Gregory, Olinthus Gilbert

Lessons, Astronomical and
Philosophical

OLD CLASS

S
G8232kx

BMED

CA.L

E^l^Senkler

CKI.KSTIAI, HEMISPHERE

LESSONS,

ASTRONOMICAL AND PHILOSOPHICAL,

FOR THE

AMUSEMENT AND INSTRUCTION

BEING

AN ATTEMPT TO EXPLAIN AND ACCOUNT FOR

THE MOST

USUAL APPEARANCES IN NATURE

IN A FAMILIAR MANNER,
FROM ESTABLISHED PRINCIPLES.

The Whole interspersed with
MORAL REFLECTIONS.

BY OLINTHUS GREGORY, LL.D.

OF THE ROYAL MILITARY ACADEMY, WOOLWICH.

-The glittering stars,

By the deep ear of Meditation heard,

Still in their midnight watches sing of HIM.

He uods a culm; the tempests blow His wrath ;

The thunder is His voice ; and the red flash

His speedy sword of justice. At His touch

The mountains flame. He shakos the solid earth,

And rocks tlie nations. Nor in these alone,

In every common instance GOD is seen. THOMSON,

THE FIFTH EDITION,

MUCH ENLARGED AND IMPROVED.

LONDON:

PRINTED FOR JOSIAH CONDER, 18. ST. PAUL'S CHURCH- YARH
LONGMAN, Ht'RST, REES, ORME, AND BROWN, PATERNOSTER
ROW; DARTON, HARVEY, AND DARTON, GRACECHURCH
STREET ; SHERWOOD, NEELY, AND JONES, PATERNOSTER
ROWJ AND LAW AND WHITAKER, A\E MARIA LANE.

1815.

Etlettoo and lleoderton, Primers,
Johnson's Court, London.

TO THE

RIGHT HON. JOHN JOSHUA PROBY,

EARL CARYSFORT,

EVER ZEALOUS IK THE PROMOTION AND ENCOURAGEMENT
OF GOOD WORK.1j

UNDER WHOSE PATRONAGE

THE FORMER EDITIONS OP THIS PERFORMANCE

MET WITH
SO FAVOURABLE A RECEPTION;

THE PRESENT IMPROVED EDITION

IS RESPECTFULLY DEDICATED
BT

HIS LORDSHIP'S

MOST OBEDIENT, AND MOST OBLIGED,
HUMBLE SERVANT,

OLTNTHLTS GREGORY.

PREFACE.

JL-T has been for a considerable time allowed
by the majority of intelligent persons, that
amongst a variety of studies there are none
of greater utility, or that afford more real
pleasure to a rational mind, than those on
Philosophical Subjects. On mature delibe-
ration it may be concluded, that this does
not so much arise from any intrinsic value of
Natural Philosophy, solely considered, as
from the peculiar use to which it may be
applied, and without which it hardly merits
the name it has obtained : and this is no
other, than regulating by it our observa-
tions upon the numerous objects of the
creation, whereby we may correct any erro-
neous notions which we may have hitherto
encouraged, either concerning them, or the

a 2 OMNIPOTENT

VI PREFACE.

OMNIPOTENT BEING by whose Will they
\vere formed.

When it is considered how liable all our
senses are to deception, and what wrong
ideas are generally formed of the different
parts of the universe from mere cursory ob-
servation, the absolute necessity of the dis-
'semination of true philosophical principles
will the more obviously appear. And if
the rudeness and imbecility of the human
mind in an uncultivated state of nature be
taken into the consideration, it will be the
more readily admitted, that every attempt
to extend the sphere of human knowledge
is laudable in its nature; and, if it be
found to answer the intention, is deserving
of encouragement.

Being duly impressed with the force of
these reflections, and also recollecting that
it is the indispensable duty of every member
of society, to render himself as serviceable
to his fellow-creatures as his abilities will
allow, I was induced to apply my leisure
hours to the execution of a performance
which might in some measure tend to the

instruction

PREFACE. Vll

instruction of the Youth of Great Britain.
And as iny principal design was to lay be-
fore them some pages of the Volume of
Nature, I judged that if this could be per-
formed in such a manner as to be also a
source of amusement, it would probably meet
with a more welcome reception, and conse-
quently have the better effect.

I have likewise been cautious in checking
any inclination to scepticism during the
study of Natural Philosophy : and in guard-
ing against a mischievous misapplication of
the word Nature. I uniformly wish this
word to be considered as an abridged form
of expressing, sometimes the results of the
laws to which the mechanism of the universe
is subjected by the Supreme Being; some-
times the collection of beings created by
him. Nature viewed thus, in its true light,
is no longer a subject of cold unproductive
speculation, with regard to morality. The
study of its productions and its phenomena
not only enlightens the mind, but warms the
heart, by exciting feelings of reverence and
admiration, at the sight of so many wonders,

bearing

Vlll PREFACE.

bearing such striking characters of unlimited
power and matchless wisdom.

Pursuant to these ideas 1 have divided the
following work into easy lessons of various
lengths, as the nature of the respective sub-
jects would admit ; and have interspersed
them with moral reflections, in prose and
verse, in order to alleviate the mind of the
student, and to lead him, by imperceptible
degrees, to reflect seriously on the several
objects around him. To the honour of our
British Poets, it must be acknowledged, I
was seldom at a loss for an Extract suitable
to my purpose ; and if my acquaintance with
their works had been more extensive, I be-
lieve there would have been no occasion for
those two or three little original pieces, which
make so dim an appearance in such brilliant
company.

These Lessons may with propriety be in-
troduced into Schools to be read before the
master in greater or less proportions, as may
be thought most proper : in which case they
will answer a double purpose, — improving
the Pupil in the Art of Reading, while they

enlarge

PREFACE. IX

enlarge the bounds of his understanding.
That they might be as much as possibly sub-
servient to the former, without raising an
impediment in the way of the latter, reflec-
tions, attendant on the several subjects, are
the more frequently introduced.

To some persons it may perhaps appear
necessary, that I should have given an ex-
planation of all the technical terms which
are found in the following pages : for in-
stance, such as centre, or center, diaphanous,
equinox, focus, glands, lacteal, peristaltic,
&c. Here I would observe, that I have not
neglected such explanation where it could
be given without leading me too circuitous
a course ; and even where it is otherwise,
the omission will not afford an objection of
great weight ; for there is scarcely a dic-
tionary in which the requisite information
may not be met with. Perhaps in schools
this raay be productive of some advantage,
as it may lead to inquiry ; but that this
may have the better effect, it may be re-
marked, that the preceptor does not pro-
perly acquit himself in his duty towards

his

X PREFACE.

his pupils, who does not indulge them in the
liberty of asking every question, the solu-
tion of which may have a tendency to in-
crease their fund of learning. Masters, by
acting thus, would undoubtedly be able to
judge in what respects their scholars were
most deficient; and could, of course, sup-
ply those deficiencies from their own know-
ledge, or from those helps which it may
naturally be supposed they have at hand.

In the composition of these Lessons, I
have not scrupled to make a free use of the
Works of several of the most esteemed Au-
thors on Astronomy and Philosophy; and
if I have not always acknowledged where
the obligation lay, I may observe that such
alterations were made, or the extracts taken
in so detached a manner, as rendered it
nearly, if not absolutely, impossible. When
we remember that the improvements in these
sciences were gradual aod not effected by
one man, or by one age ; it must be allowed
that every production (except those which
boast of new inventions and discoveries) must
be principally a compilation; and the chief

merit

PREFACE. xi

merit to which the person who undertakes
it can aspire, is that of arranging the mate-
rials before him in a manner more suitable to
his purpose, and making such reflections as
may be best adapted to the subject.

I am conscious, that in the present under-
taking many imperfections will be met with :
however, such as it is, I present it with cheer-
fulness to the public view ; and if it meet with
a favourable reception from the candid and
ingenuous, I shall have but little to fear from
the severe critic. Literary fame I want not
to acquire : zeal for the welfare of the British
Youth was the only motive which urged me
to this performance ; and if it prove to be of
service to- them, I shall think myself amply
rewarded. As to the numerous defects, I
must sue for indulgence by observing, that
I am yet but a young man; and am wil-
ling to hope that if health and leisure should
permit, I may at some future period pro-
duce something more worthy of public fa-
vour. Yet, as I am desirous to make this
Work as correct and useful as possible, I
cannot but add, that those who will be so

obliging

Xli PREFACE.

obliging as to furnish me with hints for its
improvement, will confer a lasting obliga-
tion upon me, and shall receive my grate-
ful acknowledgments.

O. G. GREGORY.

Yaxley,
May 20th 1793.

ADVER-

ADVERTISEMENT.

GRATITUDE for the favourable reception which
the first Edition of these LESSONS has experienced, has
induced the Author to give them a careful revisal, in
order that this New Edition may be found less un-
worthy of public favour. In this revisal, he has been
assisted by the polite suggestions of some of the Review-
ers, (for whose testimonials in favour of his perform-
ance he feels peculiarly obliged), and by many useful
hints which have been communicated to him in letters
from several of his literary friends ; to whom he can-
not but acknowledge his obligations, and whose names
would reflect honour upon his work, if he were per-
mitted to mention them. He is in a particular man~
ner indebted to a Nobleman of distinguished worth
and abilities, for condescending to point out several
alttratious and emendations ; all of which were of so
much importance, that his Lordship will find they
have been universally attended to. The Author has
taken care to incorporate into this Edition, all those
improvements and discoveries that have been made
since the first Edition was published, and that ap-
peared to have any connection with the subjects on
a 3 which

XlV ADVERTISEMENT.

which he has treated. Besides the numerous altera-
tions which are to be met with in almost every
Lesson, he has added three New Lessons, — one on
Electricity, one on Fountains or Springs, and one on
Plants and Vegetation. He humbly hopes that these
corrections and additions will ensure to him a con*
tinuation of that encouragement with which he ha*
Heen already honoured by an indulgent Public.

