold leaf, or piece of thread, or any 
other substance, were hung where this ball is, 



14 GRAVITATION. 

it would swing to and fro in the same manner, 
and in the same time too. Do not be startled 
at this statement ; I repeat, in the same manner 
and in the same time, and you will see by and 
by how this is. Now, that power which caused 
the water to descend in the balance — which 
made the iron weight press upon and flatten the 
bubble of air — which caused the swinging to 
and fro of the pendulum, that power is entirely 
due to the attraction which there is between 
the falling body and the earth. Let us be slow 
and careful to comprehend this. It is not that 
the earth has any particular attraction towards 
bodies which fall to it, but, that all these 
bodies possess an attraction, every one towards 
the other. It is not that the earth has any 
special power which these balls themselves have 
not, for just as much power as the earth has to 
attract these two balls [dropping two ivory 
balls], just so much power have they in propor- 
tion to their bulks to draw themselves one to 
the other ; and the only reason why they fall so 
quickly to the earth is owing to its greater size. 
Now, if I were to place these two balls near to- 
gether, I should not be able, by the most deli- 
cate arrangement of apparatus, to make you, or 



THE CENTRE OF GRAVITY. 15 

myself, sensible that these balls did attract one 
another ; and yet we know that such is the case, 
because if, instead of taking a small ivory ball, 
we take a mountain, and put a ball like this 
near it, we find that, owing to the vast size of 
the mountain, as compared with the billiard 
ball, the latter is drawn slightly towards it ; 
showing clearly that an attraction does exist, 
just as it did between the shell-lac which I 
rubbed and the piece of paper which was over- 
turned by it. 

Now, it is not very easy to make these things 
quite clear at the outset, and I must take care 
not to leave anything unexplained as I proceed, 
and, therefore, I must make" you clearly under- 
stand that all bodies are attracted to the earth, 
or, to use a more learned term, gravitate. You 
will not mind my using this word, for when I 
say that this penny-piece gravitates, I mean 
nothing more nor less than that it falls towards 
the earth, and if not intercepted, it would go on 
falling, falling, until it arrived at what we call 
the centre of gravity of the earth, which I will 
explain to you by and by. 

I want you to understand that this property 
of gravitation is never lost, that every substance 



16 GRAVITATION. 

possesses it, that there is never any change in 
the quantity of it ; and, first of all, I will take 
as illustration a piece of marble. Now this 
marble has weight — as you will see if I put it 
in these scales; it weighs the balance down, 
and if I take it off, the balance goes back again 
and resumes its equilibrium. I can decompose 
this marble and change it, in the same manner 
as I can change ice into water and water into 
steam. I can convert a part of it into its own 
steam easily, and show you that this steam from 
the marble has the property of remaining in the 
same place at common temperatures, which 
water-steam has not. If I add a little liquid to 
the marble and decompose it( 6 ), I get that which 
you see — [the Lecturer here put several lumps 
of marble into a glass jar, and poured water and 
then acid over them ; the carbonic acid imme- 
diately commenced to escape with considerable 
effervescence] — the appearance of boiling, 
which is only the separation of one part of 
the marble from another. Now this [marble] 
steam, and that [water] steam, and all other 
steams gravitate just like any other substance 
does ; they all are attracted the one towards the 
other, and all fall towards the earth, and what 



GRAVITATION OF CARBONIC ACID. 



17 



I want you to see is that this steam gravitates. 
I have here {Jig. 2) a large vessel placed upon 

Fig. 2. 




a balance, and the moment I pour this steam 
into it you see that the steam gravitates. Just 
watch the index, and see whether it tilts over or 
not. [The Lecturer here poured the carbonic 
acid out of the glass in which it was being 
generated into the vessel suspended on the 
balance, when the gravitation of the carbonic 
acid was at once apparent.] Look how it is 
going down. How pretty that is ! I poured no- 
thing in but the invisible steam, or vapour, or 
gas which came from the marble, but you see 
that part of the marble, although it has taken 
the shape of air, still gravitates as it did before. 
c 



18 GRAVITATION. 

Now will it weigh down that bit of paper? 
[Placing a piece of paper in the opposite scale.] 
Yes, more than that ; it nearly weighs down 
this bit of paper. [Placing another piece of 
paper in.] And thus you see that other forms 
of matter besides solids and liquids tend to fall 
to the earth ; and, therefore, you will accept 
from me the fact that all things gravitate, 
whatever may be their form or condition. Now 
here is another chemical test which is very 
readily applied. [Some of the carbonic acid 
was poured from one vessel into another, and 
its presence in the latter shown by introducing 
into it a lighted taper, which was immediately 
extinguished.] You see from this result also 
that it gravitates. All these experiments show 
you that, tried by the balance, tried by pouring 
like water from one vessel to another, this 
steam, or vapour, or gas, is, like all other 
things, attracted to the earth. 

There is another point I want in the next 
place to draw your attention to. I have here 
a quantity of shot; each of these falls separately, 
and each has its own gravitating power, as you 
perceive when I let them fall loosely on a sheet 
of paper. If I put them into a bottle I collect 



CENTRE OP GRAVITY. 



19 



them together as one mass, and philosophers 
have discovered that there is a certain point in 
the middle of the whole collection of shots that 
may he considered as the one point in which 
all their gravitating power is centred, and that 
point they call the centre of gravity; it is not 
at all a bad name, and rather a short one — the 
centre of gravity. Now suppose I take a sheet 
of pasteboard or any other thing easily dealt 
with, and run a bradawl through it at one 
corner A (Jig, 3) and Mr. Anderson hold that 
up in his hand before us, and I then take a 




piece of thread and an ivory ball, and hang 

C2 



20 GRAVITATION. 

that upon the awl, then the centre of gravity 
of both the pasteboard and the ball and string 
are as near as they can get to the centre 
of the earth; that is to say, the whole of the 
attracting power of the earth is, as it were, 
centred in a single point of the cardboard; 
and this point is exactly below the point of 
suspension. All I have to do, therefore, is to 
draw a line, A B, corresponding with the string, 
and we shall find that the centre of gravity is 
somewhere in that line. But where? To find 
that out all we have to do is to take another 
place for the awl {fig. 4), hang the plumb-line, 
and make the same experiment, and there [at 
the point c] is the centre of gravity — there 
where the two lines which I have traced cross 
each other; and if I take that pasteboard, and 
make a hole with the bradawl through it at 
that point, you will see that it will be supported 
in any position in which it may be placed. 
Now, knowing that, what do I do when I try 
to stand upon one leg? Do you not see that I 
push myself over to the left side, and quietly 
take up the right leg, and thus bring some 
central point in my body over this left leg. 
What is that point which I throw over? You 



CENTRE OF GRAVITY. 



21 



will know at once that it is the centre of 
gravity — that point in me where the whole 
gravitating force of my body is centred, and 
which I thus bring in a line over my foot. 

Here is a toy I happened to see the other 
day, which will, I think, serve to illustrate our 
subject very well. That toy ought to lie some- 
thing in this manner {fig. 5). And would do 
so if it were uniform in substance; but you 
see it does not, it will get up again. And now 
philosophy comes to our aid; and I am per- 



Fig. 6. 




fectly sure, without looking inside the figure, 
that there is some arrangement by which the 
centre of gravity is at the lowest point when 
the image is standing upright; and we may be 
certain when I am tilting it over (see fig. 6) 
that I am lifting up the centre of gravity (a), and 



c 3 



22 



GRAVITATION. 



raising it from the earth. All this is effected 
by putting a piece of lead inside the lower 
part of the image, and making the base of large 
curvature, and there you have the whole secret. 
But what will happen if I try to make the 
figure stand upon a sharp point? You observe 
I must get that point exactly under the centre 

Fig. 7. 




of gravity or it will fall over thus [endeavouring 
unsuccessfully to balance it]; and this you see 
is a difficult matter, I cannot make it stand 
steadily; but if I embarrass this poor old lady 



CENTKE OF GRAVITY. 



23 



with a world of trouble, and hang this wire 
with bullets at each end about her neck, it is 
very evident that, owing to there being those 
balls of lead hanging down on either side, in 
addition to the lead inside, I have lowered the 
centre of gravity, and now she will stand upon 
this point {fig. 7); and what is more, she proves 
the truth of our philosophy by standing side- 
ways. 

I remember an experiment which puzzled me 
very much when a boy. I read it in a conjur- 
ing book, and this was how the problem was 
put to us : " How," as the book said, " how to 

Fig. 8. 




hang a pail of water, by means of a stick, upon 
the side of a table" (fig. 8). Now I have here a 



c 4 



24 



GRAVITATION. 



table, a piece of stick, and a pail, and the 
proposition is, how can that pail be hung to the 
edge of this table ? It is to be done, and can 
you at all anticipate what arrangement I shall 
make to enable me to succeed ? Why this. I 
take a stick, and put it in the pail between the 
bottom and the horizontal piece of wood, and 
thus give it a stiff handle, and there it is ; and 
what is more, the more water I put into the 
pail the better it will hang. It is very true 
that before I quite succeeded I had the misfor- 
tune to push the bottoms of several pails out ; 
but here it is hanging firmly (fig. 9), and you 




now see how you can hang up the pail in the 
way which the conjuring books require. 



CENTKE OF GRAVITY. 



25 



Again, if you are really so inclined (and I do 
hope all of you are), you will find a great deal 
of philosophy in this [holding up a cork and a 
pointed thin stick about a foot long]. Do not 



Fig. 10. 




refer to your toy-books, and say you have seen 
that before. Answer me rather, if I ask you, 
have you understood it before ? It is an ex- 
periment which appeared very wonderful to me 
when I was a boy ; I used to take a piece of 
cork (and I remember, I thought at first that 
it was very important that it should be cut out 
in the shape of a man, but by degrees I got rid 
of that idea), and the problem was to balance it 



26 GRAVITATION. 

on the point of a stick. Now you will see I 
have only to place two sharp-pointed sticks one 
on each side, and give it wings, thus, and you 
will find this beautiful condition fulfilled. 

We come now to another point; — All bodies, 
whether heavy or light, fall to the earth by this 
force which we call gravity. By observation, 
moreover, we see that bodies do not occupy the 
same time in falling ; I think you will be able 
to see that this piece of paper and that ivory 
ball fall with different velocities to the table 
[dropping them] ; and if, again, I take a feather 
and an ivory ball, and let them fall, you see 
they reach the table or earth at different times ; 
that is to say, the ball falls faster than the 
feather. Now, that should not be so, for all 
bodies do fall equally fast to the earth. There 
are one or two beautiful points included in that 
statement. First of all, it is manifest that an 
ounce, or a pound, or a ton, or a thousand tons, 
all fall equally fast, no one faster than another : 
here are two balls of lead, a very light one and 
a very heavy one, and you perceive they both 
fall to the earth in the same time. Now if I 
were to put into a little bag a number of these 
balls sufficient to make up a bulk equal to the 



GRAVITATION IN MASSES. 27 

large one, they would also fall in the same time; 
for if an avalanche fall from the mountains, the 
rocks, snow and ice, together falling towards 
the earth, fall with the same velocity, whatever 
be their size. 

I cannot take a better illustration of this 
than that of gold leaf, because it brings before 
us the reason of this apparent difference in the 
time of the fall. Here is a piece of gold leaf. 
Now if I take a lump of gold and this gold leaf, 
and let them fall through the air together, you 
see that the lump of gold — the sovereign, or 
coin — will fall much faster than the gold leaf. 
But why? They are both gold, whether sove- 
reign or gold leaf. Why should they not fall 
to the earth with the same quickness? They 
would do so, but that the air around our globe 
interferes very much where we have the piece 
of gold so extended and enlarged as to offer 
much obstruction on falling through it. I will, 
however, show you that gold leaf does fall as 
fast when the resistance of the air is excluded — 
for if I take a piece of gold leaf and hang it in 
the centre of a bottle, so that the gold, and 
the bottle, and the air within shall all have an 
equal chance of falling, then the gold leaf will 



28 GRAVITATION. 

fall as fast as anything else. And if I suspend 
the bottle containing the gold leaf to a string, 
and set it oscillating like a pendulum, I may 
make it vibrate as hard as I please, and the 
gold leaf will not be disturbed, but will swing 
as steadily as a piece of iron would do; and I 
might even swing it round my head with any 
degree of force, and it would remain undis- 
turbed. Or I can try another kind of experi- 
ment: — if I raise the gold leaf in this way 
[pulling the bottle up to the ceiling of the 
theatre by means of a cord and pulley, and 
then suddenly letting it fall to within a few 
inches of the lecture table], and allow it then 
to fall from the ceiling downwards (I will put 
something beneath to catch it, supposing I 
should be rnaladroif), you will perceive that 
the gold leaf is not in the least disturbed. The 
resistance of the air having been avoided, the 
glass bottle and gold leaf all fall exactly in the 
same time. 

Here is another illustration: — I have hung 
a piece of gold leaf in the upper part of this 
long glass vessel, and I have the means, by a 
little arrangement at the top, of letting the 
gold leaf loose. Before we let it loose we will 



GRAVITATION IN VACUO. 29 

remove the air by means of an air pump, and 
while that is being done, let me show you 
another experiment of the same kind. Take 
a penny-piece, or a half-crown, and a round 
piece of paper a trifle smaller in diameter than 
the coin, and try them side by side to see 
whether they fall at the same time [dropping 
them]. You see they do not — the penny- 
piece goes down first. But, now place this 
paper flat on the top of the coin, so that it shall 
not meet with any resistance from the air, and 
upon then dropping them you see they do both 
fall in the same time [exhibiting the effect], I 
dare say if I were to put this piece of gold leaf, 
instead of the paper, on the coin, it would do 
as well. It is very difficult to lay the gold leaf 
so flat that the air shall not get under it and 
lift it up in falling, and I am rather doubtful 
as to the success of this, because the gold leaf 
is puckery ; but will risk the experiment. There 
they go together! [letting them fall] and you 
see at once that they both reach the table at 
the same moment. 

We have now pumped the air out of the ves- 
sel, and you will perceive that the gold leaf 
will fall as quickly in this vacuum as the coin 



30 GRAVITATION. 

does in the air. I am now going to let it 
loose, and you must watch to see how rapidly 
it falls. There ! [letting the gold loose] there 
it is, falling as gold should fall. 

I am sorry to see our time for parting is 
drawing so near. As we proceed, I intend to 
write upon the board behind me certain words 
so as to recall to your minds what we have 
already examined ; and I put the word Forces 
as a heading, and I will then add beneath the 
names of the special forces according to the 
order in which we consider them ; and although 
I fear that I have not sufficiently pointed out 
to you the more important circumstances con- 
nected with this force of Gravitation, espe- 
cially the law which governs its attraction (for 
which, I think, I must take up a little time at 
our next meeting), still I will put that word on 
the board, and hope you will now remember 
that we have in some degree considered the 
force of gravitation — that force which causes 
all bodies to attract each other when they are 
at sensible distances apart, and tends to draw 
them together 



31 



LECTUEE II. 

GRAVITATION. — COHESION. 

Do me the favour to pay me as much attention 
as you did at our last meeting, and I shall not 
repent of that which I have proposed to under- 
take. It will be impossible for us to consider 
the Laws of Nature, and what they effect, 
unless we now and then give our sole attention, 
so as to obtain a clear idea upon the subject. 
Give me now that attention, and then I trust 
we shall not part without your knowing some- 
thing about those Laws, and the manner in 
which they act. You recollect, upon the last 
occasion, I explained that all bodies attracted 
each other, and that this power we called gravi- 
tation. I told you that when we brought these 
two bodies [two equal-sized ivory balls sus- 
pended by threads] near together, they attracted 
each other, and that we might suppose that the 



32 GRAVITATION. 

whole power of this attraction was exerted be- 
tween their respective centres of gravity ; and, 
furthermore, you learned from me that if, in- 
stead of a small ball I took a larger one, like 
that [changing one of the balls for a much 
larger one], there was much more of this at- 
traction exerted ; or, if I made this ball larger 
and larger, until, if it were possible, it became 
as large as the Earth itself — or, I might take the 
Earth itself, as the large ball — that then the 
attraction would become so powerful as to cause 
them to rush together in this manner [dropping 
the ivory ball]. You sit there upright, and I 
stand upright here, because we keep our centres 
of gravity properly balanced with respect to the 
earth; and I need not tell you that on the 
other side of this world the people are standing 
and moving about with their feet towards our 
feet, in a reversed position as compared with 
us, and all by means of this power of gravita- 
tion to the centre of the earth. 

I must not, however, leave the subject of 
gravitation, without telling you something 
about its laws and regularity; and first, as 
regards its power with respect to the distance 
that bodies are apart. If I take one of these 



LAW OF GRAVITATION. 33 

balls and place it within an inch of the other, 
they attract each other with a certain power. 
If I hold it at a greater distance off, they at- 
tract with less power, and if I hold it at a 
greater distance still, their attraction is still less. 
Now this fact is of the greatest consequence ; 
for, knowing this law, philosophers have dis- 
covered most wonderful things. You know 
that there is a planet, Uranus, revolving round 
the sun with us, but eighteen hundred millions 
of miles off; and because there is another 
planet as far off as three thousand millions of 
miles, this law of attraction, or gravitation, still 
holds good, and philosophers actually discovered 
this latter planet, Neptune, by reason of the 
effects of its attraction at this overwhelming 
distance. Now I want you clearly to under- 
stand what this law is. They say (and they 
are right) that two bodies attract each other 
inversely as the square of the distance, — a sad 
jumble of words until you understand them ; 
but I think we shall soon comprehend what this 
law is, and what is the meaning of the " inverse 
square of the distance." 

I have here (fig. 11) a lamp a, shining most 
intensely upon this disc, b, c, d ; and this light 

D 



34 



GRAVITATION. 



acts as a sun by which I can get a shadow from 
this little screen b f (merely a square piece of 
card), which, as you know, when I place it close 
to the large screen, just shadows as much of 
it as is exactly equal to its own size ; but now 
let me take this card e, which is equal to the 

Fig. 11. 




other one in size, and place it- midway between 
the lamp and the screen ; now look at the size 
of the shadow b d, it is four times the original 
size. Here, then, comes the " inverse square of 
the distance." This distance, A e, is one, and 
that distance, A b, is two ; but that size E being 
one, this size b d of shadow is four instead of 



LAW OF GRAVITATION. 35 

two, which is the square of the distance ; and, 
if I put the screen at one third of the distance 
from the lamp, the shadow on the large screen 
would be nine times the size. Again, if I hold 
this screen here, at b f, a certain amount of 
light falls on it ; and if I hold it nearer the 
lamp at e, more light shines upon it. And 
you see at once how much — exactly the quan- 
tity which I have shut off from the part of this 
screen, b d, now in shadow; moreover, you see 
that if I put a single screen here, at a, by the 
side of the shadow, it can only receive one fourth, 
of the proportion of light which is obstructed. 
That, then, is what is meant by the inverse of 
the square of the distance. This screen e is the 
brightest because it is the nearest, and there is 
the whole secret of this curious expression 
inversely as the square of the distance. Now, 
if you cannot perfectly recollect this when you 
go home, get a candle and throw a shadow of 
something — your profile, if you like — on the 
wall, and then recede or advance, and you will 
find that your shadow is exactly in proportion 
to the square of the distance you are off the 
wall ; and then if you consider how much light 
shines on you at one distance, and how much 

D 2 



36 GRAVITATION. 

at another, you get the inverse accordingly. So 
it is as regards the attraction of these two balls, 
they attract according to the square of the 
distance, inversely. I want you to try and 
remember these words, and then you will be 
able to go into all the calculations of astrono- 
mers as to the planets and other bodies, and tell 
why they move so fast, and why they go round 
the sun without falling into it, and be prepared 
to enter upon many other interesting inquiries 
of the like nature. 