Cambridge,
May 2<)th, 1799*

Should any, who possess extensive philosophical
knowledge, honour this work with a perusal, they will
perceive that it is a juvenile production; being,
indeed, written originally before the author was 20
years of age : but, as its success has shewn its fitness
forjuveniTe minds, the Author should not think him-
self justifiable in making any alterations in the plan ;
but simply thinks himself bound to correct it as muck-
as possible, and to supply omissions by notes of refer-
ence, while the plan remains the same. The principal
additions and changes in the fourth edition, were in the
15th, imti, (24th, 28(A, 29th, and SQth Lessons. Sevc,-
ral minor corrections are made in thejlth edition.

Ro} til Military Academy,
Aug. 20tii, 1815.

CONTENTS.

Page

INTRODUCTORY LESSON ••••• I

View of the Heavens •«••• • %••• 5

On the Sun 9

Mercury • • ••• 15

Venus « 2O

TheEarth .• - •> -•••• 2*

Mars f 31

Jupiter . 34

Saturn ••- 38

Georgtum Sidus, or Herschel «.«• 41

TheMoon .-• 4S'

Comets ••• « ••«• 51

Projection and' Gravity 55.

Zclipses of the Sun and Moon 62:

The Fixed Stars, with Reflections on the Immensity

of the Universe G8

The Air and Atmosphere «•• , .... 77

Winds •• ••• 91

Sounds and Echoes ••*".*.• 98

Evaporation, Ruin, Hail, Snow, Mists, and Dew • • 108

Frostandlce 115-

Electricity »«•• 122,

Thunder and Lightning ••••• ••• •• 135

The Ignis Fatuus r 14*

The Aurora Borealis 149

Light and Colours ••• 155-

Tke Rainbow .» • • •_• •...„»• • • v •• • • • M • v.r • • • •_'• W*

XVI CONTENTS.

On Halos and Parhelia >•• 172

Fire 177

Water 190

Fountains or Springs 201

The Tide* 209

Days and Nights 214

The Seasons 218

Vegetables or Plants • • 226

Earthquakes 239

Volcanos 265

TheEje 278

Concoction • • • 286

The Circulation of the Blood 295

Concluding Lesson •••• 303

Appendix, containing Additional Remarks on Heat,

Cold, aud Light 311

LESSON I.

INTRODUCTION.

Every object of Creation

Can furnish hints to contemplation, GAY.

you, my dear young friends, have no\v ar-
rived at a period of life, in which the mental
faculties are rapidly expanding and increasing in
vigour, you will perceive an inquisitive curiosity,
which has long remained dormant in your minds,
hastily bursting forth : it will be of the utmost
importance to your happiness, both present and
future, that you be careful in directing this active
principle into its proper course.

Ever since you have been able to exercise the
power of reasoning, you cannot but have observed,
with wonder and admiration, the sun shining with
astonishing splendour, dispensing light and heat
around; — the moon, with majesty serene, gliding
along the arched heavens, scattering her gentle
rays, in the absence of the glittering luminary of
day; — and the spacious canopy bespangled with
iiumerous stars, like twinkling flames, adding to
the beauty of the scene. You must have observed,
B mih

2 INTRODUCTION. [Lesson r.

with awful astonishment, the forked lightning in
vivid motion glancing through the wide expanse;
and have heard, with fear and anxiety, the tre-
mendous thunder, shaking the firmest buildings
with its pealing crash. When you reflect upon
these and other appearances in nature, what im-
pressions do you feel ? You who have considered
these things attentively will ingeniously confess,
that you are thereby led to conceive that there
must be some First Cause which produced, governs,
and regulates the whole. The most cursory obser-
vation will have induced you to entertain a high
opinion of the wisdom, power, and goodness of the
ALMIGHTY DESIGNER ; but I can assure you, my
young friends, that the more you reflect upon the
universe, in the display of its wonders and beauties,
and the better you are acquainted with it, so much
the more will be increased your reverence and
love of the Governor of all.

Nature is but a name for an effect

Whose cause is God. COWPER.

Natural Philosophy is subservient to purposes
of a high and noble kind, and is chiefly to be
valued, as it lays a sure foundation for natural re-
ligion and moral philosophy; by leading us, in a
satisfactory manner, to the knowledge of the Au-
thor and Governor of the universe. To study na-
ture is to search into his workmanship : every new
discovery opens to us a new part of his scheme.
And while we still meet, in our inquiries, with
hints of greater things yet undiscovered, the mind

is

Lesson I. INTRODUCTION. 3

is kept in a pleasing expectation of making a fur-
ther progress ; acquiring, at the same time, higher
conceptions of that great Being, whose works are
so various, and hard to be comprehended.

It is a melancholy consideration, that too many
young persons, instead of being zealous of acquir-
ing real and useful knowledge, suffer a kind of
torpor to dwell upon their minds, and give way to
such supineness as may, if they be not quickly
roused from their lethargy, be attended with fatal
consequences. If any such persons should peruse
these Lessons, let me exhort them to shake off
their carelessness, and endeavour to furnish their
minds, ere it be too late, with a true knowledge of
the works and wonders of the creation : let them be
assured that such conduct will produce the hap-
piest effects; for philosophical contemplations will
form the safest bulwark against the insidious at-
tacks of Atheists : because the principal intention,
of such inquiries is, from a consideration of the
effects produced, to correct our ideas with respect
to the Great First Cause; or, as the poet has ex-
pressed it,

To look through Nature up to NATURE'S GOD. POPE,

In these Lessons it shall therefore be my pro-
vince to explain to you, in a concise and familiar
manner, some of the wonders of the universe : I
will first lead you to lake a survey of the heavenly
bodies; and afterwards consider some of those
objects and some of those appearances of na-
B 2 ture,

INTRODUCTION. [Lesson i.

ture which relate to the earth we inhabit : thus
shall we

See through this vast extended theatre

Of skill divine, what shining marks appear !

Creating power is all around exprest,

The GOD discover'd, and his care confest :

Nature's high birth her heav'nly beauties shew :

By every feature we the parent know.

Th' expanded spheres, amazing to the sight,

Magnificent with stars, and globes of light;

The glorious orbs which heav'n's bright host compose .

Th' imprison'd sea, resistless ebbs and flows ;

The fluctuating fields of liquid air,

With all the curious meteors hov'ring there,

And the wide regions of the land proclaim,

The POW'R DIVINE that rais'd the mighty frame.

BLACKMORE.

LESSON

LESSON II.

VIEW OF THE HEAVENS.

Heaven

Is as the book of GOD before thee set
Wherein to read his wond'rous works. MILTON.

The heav'ns declare the glory of GOD. DAVID.

AGREEABLY to my plan, I shall now endea-
vour, in the first place, to describe to you the na-
ture, size, and motion of the principal heavenly
bodies; the beauty and variety of which have no
doubt often filled you with astonishment: follow-
ing the advice of Ovid,

' We, though from heaven remote, to heaven will move

' With strength of mind, and tread th' abyss above ;

' And penetrate with an interior light,

' Those upper depths which nature hid from sight.

' Pleas'd we will be to walk along the sphere

* Of shining stars, and travel through the year."

The science which teaches the knowledge of
the celestial bodies, their magnitudes, motions,
distances, periods, eclipses, order, &c. is called
ASTRONOMY : the study of this has been pursued
with avidity in all ages, and it is now arrived at
a tolerable degree of accuracy. The hypotheses
which have, been invented by astronomers, at
different times and in different countries, are nu-
ll 3 merous,

VIEW OP THE HEAVENS. [LeSS07l II.

nierous, and the greater part of them are too futile
in their nature to d'eservea particular account : the
only one which agrees with all the phenomena is
that which was first invented by Pythagoras (who
was born 577 years before Christ), and taught in
Greece and Italy ; but this was soon buried in ob-
livion, and was set aside from the time of Ptolemy,
until it was restored about the year 1507» by
Nicholas Copernicus. The discoveries of Kepler
and Galileo tended greatly to prove its truth ; but
it was much opposed, until at length the indefati-
gable researches of Sir ISAAC NEWTON fixed it
upon too firm a basis to be easily overthrown. It
is now generally adopted by Astronomers, and is>
with a few modifications, now called the Newtonian
System ; an account of which I shall here proceed
to lay before you.

When we take a view of the heavenly bodies,
our attention is first attracted by the sun and moon,
which are distinctively named luminaries : the other
beautiful spangles in the glorious canopy are called
stars ; and of these a distinction is made into pla-
nets or wandering stars, and fixed stars. The pla-
nets, of which the earth we inhabit is one, move
in regular and uninterrupted order aro'und the sun j
some of these planets have attendants, usually
called satellites, moving around them. Sometimes
there are other stars seen, with blazing tails issu-
ing from them : these pursue very eccentric irre-
gular courses, and are called comets. The planets*

them-

* Correctly speaking, the Satellites are Planets, as well aa
those round which they revolve: for planet is a Greek word,

Lesson n.] VIEW OF THE HEAVENS. 7

themselves are frequently called primaries., and
their satellites secondaries. Tfiere are two methods
of discovering which are planets, and which are
fixed stars : every fixed star twinkles, but a planet
does not ; for the stars are to appearance only lu-
cid poinis, and therefore any opaque particle float-
ing in the air is sufficient to cause a momentary
eclipse of them f; but ihe planets, though smaller,
suffer very little apparent diminution. The pro-
per criterion, however, is this : the planets are al-
ways in motion from one part of the heavens to
the other, whereas the other stars keep constantly
the same relative distance.

The names of the planets, beginning with that
nearest the sun, are as follow : Mercury, Penus,
the Earthy Mars, Jupiter, Saturn, and Georgium
Sidus, or Herschel. These are all that are yet
discovered, though there very probably may be

signifying any thing that wanders. Agreeably to this accep-
tation, the Sun itself is a Planet; as it, like the others, has a
two-fold motion. And indeed, to complete the similarity,
Dr. Herschel has (in a paper which will be presently more
largely spoken of) asserted^ that his body is opaque, and that
it is diversified with hills and valleys.

t Although the above is the generally adopted method! of
explaining the twinkling of the fixed stars, yet it is now
thought to be inaccurate. Mr. Michell justly observes (in
the " Philosophical Transactions,") that no object can hide &
star from us, that is not large enough to exceed the apparent
diameter of the star, by the diameter of the pupil of the eye>
nay, it must be large enough to hide the star from both eyes
at the same time.

Perhaps the principal cause of this twinkling, is the
unequal refraction of light, in consequence of inequalities
and undulations in the atmosphere.

» *• more :

8 VIEW OF THE HEAVENS. [LeSSOH II.

more*: after describing to you the sun, I shall
proceed to the rest in their order.

* Since the commencement of the present century, four
other Planets have been discovered.

The first of these was discovered on the 1st of January,
1801, by M. Piazzi, of Palermo : its mean distance from the
sun is not qtiite three times that of the earth (2.768): its
revolution is performed in four years, seven months, and ten
days; and its orbit is inclined to the ecliptic in an angle
of about lOf degrees. This planet is much less in size than
our moon : its discoverer has given it the name of Ceres, but
most astronomers call it by the name of Piazzi.

The second was discovered on the 20th of March 1802, by
Dr. Olbers, of Bremen. Its distance from the sun, time of
revolution, and magnitude, are nearly the same as Piazzi's
planet; and the orbits of the two intersect each other; the
latter being inclined to the ecliptic in an angle of about 34^
degrees. It is called by the names Pallas, and Olbers.

The third was discovered on the 1st of September 1801, by
M. Harding, of Lilienthal. Its mean distance from the sun
is rather greater than that of the two former; and its size
nearly equal to that of Ceres. Its inclination is 13 degrees.
It appears like a star of the eighth magnitude. Harding has
given to this planet the name of Juno.

The- fourth was discovered by Dr. Olbers, early in 1807.
It is nearer to Mars than either of the other newly discovered
planets, its mean distance being rather more than 2| times
that of the earth ; and the revolution through its orbit is
performed in 1130 of our days. The inclination of that orbit
to the ecliptic is 7 and l-7th degrees, being rather more than
that of Mercury. The size of this planet is not known.
Astronomers have given it the name of Vesta.

LESSON

LESSON III,

ON THE SUN.

Hail sacred source of inexhausted light !

Prodigious instance of creating might !

His distance man's imagination foils ;

Numbers will scarce avail to-cotint the miles.

His globous body how immensely great!

How fierce his burnings ! how intense his heat!

As swift as thought he darts liis radiance round.

To distant worlds his system's utmost bound :

Of all the planets the directing soul,

That heightens and invigorates the whole. BROWN.

wFTEN as you hfije beheld the mid-day sun
shining in all his grandeur, disseminating his reful-
gent beams around ; and often as you have felt
the efficacy of his all -genial heat, you may never
have entertained an idea of his vast size. When
you are informed of the dimensions of this grand
dispenser of light and heat, and when you coi)ne
to be acquainted with some of the laws by which
he is governed, you will consider it as one of the
many irrefragable proofs, that the universe could
not (as atheists assert) be jumbled together by
chance ; but that the whole must have been
formed by an all-wise, all-powerful, and adorable
Creator !

The sun is a body very nearly in the form of

that solid which is by mathematicians called. a

B 5 sphere

10 • THE SUN. [Lesson in.

sphere or globe, and the observations of astrono-
mers have proved beyond a doubt, that its axis is
nearly 883,210 miles, its circumference 2,774,692
miles, and its solidity in cubic miles 360,737,732,
256,5fi4,299 : viz. three hundred and sixty thou-
sand seven hundred and thirty-seven billions,
seven hundred and thirty-two thousand two hun-
dred and fifty-six millions, five hundred and twen-
ty-four thousand two hundred and ninety-nine »
a number almost surpassing the powers of imagi-
nation !

From a cursory observation you would perhaps
be led to imagine that the sun moves round the
earth once in twenty-four hours ; but this is not the
case. The sun has two motions : the one is a peri-
odical motion, in an elliptical or very nearly a cir-
cular direction, round the common centre of all
the planetary motions. As this common centre is
found to be always exceedingly near the sun, and
most commonly within it, I shall henceforward
suppose this luminary to be the centre of the
planetary system, for in such a supposition we shall
not fall into any material error. The other mo-
tion is a revolution upon its axis, which is com-
pleted in about twenty-five days, as appears ob-
viously by paying attention to the maculce and
faculce, or spots upon his surface.

The sun was supposed, by many of the ancients,
to be the clearest image of his Maker, <( without
*' spot, or wrinkle, or any such thing." To such
a degree had this prejudice arisen, that when Gali-
leo discovered several dark spots on the surface of

the

Lesson ill.] THE strir, 1 j

the sun, and mentioned his discovery to another
philosopher, he was told that the thing was utterly
impossible, and that there must be some defect
either in his glasses or his eyes : it was added also,
as another proof of the assertor's candour and pe-
netration, that as such a circumstance was not
noticed by Aristotle, the pretended discovery could
be nothing less than presumption or deception^
However, that there are spots on the sun, has since
been indisputably confirmed, and is- now univer-
sally admitted. Of these spots, the dark ones are
ealled macula, to distinguish them from the others,
which are of a brighter appearance than the rest of
the sun's surface, and which have obtained the
name offaculce.

Concerning the nature of these spots, there have
been various opinions entertained by different per-
sons. Some have supposed maculae to be large
portions of opaque matter moving up and down in
the fiery fluid, of which the sun was thought to be
composed or surrounded, revolving near its sur-
face, and sometimes beyond it. Others have taken
them for the smoke of volcanoes in the sun, or the
scum floating upon a huge ocean of fluid matter,
Faculae, on the contrary, have been called clouds
of light, and luminous vapours j and, because ma-
culae have been sometimes observed to change into-
faculae, it has been conjectured, that the latter
were the bright flames of volcanoes rapidly blazing
out, after the dark smoky matter, which produced
the maculae, became dissipated by combustion^
These are the opinions I hat have been commonly

held

12 THE SUN. [Lesson in.

held on the subject; but it does not appear to have
been considered with much attention until very
lately. The discoveries and observations of Dr.
fierschel, have in a great measure supplied the de-
fect, and afforded ample materials for forming a
rational and plausible theory to explain and eluci-
date the appearances we are now treating upon.

This ingenious astronomer has assigned very
forcible reasons for concluding, that the opinion
commonly received, that the sun is a body of real
fire, is futile and erroneous. He susposes, on the
contrary, that it is an opaque body, surrounded by
an atmosphere of a phosphoric nature, composed
of various transparent and elastic fluids, by the
decomposition of which, light is produced, and lu-
cid appearances formed of different degrees and
intensity. The doctor even goes so far as to assert,
with much probability, that the suri is in reality an
inhabitable world; but this assertion has no con-
nection with our present inquiry, which we must
confine, for the present, to maculae and faculae.
Admitting, therefore, the precexling remarks, we
will endeavour to deduce from them a satisfactory
hypothesis to account for these appearances. The
sun, it has been said, is an opaque body, surrounded
by a lucid atmosphere : you will easily conceive,
then, that maeulse are those parts of his surface
which happen to be free from luminous decompo-
sitions, or, in other words, which are but slightlyj
if at all, covered by the shining matter, and are
for that reason exposed to our view. In most cases
the real body of the sun is supposed to be visible

through

Lesson in.] THE SUN. 13

through its transparent atmosphere, where the lu-
cid substance is not very intense, or where it is
removed by some temporary cause. As some of
the spots appear below, and others above the sur-
face of the shining fluid, it is reasonable to con-
clude that the former are the lower parts of the
sun's surface, and the latter his mountains, which
project beyond the lucid part of his atmosphere.
The former are found to vary in their situation, as
they may be hidden or rendered visible by any
cause which will accumulate or remove the shining
matter : the latter are fixed, with respect to the
sun's surface, and are those, by observations on
which {lie sun's rotation upon his axis has been
determined. From what has been here said, it is
hoped you are tolerably well acquainted with the
nature of maculae : we will now proceed to the
consideration of faculae.

Faculse, on this hypothesis, are those parts of
the solar atmosphere which are brighter, and in
general more elevated than the rest. These Dr.
Herschel supposes to be " more copious mixtures
" of such fluids as decompose each other;'* or they
may be called, larger collections of the luminous
fluids which form the solar atmosphere, according
to the quantity, brightness, and depth of which, the
faculce differ in magnitude and intensity. They are
more frequently observed near ;he borders, than to-
wards the middle of the sun's disc, because, as they
are supposed to extend beyond the usual level of his
atmosphere those which are near the middle of the
disc become edgewise to our view, and are there-
fore

14 THE SUN. [Lesson m.

fore not so easily discernible as those which ap-
proach nearer its circumference.

If the hypothesis concerning the nature of the
sun, which is recited in this lesson, be admitted, it
will readily be acknowledged that that luminary
differs but little in his nature from the planets j
and perhaps we may be allowed to call the sun, in
a popular way, the central planet, or the grand
planet) to which all the others are intimately united,
and from which, as from a copious fountain, flows
all that is necessary to support, connect, and har-
monize the various planets in the system : hence
we may advert to the beautiful and instructive ob-
servation of the poet, and say,

The planets of each system represent
Kind neighbours: mutual amity prevails;
Sweet interchange of rays, received, retuHi'd :
Enlight'ning and enlighten'd ! All at once
Attracting and attracted ! Patriot like,
None sins against the welfare of the whole:
But their reciprocal, unselfish aid,
Affords an emblem of millennial love.
Nothing in nature, much less conscious being,
Was e'er created solely for itself:
Thus man his sov'reign duty learn* in this
Material picture of be nucoltnce. Yousc,

LESSON IV.