Let us now leave this subject which I have 
written upon the board under the word Force 
— Gravitation — and go a step further. All 
bodies attract each other at sensible distances. 
I showed you the electric attraction on the last 
occasion (though I did not call it so) ; that 
attracts at a distance; and in order to make our 
progress a little more gradual, suppose I take a 
few iron particles [dropping some small frag- 
ments of iron on the table]. There, I have 
already told you that in all cases where bodies 
fall, it is the 'particles that are attracted. You 
may consider these then as separate particles 
magnified, so as to be evident to your sight ; 
they are loose from eachother — they all gravi- 



MAGNETIC ATTRACTION. 



37 



tate — they all fall to the earth — for the force 
of gravitation never fails. Now, I have here a 
centre of power which I will not name at present, 
and when these particles are placed upon it, 
see what an attraction they have for each other. 
Here I have an arch of iron filings {fig. 12) 

Fig. 12. 





* 








y 



regularly built up like an iron bridge, because 
I have put them within a sphere of action which 
will cause them to attract each other. See ! — 
I could let a mouse run through it, and yet if I 
try to do the same thing with them here [on the 
table] they do not attract each other at all. It 
is that [the magnet] which makes them hold 
together. Now, just as these iron particles hold 

D 3 



38 COHESION. 

together in the form of an elliptical bridge, so 
do the different particles of iron which constitute 
this nail hold together and make it one. And 
here is a bar of iron ; why, it is only because 
the different parts of this iron are so wrought 
as to keep close together by the attraction be- 
tween the particles that it is held together in 
one mass. It is kept together, in fact, merely 
by the attraction of one particle to another, and 
that is the point I want now to illustrate. If I 
take a piece of flint and strike it with a hammer 
and break it thus [breaking off a piece of the 
flint], I have done nothing more than separate 
the particles which compose these two pieces so 
far apart, that their attraction is too weak to 
cause them to hold together, and it is only for 
that reason that there are now two pieces in the 
place of one. I will show you an experiment 
to prove that this attraction does still exist in 
those particles, for here is a piece of glass (for 
what was true cf the flint and the bar of iron is 
true of the piece of glass, and is true of every 
other solid, they are all held together in the lump 
by the attraction between their parts), and I can 
show you the attraction between its separate 
particles, for if I take these portions of glass 



TENACITY OF IRON. 39 

which I have reduced to very fine powder, you 
see that I can actually build them up into a 
solid wall by pressure between two flat surfaces. 
The power which I thus have of building up 
this wall is due to the attraction of the particles, 
forming as it were the cement which holds them 
together; and so in this case, where I have 
taken no very great pains to bring the particles 
together, you see perhaps a couple of ounces of 
finely pounded glass standing as an upright 
wall — is not this attraction most wonderful ? 
Tlwt bar of iron one inch square has such power 
of attraction in its particles — giving to it such 
< strength — that it will hold up twenty tons 
weight before the little set of particles in the 
small space equal to one division across which 
it can be pulled apart, will separate. In this 
manner suspension bridges and chains are held 
together by the attraction of their particles, and 
I am going to make an experiment which will 
show how strong is this attraction of the parti- 
cles. [The Lecturer here placed his foot on a 
loop of wire fastened to a support above, and 
swung with his whole weight resting upon it for 
some moments.] You see while hanging here 
all my weight is supported by these little par- 

D 4 



40 COHESION. 

tides of the wire, just as in pantomimes they 
sometimes suspend gentlemen and damsels. 

How can we make this attraction of the par- 
ticles a little more simple ? There are many 
things which if brought together properly will 
show this attraction. Here is a boy's experi- 
ment (and I like a boy's experiment). — Get a 
tobacco-pipe, fill it with lead, melt it, and then 
pour it out upon a stone, and thus get a clean 
piece of lead (this is a better plan than scraping 
it — scraping alters the condition of the surface 
of the lead). I have here some pieces of lead 
which I melted this morning for the sake of mak- 
ing them clean. Now these pieces of lead hang 
together by the attraction of their particles, and 
if I press these two separate pieces close together, 
so as to bring their particles within the sphere 
of attraction, you will see how soon they become 
one. I have merely to give them a good squeeze, 
and draw the upper piece slightly round at the 
same time, and here they are as one, and all 
the bending and twisting I can give them will 
not separate them again ; I have joined the 
lead together, not with solder, but simply by 
means of the attraction of the particles. 

This however is not the best way of bringing 



COHESION OF ALUM PARTICLES. 41 

those particles together — we have many better 
plans than that, — and I will show you one that 
will do very well for juvenile experiments. 
There is some alum crystallised very beautifully 
by nature (for all things are far more beautiful 
in their natural than their artificial form), and 
here I have some of the same alum broken into 
fine powder. In it I have destroyed that force 
of which I have placed the name on this board 
— Cohesion, or the attraction exerted between 
the particles of bodies to hold them together. 
Now I am going to show you that if we take this 
powdered alum and some hot water, and mix 
them together, I shall dissolve the alum — all 
the particles will be separated by the water far 
more completely than they are here in the 
powder ; but then, being in the water, they will 
have the opportunity as it cools (for that is the 
condition which favours their coalescence) of 
uniting together again and forming one mass.( 7 ) 
Now, having brought the alum into solution, 
I will pour it into this glass basin, and you will, 
to-morrow, find that those particles of alum 
which I have put into the water, and so separated 
that they are no longer solid, will, as the water 
cools, come together and cohere, and by to-mor- 



42 COHESION. 

row morning we shall have a great deal of the 
alum crystallised out, that is to say, come back 
to the solid form. [The Lecturer here poured 
a little of the hot solution of alum into the 
glass dish, and when the latter had thus been 
made warm, the remainder of the solution was 
added.] I am now doing that which I advise 
you to do if you use a glass vessel, namelyf 
warming it slowly and gradually, and in repeat- 
ing this experiment do as I do, pour the liquid 
out gently, leaving all the dirt behind in the 
basin ; and remember that the more carefully 
and quietly you make this experiment at home, 
the better the crystals. To-morrow you will 
see the particles of alum drawn together, and 
if I put two pieces of coke in some part of the 
solution (the coke ought first to be washed very 
clean, and dried), you will find to-morrow that 
we shall have a beautiful crystallisation over 
the coke, making it exactly resemble a natural 
mineral. 

Now how curiously our ideas expand by 
watching these conditions of the attraction of 
cohesion ! — how many new phenomena it gives 
us beyond those of the attraction of gravitation ! 
See how it gives us great strength. The things 



CHANGE IN CONDITION OF COHESION. 43 

we deal with in building up the structures on 
the earth are of strength — we use iron, stone, 
and other things of great strength ; and only 
think that all those structures you have about 
you — think of the Great Eastern if you please, 
which is of such size and power as to be almost 
more than man can manage — are the result of 
this power of cohesion and attraction. 

I have here a body in which I believe you 
will see a change taking place in its condition 
of cohesion at the moment it is made. It is at 
first yellow, it then becomes a fine crimson red. 
Just watch w r hen I pour these two liquids 
together — both colourless as water. [The 
Lecturer here mixed together solutions of per- 
chloride of mercury and iodide of potassium, 
when a yellow precipitate of biniodide of mercury 
fell down, which almost immediately became 
crimson red.] Now, there is a substance which 
is very beautiful, but see how it is changing 
colour. It was reddish-yellow at first, but it 
has now become red. ( 8 ) I have previously pre- 
pared a little of this red substance, which you 
see formed in the liquid, and have put some of it 
upon paper. [Exhibiting several sheets of paper 
coated with scarlet biniodide of mercury. ( 9 )] 



44 COHESION. 

i 

There it is — the same substance spread upon 
paper, and there too is the same substance; and 
here is some more of it [exhibiting a piece of 
paper as large as the other sheets, but having 
only very little red colour on it, the greater 
part being yellow], a little more of it, you will 
say. Do not be mistaken; there is as much 
upon the surface of one of these pieces of paper 
as upon the other. What you see yellow is 
the same thing as the red body, only the attrac- 
tion of cohesion is in a certain degree changed; 
for I will take this red body, and apply heat to 
it (you may perhaps see a little smoke arise, 
but that is of no consequence), and if you look 
at it it will first of all darken — but see, how it 
is becoming yellow. I have now made it all 
yellow, and what is more, it will remain so ; but 
if I take any hard substance, and rub the yellow 
part with it, it will immediately go back again 
to the red condition. [Exhibiting the experi- 
ment.] There it is. You see the red is not 
put back, but brought back by the change in 
the substance. Now [warming it over the 
spirit lamp] here it is becoming yellow again, 
and that is all because its attraction of cohesion 
is changed. And what will you say to me 



PRINCE RUPERTS DROPS. 45 

when I tell you that this piece of common 
charcoal is just the same thing, only differently 
coalesced, as the diamonds which you wear? 
(I have put a specimen outside of a piece of 
straw which was charred in a particular way— 
it is just like black lead.) Now, this charred 
straw, this charcoal, and these diamonds, are 
all of them the same substance, changed but in 
their properties as respects the force of cohesion. 
Here is a piece of glass [producing a piece of 
plate glass about two inches square], (I shall 
want this afterwards to look to and examine its 
internal condition) — and here is some of the 
, same sort of glass differing only in its power 
of cohesion, because while yet melted it has been 
dropped into cold water [exhibiting a u Prince 
Kupert's drop( 10 ) {jig. 13)], and if I take one 
of these little tear-like pieces and break off 
ever so little from the point, the whole will at 
once burst and fall to pieces. I will now break 
off apiece of this. [The Lecturer nipped off a 
small piece from the end of one of the Kupert's 
drops, whereupon the whole immediately fell 
to pieces.] There! you see the solid glass has 
suddenly become powder, and more than that, 
it has knocked a hole in the glass vessel in 



46 



COHESION. 



which it was held. I can show the effect 
better in this bottle of water, and it is very 
likely the whole bottle will go. [A 6-oz. vial 
was filled with water, and a Kupert's drop 
placed in it with the point of the tail just pro- 
jecting out; upon breaking the tip off, the 
drop burst, and the shock being transmitted 
through the water to the sides of the bottle, 
shattered the latter to pieces.] 



Fig. 13. 



Fig. 14. 





Here is another form of the same kind of 
experiment. I have here some more glass 
which has not been annealed [showing some 
thick glass vessels ( u ) (fig. 14)], and if I take 
one of these glass vessels and drop a piece of 
pounded glass into it (or I will take some of 
these small pieces of rock crystal — they have 
the advantage of being harder than glass) and 



COHESION IN CRYSTALLINE BODIES. 47 

so make the least scratch upon the inside, the 
whole bottle will break to pieces, — it cannot 
hold together. [The Lecturer here dropped a 
small fragment of rock crystal into one of these 
glass vessels, when the bottom immediately 
came out and fell upon the plate.] There! it 
goes through, just as it would through a sieve. 

Now, I have shown you these things for the 
purpose of bringing your minds to see that 
bodies are not merely held together by this 
power of cohesion, but that they are held to- 
gether in very curious ways. And suppose I 
take some things that are held together by this 
force, and examine them more minutely. I 
will first take a bit of glass, and if I give it a 
blow with a hammer I shall just break it to 
pieces. You saw how it was in the case of the 
flint when I broke the piece off ; a piece of a 
similar kind would come off, just as you would 
expect ; and if I were to break it up still more, 
it would be as you have seen, simply a col- 
lection of small particles of no definite shape 
or form. But supposing I take some other 
thing, this stone for instance {fig. 15) [taking a 
piece of mica ( 12 )], and if I hammer this stone I 
may batter it a great deal before I can break it 



48 



COHESION. 



up. I may even bend it without breaking it ; 
that is to say, I may bend it in one particular 
direction without breaking it much, although I 
feel in my hands that I am doing it some in- 
jury. But now if I take it by the edges I find 
that it breaks up into leaf after leaf in a most 
extraordinary manner. Why should it break 
up like that ? Not because all stones do, or all 



Fig. 15. 



Fig. 16. 



Fiq. 17. 




crystals; for there is some salt (Jig. 16) — you 
know what common salt is ( 13 ) ; here is a piece 
of this salt which by natural circumstances has 
had its particles so brought together that they 
have been allowed free opportunity of combin- 
ing or coalescing, and you shall see what 
happens if I take this piece of salt and break 
it. It does not break as flint did, or as the 
mica did, but with a clean sharp angle and 



CLEAVAGE OF CRYSTALS. 49 

exact surfaces, beautiful and glittering as 
diamonds [breaking it by gentle blows with a 
hammer] ; there is a square prism which I may 
break up into a square cube. You see these frag- 
ments are all square — one side may be longer 
than the other, but they will only split up so as to 
form square or oblong pieces with cubical sides. 
Now, I go a little farther, and I find another 
stone {fig. 17) [Iceland, or calc-spar] ( u ), which 
I may break in a similar way, but not with 
the same result. Here is a piece which I 
have broken off, and you see there are plain 
surfaces perfectly regular with respect to each 
other, but it is not cubical — it is what we call 
a rhomboid. It still breaks in three directions . 
most beautifully and regularly with polished 
surfaces, but with sloping sides, not like the 
salt. Why not ? It is very manifest that this 
is owing to the attraction of the particles one 
for the other being less in the direction in 
which they give way than in other directions. 
I have on the table before me a number of 
little bits of calcareous spar, and I recommend 
each of you to take a piece home, and then 
you can take a knife and try to divide it in 
the direction of any of the surfaces already 

E 



50 COHESION. 

existing. You will be able to do it at once — 
but if you try to cut it across the crystals you 
cannot ; by hammering, you may bruise and 
break it up — but you can only divide it into 
these beautiful little rhomboids. 

Now I want you to understand a little more 
how this is — and for this purpose I am going 
to use the electric light again. You see, we 
cannot look into the middle of a body like this 
piece of glass. We perceive the outside form, 
and the inside form, and we look through it ; 
but we cannot well find out how these forms 
become so, and I want you, therefore, to take 
a lesson in the way in . which we use a ray of 
light for the purpose of seeing what is in the 
interior of bodies. Light is a thing which is, 
so to say, attracted by every substance that 
gravitates (and we do not know anything that 
does not). All matter affects light more or 
less by what we may consider as a kind of 
attraction, and I have arranged •(%. 18) a very 
simple experiment upon the floor of the room 
for the purpose of illustrating this. I have put 
into that basin a few things which those who 
are in the body of the theatre will not be able 
to see, and I am going to make use of this 



REFRACTION OF LIGHT. 51 

power, which matter possesses, of attracting a 
ray of light. If Mr. Anderson pours some 



Fig. 18. 




water, gently and steadily, into the basin, the 
water will attract the rays of light downwards, 
and the piece of silver and the sealing-wax 
will appear to rise up into the sight of those 
who were before not high enough to see over 
the side of the basin to its bottom. [Mr. 
Anderson here poured water into the basin, 
and upon the Lecturer asking whether any 
body could see the silver and sealing-wax he 
was answered by a general affirmative.] Now, 
I suppose that everybody can see that they are 
not at all disturbed, whilst from the way they 
appear to have risen up, you would imagine 
the bottom of the basin and the articles in it 
were two inches thick, although they are only 
one of our small silver dishes and a piece of 

E 2 



52 



COHESION. 



sealing-wax which I have put there. The 
light which now goes to you from that piece of 
silver was obstructed by the edge of the basin, 
when there was no water there, and you were 
unable to see anything of it; but when we 
poured in water, the rays were attracted down 
by it, over the edge of the basin, and you were 
thus enabled to see the articles at the bottom. 

I have shown you this experiment first, so 
that you might understand how glass attracts 
light, and might then see how other substances, 
like rock-salt and calcareous spar, mica, and 
other stones, would affect the light; and, if 
Dr. Tyndall will be good enough to let us use 
his light again, we will first of all show you 
how it may be bent by a piece of glass {fig. 19). 



x\c N 



Fig. 19. 



¥ 



[The electric lamp was again lit, and the beam 
of parallel rays of light, which it emitted, was 



THE PRISMATIC SPECTRUM. 53 

bent about and decomposed by means of the 
prism.] Now, here you see, if I send the 
light through this piece of plain glass, A, it 
goes straight through, without being bent (un- 
less the glass be held obliquely, and then the 
phenomenon becomes more complicated), but 
if I take this piece of glass, b [a prism], you 
see it will show a very different effect. It no 
longer goes to that wall, but it is bent to this 
screen, c, and how much more beautiful it is 
now [throwing the prismatic spectrum on the 
screen]. This ray of light is bent out of its 
course by the attraction of the glass upon it. 
And you see I can turn and twist the rays to 
and fro, in different parts of the room, just as 
I please. Now it goes there, now here. [The 
Lecturer projected the prismatic spectrum 
about the theatre.] Here I have the rays 
once more bent on to the screen, and you see 
how wonderfully and beautifully that piece of 
glass not only bends the light by virtue of its 
attraction, but actually splits it up into diffe- 
rent colours. Now, I want you to understand 
that this piece of glass [the prism] being 
perfectly uniform in its internal structure, tells 
us about the action of these other bodies which 
e a 



54 COHESION. 

are not uniform — which do not merely cohere, 
but also have within them, in different parts, 
different degrees of cohesion, and thus attract 
and bend the light with varying powers. We 
will now let the light pass through one or two 
of these things which I just now showed you, 
broke so curiously ; and, first of all, I will take 
a piece of mica. Here, you see, is our ray of 
light — we have first to make it what we call 
polarised, but about that you need not trouble 
yourselves, it is only to make our illustration 
more clear. Here, then, we have our polarised 
ray of light, and I can so adjust it as to make 
the screen, upon which it is shining, either 
light or dark, although I have nothing in the 
course of this ray of light but what is perfectly 
transparent [turning the analyser round]. I 
will now make it so that it is quite dark, and 
we will, in the first instance, put a piece of 
common glass into the polarised ray so as to 
show you that it does not enable the light to 
get through. You see the screen remains 
dark. The glass then, internally, has no effect 
upon the light. [The glass was removed, and 
a piece of mica introduced.] Now, there is the 
mica which we split up so curiously, into leaf 



ACTION OF CALOSPAR ON LIGHT. 55 

after leaf, and see how that enables the light 
to pass through to the screen, and how, as 
Dr. Tyndall turns it round in his hand, you 
have those different colours, pink, and purple, 
and green, coming and going most beautifully ; 
— not that the mica is more transparent than 
the glass, but because of the different manner 
in which its particles are arranged by the force 
of cohesion. 

Now we will see how calcareous spar acts 
upon this light, — that stone which split up into 
rhombs, and of which you are each of you going 
to take a little piece home. [The mica was 
removed, and a piece of calc-spar introduced at 
A.] See how that turns the light round and 

Fig. 20. 




A x 



f 



round, and produces these rings and that black 
cross (Jig. 20). Look at those colours, are they 

E 4 



56 COHESION. 

not most beautiful for you and for me ? (for I 
enjoy these things as much as you do). In 
what a wonderful manner they open out to us 
the internal arrangement of the particles of this 
calcareous spar by the force of cohesion. 

And now I will show you another experiment. 
Here is that piece of glass which before had no 
action upon the light. You shall see what it 
will do when we apply pressure to it. Here, 
then, we have our ray of polarised light, and I 
will first of all show you that the glass has no 
effect upon it in its ordinary state, — when I 
place it in the course of the light, the screen 
still remains dark. Now, Dr. Tyndall will press 
that bit of glass between three little points, one 
point against two, so as to bring a strain upon 
the parts, and you will see what a curious effect 
that has. [Upon the screen two white dots 
gradually appeared.] Ah ! these points show 
the position of the strain — in these parts the 
force of cohesion is being exerted in a different 
degree to what it is in the other parts, and 
hence it allows the light to pass through. How 
beautiful that is — ho wit makes the light come 
through some parts and leaves it dark in others, 
and all because we weaken the force of cohesion 



EFFECT OF HEAT OR PRESSURE ON GLASS. 57 

between particle and particle. Whether you 
have this mechanical power of straining, or 
whether we take other means, we get the same 
result, and, indeed, I will show you by another 
experiment that if we heat the glass in one 
part it will alter its internal structure, and 
produce a similar effect. Here is a piece of 
common glass, and if I insert this in the path 
of the polarised ray, I believe it will do nothing. 
There is the common glass [introducing it] — 
no light passes through — the screen remains 
quite dark ; but I am going to warm this glass 
in the lamp, and you know yourselves that 
when you pour warm water upon glass you put 
a strain upon it sufficient to break it sometimes 
— something like there was in the case of the 
Prince Eupert's drops. [The glass was warmed 
in the spirit lamp, and again placed across the 
ray of light.] Now you see how beautifully the 
light goes through those parts which are hot, 
making dark and light lines just as the crystal 
did, and all because of the alteration I have 
effected in its internal condition; for these dark 
and light parts are a proof of the presence of 
forces acting and dragging in different directions 
within the solid mass. 



53 



LECTUEE III. 

COHESION. — CHEMICAL AFFINITY. 

We will first return for a few minutes to one of 
the experiments made yesterday. You remem- 
ber what we put together on that occasion — 
powdered alum and warm water ; here is one of 
the basins then used. Nothing has been done to 
it since ; but you will find on examining it that 
it no longer contains any powder, but a multi- 
tude of beautiful crystals. Here also are the 
pieces of coke which 1 put into the other basin, 
they have a fine mass of crystals about them. 
That other basin I will leave as it is. I will not 
pour the water from it, because it will show you 
that the particles of alum have done something 
more than merely crystallise together. They 
have pushed the dirty matter from them, laying 
it around the outside or outer edge of the lower 
crystals — squeezed out as it were by the strong 



COHESION WEAKENED BY HEAT. 59 

attraction which the particles of alum have for 
each other. 

And now for another experiment. We have 
already gained a knowledge of the manner in 
which the particles of bodies — of solid bodies 
— attract each other, and we have learnt that 
it makes calcareous spar, alum, and so forth, 
crystallise in these regular forms. Now let me 
gradually lead your minds to a knowledge of the 
means we possess of making this attraction alter 
a little in its force; either of increasing, or 
diminishing, or apparently of destroying it alto- 
gether. I will take this piece of iron [a rod of 
iron about two feet long and a quarter of an 
inch in diameter], it has at present a great deal 
of strength, due to its attraction of cohesion ; 
but if Mr. Anderson will make part of this 
red hot in the fire, we shall then find that it 
will become soft, just as sealing-wax will when 
heated, and we shall also find that the more it 
is heated the softer it becomes. Ah ! but what 
does soft mean? Why, that the attraction 
between the particles is so weakened that it is 
no longer sufficient to resist the power we bring 
to bear upon it. [Mr. Anderson handed to the 
Lecturer the iron rod, with one end red-hot, 



60 COHESION. 

which he showed could be easily twisted about 
with a pair of pliers.] You see, I now find no 
difficulty in bending this end about as I like ; 
whereas I cannot bend the cold part at all. 
And you know how the smith takes a piece of 
iron and heats it, in order to render it soft for 
his purpose: he acts upon our principle of 
lessening the adhesion of the particles, although 
he is not exactly acquainted with the terms by 
which we express it. 

And now we have another point to examine ; 
and this water is again a very good substance to 
take as an illustration (as philosophers we call 
it all water, even though it be in the form of 
ice or steam). Why is this water hard ? [point- 
ing to a block of ice] because the attraction of 
the particles to each other is sufficient to make 
them retain their places in opposition to force 
applied to it. But what happens when we 
make the ice warm ? Why, in that case we 
diminish to such a large extent the power of 
attraction that the solid substance is destroyed 
altogether. Let me illustrate this : I will take 
a red-hot ball of iron [Mr. Anderson by means 
of a pair of tongs handed to the Lecturer a red- 
hot ball of iron, about two inches in diameter] 



SOLID, LIQUID, AND GASEOUS STATE. 61 

because it will serve as a convenient source of 
heat [placing the red-hot iron in the centre of 
the block of ice]. You see I am now melting 
the ice where the iron touches it. You see the 
iron sinking into it, and while part of the solid 
water is becoming liquid, the heat of the ball 
is rapidly going off. A certain part of the 
water is actually rising in steam — the attraction 
of some of the particles is so much diminished 
that they cannot even hold together in the 
liquid form, but escape as vapour. At the same 
time you see I cannot melt all this ice by the 
heat contained in this ball. In the course of a 
very short time I shall find it will have become 
quite cold. 

Here is the water which we have produced 
by destroying some of the attraction which 
existed between the particles of the ice, for 
below a certain temperature the particles of 
water increase in their mutual attraction and 
become ice; and above a certain temperature 
the attraction decreases and the water becomes 
steam. And exactly the same thing happens 
with platinum, and nearly every substance in 
nature; if the temperature is increased to a 
certain point it becomes liquid, and a further 



62 COHESION. 

increase converts it into a gas. Is it not a 
glorious thing for us to look at the sea, the 
rivers, and so forth, and to know that this same 
body in the northern regions is all solid ice and 
icebergs, while here, in a warmer climate, it has 
its attraction of cohesion so much diminished 
as to be liquid water. Well, in diminishing 
this force of attraction between the particles of 
ice, we made use of another force, namely, that 
of heat; and I want you now to understand that 
this force of heat is always concerned when 
water passes from the solid to the liquid state. 
If I melt ice in other ways I cannot do without 
heat (for we have the means of making ice 
liquid without heat; that is to say, without 
using heat as a direct cause). Suppose, for 
illustration, I make a vessel out of this piece of 
tinfoil [bending the foil up into the shape of 
a dish], I am making it metallic, because I 
want the heat which I am about to deal with 
to pass readily through it ; — and I am going 
to pour a little water on this board, and then 
place the tin vessel on it. Now if I put some 
of this ice into the metal dish, and then pro- 
ceed to make it liquid by any of the various 
means we have at our command, it still must 



ICE PRODUCED ARTIFICIALLY. 63 

take the necessary quantity of heat from some- 
thing, and in this case it will take the heat from 
the tray, and from the water underneath, and 
from the other things round about. Well, a 
little salt added to the ice, has the power of 
causing it to melt, and we shall very shortly 
see the mixture become quite fluid, and you 
will then find that the water beneath will be 
frozen — frozen because it has been forced to 
give up that heat which is necessary to keep it 
in the liquid state, to the ice on becoming 
liquid. I remember once, when I was a boy, 
hearing of a trick in a country alehouse ; the 
point was how to melt ice in a quart pot by the 
fire, and freeze it to the stool. Well, the way 
they did it was this : they put some pounded 
ice in a pewter pot and added some salt to it, 
and the consequence was, that when the salt 
was mixed with it, the ice in the pot melted 
(they did not tell me anything about the salt, 
and they set the pot by the fire, just to make 
the result more mysterious), and in a short 
time the pot and the stool were frozen together, 
as we shall very shortly find it to be the case 
here. And all because salt has the power of 
lessening the attraction between the particles of 



64 



COHESION. 



ice. Here you see the tin dish is frozen to the 
board, I can even lift this little stool up by it. 

This experiment cannot, I think, fail to im- 
press upon your minds the fact, that whenever 
a solid body loses some of that force of attraction 
by means of which it remains solid, heat is 
absorbed; and if, on the other hand, we" convert 
a liquid into a solid, e. g. water into ice, a cor- 
responding amount of heat is given out. I 
have an experiment showing this to be the 
case. Here {fig. 21) is a bulb, A, filled with air, 

Fig. 21. 




the tube from which dips into some coloured 
liquid in the vessel b. And I dare say you 
know that if I put my hand on the bulb A, and 
warm it, the coloured liquid which is now 



HEAT EVOLVED DURING SOLIDIFICATION. 65 

standing in the tube at c will travel for- 
ward. Now we have discovered a means, by 
great care and research into the properties of 
various bodies, of preparing a solution of a salt( 15 ) 
which if shaken or disturbed will at once become 
a solid; and as I explained to you just now (for 
what is true of water is true of every other 
liquid), by reason of its becoming solid, heat is 
evolved, and I can make this evident to you 
by pouring it over this bulb; — there! it is 
becoming solid, and look at the coloured liquid, 
how it is being driven down the tube, and how 
it is bubbling out through the water at the 
end; and so we learn this beautiful law of our 
philosophy, that whenever we diminish the 
attraction of cohesion we absorb heat — and 
whenever we increase that attraction heat is 
evolved. This, then, is a great step in advance, 
for you have learned a great deal in addition 
to the mere circumstance that particles attract 
each other. But you must not now suppose 
that because they are liquid they have lost their 
attraction of cohesion; for here is the fluid 
mercury, and if I pour it from one vessel into 
another, I find that it will form a stream from 
the bottle down to the glass — a continuous rod 



66 COHESION. 

of fluid mercury, the particles of which have at- 
traction sufficient to make them hold together 
all the way through the air down to the glass 
itself: and if I pour water quietly from a jug, 
I can cause it to run in a continuous stream in 
the same manner. Again, let me put a little 
water on this piece of plate glass, and then 
take another plate of glass and put it on the 
water; there ! the upper plate is quite free to 
move, gliding about on the lower one from side 
to side ; and yet, if I take hold of the upper 
plate and lift it up straight, the cohesion is so 
great that the lower one is held up by it. See 
how it runs about as I move the upper one, and 
this is all owing to the strong attraction of the 
particles of the water. Let me show you 
another experiment. If I take a little soap and 
water — not that the soap makes the particles 
of the water more adhesive one for the other, 
but it certainly has the power of continuing in 
a better manner the attraction of the particles 
(and let me advise you when about to experi- 
ment with soap-bubbles to take care to have 
everything clean and soapy). I will now blow 
a bubble, and that 1 may be able to talk and 
blow a bubble too, I will take a plate with a 



COHESION OF THE PAHTICLES OF LIQUIDS. 67 

little of the soapsuds in it, and will jnst soap 
the edges of the pipe, and blow a bubble on to 
the plate. Now, there is our bubble. Why 
does it hold together in this manner? Why, 
because the water of which it is composed has 
an attraction of particle for particle : — so great, 
indeed, that it gives to this bubble the very 
power of an india-rubber ball; for you see, if I 
introduce one end of this glass tube into the 
bubble that it has the power of contracting so 
powerfully as to force enough air through the 
tube to blow out a light {fig. 22) — the light is 
blown out. And look! see how the bubble is 
disappearing, see how it is getting smaller and 
smaller. 

There are twenty other experiments I might 
show you to illustrate this power of cohesion of 
the particles of liquids. For instance, what 
would you propose to me if, having lost the 
stopper out of this alcohol bottle, I should want 
to close it speedily with something near at hand. 
Well, a bit of paper would not do, but a piece 
of linen cloth would, or some of this cotton 
wool which I have here. I will put a tuft of it 
into the neck of the alcohol bottle, and you see 
when I turn it upside down, that it is perfectly 

F2 



68 



COHESION. 



well stoppered so far as the alcohol is concerned; 
the air can pass through, but the alcohol cannot. 
And if I were to take an oil vessel this plan 
would do equally well, for in former times they 
used to send us oil from Italy in flasks stop- 
pered only with cotton wool (at the present 
time the cotton is put in after the oil has arrived 
here, but formerly it used to be sent so stop- 
pered). Now if it were not for the particles of 



Fig. 22. 



Fig. 23. 




liquid cohering together, this alcohol would 
run out, and if I had time I could have shown 
you a vessel with the top, bottom and sides alto- 
gether formed like a sieve, and yet it would 
hold water owing to this cohesion. 

You have now seen that the solid water can 
become fluid by the addition of heat, owing to 
this lessening the attractive force between its 



BULK OF BODIES IN VAPOROUS CONDITION. 69 

particles, and yet you see that there is a good 
deal of attractive force remaining behind. I 
want now to take you another step beyond. We 
saw that if we continued applying heat to the 
water (as indeed happened with our piece of ice 
here), that we did at last break up that attraction 
which holds the liquid together, and I am about 
to take some ether (any other liquid would do, 
but ether makes a better experiment for my 
purpose,) in order to illustrate what will happen 
when this cohesion is broken up. Now this 
liquid ether, if exposed to a very low tempera- 
ture, will become a solid, but if we apply heat 
to it, it becomes vapour, and I want to show 
you the enormous bulk of the substance in this 
new form: — when we make ice into water, 
we lessen its bulk, but when we convert water 
into steam, we increase it to an enormous ex- 
tent. You see it is very clear that as I apply 
heat to the liquid I diminish its attraction of 
cohesion — it is now boiling, and I will set fire 
to the vapour, so that you may be enabled to 
judge of the space occupied by the ether in this 
form by the size of its flame, and you now see 
what an enormously bulky flame I get from 
that small volume of ether below. The heat 

1 3 



70 COHESION. 

from the spirit lamp is now being consumed, 
not in making the ether any warmer, but in 
converting it into vapour, and if I desired to 
catch this vapour and condense it (as I could 
without much difficulty), I should have to do 
the same as if I wished to convert steam into 
water and water into ice: in either case it would 
be necessary to increase the attraction of the 
particles, by cold or otherwise. So largely is 
the bulk occupied by the particles increased by 
giving them this diminished attraction, that if 
I were to take a portion of water a cubic inch 
in bulk (a, fig. 23) I should produce a volume of 
steam of that size b [1700 cubic inches ; nearly 
a cubic foot], so greatly is the attraction of co- 
hesion diminished by heat; and yet it still 
remains water. You can easily imagine the 
consequences which are due to this change in 
volume by heat — the mighty powers of steam 
and the tremendous explosions which are some- 
times produced by this force of water. I want 
you now to see another experiment which will 
perhaps give you a better illustration of the bulk 
occupied by a body when m the state of vapour. 
Here is a substance which we call iodine, and I 
am about to submit this solid body to the same 



GASES AKE ALWAYS TRANSPARENT. 71 

kind of condition as regards heat that I did the 
water and the ether [putting a few grains of 
iodine into a hot glass globe, which immediately 
became rilled with the violet vapour], and you 
see the same kind of change produced. More- 
over, it gives us the opportunity of observing 
how beautiful is the violet-coloured vapour from 
this black substance, or rather the mixture of 
the vapour with air (for I would not wish you 
to understand that this globe is entirely filled 
with the vapour of iodine). 

If I had taken mercury and converted it into 
vapour (as I could easily do), I should have a 
perfectly colourless vapour, for you must under- 
stand this about vapours, that bodies in what 
we call the vaporous, or the gaseous state, are 
always perfectly transparent, never cloudy or 
smoky ; they are, however, often coloured, and 
we can frequently have coloured vapours or 
gases produced by colourless particles themselves 
mixing together, as in this case [the Lecturer 
here inverted a glass cylinder full of binoxide of 
nitrogen ( 16 ) over a cylinder of oxygen, when the 
dark red vapour of hyponitrous acid was pro- 
duced]. Here also you see a very excellent 
illustration of the effect of a power of nature 

F 4 



72 CHEMICAL AFFINITY. 

which we haye not as yet come to, but which 
stands next on our list — Chemical Affinity. 
And thus you see we can have a violet vapour 
or an orange vapour, and different other kinds 
of vapour, but they are always perfectly trans- 
parent, or else they would cease to be vapours. 
I am now going to lead you a step beyond 
this consideration of the attraction of the par- 
ticles for each other. You see we have come to 
understand that, if we take water as an illustra- 
tion, whether it be ice, or water, or steam, it is 
always to be considered by us as water. Well, 
now prepare your minds to go a little deeper 
into the subject. We have means of searching 
into the constitution of water beyond any that 
are afforded us by the action of heat, and 
among these one of the most important is that 
force which we call voltaic electricity, which we 
used at our last meeting for the purpose of ob- 
taining light, and which we carried about the 
room by means of these wires. This force is 
produced by the battery behind me, to which 
however I will not now refer more particularly; 
before we have done we shall know more about 
this battery, but it must grow up in our know- 
ledge as we proceed. Now here (Jig. 24) is a 



CONSTITUTION OF WATER. 



73 



portion of water in this little vessel c, and be- 
sides the water there are two plates of the metal 
platinum, which are connected with the wires 
(a and b) coming outside, and I want to 

Fig. 24. 




examine that water, and the state and the 
condition in which its particles are arranged. 
If I were to apply heat to it you know what we 
should get, it would assume the state of vapour, 
but it would nevertheless remain water, and 
would return to the liquid state as soon as the 
heat was removed. Now by means of these 
wires (which are connected with the battery 
behind me, and come under the floor and up 
through the table) we shall have a certain 



74 CHEMICAL AFFINITY. 

amount of this new power at our disposal. 
Here you see it is [causing the ends of the 
wires to touch] — that is the electric light we 
used yesterday, and by means of these wires we 
can cause water to submit itself to this power ; 
for the moment I put them into metallic con- 
nection (at A and b) you see the water boiling in 
that little vessel (c), and you hear the bubbling 
of the gas that is going through the tube (d). 
See how I am converting the water into vapour, 
and if I take a little vessel (e), and fill it with 
water, and put it in the trough over the end of 
the tube (i>), there goes the vapour ascending 
into the vessel. And yet that is not steam, for 
you know that if steam is brought near cold 
water, it would at once condense, and return 
back again to water; this then cannot be steam, 
for it is bubbling through the cold water in 
this trough, but it is a vaporous substance, and 
we must therefore examine it carefully, to see 
in what way the water has been changed. And 
now, in order to give you a proof that it is not 
steam, I am going to show you that it is com- 
bustible, for if I take this small vessel to a 
light, the vapour inside explodes in a manner 
that steam could never do. 



FORMATION OF WATER FROM ITS ELEMENTS. 75 

I will now fill this large bell-jar (f) with 
water ; and I propose letting the gas ascend 
into it, and I will then show you that we can 
reproduce the water back again from the 
vapour or air that is there. Here is a strong 
glass vessel (g), and into it we will let the gas 
(from f) pass. We will there fire it by the 
electric spark, and then after the explosion you 
will find that we have got the water back again ; 
it will not be much, however, for you will 
recollect that I showed you how small a portion 
of water produced a very large volume of 
vapour. Mr. Anderson will now pump all the 
air out of this vessel (g), and when I have 
screwed it on to the top of our jar of gas (f), 
you will see upon opening the stopcocks (h'ih) 
the water will jump up, showing that some of 
the gas has passed into the glass vessel. I will 
now shut these stopcocks, and we shall be able 
to send the electric spark through the gas by 
means of the wires (i, k) in the upper part of 
the vessel, and you will see it burn with a most 
intense flash. [Mr. Anderson here brought a 
Leyden jar, which he discharged through the 
confined gas by means of the wires i, k.] You 
saw the flash, and now that you may see that 



76 CHEMICAL AFFINITY. 

there is no longer any gas remaining, if I place 
it over the jar and open the stopcocks again, up 
will go the gas, and we can have a second com- 
bustion ; and so I might go on again and again, 
and I should continue to accumulate more and 
more of the water to which the gas has returned. 
Now is not this curious? — in this vessel (c) we 
can go on making from water a large bulk of 
permanent gas, as we call it, and then we can 
reconvert it into water in this way. [Mr. An- 
derson brought in another Leyden jar, which, 
however, from some cause would not ignite the 
gas. It was therefore recharged, when the ex- 
plosion took place in the desired manner.] How 
beautifully we get our results when we are 
right in our proceedings! — it is not that Nature 
is wrong when we make a mistake. Now I will 
lay this vessel (g) down by my right hand, and 
you can examine it by and by: there is not 
very much water flowing down, but there is 
quite sufficient for you to see. 

Another wonderful thing about this mode of 
changing the condition of the water is this — 
that we are able to get the separate parts of 
which it is composed, at a distance the one from 
the other, and to examine them, and see what 



DECOMPOSITION OF WATEK. 77 

they are like, and how many of them there are ; 
and for this purpose I have here some more 
water in a slightly different apparatus to the 
former one {fig. 25), and if I place this in con- 



nection with the wires of the battery (at A b) I 
shall get a similar decomposition of the water 
at the two platinum plates. Now I will put 
this little tube (o) over there, and that will col- 
lect the gas together that comes from this side 
(a), and this tube (h) will collect the gas that 
comes from the other side (b), and I think we 
shall soon be able to see a difference. In this ap- 
paratus, the wires are a good way apart from each 
other, and it now seems that each of them is capa- 
ble of drawing off particles from the water and 
sending them off, and you see that one set of 
particles (h) is coming off twice as fast as those 



78 CHEMICAL AFFINITY. 

collected in the other tube (o). Something is 
coming out of the water there (at h) which 
burns [setting fire to the gas], but what comes 
out of the water here (at o), although it will not 
burn, will support combustion very vigorously. 
[The Lecturer here placed a match with a 
glowing tip in the gas, when it immediately 
rekindled.] 