ON MERCURY.

First Mercury amidst full tides of light,

Rolls next the Sun, through his small circle bright;

All that dwell there must be refin'd and pure ;

Bodies like ours, such ardour can't endure;

Onr earth would blaze beneath so fierce a ray,

And all its marble mountains waste away. BAKER.

JlOWEVER ignorant we are of the nature of
qualities, and how much soever their mode of ope-
ration is concealed from us, if it be but admitted
that they act in right lines, and that they are pro-
pagated from a point, or body, as from a center,
then it may be demonstrated in a strictly geome-
trical manner, that their energy, or intensity, di-
minishes in a duplicate proportion of the distance
from that center. Thus, for instance, suppose a
person whom I will call Thomas, stands at ten feet
distance from a fire, and another, whom I will call
James, stands twenty feet from the fire ; if they
are similarly situated in all respects but that of
distance, it may be demonstrated, that the fire will
impart four times as much heat to Thomas as to
James ; that is, Thomas's heat is to James's, as
the square of James's distance from the fire is to
the square of Thomas's distance from it.

Considering the sun as the center from whence
proceed those rays, or particles, which meeting

with

j6 MERCURY. [Lesson iv.

with proper substances, produce light and heat at
the planets, and calculating by the theorem above
mentioned, it has been concluded, that if the
earth were placed in the situation of Mercury, its
medium of heat : would be sevca limes more intense
than the greatest heat uf our torrid zone is in its
present situation. And hence it has been asserted,
that if the materials of which Mercury is com-
posed were exactly of the same nature as those of
the earth, they could not long remain without be-
ing either melted into a fluid, and dissipated into
vapour, or vitrified. Have we not then, in the
formation o£ this planet, another proof of infinite
wisdom ? For, if the world were formed by chance,
or, as atheistical writers express it, by the fortui-
tous concourse of atoms, whence comes it, that
Mercury and the Earth should have the materials
of which they are composed, so adjusted and ar-
ranged as to make them so well adapted for their
respective situations, as we have abundant reason
to conclude they are?

It will be necessary to premise, that, though the
motions of the planets are tolerably uniform and
regular, yet they are not exactly so :. nor are their
orbits, or the tracks in which they describe their
periodical motions, strictly circular, but rather
elliptical j their bodies are not globes, but sphe-
riods, being flatted at the ends of their axes, which
are called poles, and more protuberant at their
middle parts or equator? : their orbits are not all in
the same plane, but are variously inclined to each
other. However, as it is foreign from my design

to

Lesson iv.] MERCUHY. 17

to treat upon them in so particular a manner, I
shall content myself with referring you to places
where you may find abundant information in these
respects. (See the books recommended towards
the end of these Lessons.)

Those planets which move in orbits within that
of the earth, are called inferior, perhaps more
properly Interior planets : those whose orbits en-
close the earth's are called superior, or more pro-
perly exterior planets.

Mercury is the smallest of the inferior planets,
and the nearest to the sun, about which he is car-
ried with a very rapid motion. Hence it was
that this planet was considered mythologically
as the messenger of the gods : hev was repre-
sented emblematically by the figure of a youth
with wings at his head and feet, and his cadu-
ceus entwined by winged serpents. The cha-
racter $ in present use for this planet i» also de-
rived from the mythological description. Though
small, he has a bright appearance, with a light
tinct of blue : he never departs 28° from the sun,
and on that account is usually hid in the splen-
dour of that luminary.

The mean distance of Mercury from the sun,
is to that of 'the earth from the sun, as 387 to
1000: hence his distance is about 37 millions of
miles. The sun's diameter will appear at Mer-
cury nearly three times as large as at the earth :
and the sun's light and heat received there, is,
as before observed, about seven times those at
the earth.

The

18 MERCURY. [Lesson iv.

The diamtter of this planet is nearly one-third
of the diameter of the eanh, or about 3000 miles.
Hence the surface of Mercury is nearly 1-gth,
and his magnitude or bulk l-27th of that of the
earth.

His period of revolution round the sun is 87
days, 23 hours, and l-4th : hence you may find
that he moves in his orbit about the sun at the
amazing rate of more than 95,OOO miles in an
hour. His length of day, or time of rotation on his
axis, inclination of axis to his orbit, &cc. are yet
unknown.

Mercury changes his phases in a manner simi-
lar to the moon, according as he is differently
stationed, with regard to the earth and sun : though
we may observe that he never appears quite full,
because his bright side is only turned directly to-
wards us, when he is so near the sun as to be lost
from our sight in his beams. These different
phases of his make it obvious that he does not
shine by any light of his own 5 for if he did, he
would always appear round.

As the orbit of this planet is between the earth's
orbit and the sun, if it were in the same plane
as the orbit of the earth, Mercury would fre-
quently be seen to move across the face or diac
of the sun. But as the planes of their orbits are
not coincident, this appearance happens less com-
monly ; it is denominated by astronomers, a
transit of Mercury over the sun's disc, the planet
then appearing like a black spot on the face of the
sun. The last transit of Mercury happened in the

year

-Lesson iv.] .MKHOURY. 19

year 1802 : other transits will happen on the 12th
of November in the present year 1815 ; Novem-
ber 5th, 1822; May 5th, 1832; November 7th,
1835; May 8th, 1845; May 9th, 1S-18; No-
vember 12th, 1861 ; November 5th, 1868 ; May
6th, 1878; November 8th, 1881; May 10th,
1891; and November 10th, 1894. These are all
which wjfl occur hi the course of the present ceil',
tury.

LESSON

LESSON V.

ON VENUS.

»

Fair Venus next fulfils her larger round,
With softer beams, and milder glory crown'd ;
Friend to mankind, she glitters from afar,
Now the bright evening, now the morning star.

BAKER.

VENUS, the second planet from the sun, is
the next which comes under our consideration :
the character by which she is denoted in astro-
nomical performances is ? , which is the same as
that which the chemists make use of to denote
copper.

The mean distance of this planet from the sun
is about 69 millions of miles, and her magnitude
is nearly the same as the earth's, her diameter be-
ing something more than 7?900 miles. Astrono-
mers have discovered mountains on her surface ;
and some dark moveable spots, which have been
observed on her disc, give us great reason to sup-
pose she has an atmosphere. Her periodical course
round the sun is completed in less than 225 days.
The time of a complete rotation on her axis was by
Bianchini assigned to be 24 days and 6 hours :
but Cassi?ii, with a much stronger appearance of
probability, says the rotation is performed in about

23

Lesson v.] VENUS. 2JL

23 hours ; and this assertion is supported by some
late observations accurately made by Shroeter,
from which he has determined the time of one ro-
tation to be nearly 24 hours. Delamlre assigns it
at 24 hours 5| minutes.

Venus when viewed through a telescope, is
rarely seen to shine with a full face ; but has phases
changing in like manner with the moon : being
now gibbous, now horned ; and her illumined
part is constantly toward the sun. To the naked
eye this planet is easily distinguishable, on ac-
count ot her brightness and whiteness, which ex-
ceeds that of any other planet ; nay, her lustre
is so considerable, that when she is about 40 de-
grees removed from the sun, it is hardly equalled
by that of the moon, which is frequently a dull
light when compared with the vigour and bright-
ness of the beams of the planet. In this state she
has been often mistaken for a comet, and is fre-
quently seen in the day time when the sun shines :
a phenomenon which is taken notice of by some
of our philosophical poets.

No stars besides their radiance can display
In Phoebus' presence, the dread lord of day :
Ev'n Cynthia's self, though regent of the night,
Is quite obscur'd by his emergent light :
But Venus only, as if more divine,
With Phoebus dares in partnership to shine."

This planet is a morning star, when she appears
westward of the sun, for she then rises before
himj at these times she is among poets called

Phosphorus

22 VENUS. [Lesson v.

Phosphorus or Lucifer; but when eastward of
the sun, she shines in the evening after he sets,
and then is called popularly the evening star ; but
poets then give her the name Hesperus or Vesper.
She retains each of these names in its turn about
290 days.

Venus, as well as Mercury, is sometimes seen
to transit the sun's disc, in form of a dark round
spot. These transits of Venus happen but seldom.
One was seen in England iir 1639 ; and two in
the last century, viz. the one in 1761, and the
other in 1/69: there will not happen another
until December gth, 1874; and after that, only
one more, namely, on December 7th, 1882, before
the close of the present century.

None of the wandering stars are more cele-
brated and admired among the ancients, than the
one we are now reflecting upon : they had a pro-
digious veneration for her, making her their fa-
vourite goddess, paying her adoration, and all that
Deity could claim ; they even thought that her
power supplied earth, air, and sea, and that clouds
and tempests disappeared at her presence. But
those who direct their contemplations into a
proper channel will strip the planet of these ima-
ginary honours, and place them where they are
really due : we must consider her in all her va-
ried and attendant beauties, as a part, a small
part only, of the divine workmanship of HIM
" who covers himself with light, as with a gar-
*' nient, and has stretched out the heavens like a
« curtain.'* By thus examining with attention

the

Lesson v.J VENUS, 23

the separate parts of his wonderful performances,
we shall reflect with greater pleasure on the whole,
and be induced to exclaim,

These are thy glorious works, Parent of Good,

Almighty ; thine this universal frame,

Thus woaderous fair ! THYSELF how vvond'rous then !

MILTON.

LESSON

LESSON vi.

ON THE EARTH.

More distant still our earth comes rolling on,
And forms a wider circle round the sun ;
With her the moon, companion ever dear !
Her course attending through the shining year.

BAKER.