Here, then, we have two things, neither of 
them being water alone, but which we get out 
of the water. Water is therefore composed of 
two substances different to itself, which appear 
at separate places when it is made to submit to 
the force which I have in these wires, and if I 
take an inverted tube of water and collect this 
gas (h), you will see that it is by no means the 
same as the one we collected in the former ap- 
paratus (fig. 24). That exploded with a loud 
noise when it was lighted, but this will burn 
quite noiselessly — it is called hydrogen; and 
the other we call oxygen — that gas which so 
beautifully brightens up all combustion, but 
does not burn of itself. So now we see that 
water consists of two kinds of particles attracting 
each other in a very different manner to the 
attraction of gravitation or cohesion, and this 



PREPARATION OF OXYGEN. 79 

new attraction we call chemical affinity, or the 
force of chemical action between different 
bodies ; we are now no longer concerned with 
the attraction of iron for iron, water for water, 
wood for wood, or like bodies for each other as 
we were when dealing with the force of cohesion ; 
we are dealing with another kind of attraction, 
— the attraction between particles of a different 
nature one to the other. Chemical affinity 
depends entirely upon the energy with which 
particles of different kinds attract each other. 
Oxygen and hydrogen are particles of different 
kinds, and it is their attraction to each other 
which makes them chemically combine and 
produce water. 

I must now show you a little more at large 
what chemical affinity is. I can prepare these 
gases from other substances as well as from 
water ; and we will now prepare some oxygen : 
here is another substance which contains oxygen 
— chlorate of potash ; I will put some of it into 
this glass retort, and Mr. Anderson will apply 
heat to it : we have here different jars filled with 
water, and when by the application of heat the 
chlorate of potash is decomposed, we will dis- 
place the water, and fill the jars with gas. 



80 



CHEMICAL AFFINITY. 



Now when water is opened out in this way by 
means of the battery ; which adds nothing to it 
materially, which takes nothing from it mate- 
rially (I mean no matter, I am not speaking of 
force) ; which adds no matter to the water ; it 
is changed in this way — the gas which you saw 
burning a little while ago, called hydrogen, is 
evolved in large quantity, and the other gas, 
oxygen, is evolved in only half the quantity; so 
that these two areas represent water, and these 
are always the proportions between the two 
gases. 



1 

Hydrogen. 


8 
Oxygen. 


9 



Oxygen 


. 88-9 


Hydrogen . 


. IM 


Water . 


. lOO'O 



But oxygen is sixteen times the weight of 
the other — eight times as heavy as the par- 
ticles of hydrogen in the water ; and you there- 
fore know that water is composed of nine parts 
by weight — one of hydrogen and eight of oxy- 
gen ; thus : — 



PROPERTIES OF OXYGEN. 81 



Hydrogen . 


. 46*2 cubic inches 


. = 1 grain. 


Oxygen 


. 231 „ „ . 


. = 8 grains. 


Water {steam) 


. 69'3 „ „ . 


. = 9 grains. 



Now Mr. Anderson has prepared some oxygen, 
and we will proceed to examine what is the 
character of this gas. First of all you remem- 
ber I told you that it does not burn, but that it 
affects the burning of other bodies. I will just 
set fire to the point of this little bit of wood, 
and then plunge it into the jar of oxygen, and 
you will see what this gas does in increasing the 
brilliancy of the combustion. It does not burn, 
it does not take fire as the hydrogen would, but 
how vividly the combustion of the match goes 
on. Again, if I were to take this wax taper 
and light it, and turn it upside down in the air, 
it would in all probability put itself out, owing 
to the wax running down into the wick. [The 
Lecturer here turned the lighted taper upside 
down, when in a few seconds it went out.] Now 
that will not happen in oxygen gas ; you will 
see how differently it acts {fig. 26). [The taper 
was again lighted, turned upside down, and then 
introduced into a jar of oxygen.] Look at that ! 
see how the very wax itself burns, and falls down 
a 



82 



CHEMICAL AFFINITY. 



in a dazzling stream of fire, so powerfully does 
the oxygen support combustion. Again, here is 

Fig. 26. 




another experiment which will serve to illus- 
trate the force, if I may so call it, of oxygen, 
I have here a circular flame of spirit of wine, 
and with it I am about to show you the way in 
which iron burns, because it will serve very well 
as a comparison between the effect produced by 
air and oxygen. If I take this ring flame, I 
can shake by means of a sieve the fine particles 
of iron filings through it, and you will see the 
way in which they burn. ' [The Lecturer here 
shook through the flame some iron filings which 
took fire and fell through with beautiful scintil- 
lations.] But if I now hold the flame over a 
jar of oxygen [the experiment was repeated over 



PROPERTIES OF OXYGEN. 



83 



a jar of oxygen, when the combustion of the 
filings as they fell into the oxygen became almost 
insupportably brilliant], you see how wonder- 
fully different the effect is in the jar, because 
there we have oxygen instead of common air. 



O 2 



84 



LECTURE IV. 

CHEMICAL AFFINITY HEAT. 

We shall have to pay a little more attention to 
the forces existing in water before we can have 
a clear idea on the subject. Besides the at- 
traction which there is between its particles to 
make it hold together as a liquid or a solid, 
there is also another force, different from the 
former ; — one which, yesterday, by means of 
the voltaic battery, we overcame, drawing from 
the water two different substances, which, when 
heated by means of the electric spark, attracted 
each other, and rushed into combination to 
reproduce water. Now I propose to-day to 
continue this subject, and trace the various 
phenomena of chemical affinity ; and for this 
purpose, as we yesterday considered the cha- 
racter of oxygen, of which I have here two jars 
(oxygen being those particles derived from the 



PREPARATION OF HYDROGEN. 



85 



water which enable other bodies to burn), we 
will now consider the other constituent of water, 
and without embarrassing you too much with 
the way in which these things are made, I will 
proceed now to show you our common way of 
making hydrogen. (I called it hydrogen yes- 
terday — it is so called because it helps to gene- 
rate water.)* I put into this retort some zinc, 
water, and oil of vitriol, and immediately an 
action takes place, which produces an abundant 
evolution of gas, now coming over into this jar, 
and bubbling up in appearance exactly like the 
oxygen we obtained yesterday. 

Fig. 27. 




The processes you see are very different, 



* £5cop, " water," and 7ewaw, " I generate." 
G 3 



86 CHEMICAL AFFINITY. 

though the result is the same in so far as it 
gives us certain gaseous particles. Here then 
is the hydrogen. I showed you yesterday cer- 
tain qualities of this gas, now let me exhibit 
you some other properties. Unlike oxygen, 
which is a supporter of combustion, and will 
not burn, hydrogen itself is combustible. There 
is a jar full of it, and if I carry it along in this 
manner, and put a light to it, I think you will 
see it take fire, not with a bright light, — you 
will at all events hear it if you do not see it. 
Now that is a body entirely different from oxy- 
gen ; it is extremely light ; for although yester- 
day you saw twice as much of this hydrogen 
produced on the one side as on the other, by 
the voltaic battery, it was only one eighth the 
weight of the oxygen. I carry this jar upside 
down. Why? Because I know that it is a 
very light body, and that it will continue in 
this jar upside down quite as effectually as the 
water will in that jar which is not upside down ; 
and just as I can pour water from one vessel 
into another in the right position to receive it, 
so can I pour this gas from one jar into another 
when they are upside down. See what I am 
about to do. There is no hydrogen in this jar 



PROPERTIES OF HYDROGEN. 87 

at present, but I will gently turn this jar of 
hydrogen up under this other jar (fig. 28) and 
then we will examine the two. We shall see, 
on applying a light, that the hydrogen has left 

Fig. 28. 




the jar in which it was at first, and has poured 
upwards into the other, and there we shall 
find it. 

You now understand that we can have par- 
ticles of very different kinds, and that they can 
have different bulks and weights ; and there are 
two or three very interesting experiments which 
serve to illustrate this. For instance, if 1 blow 
soap bubbles with the breath from my mouth 
you will see them fall, because I fill them with 
common air, and the water which forms the 
bubble carries it down. But now if I inhale 
hydrogen gas into my lungs (it does no harm 

G 4 



88 



chemical Affinity. 



to the lungs, although it does no good to them), 
see what happens. [The Lecturer inhaled 
some hydrogen, and after one or two ineffectual 
attempts, succeeded in blowing a splendid 
bubble, which rose majestically and slowly to 
the ceiling of the theatre, where it burst.] That 
shows you very well how light a substance this 
is ; for notwithstanding all the heavy bad air 
from my lungs, and the weight of the bubble, 
you saw how it was carried up. I want you 
now to consider this phenomenon of weight as 
indicating how exceedingly different particles 



Fig. 29. 
Hydrogen. 



Flat in um. 



Water 

Q 




are one from the other : and I will take as 
illustrations these very common things, air, 



BULK OF EQUAL WEIGHTS OF BODIES. 



89 



water, the heaviest body, platinum — and this 
gas, and observe how they differ in this re- 
spect ; for if I take a piece of platinum of that 
size (fig. 29), it is equal to the weight of portions 
of water, air, and hydrogen of the bulks I have 
represented in these spheres ; and this illustra- 
tion gives you a very good idea of the extra- 
ordinary difference with regard to the gravity 
of the articles having this enormous difference 
in bulk. [The following tabular statement hav- 
ing reference to this illustration appeared on 
the diagram board.] 



Hydrogen 


1 






Air 


14-4 


1 




Water 


11943 


829 


1 


Platinum 


256774 


17831 


21*5 



Whenever oxygen and hydrogen unite to- 
gether they produce water, and you have seen 
the extraordinary difference between the bulk 
and appearance of the water so produced and 



90 



CHEMICAL AFFINITY. 



the particles of which it consists chemically. 
Now we have never yet been able to reduce 
either oxygen or hydrogen to the liquid state ; 
and yet their first impulse when chemically 
combined is to take up first this liquid condition 
and then the solid condition. We never com- 
bine these different particles together without 
producing water ; and it is curious to think how 
often you must have made the experiment of 
combining oxygen and hydrogen to form water 
without knowing it. Take a candle, for in- 
stance, and a clean silver spoon (or a piece of 
clean tin will do), and if you hold it over the 
flame you immediately cover it with dew — not 

Fig. 30. 




a smoke — which presently evaporates. This 
perhaps will serve to show it better. Mr. An- 



EFFECTS OF CHEMICAL AFFINITY. 91 

derson will put a candle under that jar, and you 
will see how soon the water is produced {fig. 30). 
Look at that dimness on the sides of the glass, 
which will soon produce drops, and trickle 
down into the plate. Well, that dimness and 
these drops are water, formed by the union of 
the oxygen of the air with the hydrogen exist- 
ing in the wax of which that candle is formed. 
And now, having brought you in the first 
place to the consideration of chemical attrac- 
tion, I must enlarge your ideas so as to include 
all substances which have this attraction for 
each other — for it changes the character of 
bodies^ and alters them in this way and that 
way, in the most extraordinary manner; and 
produces other phenomena wonderful to think 
about. Here is some chlorate of potash, and 
there some sulphuret of antimony. ( 17 ) We will 
mix these two different sets of particles together, 
and I want to show you in a general sort of 
way, some of the phenomena which take place 
when we make different particles act together. 
Now I can make these bodies act upon each 
other in several ways. In this case I am going 
to apply heat to the mixture, but if I were to 
give a blow with a hammer the same result 



92 CHEMICAL AFFINITY. 

would follow. [A lighted match was brought 
to the mixture, which immediately exploded 
with a sudden flash, evolving a dense white 
smoke.] There you see the result of the action 
of chemical affinity, overcoming the attraction of 
cohesion of the particles. Again, here is a little 
sugar ( 18 ), quite a different substance from the 
black sulphuret of antimony, and you shall see 
what takes place when we put the two together. 
[The mixture was touched with sulphuric acid, 
when it took fire and burnt gradually and with 
a brighter flame than in the former instance.] 
Observe this chemical affinity travelling about 
the mass, and setting it on fire, and throwing 
it into such wonderful agitation! 

I must now come to a few circumstances 
which require careful consideration. We have 
already examined one of the effects of this 
chemical affinity — but to make the matter 
more clear we must point out some others. 
And here are two salts dissolved in water. ( l9 ) 
They are both colourless solutions, and in these 
glasses you cannot see any difference between 
them. But if I mix them, I shall have chemical 
attraction take place. I will pour the two 
together into this glass, and you will at once 



SOLID PRODUCED FROM TWO LIQUIDS. 93 

see, I have no doubt, a certain amount of 
change. Look, they are already becoming 
milky, but they are sluggish in their action — 
not quick as the others were — for we have 
endless varieties of rapidity in chemical action. 
Now, if I mix them together, and stir them so 
as to bring them properly together, you will 
soon see what a different result is produced. 
As I mix them they get thicker and thicker, 
and you see the liquid is hardening and stiffen- 
ing, and before long I shall have it quite hard ; 
and before' the end of the lecture it will be a 
solid stone — a wet stone no doubt, but more 
or less solid — in consequence of the chemical 
affinity. Is not this changing two liquids into 
a solid body a wonderful manifestation of 
chemical affinity ? 

There is another remarkable circumstance in 
chemical affinity, which is that it is capable of 
either waiting or acting at once. And this is 
very singular, because we know of nothing of 
the kind in the forces either of gravitation or 
cohesion. For instance, here are some oxygen 
particles, and here is a lump of carbon particles. 
I am going to put the carbon particles into the 
oxygen they can act, but they do not — they 



94 CHEMICAL AFFINITY. 

are just like this unlighted candle. It stands 
here quietly on the table, waiting until we 
want to light it. But it is not so in this other 
case: here is a substance, gaseous like the 
oxygen, and if I put these particles of metal 
into it the two combine at once. The copper 
and the chlorine unite by their power of chemi- 
cal affinity, and produce a body entirely unlike 
either of the substances used. And in this 
other case, it is not that there is any deficiency 
of affinity between the carbon and oxygen, for 
the moment I choose to put them in a condi- 
tion to exert their affinity, you will see the 
difference. [The piece of charcoal was ignited, 
and introduced into the jar of oxygen, when the 
combustion proceeded with vivid scintillations.] 
Now this chemical action is set going exactly 
as it would be if I had lighted the candle, or 
as it is when the servant puts coals on and 
lights the fire : the substances wait until we do 
something which is able to start the action. 
Can anything be more beautiful than this com- 
bustion of charcoal in oxygen? You must 
understand that each of these little sparks is a 
portion of the charcoal, or the bark of the 
charcoal, thrown off white hot into the oxygen, 



COMBUSTION IN OXYGEN. 9 5 

and burning in it most brilliantly, as you see. 
And now let me tell you another thing, or you 
will go away with a very imperfect notion of 
the powers and effects of this affinity. There 
you see some charcoal burning in oxygen. 
Well, a piece of lead will burn in oxygen just 
as well as the charcoal does, or indeed better, 
for absolutely that piece of lead will act at once 
upon the oxygen as the copper did in the other 
vessel with regard to the chlorine. And here 
also a piece of iron ; if I light it and put it into 
the oxygen, it will burn away just as the carbon 
did. And I will take some lead and show you 
that it will burn in the common atmospheric 
oxygen at the ordinary temperature. These 
are the lumps of lead which you remember we 
had the other day — the two pieces which 
clung together. Now these pieces, if I take 
them to day and press them together, will not 
stick, and the reason is that they have attracted 
from the atmosphere a part of the oxygen there 
present, and have become coated as with a 
varnish by the oxide of lead, which is formed 
on the surface, by a real process of combustion 
or combination. There you see the iron burn- 
ing very well in oxygen, and I will tell you the 



96 CHEMICAL AFFINITY. 

reason why those scissors and that lead do not 
take fire whilst they are lying on the table. 
Here the lead is in a lump, and the coating of 
oxide remains on its surface, whilst there you 
see the melted oxide is clearing itself off from 
the iron, and allowing more and more to go on 
burning. In this case, however [holding up a 
small glass tube containing lead pyropliorus ( 20 )], 
the lead has been very carefully produced in 
fine powder, and put into a glass tube and 
hermetically sealed so as to preserve it, and I 
expect you will see it take fire at once. This 
has been made about a month ago, and has 
thus had time enough to sink down to its 
normal temperature — what you see therefore 
is the result of chemical affinity alone. [The 
tube was broken at the end, and the lead 
poured out on to a piece of paper, whereupon 
it immediately took fire.] Look, look, at the 
lead burning ; why it has set fire to the paper ! 
Now that is nothing more than the common 
affinity always existing between very clean lead 
and the atmospheric oxygen ; and the reason 
why this iron does not burn until it is made 
red hot, is because it has got a coating of oxide 
about it, which stops the action of the oxygen, 



COMBUSTION AND CHEMICAL AFFINITY. 97 

— putting a varnish, as it were, upon its surface, 
as we varnish a picture — absolutely forming 
a substance which prevents the natural che- 
mical affinity between the bodies from acting. 

I must now take you a little further in this 
kind of illustration, or consideration, I would 
rather call it, of chemical affinity. This attrac- 
tion between different particles exists also most 
curiously in cases where they are previously 
combined with other substances. Here is a 
little chlorate of potash containing the oxygen 
which we found yesterday could be procured 
from it ; it contains the oxygen there combined 
and held down by its chemical affinity with 
other things ; but still it can combine with 
sugar, as you saw. This affinity can thus 
act across substances, and I want you to see 
how curiously what we call combustion acts 
with respect to this force of chemical affinity. 
If I take a piece of phosphorus and set fire to 
it, and then place a jar of air over the phos- 
phorus, you see the combustion which we are 
having there on account of chemical affinity 
(combustion being in all cases the result of 
chemical affinity). . The phosphorus is escaping 
in that vapour, which will condense into a 
H 



98 CHEMICAL AFFINITY. 

snow-like mass at the close of the lecture. 
But suppose I limit the atmosphere, what 
then? why, even the phosphorus will go out. 
Here is a piece of camphor which will burn 
very well in the atmosphere, and even on water 
it will float about and burn, by reason of some 
of its particles gaining access to the air. But 
if I limit the quantity of air by placing a jar 
over it, as I am now doing, you will soon find 
the camphor will go out. Well, why does it 
go out ? not for want of air, for there is plenty 
of air remaining in the jar. Perhaps you will 
be shrewd enough to say for want of oxygen. 

This therefore leads us to the inquiry as to 
whether oxygen can do more than a certain 
amount of work. The oxygen there (Jig. 30) 
cannot go on burning an unlimited quantity of 
candle, for that has gone out, as you see ; and 
its amount of chemical attraction or affinity is 
just as strikingly limited ; it can no more be 
fallen short of or exceeded than can the attrac- 
tion of gravitation. You might as soon attempt 
to destroy gravitation, or weight, or all things 
that exist, as to destroy the exact amount of 
force exerted by this oxygen. And when I 
pointed out to you that 8 by weight of oxygen 
to 1 by weight of hydrogen went to form water, 



COMBUSTION IN DEFINITE PROPORTIONS. 99 

I meant this, that neither of them would com- 
bine in different proportions with the other, for 
you cannot get 10 of hydrogen to combine with 
6 of oxygen, or 10 of oxygen to combine with 
6 of hydrogen — it must be 8 of oxygen and 1 
of hydrogen. Now suppose I limit the action 
in this way; this piece of cotton wool burns, 
as you see, very well in the atmosphere ; and I 
have known of cases of cotton-mills being fired 
as if with gunpowder, through the very finely- 
divided particles of cotton being diffused through 
the atmosphere in the mill, when it has some- 
times happened that a flame has caught these 
raised particles, and it has run from one end of 
the mill to the other and blown it up. That then 
is on account of the affinity which the cotton 
has for the oxygen ; but suppose I set fire to 
this piece of cotton which is rolled up tightly ; 
it does not go on burning, because I have limited 
the supply of oxygen, and the inside is pre- 
vented from having access to the oxygen, just 
as it was in the case of the lead by the oxide. 
But here is some cotton which has been imbued 
with oxygen in a certain manner. I need not 
trouble you now with the way it is prepared ; 
it is called gun-cotton. ( 21 ) See how that burns 

H 2 



100 CHEMICAL AFFINITY. 

[setting fire to a piece] ; it is very different from 
the other, because the oxygen that must be 
present in its proper amount is put there before- 
hand. And I have here some pieces of paper 
which are prepared like the gun-cotton ( 22 ), and 
imbued with bodies containing oxygen. Here 
is some which has been soaked in nitrate of 
strontia — you will see the beautiful red colour 
of its flame ; and here is another which I think 
contains baryta, which gives that fine green 
light; and I have here some more which has 
been soaked in nitrate of copper, — it does not 
burn quite so brightly, but still very beautifully. 
In all these cases the combustion goes on inde- 
pendent of the oxygen of the atmosphere. And 
here we have some gunpowder put into a case, 
in order to show that it is capable of burning 
under water. You know that we put it into a 
gun, shutting off the atmosphere, with shot, 
and yet the oxygen which it contains supplies 
the particles with that without which chemical 
action could not proceed. Now I have a vessel 
of water here, and am going to make the ex- 
periment of putting this fuse under the water, 
and you will see whether that water can extin- 
guish it ; here it is burning out of the water, 



LAWS OF CHEMICAL AFFINITY. 101 

and there it is burning under the water ; and so 
it will continue until exhausted, and all by 
reason of the requisite amount of oxygen being 
contained within the substance. It is by this 
kind of attraction of the different particles one 
to the other that we are enabled to trace the 
laws of chemical affinity, and the wonderful 
variety of the exertions of these laws. 

Now I want you to observe that one great 
exertion of this power which is known as chemical 
affinity is to produce heat and light; you know, 
as a matter of fact, no doubt, that when bodies 
burn they give out heat, but it is a curious thing 
that this heat does not continue — the heat goes 
away as soon as the action stops, and you see 
thereby that it depends upon the action during 
the time it is going on. It is not so with gravi- 
tation; this force is continuous, and is just as 
effective in making that lead press on the table 
as it was when it first fell there. Nothing occurs 
there which disappears when the action of falling 
is over; the pressure is upon the table, and will 
remain there until the lead is removed ; whereas, 
in the action of chemical affinity to give light 
and heat, they go away immediately the action 
is over. This lamp see r ms to evolve heat and 

H 3 



102 HEAT. 

light continuously, but it is owing to a constant 
stream of air coming into it on all sides, and 
this work of producing light and heat by chemi- 
cal affinity will subside as soon as the stream of 
air is interrupted. What then is this curious 
condition of heat ? Why it is the evolution of 
another power of matter, of a power new to us, 
and which we must consider as if it were now 
for the very first time brought under our notice. 
What is heat ? We recognise heat by its power 
of liquefying solid bodies and vaporising liquid 
bodies, by its power of setting in action, and 
very often overcoming, chemical affinity. Then 
how do we obtain heat? We obtain it in 
various ways ; most abundantly by means of the 
chemical affinity we have just before been speak- 
ing about, but we can also obtain it in many other 
ways. Friction will produce heat. The Indians 
rub pieces of wood together until they make 
them hot enough to take fire ; and such things 
have been known as two branches of a tree 
rubbing together so hard as to set the tree on 
fire. I do not suppose I shall set these two 
pieces of wood on fire by friction ; but I can 
readily produce heat enough to ignite some 
phosphorus. [The Lecturer here rubbed two 



VARIOUS METHODS OF OBTAINING HEAT. 103 

pieces of cedar wood strongly against each other 
for a minute, and then placed on them a piece 
of phosphorus, which immediately took 
fire.] And if you take a smooth metal tg ' s ' 
button stuck on a cork, and rub it on 
a piece of soft deal wood, you will 
make it so hot as to scorch wood and 
paper, and burn a match. 

I am now going to show you that we 
can obtain heat not by chemical affi- 
nity alone, but by the pressure of air. 
Suppose I take a pellet of cotton and 
moisten it with a little ether, and put 
it into a glass tube (fig. 31), and then 
take a piston and press it down suddenly, I expect 
I shall be able to burn a little of that ether in 
the vessel. It wants a suddenness of pressure, 
or we shall not do what we require. [The 
piston was forcibly pressed down, when a flame 
due to the combustion of the ether was visible 
in the lower part of the syringe.] All we want 
is to get a little ether in vapour, and give fresh 
air each time, and so we may go on again and 
again getting heat enough by the compression 
of air to fire the ether-vapour. 

This, then, I think, will be sufficient, accom- 

H 4 



104 HEAT. 

panied with all you have previously seen, to show 
you how we procure heat. And now for the effects 
of this power. We need not consider many of 
them on the present occasion, because when you 
have seen its power of changing ice into water 
and water into steam, you have seen the two 
principal results of the application of heat. I 
want you now to see how it expands all bodies 
— all bodies but one, and that under limited 
circumstances. Mr. Anderson will hold a lamp 
under that retort, and you will see the moment 
he does so that the air will issue abundantly 
from the neck which is under water, because the 
heat which he applies to the air causes it to ex- 
pand. And here is a brass rod ( fig. 32) which 

Fig. 32. 




tL 



goes through that hole and fits also accurately 
into this gauge; but if I make it warm with 



EXPANSION BY HEAT. 105 

this spirit-lamp it will only go in the gauge or 
through the hole with difficulty ; and if I were 
to put it into boiling-water it would not go 
through d,t all. Again; as soon as the heat 
escapes from bodies they collapse ; see how the 
air is contracting in the vessel now that Mr. 
Anderson has taken away his lamp : the stem 
of it is filling with water. Notice too, now, that 
although I cannot get the tube through this 
hole or into the gauge, the moment I cool it by 
dipping it into water, it goes through with per- 
fect facility, so that we have a perfect proof of 
this power of heat to contract and expand bodies. 



106 



LECTUKE V. 

MAGNETISM — ELECTRICITY. 

I wonder whether we shall be too deep to-day or 
not. Kemember, that we spoke of the attraction 
by gravitation of all bodies to all bodies by their 
simple approach. Kemember, that we spoke 
of the attraction of particles of the same kind 
to each other, — that power which keeps them 
together in masses, — iron attracted to iron, 
brass to brass, or water to water. Remember, 
that we found, on looking into water, that there 
were particles of two different kinds attracted 
to each other ; and this was a great step beyond 
the first simple attraction of gravitation; be- 
cause here we deal with attraction between 
different kinds of matter. The hydrogen could 
attract the oxygen and reduce it to water, but 
it could not attract any of its own particles, so 
that there we obtained a first indication of the- 
existence of two attractions. 



DIFFEEENT FORMS OF ATTRACTION. 107 

To-day we come to a kind of attraction even 
more curious than the last, namely, the attrac- 
tion which we find to be of a double nature — 
of a curious and dual nature. And I want first 
of all to make the nature of this doubleness 
clear to you. Bodies are sometimes endowed 
with a wonderful attraction, which is not found 
in them in their ordinary state. For instance, 
here is a piece of shellac, having the attraction 
of gravitation, having the attraction of cohesion, 
and if I set fire to it, it would have the attrac- 
tion of chemical affinity to the oxygen in the 
atmosphere. Now all these powers we find in 
it as if they were parts of its substance ; but 
there is another property which I will try and 
make evident by means of this ball, this bubble 
of air [a light india-rubber ball, inflated and 
suspended by a thread]. There is no attraction 
between this ball and this shellac at present ; 
there may be a little wind in the room slightly 
moving the ball about, but there is no attrac- 
tion. But if I rub the shellac with a piece of 
flannel [rubbing the shellac, and then holding 
it near the ball], look at the attraction which 
has arisen out of the shellac, simply by this 
friction, and which I may take away as easily 



108 ELECTRICITY. 

by drawing it gently through my hand. [The 
Lecturer repeated the experiment of exciting 
the shellac, and then removing the attractive 
power by drawing it through his hand.] Again 
you will see I can repeat this experiment with 
another substance ; for if I take a glass rod and 
rub it with a piece of silk covered with what 
we call amalgam, look at the attraction which 
it has, how it draws the ball towards it ; and 
then, as before, by quietly rubbing it through 
the hand, the attraction will be all removed 
again to come back by friction with this silk. 

But now we come to another fact. I will 
take this piece of shellac, and make it attractive 
by friction; and remember that whenever we 
get an attraction of gravity, chemical affinity, 
adhesion, or electricity (as in this case), the 
body which attracts is attracted also, and just 
as much as that ball was attracted by the 
shellac, the shellac was attracted by the ball. 
Now I will suspend this piece of excited shellac 
in a little paper stirrup, in this way {fig. 33), in 
order to make it move easily, and I will take 
another piece of shellac, and after rubbing it 
with flannel, will bring them near together : 
you will think that they ought to attract each 



ELECTRICAL ATTRACTION AND REPULSION. 109 

other ; but now what happens ? It does not 
attract ; on the contrary, it very strongly repels, 

Fig. 33. 




and I can thus drive it round to any extent. 
These, therefore, repel each other, although 
they are so strongly attractive — repel each 
other to the extent of driving this heavy piece 
of shellac round and round in this way. But 
if I excite this piece of shellac as before, and 
take this piece of glass and rub it with silk, and 
then bring them near, what think you will 
happen ? [The Lecturer held the excited glass 
near the excited shellac, when they attracted 
each other strongly.] You see, therefore, what 
a difference there is between these two attrac- 
tions, — they are actually two kinds of attraction 



110 



ELECTRICITY. 



concerned in this case, quite different to any- 
thing we have met with before ; but the force 
is the same. We have here then a double at- 
traction — a dual attraction or force — one at- 
tracting and the other repelling. 

Again, to show you another experiment 
which will help to make this clear to you. 
Suppose I set up this rough indicator again 
[the excited shellac suspended in the stirrup] ; 
it is rough, but delicate enough for my pur- 
pose ; and suppose I take this other piece of 
shellac, and take away the power, which I can 



Fig. 34. 





do by drawing it gently through the hand ; and 
suppose I take a piece of flannel (%. 34) which 



EYOLUTION OF ELECTRICITY. Ill 

I have shaped into a cap for it and made dry. 
I will put this shellac into the flannel, and here 
comes out a very beautiful result. I will rub 
this shellac and the flannel together (which 
I can do by twisting the shellac round), and 
leave them in contact ; and then, if I ask, by 
bringing them near our indicator, what is the 
attractive force ? — it is nothing ! But if I take 
them apart, and then ask what will they do 
when they are separated, — why the shellac is 
strongly repelled, as it was before, but the cap 
is strongly attractive ; and yet if I bring them 
both together again, there is no attraction — it 
has all disappeared [the experiment was re- 
peated]. Those two bodies therefore still con- 
tain this attractive power — when they were 
parted it was evident to your senses that they 
had it, though they do not attract when they 
are together. 

This then is sufficient in the outset to give 
you an idea of the nature of the force which we 
call electricity. There is no end to the things 
from which you can evolve this power. When 
you go home take a stick of sealing-wax — I 
have rather a large stick, but a smaller one will 
do — and make an indicator of this sort (fig* 35). 



112 ELECTRICITY. 

Take a watch-glass (or your watch itself will do, 
you only want something which shall have a 

Fig. 35. 




round face), and now if you place a piece of 
flat glass upon that, you have a very easily 
moved centre ; and if I take this lath and put 
it on the flat glass (you see I am searching for 
the centre of gravity of this lath, I want to 
balance it upon the watch-glass), it is very 
easily moved round, and if I take this piece of 
sealing-wax and rub it against my coat, and 
then try whether it is attractive [holding it near 
the lath], you see how strong the attraction is ; 
I can even draw it about. Here then you have 
a very beautiful indicator, for I have with a 
small piece of sealing-wax and my coat pulled 
round a plank of that kind, so you need be in 
no want of indicators to discover the presence 
of this attraction. There is scarcely a substance 



ELECTRICAL ATTRACTION. 113 

which we may not use. Here are some indica- 
tors {fig. 36). I bend round a strip of paper into 

Fig. 36. 




a hoop, and we have as good an indicator as can 
be required ; see how it rolls along, travelling 
after the sealing-wax. If I make them smaller, 
of course we have them running faster, and 
sometimes they are actually attracted up into 
the air. Here also is a little collodion balloon. 
It is so electrical that it will scarcely leave my 
hand unless to go to the other. See, how 
curiously electrical it is ; it is hardly possible 
for me to touch it without making it electrical ; 
and here is a piece which clings to anything it 
is brought near, and which it is not easy to lay 
down. And here is another substance, gutta- 
percha, in thin strips ; it is astonishing how by 
rubbing this in your hands you make it electri- 
cal ; but our time forbids us to go further into 
I 



114 MAGNETISM. 

this subject at present ; you see clearly there 
are two kinds of electricities which may be 
obtained by rubbing shellac with flannel or glass 
with silk. 

Now, there are some curious bodies in nature 
(of which I have two specimens on the table) 
which are called magnets or loadstones; ores of 
iron, of which there is a great deal sent from 
Sweden. They have the attraction of gravita- 
tion, and attraction of cohesion, and certain 
chemical attraction ; but they also have a great 
attractive power, for this little key is held up 
by this stone. Now, that is not chemical at- 
traction, it is not the attraction of chemical 
affinity, or of aggregation of particles,, or of 
cohesion, or of electricity (for it will not attract 
this ball if I bring it near it), but it is a sepa- 
rate and dual attraction, and what is more, one 
w r hich is not readily removed from the substance, 
for it has existed in it for ages and ages in the 
bowels of the earth. Now we can make arti- 
ficial magnets (you will see me to-morrow make 
artificial magnets of extraordinary power). And 
let us take one of these artificial magnets, and 
examine it, and see where the power is in the 
mass, and whether it is a dual power. You see 



MAGNETIC ATTKACTION. 115 

it attracts these keys, two or three in succession, 
and it will attract a very large piece of iron. 
That then is a very different thing indeed to 
what you saw in the case of the shellac, for that 
only attracted a light ball, but here I have 
several ounces of iron held up. And if we come 
to examine this attraction a little more closely, 
we shall find it presents some other remarkable 
differences ; first of all, one end of this bar (fig. 
37) attracts this key, but the middle does not 
attract. It is not then the whole of the sub- 
stance which attracts. If I place this little key 
in the middle it does not adhere; but if I place 
it there, a little nearer the end, it does, though 
feebly. Is it not then very curious to find that 
there is an attractive power at the extremities 
which is not in the middle ! — to have thus in 
one bar two places in which this force of attrac- 
tion resides. If I take this bar and balance it 
carefully on a point, so that it will be free to 
move round, I can try what action this piece of 
iron has on it. Well, it attracts one end, and 
it also attracts the other end, just as you saw 
the shellac and the glass did, with the exception 
of its not attracting in the middle. But if now, 
instead of a piece of iron, I take a magnet, and 
I 2 



116 MAGNETISM. 

examine it in a similar way, you see that one of 
its ends repels the suspended magnet; the force 

Fig. 37. Fig. 38. 





then is no longer attraction but repulsion ; but, 
if I take the other end of the magnet and 
bring it near, it shows attraction again. 

You will see this better, perhaps, by another 
kind of experiment. Here (fig. 38) is a little 
magnet, and I have coloured the ends differently 
so that you may distinguish one from the other. 
Now this end (s) of the magnet (fig. 37) attracts 
the uneoloured of the little magnet. You see 
it pulls it towards it with great power. And as 
I carry it round, the uneoloured end still follows. 
But now if I gradually bring the middle of the 
bar magnet opposite the uneoloured end of the 
needle, it has no effect upon it, either of attrac- 
tion or repulsion, until, as I come to the oppo- 



DOUBLE POWER OF THE MAGNET. 



117 



site extremity (n) you see that it is the coloured 
end of the needle which is. pulled towards it. 
We are now therefore dealing with two kinds of 
power, attracting different ends of the magnet 
— a double power, already existing in these 
bodies, which takes up the form of attraction 
and repulsion. And now when I put up this 
label with the word magnetism, you will under- 
stand that it is to express this double power. 

Now with this loadstone you may make mag- 
nets artificially. Here is an artificial magnet 
{fig. 39) in which both ends have been brought 

Fig. 39. 




together in order to increase the attraction. 
This mass will lift that lump of iron, and what 
is more, by placing this keeper, as it is called, 

I 3 



118 MAGNETISM. 

on the top of the magnet, and taking hold of 
the handle it will adhere sufficiently strongly to 
allow itself to be lifted up, so wonderful is its 
power of attraction. If you take a needle, and 
just draw one of its ends along one extremity 
of the magnet, and then draw the other end 
along the other extremity, and then gently place 
it on the surface of some water (the needle will 
generally float on the surface, owing to the 
slight greasiness communicated to it by the 
fingers) you will be able to get all the pheno- 
mena of attraction and repulsion, by bringing 
another magnetised needle near to it. 

I want you now to observe that although I 
have shown you in these magnets that this 
double power becomes evident principally at the 
extremities, yet the whole of the magnet is con- 
cerned in giving the power. That will at first 
seem rather strange ; and I must therefore show 
you an experiment to prove that this is not an 




accidental matter, but that the whole of the 
mass is really concerned in this force, just as in. 



DISTRIBUTION OF POWER IN MAGNETS. 119 

falling the whole of the mass is acted upon by 
the force of gravitation. I have here {fig. 40) a 
steel bar, and I am going to make it a magnet, 
by rubbing it on the large magnet {fig. 39). I 
have now made the two ends magnetic in oppo- 
site ways. I do not at present know one from 
the other, but we can soon find out. You see 
when I bring it near our magnetic needle {fig. 38) 
one end repels and the other attracts ; and the 
middle will neither attract nor repel — it cannot, 
because it is half way between the two ends. 
But now, if I break out that piece (n. s.) and 
then examine it — see how strongly one end {n) 
pulls at this end {sfig. 38) and how it repels the 
other end (n). And so it can be shown that 
every part of the magnet contains this power of 
attraction and repulsion, but that the power is 
only rendered evident at the end of the mass. 
You will understand all this in a little while, 
but what you have now to consider is that every 
part of this steel is in itself a magnet. Here is 
a little fragment which I have broken out of the 
very centre of the bar, and you will still see 
that one end is attractive and the other is re- 
pulsive. Now, is not this power a most wonder- 
ful thing? And very strange, the means of 
i 4 



120 



ELECTRICITY. 



taking it from one substance and bringing it to 
other matters. I cannot make a piece of iron 
or anything else heavier or lighter than it is ; 
its cohesive power it must and does have ; but, 
as you have seen by these experiments, we can 
add or subtract this power of magnetism, and 
almost do as we like with it. 