IN the earliest ages of the world the generality
of mankind entertained very strange notions con-
cerning the form and dimensions of the earth we
inhabit : and even in the present enlightened age
it is not unusual to meet with persons whose ideas
in this respect are very far from the truth. Those
who have not been in the habit of considering
this subject in an astronomical point of view, look
upon the earth as a very extensive plane, here and
there interspersed with hills and vales ; they have
also a confused notion of its being fixed firmly
upon something ; but upon what, or in what man-
ner, it is impossible for them to tell.

But I would wish you, my young friends, to re-
flect upon the subject in a more correct manner.
To you 1 must therefore observe, that the earth is
in form nearly globular, and partakes of two con-
stant motions; the one about its axis, and the other
through its orbit round the sun, like the other
planets. To this perhaps some of you may ob-
ject,

Lessonvi.] THE EARTH. 23

ject, and you may advance several reasons for
the objection, the principal of which will be like
the following: — l.'It is repugnant to our senses,
which represent the earth to be flat and immove-
able ', and 2. It is contrary to the words of Scrip-
ture.

The first of these reasons may be obviated with
ease, if the subject be considered with a proper
attention. Thus, the roundness of the Earth is con-
firmed by recollecting that it has been frequently
circumnavigated : that it is round is also proved
by considering that its shadow, as projected upon
the Moon in a lunar eclipse, always appears nearly
circular, which would not happen if the Earth
were not nearly spherical j — but the most mani-
fest proof is derived from the considerations di-
rectly following. If we stand upon the sea shore
and notice a ship sailing from us, we shall first lose
sight of the hull or body of the vessel, then of
the lower pajts of the masts and rigging, and as
she goes farther off, the upper parts of the masts
disappear : so again, when a ship comes towards
port, the steeples and highest buildings are first seen
by the sailors ; as the vessel comes nearer, they per-
ceive the houses and lower buildings ; and pre-
sently after the surface of the ground "appears.
Thus it is obvious that the earth is nearly spheri-
cal : and the diversifications of its surface with
mountains and valleys have no sensible effect in
destroying its sphericity; for the greatest hills,
when compared with its magnitude, bear no greater
proportion to the whole, than the little protu-
c berances

3<> THE EAKTH. [LeSSOH VI.

— - — i—f- — • .

beranccs on the coat of an orange to the bulk
thereof.

The argument alleged against the earth's mo-
tion, " that no such motion is evident to our
semises,-" 03 too weak and frivolous to deserve a
particular answer ; for it is well known that we
meet with deceptions in the sense of vision, in a
variety of instances where the objects viewed are
quite familiar to us ; and when the fallacy is dis-
covered, we have been surprised that we should
be so easily deceived.

As to the second reason before advanced, those
who oppose the astronomical principles concern-
ing the shape and motion of the Earth, because
they think them contrary to Revelation, would
do well to consider for what purpose the holy
Scriptures were written. Were they written as a
measure of faith, or as a rule to regulate our phi-
losophical opinions ? Gassendus does not give a
direct answer to the question ; but he has made
some very pertinent observations on the subject,
with which I shall here present you. " There are,"
says he, " two sacred volumes ; the one written,
" called the Bible, — the other Nature, or the
" World; GOD having manifested himself by two
" lights, the one of revelation, and the other of
"demonstration: accordingly the interpreters of
*' the former are divines, of the latter mathemati-
** cians. As to matters of natural knowledge,
*' the mathematicians are to be consulted, — and
" as to objects of faith, the prophets j the for-
«• aaer being no less interpreters, or apostles, from

" God

Lesson vu] THE EARTH. 27

" God to men than the latter. And as the ma-
" thematician would be judged to wander out of
" his province, if he should pretend to controvert,
" or set aside any article of faith from principles
" of geometry ; so it must be granted, the divines
ft are no less out of their limits, when they ven-
" lure to pronounce on a point of natural know-
*' ledge, beyond the reach of any ftot versed in
" geometry and optics, merely from holy Scrip-
" ture, which does not pretend to teach any thing
" of the matter."

I shall now proceed to exhibit to you the Earth
in an astronomical point of view; for I am con-
vinced, that the more attentively you consider it in
this light, the more willingly you will throw aside
the common prejudices, and place the true result
of philosophical reasoning in their stead.

The earth, considered as an element, after the
manner of Aristotle, is called Terra: but amongst
astronomers it has obtained the name Tellus, and
is denoted by the character ® ; it is the third pla-
net from the Sun, its mean distance from him
being 95 millions of miles; and its diameter is
found to be 7970 miles*. It is nearly 365| days in
completing a revolution through its orbit,
is the length of our year : and a complete rof
upon its axis is performed in the compass of a:na-

* Strictly speaking, the Earth, and indeed all toe planets
are spheroids formed by the rotation of ellipses of small
ellrpticity upon their minor axes ; but their deviation from
the spherical form is too minute to need any particular spe-
cification in a populai work like this.

"e 2 tural

28 THE EARTH. \LesSOH VI.

tural day, or 24 hours. From mathematical prin-
ciples it has been demonstrated that the length
of the day is somewhat different at different parts
of the year, but the difference is very inconsider-
able ; one day when the Sun is in the equinoctial
being shorter by 40 seconds than when he is in
the tropics. There is also another motion of the
Earth, which occasions the precession of the equi-
noxes; but it is of too abstruse a nature to be
explained to you in a satisfactory manner, until
you have gained a better acquaintance with astro-
nomy.

Here let us pause, and contemplate with humi-
lity, mingled with satisfaction, the abundant good-
ness of HIM " who hangeth the earth upon
if nothing," to us his creatures. He compels the
huge mass of inert matter on which we dwell, to
travel with wonderful regularity through the abyss
of space ; and in its progress the various parts
thereof are, by means of the diurnal rotation,
made to feel the. effects of the invigorating foun-
tain of light and heat. Were it not for this we
should sensibly feel the want of the returning sea-
Sons : no more should we see the valleys standing
thick with com ; nor should we behold the beau-
tiful verdure of the fertile meadow ; — no more
would the trees spread forth their foliage, nor
would the plants be ornamented with flowers. Or
as it is expressed in the lang|tege of inspiration,
— " No longer would the fig-tree blossom, nor
" fruit be in the vine : the labour of the olive
" would fail, and the fields could yield no meat :

"the

Lesson v*.] THE EARTH.

" the flocks must be cut off from the fold, and
" there would be no herd in the stalls/'

Consider this, ye perverse mortals! who argue
against conviction : consider, and tell us, if the
above gloomy picture would not be realized, were
the chance, which you so blindly extol, to preside
over us. But thanks to the beneficence of the all-
wise PROTECTOR of erring men, the evils which
would be brought upon us under the dominion of
chance, are averted : directed by an ALMIGHTY
command, the earth is carried gradually along^
and its motions are regulated in such a manner
as are most conducive to the general design :
the varied seasons of the year and the vicissi-
tudes of day and night follow each other in pleas-
ing gradations : the whole move on with astonish-
ing harmony; and through every part of their pro-
gress, the omnipotent Conductor is administering
to our wants, and bestowing upon us additional
blessings. " Oh ! that men would praise the Lord
" for his goodness, and for his wonderful works
" to the children of men * 1"

The

* It has been customary, when speaking of the benefits we
enjoy, to mention the convenient situation of the earth in the
system, with respect to light and heat : and in particular, with
regard to heat, it has been said that were we nearer the sun,
the earth would be burnt ; and were it farther off, we should
be frozen. This method of reasoning might be applied with
propiiety, when it was thought that the sun was a globe of
fire ; but as modern discoveries have led philosophers to dis-
pute the truth of such an opinion, it was thought better to
omit the argument here hinted at. However, I have in some
parts of these Lessous spoken of the dcgreesof light and heat,
C3 m

THE EARTH. [Lesson VI.

The Earth is attended with a satellite, which
adds greatly to our comforts and greatly to our
pleasures : I dare say you will wish to be ac-
quainted with its nature and size, when I tell you
that this satellite is no other than the Moon, which
with a

— - — pleasing light
Shadowy sets off the face of things. MILTO.V.

But as this heavenly body is of such importance
as to deserve a separate description, I shall gratify
your curiosity in a future Lesson.

iu a manner conformable to the most generally received opi-
nion : I have also, in those places where I have spoken of
the heat produced by the action of the Sun's rays, generally
called it the solar heat; as it would not be right to alter
the mode of expression most commonly used, until the
premises upon which such alteration is grounded, are entirely
acceded to.

LESSON

LESSON VII.

ON MARS,

In larger circuit rolls the orb ot" Mars,
Guiltless of stern debate, and wasteful wars,
As some have erring taught: he journeys on,
ImpelPd and nourish'd by the attractive sun ;
Like us, his seasons and his day he owes
To the vast bounty which from Phoebus flows .

Bnowx.

1 HE next planet which falls under our consi-
deration, is called by the same name as Mars, the
heathen god of war ; and very probably, because
he appears with a ruddy fiery countenance : among
astronomers he is characterised by this mark <?,
which seems to be a rude sketch of a man holding
a spear protended. Mars is the first of the four
superior planet.s, his orbit being immediately
above that of the earth : his mean distance from
the sun is about 152 of those parts, of which the
mean distance of the earth from that luminary is
100: hence his real distance is about 144 millions
of miles. He performs his revolution round his
orbit in about 687 of our days, or 66/| of his own
days, which is the length of his year. The light
and heat at this planet (calculating after the man-
ner described in the fourth Le'sson) are in propor-
c 4 tloa

32 MARS. [Lesson vn.

tion to the light arid heat at the earth, nearly as
43 to 100. His diameter or axis is nearly 4200
miles, from hence it may be shewn that his bulk
is 7-24ths of the Earth's. Dr. Hooke, in the year
1665, observed several spots in Mars : observations
on these spots and their motion, by the noted
astronomers Cassini and Herschel, have at length
determined the rotation of this planet on his axis
to be performed in 24 hours f very nearly, which
is the length of his day.