And now we will return for a short time to 
the subject treated of at the commencement of 
this lecture. You see here (fig. 41) a large 

Fig 41. 




machine arranged for the purpose of rubbing 
glass with silk, and for obtaining the power 
called electricity ; and the moment the handle 



TRANSFERENCE OF ELECTRICITY. 121 

of the machine is turned a certain amount of 
electricity is evolved, as you will see by the rise 
of the little straw indicator (at a). Now I know 
from the appearance of repulsion of the pith 
ball at the end of the straw that electricity is 
present in those brass conductors (b b), and I 
want you to see the manner in which that elec- 
tricity can pass away [touching the conductor 
(b) with his finger, the Lecturer drew a spark 
from it, and the straw electrometer immediately 
fell]. There, it has all gone ; and that I have 
really taken it aw T ay you shall see by an experi- 
ment of this sort. If I hold this cylinder of 
brass by the glass handle and touch the con- 
ductor with it I take away a little of the electri- 
city. You see the spark in which it passes, and 
observe that the pith-ball indicator has fallen a 
little, which seems to imply that so much elec- 
tricity is lost; but it is not lost, it is here in this 
brass, and I can take it away and carry it about, 
not because it has any substance of its own, but 
by some strange property which we have not 
before met with as belonging to any other force. 
Let us see whether we have it here or not. [The 
Lecturer brought the charged C}dinder to a jet 
from which gas was issuing ; the spark was seen 



122 ELECTKICITT. 

to pass from the cylinder to the jet, but the gas 
did not light.] Ah ! the gas did not light, but 
you saw the spark ; there is perhaps some draught 
in the room which blew the gas on one side, or 
else it would light ; we will try this experiment 
afterwards. You see from the spark that I can 
transfer the power from the machine to this 
cylinder, and then carry it away and give it to 
some other body. You know very well as a 
matter of experiment that we can transfer the 
power of heat from one thing to another ; for if 
I put my hand near the fire it becomes hot. I 
can show you this by placing before us this ball 
which has just been brought red-hot from the 
fire. If I press this wire to it some of the heat 
will be transferred from the ball, and I have 
only now to touch this piece of gun-cotton with 
the hot wire and you see how I can transfer the 
heat from the ball to the wire and from the 
wire to the cotton. So you see that some 
powers are transferable and others are not. Ob- 
serve how long the heat stops in this ball. I 
might touch it with the wire, or with my finger, 
and if I did so quickly, I should merely burn 
the surface of the skin ; whereas if I touch that 
cylinder, however rapidly, with my finger, the 



CONDUCTION OF ELECTRICITY AND HEAT. 123 

electricity is gone at once — dispersed on the 
instant, in a manner wonderful to think of. 

I must now take up a little of your time in 
showing you the manner in which these powers 
are transferred from one thing to another ; for 
the manner in which force may be conducted 
or transmitted is extraordinary, and most es- 
sential for us to understand. Let us see in what 
manner these powers travel from place to place. 
Both heat and electricity can be conducted ; and 
here is an arrangement I have made to show 
how the former can travel. It consists of a bar 
of copper {fig. 42), and if I take a spirit-lamp 

Fig. 42. 




(this is one way of obtaining the power of heat) 
and place it under that little chimney, the flame 
will strike against the bar of copper and keep it 



124 ELECTRICITY. 

hot. Now you are aware that power is being 
transferred from the flame of that lamp to the 
copper, and you will see by and by that it is 
being conducted along the copper from particle 
to particle; for, inasmuch as I have fastened 
these wooden balls by a little wax at particular 
distances from the point where the copper is 
first heated, first one ball will fall and then the 
more distant ones, as the heat travels along, 
and thus you will learn that the heat travels 
gradually through the copper. You will see 
that this is a very slow conduction of power as 
compared with electricity. If I take cylinders 
of wood and metal, joined together at the ends, 
and wrap a piece of paper round and then apply 
the heat of this lamp to the place where the 
metal and wood join, you will see how the heat 
will accumulate where the wood is, and burn 
the paper with which I have covered it; but 
where the metal is beneath, the heat is con- 
ducted away too fast for the paper to be burned. 
And so if I take a piece of wood and a piece of 
metal joined together, and put it so that the 
flame shall play equally both upon one and the 
other, we shall soon find that the metal will 
become hot before the wood; for if I put a 



CONDUCTION OF ELECTKICITY. 125 

piece of phosphorus on the wood, and another 
piece on the copper, you will find that the 
phosphorus on the copper will take fire before 
that on the wood is melted ; and this shows you 
how badly the wood conducts heat. But with 
regard to the travelling of electricity from place 
to place its rapidity is astonishing. I will, first 
of all, take these pieces of glass and metal, and 
you will soon understand how it is that the 
glass does not lose the power which it acquired 
when it is rubbed by the silk ; by one or two 
experiments I will show you. If I take this 
piece of brass and bring it near the machine, 
you see how the electricity leaves the latter and 
passes to the brass cylinder. And again, if I 
take a rod of metal and touch the machine with 
it I lower the indicator, but when I touch it 
with a rod of glass no power is drawn away, 
showing you that the electricity is conducted by 
the glass and the metal in a manner entirely 
different ; and to make you see that more 
clearly we will take one of our Leyden jars. 
Now, I must not embarrass your minds with 
this subject too much, but if I take a piece of 
metal and bring it against the knob at the top 
and the metallic coating at the bottom, you will 



126 ELECTRICITY. 

see the electricity passing through the air as a 
brilliant spark. It takes no sensible time to 
pass through this, and if I were to take a long 
metallic wire, no matter what the length, at 
least as far as we are concerned ; and if I make 
one end of it touch the outside, and the other 
touch the knob at the top — see how the elec- 
tricity passes ! — it has flashed instantaneously 
through the whole length of this wire. Is not 
this different from the transmission of heat 
through this copper-bar {fig. 42), which has 
taken a quarter of an hour or more to reach 
the first ball ? 

Here is another experiment, for the purpose 
of showing the conductibility of this power 
through some bodies and not through others. 
Why do I have this arrangement made of brass? 
[pointing to the brass work of the electrical 
machine,^. 41]. Because it conducts electri- 
city. And why do I have these columns made 
of glass ? Because they obstruct the passage of 
electricity. And why do I put that paper tassel 
(fig. 43) at the top of the pole, upon a glass 
rod, and connect it with this machine by> means 
of a wire ? You see at once that as soon as the 
handle of the machine is turned, the electricity 



ELECTRICAL REPULSION. 



127 



which is evolved travels along this wire and up 
the wooden rod, and goes to the tassel at the 
top, and you see the power of repulsion with 

Fig. 43. 




which it has endowed these strips of paper, each 
spreading outwards to the ceiling and sides of 



123 ELECTRICITY. 

the room. The outside of that wire is covered 
with gutta-percha ; it would not serve to keep 
the force from you when touching it with your 
hands, because it would burst through, but it 
answers our purpose for the present. And so 
you perceive how easily I can manage to send 
this power of electricity from place to place by 
choosing the materials which can conduct the 
power. Suppose I want to fire a portion of 
gunpowder, I can readily do it by this transfer- 
able power of electricity. I will take a Leyden 
jar, or any other arrangement which gives us 
this power, and arrange wires so that they may 
carry the power to the place I wish ; and then 
placing a little gunpowder on the extremities of 
the wires, the moment I make the connection 
by this discharging rod, I shall fire the gun- 
powder [the connection was made and the gun- 
powder ignited]. And if I were to show you a 
stool like this, and were to explain to you its 
construction, you could easily understand that 
we use glass legs, because these are capable of 
preventing the electricity from going away to 
the earth. If, therefore, I were to stand on this 
stool, and receive the electricity through this 
conductor, I could give it to anything that I 



CONDUCTION OF ELECTRICITY. 129 

touched. [The Lecturer stood upon the in- 
sulating stool, and placed himself in connection 
with the conductor of the machine.] Now, I am 
electrified, I can feel my hair rising up as the 
paper tassel did just now. Let us see whether 
I can succeed in lighting gas by touching the 
jet with my finger. [The Lecturer brought his 
finger near a jet from which gas was issuing, 
when after one or two attempts the spark which 
came from his finger to the jet set fire to the 
gas.] You now see how it is that this power of 
electricity can be transferred from the matter in 
which it is generated, and conducted along wires 
and other bodies, and thus be made to serve new 
purposes utterly unattainable by the powers we 
have spoken of on previous days ; and you will 
not now be at a loss to bring this power of elec- 
tricity into comparison with those which we have 
previously examined, and to-morrow we shall be 
able to go further into the consideration of these 
transferable powers. 



130 



LECTUEE VI. 

THE CORRELATION OF THE PHYSICAL FORCES. 

We have frequently seen, during the course of 
these lectures, that one of those powers or forces 
of matter, of which I have written the names on 
that board, has produced results which are due 
to the action of some other force. Thus, you 
have seen the force of electricity acting in other 
ways than in attracting; you have also seen it 
combine matters together or disunite them by 
means of its action on the chemical force ; and 
in this case, therefore, you have an instance in 
which these two powers are related. But we 
have other and deeper relations than these ; we 
have not merely to see how it is that one power 
affects another — how the force of heat affects 
chemical affinity, and so forth, but we must try 
and comprehend what relation they bear to 
each other, and how these powers may be 



HEAT AND CHEMICAL AFFINITY. 131 

changed one into the other ; and it will to-day 
require all my care, and your care too, to make 
this clear to your minds. I shall be obliged 
to confine myself to one or two instances, be- 
cause to take in the whole extent of this 
mutual relation and conversion of forces would 
surpass the human intellect. 

In the first place, then, here is a piece of fine 
zinc-foil, and if I cut it into narrow strips and 
apply to it the power of heat, admitting the 
contact of air at the same time, you will find 
that it burns ; and then, seeing that it burns, 
you will be prepared to say that there is 
chemical action taking place. You see all I 
have to do is to hold the piece of zinc at the 
side of the flame, so as to let it get heated, and 
yet to allow the air which is flowing into the 
flame from all sides to have access to it; — there 
is the piece of zinc burning just like a piece of 
wood, only brighter. A part of the zinc is 
going up into the air, in the form of that white 
smoke, and part is falling down on to the table. 
This, then, is the action of chemical affinity 
exerted between the zinc and the oxygen of the 
air. I will show you what a curious kind of 
affinity this is by an experiment, which is 

K 2 



132 CORRELATION OF THE PHYSICAL FORCES. 

rather striking when seen for the first time. I 
have here some iron filings and gunpowder, and 
will mix them carefully together, with as little 
rough handling as possible ; now we will com- 
pare the combustibility, so to speak, of the two. 
I will pour some spirit of wine into a basin and 
set it on fire: and, having our flame, I will 
drop this mixture of iron filings and gunpowder 
through it, so that both sets of particles will 
have an equal chance of burning. And now 
tell me which of them it is that burns? — you 
see a plentiful combustion of the iron filings; 
but I want you to observe, that though they 
have equal chances of burning, we shall find 
that by far the greater part of the gunpowder 
remains untouched ; I have only to drain off 
this spirit of wine, and let the powder which 
has gone through the flame dry, which it will 
do in a few minutes, and I will then test it with 
a lighted match. So ready is the iron to burn, 
that it takes, under certain circumstances, even 
less time to catch fire than gunpowder. [As 
soon as the gunpowder was dry, Mr. Anderson 
handed it to the Lecturer, who applied a lighted 
match to it, when a sudden flash showed how 
large a proportion of gunpowder had escaped 



CHEMICAL AFFINITY AND ELECTRICITY. 133 

combustion when falling through the flame of 
alcohol.] 

These are all cases of chemical affinity, and I 
show them to make you understand that we 
are about to enter upon the consideration of a 
strange kind of chemical affinity, and then to 
see how far we are enabled to convert this force 
of affinity into electricity or magnetism, or any 
other of the forces which we have discussed. 
Here is some zinc (I keep to the metal zinc as 
it is very useful for our purpose), and I can 
produce hydrogen gas by putting the zinc and 
sulphuric acid together, as they are in that re- 
tort ; there you see the mixture which gives us 
hydrogen — the zinc is pulling the water to 
pieces and setting free hydrogen gas. Now we 
have learned by experience that if a little mer- 
cury is spread over that zinc, it does not take 
away its power of decomposing the water, but 
modifies it most curiously. See how that mix- 
ture is now boiling, but when I add a little 
mercury to it the gas ceases to come off. We 
have now scarcely a bubble of hydrogen set 
free, so that the action is suspended for the 
time. We have not destroyed the power of 
chemical affinity, but modified it in a wonderful 

X 3 



134 CORRELATION OF THE PHYSICAL FORCES. 

and beautiful manner. Here are some pieces 
of zinc covered with mercury, exactly in the 
same way as the zinc in that retort is covered ; 
and if I put this plate into sulphuric acid I get 
no gas, but this most extraordinary thing occurs, 
that if I introduce along with the zinc another 
metal which is not so combustible, then I re- 
produce all the action. I am now going to put 
to the amalgamated zinc in this retort some 
portions of copper wire (copper not being so 
combustible a metal as the zinc), and observe 
how I get hydrogen again, as in the first 
instance — there, the bubbles are coming over 
through the pneumatic trough, and ascending 
faster and faster in the jar; the zinc now is 
acting by reason of its contact with the copper. 
Every step we are now taking brings us to a 
knowledge of new phenomena. That hydrogen 
which you now see coming off so abundantly 
does not come from the zinc as it did before, 
but from the copper. Here is a jar containing 
a solution of copper. If I put a piece of this 
amalgamated zinc into it, and leave it there, it 
has scarcely any action, and here is a plate of 
platinum which I will immerse in the same 
solution, and might leave it there for hours, 



TRANSFERENCE OF CHEMICAL AFFINITY. 135 

days, months, or even years, and no action 
would take place. But by putting them both 
together and allowing them to touch {fig. 44), 



Fig. 44. 



Fig. 45. 





you see what a coating of copper there is im- 
mediately thrown down on the platinum. Why 
is this ? The platinum has no power of itself 
to reduce that metal from that fluid, but it has 
in some mysterious way received this power by 
its contact with the metal zinc. Here then you 
see a strange transfer of chemical force from one 
metal to another — the chemical force from the 
zinc is transferred, and made over to the plati- 
num by the mere association of the two metals. 
I might take instead of the platinum, a piece 
of copper or of silver, and it would have no 
action of its own on this solution, but the mo- 
ment the zinc was introduced and touched the 



K 4 



136 CORRELATION OF THE PHYSICAL FORCES. 

other metal, then the action would take place, 
and it would become covered with copper. 
Now, is not this most wonderful and beautiful 
to see ? We still have the identical chemical 
force of the particles of zinc acting, and yet in 
some strange manner we have power to make 
that chemical force, or something it produces, 
travel from one place to another — for we do 
make the chemical force travel from the zinc to 
the platinum by this very curious experiment 
of using the two metals in the same fluid in 
contact with each other. 

Let us now examine these phenomena a little 
more closely. Here is a drawing {Jig. 45) in 
which I have represented a vessel containing 
the acid liquid and the slips of zinc and plati- 
num or copper, and I have shown them touchiDg 
each other outside by means of a wire coming 
from each of them (for it matters not whether 
they touch in the fluid or outside — by pieces of 
metal attached, they still by that communication 
between them have this power transferred from 
one to the other). Now, if instead of only using 
one vessel, as I have shown there, I take 
another, and another, and put in zinc and 
platinum, zinc and platinum, zinc and platinum, 



TRANSFERENCE OF CHEMICAL AFFINITY. 137 

and connect the platinum of one vessel with the 
zinc of another, the platinum of this vessel 
with the zinc of that, and so on, we should only 
be using a series of these vessels instead of one. 
This we have done in that arrangement which 
you see behind me. I am using what we call a 
Grove's voltaic battery, in which one metal is 
zinc, and the other platinum, and I have as 
many as forty pairs of these plates all exercising 
their force at once in sending the whole amount 
of chemical power there evolved through these 
wires under the floor and up to these two rods 
coming through the table. We need do no more 
than just bring these two ends in contact, when 
the spark shows us what power is present ; and 
what a strange thing it is to see that this force 
is brought away from the battery behind me, 
and carried along through these wires. I have 
here an apparatus {fig. 46) which Sir Humphry 
Davy constructed many years ago, in order to 
see whether this power from the voltaic battery 
caused bodies to attract each other in the same 
manner as the ordinary electricity did. He 
made it in order to experiment with his large 
voltaic battery, which was the most powerful 
then in existence. You see there are in this 



138 CORRELATION OF THE PHYSICAL FORCES. 

glass jar two leaves of gold, which I can cause 
to move to and fro by this rack work. I will 



Fig. 46. 



Fig. 47. 





connect each of these gold leaves with separate 
ends of this battery, and if I have a sufficient 
number of plates in the battery I shall be able 
to show you that there will be some attraction 
between those leaves even before they come in 
contact : if I bring them sufficiently near when 
they are in communication with the ends of the 
battery, they will be drawn gently together, and 
you will know when this takes place, because 



POLAR ATTRACTION OF THE BATTERY. 139 

the power will cause the gold leaves to burn 
away, which they could only do when they 
touched each other. Now I am going to cause 
these two leaves of gold to approach gradually, 
and I have no doubt that some of you will see 
that they approach before they burn, and those 
who are too far off to see them approach will 
see by their burning that they have come to- 
gether. Now they are attracting each other, 
long before the connection is complete, and 
there they go ! burnt up in that brilliant flash, 
so strong is the force. You thus see, from the 
attractive force at the two ends of this battery, 
that these are really and truly electrical pheno- 
mena. 

Now, let us consider what is this spark. I 
take these two ends and bring them together, 
and there I get this glorious spark like the 
sunlight in the heavens above us. What is 
this ? It is the same thing which you saw 
when I discharged the large electrical machine, 
when you saw one single bright flash ; it is the 
same thing, only continued, because here we 
have a more effective arrangement. Instead 
of having a machine which we are obliged to 
turn for a long time together, w r e have here a 



140 CORRELATION OF THE PHYSICAL FORCES. 

chemical power which sends forth the spark — 
and it is wonderful and beautiful to see how 
this spark is carried about through these wires. 
I want you to perceive, if possible, that this 
very spark and the heat it produces (for there 
is heat), is neither more nor less than the 
chemical force of the zinc — its very force 
carried along wires and conveyed to this place. 
I am about to take a portion of the zinc and 
burn it in oxygen gas for the sake of showing 
you the kind of light produced by the actual 
combustion in oxygen gas of some of this 
metal. [A tassel of zinc-foil was ignited at a 
spirit-lamp and introduced into a jar of oxygen, 
when it burnt with a brilliant light.] That 
shows you what the affinity is when we come 
to consider it in its energy and power. And 
the zinc is being burned in the battery behind 
me at a much more rapid rate than you see in 
that jar, because the zinc is there dissolving 
and burning, and produces here this great 
electric light. That very same power which in 
that jar you saw evolved from the actual com- 
bustion of the zinc in oxygen, is carried along 
these wires and made evident here, and you 
may if you please consider that the zinc is 



THE ELECTRIC LIGHT. 141 

burning in those cells, and that this is the light 
of that burning [bringing the two poles in con- 
tact and showing the electric light]; and we 
might so arrange our apparatus as to show that 
the amounts of power evolved in either case 
are identical. Having thus obtained power 
over the chemical force, how wonderfully we are 
able to convey it from place to place! When 
we use gunpowder for explosive purposes, we 
can send into the mine chemical affinity by 
means of this electricity ; not having provided 
fire beforehand, we can send it in at the mo- 
ment we require it. Now here (fig. 47) is a 
vessel containing two charcoal points, and I 
bring it forward as an illustration of the won- 
derful power of conveying this force from place 
to place. I have merely to connect these by 
means of wires to the opposite ends of the 
battery, and bring the points in contact. See 
what an exhibition of force we have ! We have 
exhausted the air so that the charcoal cannot 
burn, and therefore the light you see is really 
the burning of the zinc in the cells behind me 
— there is no disappearance of the carbon, 
although we have that glorious electric light ; 
and the moment I cut off the connection it 



142 CORRELATION OF THE PHYSICAL FORCES. 

stops. Here is a better instance to enable some 
of you to see the certainty with which we can 
convey this force, where, under ordinary cir- 
cumstances, chemical affinity would not act. 
We may absolutely take these two charcoal 
poles down under water, and get our electric 
light there; — there they are in the water, and 
you observe when I bring them into connection 
we have the same light as we had in that glass 
vessel. 

Now, besides this production of light we have 
all the other effects and powers of burning zinc. 
I have a few wires here which are not combus- 
tible, and I am going to take one of them, a 
small platinum wire, and suspend it between 

Fig. 48. 




these two rods which are connected with the 
battery, and when contact is made at the bat- 






HEAT, ELECTRICITY, AND CHEMICAL ACTION. 143 

tery see what heat we get (Jig. 48). Is not that 
beautiful? — it is a complete bridge of power. 
There is metallic connection all the way round 
in this arrangement, and where I have inserted 
the platinum, which offers some resistance to 
the passage of the force, you see what an amount 
of heat is evolved, — this is the heat which the 
zinc would give if burnt in oxygen, but as it is 
being burnt in the voltaic battery it is giving it 
out at this spot. I will now shorten this wire 
for the sake of showing you that the shorter 
the obstructing wire is, the more and more 
intense is the heat, until at last our platinum 
is fused and falls down, breaking off the circuit. 
Here is another instance. I will take a piece 
of the metal silver, and place it on charcoal con- 
nected with one end of the battery, and lower 
the other charcoal pole on to it. See how bril- 
liantly it burns (Jig. 49). Here is a piece of 
iron on the charcoal, see what a combustion is 
going on; and we might go on in this way 
burning almost everything we place between the 
poles. Now I want to show you that this 
power is still chemical affinity — that if we call 
the power which is evolved at this point heat, or 
electricity, or any other name referring to its 



144 CORRELATION OF THE PHYSICAL FORCES. 

source, or the way in which it travels, we still 
shall find it to be chemical action. Here is a 

Fig. 49. 




coloured liquid which can show by its change 
of colour the effects of chemical action ; I will 
pour part of it into this glass and you will find 
that these wires have a very strong action. I 
am not going to show you any effects of combus- 
tion or heat, but I will take these two platinum 
plates, and fasten one to the one pole and the 
other to the other end, and place them in this 
solution, and in a very short time you will see 
the blue colour will be entirely destroyed. See, 
it is colourless now! — I have merely brought 
the end of the wires into the solution of indigo, 
and the power of electricity has come through 
these wires and made itself evident by its che- 
mical action. There is also another curious 



CHEMICAL ACTION OF THE BATTERY. 145 

thing to be noticed now we are dealing with the 
chemistry of electricity, which is that the chemi- 
cal power which destroys the colour is only due to 
the action on one side. I will pour some more 
of this sulphindigotic acid ( 23 ) into a flat dish 
and will then make a porous dyke of sand sepa- 
rating the two portions of fluid into two parts 
(fig. 50), and now we shall be*able to see whether 

Fig. 50. 




there is any difference in the two ends of the 
battery, and which it is that possess this peculiar 
action. You see it is the one on my right 
hand which has the power of destroying the blue, 
for the portion on that side is thoroughly 
bleached, while nothing has apparently occurred 
on the other side. I say apparently, for you 
must not imagine, that because you cannot per- 
ceive any action none has taken place. 

Here we have another instance of chemical 

L 



146 CORRELATION OF THE PHYSICAL FORCES. 

action. I take these platinum plates again and 
immerse them in this solution of copper from 
which we formerly precipitated some of the 
metal, when the platinum and zinc were both 
put in it together. You see that these two 
platinum plates have no chemical action of any- 
kind, they might remain in the solution as long 
as I liked, without- having any power of them- 
selves to reduce the copper ; but the moment I 
bring the two poles of the battery in contact 
with them, the chemical action which is there 
transformed into electricity and carried along 
the wires, again becomes chemical action at the 
two platinum poles, and now we shall have the 
power appearing on the left hand side, and 
throwing down the copper in the metallic state 
on the platinum plate ; and in this way I might 
give you many instances of the extraordinary 
way in which this chemical action or electricity 
may be carried about. That strange nugget of 
gold, of which there is a model in the other 
room, and which has an interest of its own in 
the natural history of gold, and which came 
from Ballarat, and was worth 80001. or 9000Z. 
when it was melted down last November, was 
brought together in the bowels of the earth, 
perhaps ages and ages ago, by some such power 



MAGNETISM AND CHEMICAL AFFINITY. 14 7 

as this. And there is also another beautiful re- 
sult dependent upon chemical affinity in that fine 
lead-tree ( 24 ), the lead growing and growing by 
virtue of this power. The lead and the zinc are 
combined together in a little voltaic arrangement, 
in a manner far more important than the power- 
ful one you see here, because in nature these 
minute actions are going on for ever, and are of 
great and wonderful importance in the precipi- 
tation of metals and formation of mineral veins, 
and so forth. These actions are not for a 
limited time, like my battery here, but they act 
for ever in small degrees, accumulating more 
and more of the results. 

I have here given you all the illustrations 
that time will permit me to show you of 
chemical affinity producing electricity, and 
electricity again becoming chemical affinity. 
Let that suffice for the present ; and let us now 
go a little deeper into the subject of this chemical 
force, or this electricity — which shall I name first 
— the one producing the other in a variety of 
ways. These forces are also wonderful in their 
power of producing another of the forces we have 
been considering, namely, that of magnetism, and 
you know that it is only of late years, and long 

L 2 



148 CORRELATION OF THE PHYSICAL FORCES. 

since I was born, that the discovery of the 
relations of these two forces of electricity and 
chemical affinity to produce magnetism have 
become known. Philosophers had been sus- 
pecting this affinity for a long time, and had 
long had great hopes of success — for in the 
pursuit of science we first start with hopes and 
expectations; these we realise and establish 
never again to be lost, and upon them we found 
new expectations of further discoveries, and so 
go on pursuing, realising, establishing, and 
founding new hopes again and again. 

Now observe this: here is a piece of wire 
which I am about to make into a bridge of force, 
that is to say, a communicator between the two 
ends of the battery. I^t is copper wire only, and 

Fig. 51. 




is therefore not magnetic of itself. We will 
examine this wire with our magnetic needle 



RELATION OF MAGNETISM TO ELECTRICITY. 149 

(fig. 51), and though connected with one extreme 
end of the battery, you see that before the circuit 
is completed it has no power over the magnet. 
But observe it when I make contact ; watch the 
needle, see how it is swung round, and notice 
how indifferent it becomes if I break contact 
again ; so you see we have this wire evidently 
affecting the magnetic needle under these cir- 
cumstances. Let me show you that a little 
more strongly. I have here a quantity of wire 
which has been wound into a spiral, and this 
will affect the magnetic needle in a very curious 
manner, because, owing to its shape, it will act 
very like a real magnet. The copper spiral has 
no power over that magnetic needle at present ; 
but if I cause the electric current to circulate 
through it, by bringing the two ends of the bat- 
tery in contact with the ends of the wire which 
forms the spiral, what will happen ? Why one 
end of the needle is most powerfully drawn to 
it ; and if I take the other end of the needle it 
is repelled ; so you see I have produced exactly 
the same phenomena as I had with the bar 
magnet, — one end attracting and the other 
repelling. Is not this then curious to see that 
we can construct a magnet of copper? Further- 

L 3 



150 CORRELATION OF THE PHYSICAL FORCES. 

more, if I take an iron bar, and put it inside 
the coil, so long as there is no electric current 
circulating round, it has no attraction, — as you 
will observe if I bring a little iron filings or 
nails near the iron. But now if I make contact 
with the battery they are attracted at once. It 
becomes at once a powerful magnet, so much so 
that I should not wonder if these magnetic 
needles on different parts of the table pointed to 
it. And I will show you by another experiment 
what an attraction it has. This piece and that 
piece of iron and many other pieces are now 
strongly attracted {fig. 52), but as soon as I break 

Fig. 52. 




contact the power is all gone and they fall. 
What then can be a better or a stronger proof 



ELECTRO-MAGNETISM. 1 51 

than this of the relation of the powers of mag- 
netism and electricity ? Again, here is a little 
piece of iron which is not yet magnetised. It 
will not at present take up any one of these 
nails ; but I will take a piece of wire and coil it 
round the iron (the wire being covered with 
cotton in every part it does not touch the iron), 
so that the current must go round in this spiral 
coil — I am, in fact, preparing an electro-magnet 
(we are obliged to use such terms to express our 
meaning, because it is a magnet made by elec- 
tricity, — because we produce by the force of 
electricity a magnet of far greater power than a 
permanent steel one). It is now completed and 
I will repeat the experiment which you saw the 
other day, of building up a bridge of iron nails ; 
the contact is now made and the current is 
going through ; it is now a powerful magnet ; 
here are the iron nails which we had the other 
day, and now I have brought this magnet near 
them they are clinging so hard that I can 
scarcely move them with my hand {fig. 53). 
But when the contact is broken, see how they 
fall. What can show you better than such an 
experiment as this the magnetic attraction with 
which we have endowed these portions of iron ? 

L 4 



152 CORRELATION OF THE PHYSICAL FORCES. 

Here again is a fine illustration of this strong 
power of magnetism. It is a magnet of the 

Fig. 53. 




same sort as the one you have just seen. I am 
about to make the current of electricity pass 
through the wires which are round this iron for 
the purpose of showing you what powerful 
effects we get. Here are the poles of the mag- 
net ; and let us place on one of them this long 
bar of iron. You see as soon as contact is made 
how it rises in position (Jig. 54) ; and if I take 
such a piece as this cylinder, and place it on, 
woe be to me if I get my finger between ; I can 
roll it over, but if I try to pull it off, I might 



ELECTKO-MAGNETISM. 



153 



lift up the whole magnet, but I have no power 
to overcome the magnetic power which is here 

Fig. 54. 




evident. I might give you an infinity of illus- 
trations of this high magnetic power. There is 
that long bar of iron held out, and I have no 
doubt that if I were to examine the other end 
I should find that it was a magnet. See what 
power it must have to support not only these 
nails, but all those lumps of iron hanging on to 
the end. "What then can surpass these evidences 
of the change of chemical force into electricity, 
and electricity into magnetism ? I might show 
you many other experiments whereby I could 
obtain electricity and chemical action, heat and 



154 CORRELATION OF THE PHYSICAL FORCES, 

light from a magnet, but what more need I show 
you to prove the universal correlation of the 
physical forces of matter, and their mutual con- 
version one into another ? 

And now let us give place as juveniles to the 
respect we owe to our elders ; and for a time let 
me address myself to those of our seniors who 
have honoured me with their presence during 
these lectures. I wish to claim this moment 
for the purpose of tendering our thanks to them, 
and my thanks to you all for the way in which 
you have borne the inconvenience that I at 
first subjected you to. I hope that the insight 
which you have here gained into some of the 
laws by which the universe is governed, may be 
the occasion of some amongst you turning your 
attention to these subjects; for what study is 
there more fitted to the mind of man than that 
of the physical sciences? And what is there 
more capable of giving him an insight into the 
actions of those laws, a knowledge of which 
gives interest to the most trifling phenomenon 
of nature, and makes the observing student find 

" tongues in trees, books in the running brooks, 

Sermons in stones, and good in everything " ? 



155 



LECTUEE 



LIGHTHOUSE ILLUMINATION — THE ELECTRIC 
LIGHT. 

[Delivered before the Royal Institution on Friday, 9th March, 
I860.] 

There is no part of my life which gives me 
more delight than my connection with the 
Trinity House. The occupation of nations 
joined together to guide the mariner over the 
sea, to all a point of great interest, is infinitely 
more so to those who are concerned in the ope- 
rations which they carry into effect, and it cer- 
tainly has astonished me since I have been 
connected with the Trinity House to see how 
beautifully and how wonderfully shines forth 
amongst nations at large the desire to do good ; 
and you will not regret having come here 
to-night, if you follow me in the various 
attempts which have been made to carry out 
the great object of guiding in safety all people 
across the dark and dreary waste of waters. It 



156 LIGHTHOUSE ILLUMINATION. 

is wonderful to think how eagerly efforts at 
improvement are made by the various public 
bodies — the Trinity House in this country, and 
commissions in France and other nations ; and 
whilst the improvements progress we come to 
the knowledge of such curious difficulties and 
such odd modes of getting over those difficulties 
as are not easy to be conceived. I must ask 
you this evening to follow me from the simplest 
possible method of giving a sign by means of a 
light to persons at a distance, to the modes at 
which we have arrived in the present day ; and 
to consider the difficulties which arise when 
carrying out these improvements to a practical 
result, and the extraordinary care which those 
who have to judge on these points must take 
in order to guard against the too hasty adoption 
of some fancied improvement, thus, as has 
happened in some few cases, doing harm instead 
of good. 

If I try to make you understand these things 
partly by old models, and partly by those which 
we have here, it is only that I may the better 
be enabled to illustrate that which I look for- 
ward to as the higher mode of lighting, by 
means of the electric lamp and the lime light. 

There is nothing more simple than a candle 



REFLECTION OF LIGHT. 



157 



being set down in a cottage window to guide a 
husband to his home, but when we want to 
make a similar guide on a large scale, not 
merely over a river or over a moor, but over 
large expanses of sea, how can we then make 
the signal using only a candle ? I have shown 
in this diagram (fig. 55) what we may imagine 

Fig. 55. 




to be the rays of a candle or any other source 
of light emanating from the centre of a sphere 
in all directions round to infinite distances. 
After this simple kind of light had been used 
for some time, it being found to be liable to be 
obscured by fogs, or distance, or other circum- 
stance, there arose the attempt to make larger 



158 LIGHTHOUSE ILLUMINATION. 

lights by means of fires ; and after that there 
was introduced a very important refinement in 
the mode of dealing with the light, namely the 
principle of reflection ; — for understand this 
(which is not known by all, and not known by 
many who should know it), that when we take 
a source of light, a single candle, for instance, 
giving off any quantity of light, we can by no 
means increase that light : we can make ar- 
rangements around and about the light, as you 
see here, but we can by no means increase the 
quantity of light. The utmost I can do is to 
direct the light which the lamp gives me by 
taking a certain portion of the rays going off on 
one side and reflecting them on to the course of 
the rays which issue in the opposite direction. 
First of all, let us consider how we may gather 
in the rays of light which pass off from this 
candle. You will easily see that if I could take 
the half rays on the one side and could send 
them by any contrivance over to the other side, 
I should gain an advantage in light on the side 
to which I directed them. This is effected in 
a beautiful manner by the parabolic mirror, by 
means of which I gather all that portion of the 
rays which are included in it ; upwards, down- 



KEFRACTION OF LIGHT. 159 

wards, sideways, anywhere within its sphere of 
action ; they are all picked up and sent forward. 
You thus see what a beautiful and important 
invention is that of the parabolic reflector for 
throwing forward the rays of light. 

Before I go further into the subject of reflec- 
tion let me point out a further mode of dealing 
with the direction of the light. For instance, 
here is a candle, and I can employ the principle 
of refraction to bend and direct the rays of 
light, and if I want to increase the light in any 
one direction, I must either take a reflector or 
use the principle of refraction. I will place 
this lens {fig. 56) in front of the candle and you 

Fig. 56. 




will easily see that by its means I can throw on 
to that sheet of paper a great light, that is to 
say, that instead of the light being thrown all 
about, it is refracted and concentrated on to 
that paper ; so here I have another means of 
bending the light and sending it in one direc- 



160 LIGHTHOUSE ILLUMINATION. 

tion ; and you see above a still better arrange- 
ment for the same purpose, — one which comes 
up to the maximum, I may say, of the ability 
of directing light by this means. You are aware 
that without that arrangement of glass the light 
would be dispersed in all directions, but the lens 
being there, all the light which passes through 
it is thrown into parallel beams and cast hori- 
zontally along. There is consequently no loss 
of light, the beam goes forward of the same 
dimensions, and will consequently continue to 
go forward for five or ten miles, or so long as the 
imperfection of the atmosphere does not absorb 
it ; and see ! What a glorious power that is, to 
be able to convert what was just now darkness 
on that paper into brilliant light. 

Whenever we have refraction of this sort we 
are liable to an evil consequent upon the ne- 
cessary imperfections in the form of the lens ; 
and Dr. Tyndall will take this lens, and will 
show you even in this small and perfect appara- 
tus what is the evil of spherical aberration with 
which we have to fight. This can be illustrated 
by means of the electric lamp ; if you look at 
the screen, you will see produced, by means of 
this lens, a figure of the coal points. This 



POLYZONAL LENSES. 161 

image is produced by the rays which pass 
through the middle of the lens, a piece of card 
with a hole in the centre being placed in front ; 
but if, keeping the rest of the apparatus in the 
same position, I change this card for another 
piece which will only allow the rays to pass 
through the edge of the lens, you observe how 
inferior the image will be. In order to get it 
distinct I have to bring the screen much nearer 
the lamp ; and so if I take the card away alto- 
gether, and allow the light to pass through all 
parts of the lens, we cannot get a perfect image, 
because the different parts of the lens are not 
able to act together. This spherical aberration 
is, therefore, what we try to avoid by building 
up compound lenses in the manner here shown 
(fig. 58). Look at this beautiful apparatus, is it 
not a most charming piece of workmanship? 
Buffon first and Fresnel afterwards, built up 
these kind of lenses, ring within ring, each at 
its proper adjustment, to compensate for the 
effects of spherical aberration ; the ring round 
that centre lens is ground so as to obviate what 
would otherwise give rise to spherical aberration, 
and the next ring, being corrected in the same 
manner, you will perceive, if you look at the 

M 



162 



LIGHTHOUSE ILLUMINATION. 



disc of light thrown by the apparatus upstairs, 
that there is nothing like the amount of aberra- 
tion that there would have been if it had been 
one great bull's-eye. Here is one of Fresnel's 
lamps of the fourth order so constructed (Jig. 57): 

Fig. 57. 




observe the fine effect obtained by these differ- 
ent lenses as you see them revolve before you, 
and understand that all this upper part is made 
to form part of the lens, each prism throwing 
its rays to increase the effect, and, although you 
may think it is imperfect because if you happen 



FRESNEL's CONSTRUCTION OF LAMPS. 163 

to sit below or above the horizontal line, you 
perceive but little if any of the light, yet you 
must bear in mind that we want the rays to go 
in a straight line to the horizon. So that all 
that building up of rings of glass is for the 
purpose of producing one fine and glorious lens 
of a large size, to send the rays all in one direc- 
tion. Here is another apparatus used to pull 
the rays down to a horizontal sheet of light, so 
that the mariner may see it as a constant and 
uniform fixed light ; the former lamp is a re- 
volving one, and the light is seen only at certain 
times as the lenses move round, and these are 
the points which make them valuable in their 
application. 

There are various orders and sizes of lights in 
lighthouses to shine for twenty or thirty miles 
over the sea, and to give indications according 
to the purposes for which they are required; 
but suppose we want more effect than is pro- 
duced by these means, how are we to get more 
light ? Here comes the difficulty. We cannot 
get more light, because we are limited by the 
condition of the burner. In any of these cases^ 
if he spreading of the ray, or divergence as it is 
called, is not restrained, it soon fails from weak* 
>x 2 



164 LIGHTHOUSE ILLUMINATION. 

ness, and if it does not diverge at all, it makes 
the light so small, that perhaps only one in 
a hundred can see it at the same time. The 
South Foreland lighthouse is, I think, 300 or 400 
feet above the level of the sea, and therefore it 
is necessary to have a certain divergence of the 
beam of light in order that it may shine along 
the sea to the horizon. I have drawn here two 
wedges, one has an angle of 15°, and shows you 
the manner in which the light opens out from 
this reflector seen at the distance of half a mile 
or more, the other wedge has an angle of 6°, 
which is the beautiful angle of Fresnel. When 
the angle is less than 6°, the mariner is not 
quite sure that he will see the light — he may 
be beneath or above it; and in practice it is 
found that we cannot have a larger angle than 
15°, or a less one than 6°. In order, therefore, to 
get more light, we must have more combustion, 
more cotton, more oil ; ' but already there are in 
that lamp four wicks put in concentric rings, 
one within the other, and we cannot increase 
them much more, owing to the divergence 
which would be caused by an increase in the 
size of the light — the more the divergence, the 
more the light is diffused and lost. We are, 



THE ELECTRIC LIGHT. 165 

therefore, restrained by the condition of the light 
and the apparatus to a certain sized lamp. At 
Teignmouth, some of the revolving lights have 
ten lamps and reflectors, all throwing their light 
forward at once. But even with ten lamps and 
reflectors we do not get sufficient light, and we 
want, therefore, a means of getting a light more 
intense than a candle in the space of a candle — 
not merely an accumulation of candle upon 
candle, but a concentration into the space of a 
candle, of a greater amount of light, and it is here 
that the electric light comes to be of so much 
value. 