Mars, when observed through a telescope is seen
•to increase and decrease like the Moon, with this
exception that he is never cornicular, or horned :
from this we may infer that he shines not by his
own light, and that his orbit includes that of the
Earth.

This planet when viewed by the unassisted eye,
appears smaller than Venus, and redder ; having
a ruddy troubled colour : whether this arises from
the planet being of such a nature as to reflect the
red rays of light best, or from a thick atmosphere
attending it, is rather uncertain. But be this as
it will, it appears pretty manifest that his sanguine
complexion has obtained him a post of eminence
among the pagan deities.

Virgil, and some other of the ancient poets, give
us lively descriptions of him : they represent him
as riding in a high chariot drawn by two horses,
Fear and Terror; and, that the god may sit at
his ease, his sister Bellona is employed in hold-
ing the reins and driving. However, though
earthly poets have honoured him with these at-
tendants,

Lesson vu.] MARS. 33

tendants, it does nor appear likely that he has any
in the heavens : for no satellites of his have yet
been discovered ; though he is the only one of the
superior planets that travels through his annual
round without attendance.

c 3 LESSON

LESSON VIIT.

ON JUPITER.

Next Jove, prodigious planet of the skies !

His orb presents, of huge amazing size,

In bulk none equals his enormous mass :

The whole joint system his contents surpass. BROWN,

1 HUS sang the poet: his assertion was strictly
true, when the general opinion was that there were
only six primary planets ; but as there has a se-
venth lately been discovered, and that a large one,
there now remains some doubt: however, as the
diameters of each of the planets are given in these
Lessons, my young readers may find if Mr. B — 's
assertion will now hold good, when they have lei-
sure to perform the necessary operations.

This planet has the sa.ne name as the grand
heathen deity, viz. Jupiter, the character by which
he is denoted is It, to represent the thunderbolts,
as some people suppose ; this mark is the same as
that by which the chemists denote tin.

Jupiter is situated between Mars and Saturn
and is the fifth primary planet, reckoning from the
Sun : his mean distance from the Sun is 52 of those
parts, of which the Earth's distance is 10: hence
his real distance is about 490 millions of miles.
His annual revolution about the Sun is performed

in

Lesson vni.] -JUPITER. 35

in about 4332 days and }, being nearly 12 of our
years ; moving in his orbit at the rate of more than
' 25 thousand miles per hour. The light and heat
received from the sun at Jupiler, are in propor-
tion to those received at the earth, as 37 to 1000 :
hence, it is a very providential circumstance that
he is attended by satellites ; otherwise his inhabi-
tants (I shall give reasons for supposing, he ha»
inhabitants, in another place) would be in a very
dreary situation.

Jupiter's diameter or axis is. more than 10 times
that of the earth, and therefore his magnitude
more than 1000 times the earth's : his diameter in
English miles is 89,170; he performs his diurnal
rotation on his axis in the short interval of Q hours
and 56 minutes, by which mean his equatoreal
parts are carried round with about 25 times the
velocity of the like parts of our Eartli ; being car-
ried at the amazing rate of 26 thousand miles per
hour. This quick succession of days will' also be
viewed by the attentive philosopher as another in-
stance of Divine wisdom : for, as the poei observes,

— In ample compass- Jotv conducts his sphere,

And later finishes his tedious year;

Yet swiftly on hi« a*Ie turn'tl regains,

The frequent aid of day to warm his plains. Bnowv.

But how will the hearts of all religious youths-
glow with admiration, when they are informed*
that the axis of Jupiter is' so nearly perpendicular
to his orbit, that he has no Sensible change of
seasons ! can this be the work of chance ? ho\v

wisely

36 JUPITER. [Lesson viu.

wisely ordered ! for if the axis of this planet were
inclined any considerable number of degrees, so
many degrees round each pole would be almost six
years together in darkness. And as each degree
of a great circle on this planet, contains more than
700 miles; it is natural to conceive, that vast
tracts of land would be rendered uninhabitable, by
any considerable inclination of his axis.

Jupiter, when viewed through a telescope, is •
found to be surrounded by faint substances called
zones or belts. These belts are generally parallel
to its equator, which is very nearly parallel to the
ecliptic : they are subject to great variations, both
in respect to their number and figure: sometimes
eight have been seen at once, and sometimes only
one; sometimes they continue for three months
without any variation, and sometimes a new belt
has been formed in less than two hours. From
their being subject to such changes, it is very pro-
bable that they do not adhere to the body of Jupi-
ter, but exist in his atmosphere. Dr. Smith in his
Optics has given a curious, account of these bells;
and the greater part of the writers on astronomy
have presented descriptions of them.

This planet, when viewed by the unassisted eye,
is remarkable for its pure white brightness; indeed
it is the brightest of all the planets, except some-
times Venus. This may appear singular when we
remember his great distance from the sun ; but
when we also consider his enormous bulk, the
wonder will cease.

In the year 1610, Galileo discovered that Ju-
piter

Lesson via.] JUPITER. 37

piter had four satellites, which he called Medicean
Stars, m honour of the family of the Medici, his
patrons. This was a discovery very important in
its consequences, as it afforded a method of deter-
mining the longitude of places on the earth (by
means of the eclipses of these satellites) with
greater facility and accuracy than by any other
method yet known. These eclipses also enabled
M. Roemer to discover and ascertain the progres-
sive motion of light; and hence Dr. Bradley was
enabled to explain an apparent motion in the fixed
stars, which could not otherwise have been ac-
counted for, and which philosophers characterize
by the term aberration.

LESSON

LESSON IX.

ON SATURN,.

Still further off, scarce warm'd by Phoebus' ray.
Through his wide orbit, Saturn wheels away.
How great the change, could we be wafted there,
How slow the seasons ! and how long the year !

% BAKER..

1 HE sixth planet has obtained the same name
as Saturn, the supposed father of the heathen godsr
amongst astronomers he is represented by the cha-
racter T?, to imitate an old man supporting him-
self upon a staff; the same character among the
chemists denotes lead \ and indeed there is some
affinity belvveen the colour of that metal, and the
light, dusky colour of the planet.

Saturn's mean distance from the Sun is about
9} times farther than the mean distance of the
Earth from that luminary ; being nearly 900 mil-
lions of miles : and of course the light and heat he
derives from the Sun are about ninety times less
than at the Earth.

This planet performs his annual revolution in
about 1O,75U of our days 5 being not far short
of thirty years. His diameter or axis is more
than 7 [) ,000 miles, and his magnitude is almost
1000 times that of the earth As it is agreeable to

the

Lesson ix.] SATURN. 39

the nature of a planet to revolve on its axis, Cas-
sitii and others supposed that Saturn had a rotation
of this kind, the time of which they endeavoured
to determine, but without success. This point
has, however, been at length ascertained by the
observations of Dr. Herschel, from which he has
found that Saturn revolves about his axis in ten
hours and sixteen minutes.

Saturn has seven satellites or moons, attendant
upon him; but the most surprizing thing observed
about this planet is a kind of ring which encom-
passes his body: astronomers have noticed it very
attentively, and some of .them have determined it
to be about twenty-one thousand miles distant
from Saturn, and to be nearly thirty thousand miles
in breadth. After paying a very minute attention
to this ring, Dr. Herschel thinks himself authorised
to say, that it is divided into two concentric
rings, situated in one plane, which is not much
inclined to the equator of the planet. M. Laplace
extends this conjecture, and affirms that there
are several concentric rings, adjusted nearly to one
plane.

There are several conjectures with regard to the
uses of this ring; and amongst them, the one
which lends most to evince the wisdom of the
Almighty I shall give you in the words of a poet,
who has evinced an extensive acquaintance with
philosophy, united with that rational devotion
which is generally the result of an attentive con-
templation of the works of nature.

Muse!

40 SATURN. [Lesson ix.

Muse ! raise thy voice, mysterious truth to sing,

How o'er the copious orb a lucid ring,

Opake and broad is seen its arch to spread

Hound the big globe at stated periods l«d ;

Perhaps (its use unknown) with gathered heat

To aid the regions of that gilded seat,

The want of nearer Phoebus to supply,

And warm with reflex beams his summer sky j

Else might the high-placed, world, exposed to frost,

Lie waste, in one eternal winter lost. BROWN.

Some persons, who object to this, observe, that
the inhabitants of Saturn have undoubtedly consti-
tutions suited to the globe they inhabit : but these
objectors may be reminded, that the nature of Sa-
turn's inhabitants may be so tempered as continu-
ally to require the aid of this ring to keep them
sufficiently warm ; it may also serve to remind
them in what a deplorable state they would be,
were it not for the continual superintendance and
presence of the adorable Creator.

LESSON X.

ON GEORGIUM SIDVS, OR HERSCHEL.

Muthesis with uplifted eye,

Tracing the wonders of the sky,

Now shews the mariner to guide

His vessel through the Irackless tide}

Now gazing on the blue profound,

Where whirl the stars in endless round,

Beholds new constellations rise,

New systems crown the argent skies ;

Views with new lustre round the glowing pole,

Wide his stupendous orb the Georgian planet roll.

PYE.

1-T was for ages supposed that there were only
six planets in the solar system: and the ingenious
Kepler, a very eminent astronomer, was so firmly
persuaded there were no more, that he confesses,
one of the three things which he anxiously sought
to find the reason of, was, — why the planets were
six in number ?

It is to the indefatigable application of an astro-
nomer, who has long resided in this country (and
whom I have had frequent occasion to mention),
Dr. William Hersshel, that we are indebted,
amongst other; brilliant discoveries, for that of a
planet, which is the fourth of the superior ones,
and the farthest from the sun of any yet disco-
vered.