Let me now show you what are the proper- 
ties of that light which make it useful for light- 
house illumination, and which has been brought 
to a practical condition by the energy and con- 
stancy of Professor Holmes. I will first of all 
show you the image of the charcoal points on 
the screen, and draw your attention to the spot 
where the light is produced. There are the 
coal points. The two carbons are brought 
within a certain distance ; the electricity is 
being urged across by the voltaic battery, and 
the coal points are brought into an intense 
state of ignition. You will observe that the 

M 3 



166 THE ELECTKIC LIGHT. 

light is essentially given by the carbons ; you 
see that one is much more luminous than the 
other, and that is the end which principally 
forms the spark, the other does not shine so 
much, and there is a space between the two 
which, although not very luminous, is most 
important to the production of the light. Dr. 
Tyndall will help me in showing you that a 
blast of wind will blow out that light; the 
electric light can in fact be blown out easier 
than a candle. We have the power of getting 
our light where we please ; if I cause the elec- 
tricity to pass between carbon and mercury I 
get a most intense and beautiful light, most of 
it being given off from the portion of the mer- 
cury between the liquid and the solid pole. I 
can show you that the light is sometimes pro- 
duced by the vapour between the two poles, 
better if I take silver than when I use mercury. 
Here is the carbon pole, there is the silver, and 
there is the beautiful green light which comes 
from the intervening portions. Now that light 
is more easily blown out than the common 
lamp, the slightest puff of wind being sufficient 
to extinguish it, as you will see if Dr. Tyndall 
breathes upon it. 



ADVANTAGES OF THE ELECTRIC LIGHT. 167 

You see, therefore, how we are able, by using 
this electric spark, to get, first of all, the light 
into a very small space. That oil lamp 
has a burner 3| inches in diameter ; compare 
the size of the flame with the space occupied by 
this electric light. Next compare the intensity 
of this light with any other; if I take this 
candle and place it by the side, I actually seem 
to put out the candle. We are thus able to 
get a light which, while it surpasses all others 
in brilliancy, is at the same time not too large, 
for I might put this light into an apparatus not 
larger than a hat, and yet I could count upon 
the rays being useful. Moreover, when such 
large burners are used in a lantern, we have to 
consider whether the bars of the window do not 
interfere to throw a shadow or otherwise ; but 
with this light there will be no difficulty of that 
sort, as a single small speculum no larger than 
a hat will send it in any direction we please ; 
and it is wonderful what advantages, by reason 
of its small bulk, we have in the consideration 
of the different kinds of apparatus required, re- 
flecting or refracting, irrespective of other reasons 
for using the electric light. And it is these 
kind of things which make us decide most 

M 4 



168 



THE ELECTRIC LIGHT. 



earnestly and carefully in favour of the electric 
light. 

I am going to show you the effect that will 
take place with that large lens when we throw 
the oil lamp out of action, and put the electric 
light into use. It is astonishing to find how 
little the eye can compare the relative inten- 
sities of two lights ; look at that screen and try 
to recollect the amount of light thrown upon it 
from the 3| inch lamp of Fresnel, and now, 
when we shift the lens sideways, look at the 
glorious light arising from that small carbon 
point {fig. 58) ; see how beautifully it shines in 



tM 



wm> 



Fig. 58. 



the focus of that lens and throws the rays for- 
ward. At present the electric light is put at 
just the same distance as the oil light, and 
therefore, being in the focus of the lens, we 



THE MAGNETO ELECTRIC MACHINE. 169 

iiave parallel rays which are thrown forward in 
a perfectly straight line, as you will see by com- 
paring the size of the lens with that of the 
light thrown on the screen. You will now see 
how far we can affect this beam of light by in- 
creasing or diminishing the distance of the 
lamp. We are able by a small adjustment to 
get a beam of a large or small angle, and observe 
what power I have now over it ; for if I want to 
increase the degrees of divergence, I am limited 
by the power of light in the case of the oil lamp, 
but with the electric light, I can make it spread 
over any width of the horizon by this simple 
adjustment. These then are some of the reasons 
which make it desirable to employ the electric 
light. 

By means of a magnet, and of motion, we 
can get the same kind of electricity as I have 
here from the battery ; and under the authority 
of the Trinity House, Professor Holmes has 
been occupied in introducing the magneto- 
electric light in the lighthouse at the South 
Foreland ; for the voltaic battery has been tried 
under every conceivable circumstance, and I 
take the liberty of saying it has hitherto proved 
a decided failure. Here, however, is an in- 



170 THE ELECTRIC LIGHT. 

strument wrought only by mechanical motion. 
The moment we give motion to this soft iron 
in front of the magnet, we get a spark. It is 
true in this apparatus it is very small, but it is 
sufficient for you to judge of its character. It 

Fig. 59. 




is the magneto-electric light, and an instrument 
has been constructed as there shown (fig. 59) 
which represents a number of magnets placed 
radially upon a wheel — three wheels of magnets 



THE MAGNETO-ELECTKIC LIGHT. 171 

and two sets of helices. When the machine, 
which is worked by a two-horse power engine, 
is properly set in motion, and the different cur- 
rents are all brought together, and thrown by Pro- 
fessor Holmes up into the lantern, we have a 
light equal to the one we have been using this 
evening. For the last six months the South 
Foreland has been shining by means of this 
electric light — beyond all comparison better 
than its former light. It has shone into France, 
and has been seen there and taken notice of by 
the authorities, who work with beautiful accord 
with us in all these matters. Never for once 
during six months has it failed in doing its 
duty ; — never once, more than was expected 
by the inventor. It has shone forth with its 
own peculiar character, and this even with the 
old apparatus — for as yet no attempt has been 
made to construct special reflectors or refractors 
for it, because it is not yet established. I will 
not tell you that the problem of employing the 
magneto-electric spark for lighthouse illumina- 
tion is quite solved yet, although I desire it 
should be established most earnestly (for I 
regard this magnetic spark as one of my own 
offspring). The thing is not yet decidedly ac- 



172 THE ELECTRIC LIGHT. 

complished, and what the considerations of ex- 
pense and other matters may be, I cannot tell. 
I am only here to tell you as a philosopher, how 
far the results have been carried, but I do hope 
that the authorities will find it a proper thing 
to carry out in full. If it cannot be introduced 
at all the lighthouses, if it can only be used at 
one, why really it will be an honour to the 
nation which can originate such an improvement 
as this, — one which must of necessity be fol- 
lowed by other nations. 

You may ask, what is the use of this bright 
light ? It would not be useful to us were it 
not for the constant changes which are taking 
place in the atmosphere, which is never pure. 
Even when we can see the stars clearly on a 
bright night it is not a pure atmosphere. The 
light of a lighthouse, more than any other, is 
liable to be dimmed by vapours and fogs, and 
where we most want this great power, is not in 
the finest condition of the atmosphere, but 
when the mariner is in danger, when the sleet 
and rain are falling, and the fogs arise, and the 
winds are blowing, and he is nearing coasts 
where the water is shallow and abounds with 
rocks — then is his time of danger, when he 



WHEN OF MOST VALUE. 173 

most wants this light. I am going to show you 
how, by means of a little steam, I can com- 
pletely obscure this glorious sun, this electric 
light which you see. The cloud now obscuring 
the light on the screen is only such a cloud as 
you see when sitting in a train on a fine summer's 
day ; you may observe that the vapour, passing 
out of the funnel, casts as deep a shadow on 
the ground as the black funnel; the very sun 
itself is extinguished by the steam from the 
funnel, so that it cannot give any light; and 
the sun itself if set in the lighthouse would not 
be able to penetrate such a vapour. 

Now the haze of this cloud of steam is just 
what we have to overcome, and the electric 
light is as soon, proportionally, extinguished 
by an obstruction of this kind as any other 
light. If we take two lights, one four times the 
intensity of the other, and we extinguish half 
of one by a vapour, we extinguish half of the 
other, and that is a fact which cannot be set 
aside by any arrangement. But then we fall 
back upon the amount of light which the 
electric spark does give us in aid of the power of 
penetrating the fog, for the light of the electric 
spark shines so far at times, that even before it 



174 THE ELECTRIC LIGHT. 

has arisen above the horizon twenty five miles 
off, it can be seen. This intense light has, there- 
fore, that power which we can take advantage of, 
— of bearing a great deal of obstruction before 
it is entirely obscured by fogs or otherwise. 

Taking care that we do not lead our author- 
ities into error by the advice given, we hope 
that we shall soon be able to recommend the 
Trinity House, from what has passed, to esta- 
blish either one or more good electric lights in 
this country. 



175 



NOTES. 



LECTUEE I. 

(*) Page 1. The opening lecture was twice post- 
poned on account of Dr. Faraday's illness. 

( 2 ) Page 9. Platinum, with one exception the heaviest 
body known, is 21 J times heavier than water. 

( 3 ) Page 10. Aluminium is 2j times heavier than 
water. 

( 4 ) Pages 10 and 11. Power or property in water. 
This power — the heat by which the water is kept in & fluid 
state, is said, under ordinary circumstances, to be latent 
or insensible. When, however, the water changes its 
form, and, by uniting with the lime or sulphate of copper, 
becomes solid, the heat which retained it in a liquid state 
is evolved. 

( 5 ) Page 10. Anhydrous sulphate of copper: sulphate 
of copper deprived of its water of crystallisation. To 
obtain it the blue sulphate is calcined in an earthen 
crucible. 

( 6 ) Page 16. Add a little liquid to the marble and de- 
compose it. Marble is composed of carbonic acid and lime, 



176 NOTES. 

and, in chemical language, is called carbonate of lime. 
When sulphuric acid is added to it, the carbonic acid is set 
free, and the sulphuric acid unites with the lime to form 
sulphate of lime. 

Carbonic acid } under ordinary circumstances, is a colour- 
less invisible gas, about half as heavy again as air. Dr. 
Faraday first showed that under great pressure it could 
be obtained in a liquid state. Thilorier, a French che- 
mist, afterwards found that it could be solidified. 



LECTURE II. 

( 7 ) Page 41. Crystallisation of alum. The solution 
must be saturated — that is, it must contain as much alum 
as can possibly be dissolved. In making the solution it 
is best to add powdered alum to hot water as long as it 
dissolves ; and when no more is taken up, allow the so- 
lution to stand a few minutes and then pour it off from 
the dirt and undissolved alum. 

( 8 ) Page 43. Red precipitate of biniodide of mercury. 
A little care is necessary to obtain this precipitate. The 
solution of iodide of potassium should be added to the 
solution of perchloride of mercury (corrosive sublimate) 
very gradually. The red precipitate which first falls is 
redissolved when the liquid is stirred: when a little 
more of the iodide of potassium is added a pale red pre- 
cipitate is formed, which, on the further addition of the 
iodide, changes into the brilliant scarlet biniodide of mer- 
cury. If too much iodide of potassium is added, the 
scarlet precipitate disappears, and a colourless solution is 
left. 

( 9 ) Page 43. Paper coated with scarlet biniodide of 
mercury. In order to fix the biniodide on paper, it must 



NOTES. 177 

be mixed with a little weak gum water, and then spread 
over the paper, which must be dried without heat. 

Biniodide of mercury is said to be dimorphous ; that is, 
is able to assume two different forms. 

( 10 ) Page 45. (i Prince Rupert's Drops." These are 
made by pouring drops of melted green glass into cold 
water. They were not, as is commonly supposed, invented 
by Prince Rupert, but were first brought to England by 
him in 1660. They excited a great deal of curiosity, and 
were considered u a kind of miracle in nature. " 

( n ) Page 46. Thick glass vessels. They are called 
Proofs or Bologna phials. 

( 12 ) Page 47. Mica. A silicate of alumina and mag- 
nesia. It has a bright metallic lustre, hence its name, 
from micoj to shine. 

( 13 ) Page 48. Common salt or chloride of sodium 
crystallises in the form of solid cubes, which aggregated 
together, form a mass, which may be broken up into the 
separate cubes. 

( 14 ) Page 49. Iceland or calc spar. Native carbonate 
of lime in its primitive crystalline form. 



LECTURE IIL 

* 

( 15 ) Page 65. Solution of a salt. Acetate of soda. A 

solution saturated, or nearly so, at the boiling point, is 
necessary, and it must be allowed to cool, and remain at 
rest until the experiment is made. 

( 16 ) Page 71. Binoxide of nitrogen and hyponitrous 
acid. Binoxide of nitrogen is formed when nitric acid 
and a little water are added to some copper turnings. 



178 NOTES. 

It produces deep red fumes as soon as it comes in contact 
with the air, by combining with the oxygen of the latter 
to form hyponitrous acid. Binoxide of nitrogen is com- 
posed of two parts oxygen and one part of nitrogen; 
hyponitrous acid is composed of one part of nitrogen and 
three parts of oxygen. 



LECTUEE IV. 

( 17 ) Page 91. Chlorate of Potash and Sutyhiiret of An- 
timony. Great care must be taken in mixing these sub- 
stances, as the mixture is dangerously explosive. They 
must be powdered separately and mixed together with 
a feather on a sheet of paper, or by passing them several 
times through a small sieve. 

( 18 ) Page 92. The mixture of chlorate of potash and 
sugar does not require the same precautions. They may 
be rubbed together in a pestle and mortar without fear. 
One part of chlorate of potash and three parts of sugar 
will answer. The mixture need only be touched witli 
a glass rod dipped in oil of vitriol. 

( 19 ) Page 92. Two salts dissolved in water. Sulphate 
of soda and chloride of calcium. The solutions must be 
saturated for the experiment to succeed well. 

( 20 ) Page 96. Lead pyrophorous. This is tartrate of 
lead which has been heated in a glass tube to dull red- 
ness as long as vapours are emitted. As soon as they 
cease to be evolved the end of the tube is sealed, and it 
is allowed to cool. 

( 21 ) Page .99. Gkm cotton is made by immersing cot- 
ton-wool in a mixture of sulphuric acid and the strongest 
nitric acid, or of sulphuric acid and nitrate of potash. 



NOTES. 179 

( 22 ) Page 100. Paper prepared like gun cotton. It 
should be bibulous paper, and must be soaked for ten 
minutes in a mixture of ten parts by measure of oil of 
vitriol with five parts of strong fuming nitric acid. The 
paper must afterwards be thoroughly washed with warm 
distilled water and then carefully dried at a gentle heat. 
The paper is then saturated with chlorate of strontia, or 
chlorate of baryta, or nitrate of copper, by immersion in 
a warm solution of these salts. (See Chemical News 
Vol. I. page 36.) 

LECTURE VI. 

( 23 ) Page 145., Sulphindigotic acid. A mixture of 
one part of indigo and fifteen parts of concentrated oil of 
vitriol. It is bleached on the side at which hydrogen gas is 
evolved in consequence of the liberated hydrogen with- 
drawing oxygen from the indigo, thereby forming a colour- 
less deoxidised indigo. In making the experiment, only 
enough of the sulphindigotic acid must be added to give 
the water a decided blue colour. 

( 24 ) Page 147. Lead tree. To make a lead tree, pass 
a bundle of brass wires through the cork of a bottle, and 
fasten a plate of zinc round them just as they issue from 
the cork, so that the zinc may be in contact with every 
one of the wires. Make the wires to diverge so as to 
form a sort of cone, and having filled the bottle quite 
full of a solution of sugar of lead, insert the wires and 
cork and seal it down, so as to perfectly exclude the air. 
In a short time the metallic lead will begin to crystallise 
around the divergent wires, and form a beautiful object. 



THE END. 



LONDON 

PRINTED BY SPOTTISWOODE AND CO. 

NEW-STREET SQUARE 



MUTANT -WittS 


PUBLISHED BY 


RICHARD GRIFFIN & CO. 


^aMigjjers to % Knitaitg of (Ulasgofo 


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LONDON, E.C. GLASGOW. 


COMPEISING 


Applied Science 


Geology and Physical 


Jfotany 


Geography 


Chemistry- 
General Science 


Mathematics 
Physical Science 
Zoology 


1860 



INDEX. 




Applied Science — 




General Science — 




Aitken's Medicine 

Anderson's Applied Chemistry . . . 
.Barlow's Manufactures 


. S 
. 3 
. 3 


Mental Science . . 


6 
6 
6 


Napier's Metallurgy of the Bihle 

Olmstead's Noah 


Book of Trades 


1 


Palace of the Great King 


7 




4 


Paley's Natural Theology 

Senior's Political Economy 


6 


Bronner's Chemistry of Food 


. 4 


7 


Davy's Agricultural Chemistry . . . 


. 4 


Smedley's Occult Sciences 


7 




. 4 
. 5 
. 5 


Geology & Physical Geography 


— 


Hunt's Manual of Photography . . . 
„ Practice of Photography. . . 


Imray's Practical Mechanics 


. 5 


Ansted's Inanimate Creation 


3 


„ Steam Engine 


5 


,, Geology 


3 


Martin's Photography 


. 6 


Bryce's Cyclopaedia 

„ Physical Geography 

Griffin's Crystallography 


4 




. 6 
. 6 


4 
5 


„ „ Receipts 


„ Electro-Metallurgy 


. 6 


Hitchcock's Religion and Geology. . 
Kitto's Physical Geography 


5 


Phillips's Metallurgy 


. 7 


5 


„ Gold Mining 


. 7 


Phillips's Geology 


7 


„ Records of Mining 


. 7 


Schoedler's Geology 


8 


Rankine's Applied Mechanics 


. 7 


Tennent's Mineralogy 


8 


„ Civil Engineering 


. 7 


Wittich's Physical Geography 


8 


„ Steam Engine 

Scoffern's Artificial Light 


. V 

. 7 


Mathematics— 




Spooner's Veterinary Art 

Thomson's Medicine 


. 7 


Airy's Trigonometry 


3 


. 8 


Brougham s Tracts 


4 


Young's Navigation 


. 8 


Copland's Arithmetic 


4 






Jardine's Geometry 


5 


Botany — 




Peacock's Arithmetic 


7 


Balfour's Botany 


. 3 
. 4 

. 8 
. 7 




8 
8 
8 
8 
8 


„ Trigonometry 

Young's Arithmetic 

„ Algebra 

„ Geometry 


Schoedler's Botany 

Smith's Botany 


Chemistry — 




Physical Science— 




Anderson's Applied Chemistry . . . 


. 3 


Bakewell's Electricity 


3 


Bronner's Chemistry of Food 


. 4 


Breen's Astronomy 


4 


Davy's Agricultural Chemistry . . . 


. 4 


Faraday's Physical Forces 


4 


Griffin's Chemical Recreations . . . 


. b 


Herschel on Light 


5 


„ Radical Chemistry 


. 5 


„ on Sound 


5 


Napier's Chemistry of Dveing 


. 6 


Lowe's Meteorology 


5 


Phillips's Chemistry of the Metals 
Schoedler's Elementary Chemistrj 


. 7 


Mitchell's Statics 


6 


f 8 


„ Astronomy 


6 


Scoffern's Elementary Chemistry . 

„ Inorganic Bodies 

„ Artificial Light 


. 7 


Nicnol's Physical Sciences 


6 


. 7 


Schoedler's Astronomy 

„ N atural Philosophy 


8 


. 7 


8 


Thomson's Dictionary of Chemistr 


V 8 


„ Physical Science 


8 






Thomson's Electricity 


8 


General Science— 




Young's Dynamics 


8 


Book of Nature 


. 3 

. 4 

. 4 

4 


„ Nautical Astronomy 

Zoology— 

Baird's Natural History 


8 
3 


Brougham's Natural Theology . . . 
Circle of the Sciences 


Dick's Christian Philosopher 


Fleming's Moral Philosophy 


. 4 


Broderip's Zoological Recreations. . 


4 


Greek and Roman Science 


5 


Bushnan's Physiology 


4 


Harry's Vacation 

Hitchcock's Religious Truth 


. 7 
. 5 




4 
5 


Knight's Natural History 


Hughes's Reading Lessons 

Keddie's Scientific Anecdotes 


. 1 


Latham's Ethnology 


5 


6 


Owen's Skeleton and Teeth 


6 


Maurice's Moral Philosophy 


. 6 


Schoedler's Zoology 


8 



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