42 GEORGIUM SIDUS. [Lesson X-

vered. This new-found planet was discovered on
the 13th of March, 1801, and is known by two
titles : the one of Gcorg'mm Sidus, was bestowed
upon it by the discoverer, in honour of our present
Sovereign. The other of Herschel was long given
it by the chief astronomers of all nations, as a
proper testimony of respect to the assiduity and
abilities of the person who discovered it. The
name by which it is now designated by continen-
tal astronomers, is Uranus.

Georgium Sidus, or Herschel, is characterized
by the mark $ , being the initial of the discoverer's
name, with a cross bar, intersecting the horizontal
bar of the H, to represent a cross, and thereby to
denote that the discovery of this planet was after
the birth of Christ. Herschel's mean distance
from the sun is about nineteen times that of the
earth, viz. about 1800 millions of miles ; he per-
forms a revolution through his orbit in 30,68"9
days very nearly, being almost ninety of our
years ; the light and heat he derives from the sun
are about the 362d part of those at the earth, cal-
culating on the hypothesis before explained. This
planet appears of a bluish white colour, and its
brilliancy is between that of Venus and the
Moon. With a telescope that magnifies about
300 times, he appears to have a very well defined
visible disc. In a very fine clear night, when the
moon is absent, he may be perceived by a good
eye without a telescope.

The time of this planet's diurnal rotation is not
yet discovered : his axis is found to be 35,865

English

Lesson x.] GEORGIUM sinus 43

English miles, and his solidity 24155283745628
cubic miles. How amazing must be the power
that could hurl this and the other planets with such
rapidity through the liquid ether ! but let your ad-
miration not yet cease, for " these are only part
" of his ways." Our contemplations on the starry
canopy are not yet completed j —

Night opes the nobkst scenes, and sheds an awe,
Which gives those venerable scenes full weight,
And deep reception in the entender'd heart. YOUNG.

Georgium Sidus has six satellites already disco-
vered, which are probably of very great utility to
his inhabitants. For it is very reasonable to con-
clude, that there is scarcely any part of this large
planet, but what is constantly enlightened by one
or other of these moous*.

* That the system which is described in the first eleven
Lessons, claims a preference to all others, will, I think, ap-
pear obvious from the following considerations.

I. The planet Venus moves round the Sun, and not round
the Earth. For through a telescope, it sometimes appears
with a bright and round face like the full Moon, and some-
times horned like the new Moon ; and when it appears full,
it is seen near the body of the Sun, as well as when it appears
horned : whic«h could not be, did it move round the Earth
alone, or round neither the Sun nor the Earth. For, if it
moved round the Earth alone, or round both the Sun and
the Earth, it must be seen sometimes in that part of the
Heavens which is opposite to the Sun. If it moved round
neither the Sun nor the Earth, it could not appear both
horned and full when it is seen near the body of the
Sun: it remains, therefore, that it revolves about the Sun,
and not about the Earth. Hence its orbit includes the
Sun, and is within the orbit of the Earth.

II. Applying

44 GEORGIUM siDUs. [Lesson x.

II. Applying a similar mode of reasoning, we may conclude^
that Mercury moves round the Sun in a less orbit than that of
I'tnus; because it puts on the same phases with Venus, and
is never seen so far from the sun as that planet is.

III. The orbit of Mars includes both the Earth and the
Sun ; and the Earth is not in the centre thereof. For this
planet is capable of appearing opposite to the Sun, or in any
other situation with respect to that luminary ; which could
not be, unless it moved round the Earth: and it always appears
full, or nearly so ; which it could not do if it ever came be-
tween the Sun and the Earth ; hence, it moves also round the
Sun. And farther, when Mars is in the opposite part of the
Heavens to the Sun, it appears about five times larger than
when it is near the Sun ; which shews that it is much nearer
the Earth in one situation than in the other : the Earth, there-
fore, is not in the centre of its motion.

IV. The like being observable of Jupiter, Saturn, and Her-
schel, (though, on account of their greater distance from the
Sun and us, the diversity in their apparent magnitudes in dif-
ferent parts of their orbits, is not so great as in Mars), it is
reasonable to conclude, that these planets also have both the
Earth and the Sun within their orbits, and that the Sun, rather
than the Earth, is in the centre of the same.

V. Since then, the Earth is placed within the orbits of Mars
Jupiter, Saturn, and Hersche I, these planets cannot appear to us
to stand still, or to go backward, as observations shew they
sometimes do appear, unless the earth moves : and since, as
has been shewn, Venus and Mercury revolve about the Sun,
and not about the Earth ; since also, the Earth is placed be-
tween the orbits of Mars and Venus, and the periodical time
of the Earth, if it does move, is, in point of magnitude, be-
tween the periodical times of those two, it seems quite rea-
sonable to suppose that the Earth revolves about the Sun in
the same manner as the .planets do : it is therefore reckoned
in the number of them.

VI. But what very much confirms this conclusion is, that
astonishing harmony,which,upon this supposition, runs through
the whole solar system: for it is known that the motions of all
the planets, both primary and secondary, are in conformity

to

Lesson*..] GKORGIUM SIDUS.

43

to one and the same law ; which is, that the squares of tht
periodical times of the primary planets, are proportional to tlie
cubes of their mean distances from the Sun ; and that t he squares
of the periodical limes of the secondaries of any primary, are to each
other, as the cubes of their distances from their primary. By no other
hypothesis which has been yet invented, can the motions of
the heavenly bodies be accounted for with such beauty and
simplicity, as by this ; nor is there any other system which
exhibits the fabric of the universe, in that regularity and
harmony, which is worthy the DIVINE ARCHITECT.

It may not be improper to mention in this note, that the
planets differ in density as well as in magnitude, a circum-
stance which will make the ratio of their absolute masses
different from that of their apparent bulk or volume : assum-
ing that of the Earth as unity, the others will be expressed
in integers and decimals in the following table.

Mercury • <
Venus
The Earth
Mars

Jupiter •• •
Saturn
Uranus •••

Sun

Moon • • • •

Volumes.

0.05G5.

0.8828-

1.0000-

0.1380-

1280.9 •••

974.78 ••

S1.2G".

•1395324.

0.2035

Masses.

0.1627

0.9248

1.0000

0.1294

•••308.94

93.271

1.6904

•329630. "
..-.'•0.0801

LESSON

LESSON XI.

ON THE MOON.

He smooth'd the rough-cast Moon's imperfect mold,

And comb'd her beamy locks with sacred gold :

Be thou, said he, Queen of the mournful night:

And as he spoke, she rose oer'clad with light,

With thousand stars attending OH her train. COWLEY.

AMID the beauteous scenes which deck the
face of nature, there are very few that have a
more pleasing effect, than those which are viewed
by the light of the Moon. Several of the poets
have given noble descriptions of the delightful
appearance and effect of a moon-light evening;
one of which, by the ancient poet Homer , I shall
here insert.

'. So when the Moon, refulgent lamp of night,

O'er heaven's clear azure spreads her sacred light,
AVhen not a breath disturbs the' deep serene,
And not a cloud o'ercasts the solemn scene j
Around her throne the vivid planets rpll,
And stars unnnmber'd gild the glowing pole.
O'er the dark trees a yellower verdure shed,
And tip with silver every mountain's head :

Then

Lesson xi.] THE MOON. 47

Then shine the vales ; the rocks in prospect rise;
A flood of glory bursts from all the skies;
The conscious swains, rejoicing in the sight,
Eye the blue vault, and bless the useful light.

POPE'S HOMER.

. Mr. Pope observes that these lines exhibit, in
the original, the finest night-piece in poetry: the
reader may judge that in the translation they do
not appear disadvantageously.

This beautiful luminary, whose gentle beams
render the summer evenings more agreeable, and
the winter nights less unpleasant, is a secondary
planet ; being a satellite to the Earth we inhabit,
about which she revolves in an elliptical orbit from
one new Moon to another in twenty-nine days
twelve hours forty-four minutes very nearly. Her
mean distance from the earth is 240,000 miles,
and she moves in her orbit at the rate of about
229O miles in an hour: her diameter is about
2180 miles; and her rotation on her axis is per-
formed in the same time as her revolution through
her orbit ; hence it appears that her day and
night taken together are just as long as our lunar
month.

You have without doubt, very frequently taken
notice of the various changes the Moon undergoes,
and you very probably are anxious to see them
accounted for : I shall here endeavour to satisfy
your curiosity. The Moon is a dark, or opake
body, shining principally with the light she re-
ceives from the Sun ; hence, only that half which
is turned towards him at any time can be illumi-
nated;

48 THB MOON. [Lesson XI.

nated, the opposite half remaining dark : then, as
the face of the Moon visible on the Earth, is that
part of her body turned towards us, we shall, ac-
cording to the different positions of the Moon,
with regard to the Sun and Earth, perceive dif-
ferent degrees of illumination. Hence the Moon
appears sometimes increasing sometimes waning;
sometimes horned, then half round; sometimes
gibbous, then full and round. At the time of
new Moon, the Moon is between the Earth and
Sun ; and at the time of full Moon, the Earth is
between the Moon and Sun.

This may be familiarly illustrated by means of
an ivory ball, which, being held before a candle in
various positions, will present a greater or less
portion of its illumined hemisphere to the view of
the observer. The Ear^h presents the same
phases to a spectator on the Moon, as she does to
us, only in a contrary order, the one being full
when the other changes, &c. and in a greater de-
gree, the Earth giving thirteen times as much
light as the Moon.

The face of the Moon, as you may have often
observed, appears to have shades of different
colours : when viewed through a telescope these
shades are found to be the diversifications of
hills and valleys; the same are also shewn by the
border of the Moon appearing indented or jag-
ged, especially about the edge of the illumined
part when the Moon is either horned or gibbous.
Dr. Herschel has measured the heights of several
of the lunar prominences with greater precision

than

Lessen XL] THK MOON. 49

than any of the former astronomers : he has de-
termined that very few of them exceed half a mile
iu their perpendicular elevation. He has also ob-
served several volcanoes on the Moon, emitting
fire, as those on the Earth do : and indeed there
seems no reason to doubt, that, to complete the
similarity between her and the Earth, she has also
seas, rivers, and an atmosphere.

Christianas Huygens, in his excellent Conjec-
tures concerning the Planetary World, says, " Tis
" certain that the Moon has no atmosphere sur-
" rounding her." He then proceeds to give his
reasons for such an assertion. But he has in this
instance fallen far short of his usual sagacity j for
the existence of a lunar atmosphere has been fre-
quently proved, by later writers, from the most
manifest considerations.

If the Moon shone by a light of her own, we
should feel a sensible warmth from her rays : but
it is a light reflected from the Sun with which she
shines, and is so exceedingly weak and languid,
that the most powerful burning glass will not collect
enough to make any sensible degree of heat. This
has been accounted for j and those who have gone
through the computation assert, that the light of
the full Moon is ninety thousand times less than
day-light. How wonderfully is infinite goodness
and wisdom displayed in this instance ! For if the
Moon's reflected rays produced heat, as the air of
the night would then have a continual warmth, it
is obvious that it would be prejudicial to the health
of mankind.

» The

50 THE MOON. [Lesson Xf.

The effect of moonlight in diversifying the
scenery of nature, and the changes which that
luminary herself undergoes, have furnished the
poets with some of their most beautiful and touch-
ing images. The following describes, with great
felicity, the separation of the spirit from the body
of a pious young female : —

But she was waning to the tomb ;

The worm of death was in her bloom :

Yet as the mortal frame declin'd,

Strong through the ruins rose the mind •

As the dim Moon, when night ascends,

Slow in the east the darkness rends,

Through melting clouds, by gradual gleams,

Pours the mild splendour of her beams,

Then bursts in triumph o'er the pole,

Free as a disembodied soul!

Thus while the veil of flesh decay'd,

Her beauties brighten'd through the shade ;

Charms which her lowly heart conceal'd ;

In Nature's weakness were reveal'd !

And still the unrobing spirit cast

Diviner glories to the last ;

Dissolv'd its bonds, and clear'd its flight,

Emerging into perfect light. MONTGOMERY.

LESSON

LESSON XII.

ON COMETS.

At his command, affrighting human kind,
Comets drag on their blazing lengths behind;
Nor, as we think, do they at random rove,
But in determin'd times, through long ellipses move ;
And though sometimes they near approach the SUH,
Sometimes beyond our system's orbit run,
Throughout their race they act their Maker's will,
His power declare, his purposes fulfil. BAKER,

Hark! from the world's exploding centre driv'n,
With sounds that shook the firmament of heav'n,
Careers the fiery giant fast and far,
On bick'ring wheels and adamantine car :
From planet whirl'd, to planet more remote,
He visits realms beyond the reach of thought ;
But wheeling homeward when his course is run,
Curbs the red yoke, and mingles with the sun!

CAMPBELL.

kind of wandering bodies is known
by the name of Comets. These the common peo-
ple call blazing stars, because they generally' have
long tails blazing or streaming from them. As
these extraordinary bodies are but seldom seen,
they are by many persons thought portentous,
presaging some extraordinary event ; some look
upon them as bloody signs hung out by Divine re-
sentment over a guilty world: some read in their
appearance the fate of nations and the fall of
monarchies ; others imagine they foretel desolat-
ing plagues, famines, or wars. They must, how-
ever, be acquitted of all tendency of this kind.
D 2 Nor

5* COMETS. [Lesson xiz.

Nor indeed is there any occasion for apprehension
that they should at all injure the earth we inhabit.
The probability is some millions to one against a
cometary and a planetary body corning into con-
tact : and even the tail of a comet cannot come
near our atmosphere, unless the Comet be at its
inferior conjunction very nearly at the time when,
it is in a node j circumstances extremely unlikely
to happen together.

Among the various opinions which have been
entertained concerning the nature of Comets, that
of NRVVTON was, till Jatdy, most generally adopt-
ed. According to his hypothesis, Comets consist
of a very compact, durable, and solid substance,
capable of bearing most exceedingly great degrees
of heat and cold without dissolution : they are
of anopakenature,shining by reflection of the Sun's
light, as the planets do. They move in stated
periods in very long elliptical orbits, having the
Sun in one of their Foci j in one part of their or-
bits they approach extremely near to the Sun, and
in another part they are immensely distant from
him ; sometimes they come much nearer to the
Sun than Mercury's orbit, at other times they are
greaily farther from the Sun than Georgium Sidus.
Comets differ much in their magnitude, though
most of those which have been observed are con-
siderably less than the Moon ; but their dimensions
are not determined with accuracy ; neither are their
periods : — for as one person's life is seldom longer
than a Comet's period, and very frequently not so
long, there is but little probability of his again
seeing a Comet, when it returns near the Sun after

another

Lesson xn.] COMETS. 53

another revolution through its orbit; and, of course,
their periods are not precisely ascertained.

The tail of a Comet, which is generally its most
conspicuous part, is thought by NEWTON to be a
prodigious quantity of fume and vapours, flying
oft" from its body, as it becomes more and more
heated in its approach to the Sun. These tails
arc sometimes exceedingly long, some having been
computed to be 80 millions of miles in length :
that they are vapours was thought evident from
these considerations.; first, the fixed stars are often
seen through them ; secondly, they appear broader
on their upper part than near the head of the Co-
met; thirdly, the tails lie always towards those
parts which the Comets have just left ; and fourth-
ly, they seem most splendid and large immediately
after they return from the Sun; — all which is
agreeable to the nature of smoke and vapour.

The hypothesis of NEWTON, as above recited,
fcas been objected to by Dr. Hattey and Dr. Ha-
milton, who think that the tail of a Comet is
formed of matter which has not the power of re-
fracting and reflecting the rays of light; but that
it is a lucid, or self-shining substance: and from
its similarity to the aurora borealis, they think it
probable that it is produced by a similar cause, and
is properly an electrical phenomenon.

A more recently advanced opinion is that of Dr.
Herschel, who has affirmed, that, after a very dili-
gent examination, he could not perceive the least
appearance of any solid nucleus ; Comets seeming
to be mere collections of vapours condensed about
the centre of each. J3e farther supposed that the
D 3 orbits

54 COURTS. [Lesson xn.

orbits of Comets are not regular and determinate,
as they have been generally imagined to be, be-
cause, he says, they are liable to be changed con-
siderably by the perturbation of the planets. Per-
haps, the non-appearance of some Comets, which
•were predicted tx) appear in these last few years,
may serve to confirm this suggestion.

After all, it must be acknowledged, that the phi-
losophy of Comets is, at present, very imperfect.
The discoveries which have hitherto been made
Bowing to the long intervals which frequently pre-
cede the return of Comets, and their irregular mo-
tions), are not sufficiently important to afford any
thing decisive. The prediction of Seneca remains
vet to be accomplished, wherein he says, " The
" time will come when the nature of Comets, and
u their magnitudes, will be demonstrated, and the
" routes they take, so different from the planets,
»f explained. Posterily will then wonder, that the
ic preceding ages should be ignorant of matters
" so plain and easy to be known *."

* M. LAMBERT, in his Letters on Cosmogony, takes for
granted the principle that the universe ought to be as popu-
lous as possible, and contain us many moving bodies as it
o.in without confusion and disorder. "Hence," says he, "the
most perfect plan of our system will be that into which enters
the greatest number of orbits, all separated from one an-
other, and which in no point intersect each other. If, then,
we should be able to prove that the orbits of comets corre-
spond to this end better than those of the planets, the reason
of their superiority in point of number must be seen and ad-
mitted." This, in fact, he does prove, and thus shews that the
vf-ry elliptic orbits of Comets, instead of being irreconcilea.
Lie with the wisdom which is otherwise manifest in the works
of creation, are additional proofs that the highest possible
perfection obtains in the universe at large.

LESSON

LESSON XIII.

ON GRAVITY, WEIGHT, <$-c.

This problem let philosophers resolve,
What makes the globes from east to west revolve?
What is the strong impulsive cause declare,
That rolls tUe pond'rous orbs so swift in air.

BLACKMORE.

VY HILST you are reflecting upon tbfe planetary
bodies, and considering the regularity of their re-
turning periods, these inquiries will very naturally
be suggested to your mind. As a research of this
kind cannot be unpleasing, the present Lesson will
be appropriated to it. Sir Isaac Newton has left
us no room to doubt that the bodies in the solar
system are

All combin'd

And rul'd unerring, by that simple power
Which draws the stone projected to the ground.

THOMSON.

The sagacious Kepler had determined from ob-
servations, that the planetary motions agree with
this regular law, viz. The squares of their perio-
dical times are as the cubes of their mean distances
from the Sun or focus of their orbits; and this law
has been since demonstrated by Newton, from the
principles of attraction and projectile motion. If
we carry back our researches to the creation of the
D 4 worldj

56 GRAVITY, WEIGHT, &C. [LfSSOH XIII.

world, we might reason in a manner similar to the
following: In the beginning the G<<AND MOVF.R
imp;essed such a degree of motion upon these
bodies, as, if not controuled, would have whirled
them onward in straight lines, and to endless
lengihs, till they would have been lost to imagina-
tion in the abyss of space. But the gravitating
property (which acts in reciprocal proportion to
the square of its distance from the attractive cen-
tre), heinvr combined with the projectile force, de-
termined their courses to an elliptical form, and
obliged these bodies to perform their destined
rounds. Were euher of these causes to have its
action suspended, the harmony of these motions
would be disconcerted : were the projectile force
suspended, the planets would be drawn by the
attractive power till they fell upon the central
body : and if the gravitating force were sus-
pended, they would be rapidly hurled to an incon-
ceivable distance, and perhaps would be dissipated
into atoms.

How admirable, how extensive, and diversified
is the efficacy of the single principle — Gravity/
It is this which penetrates the minutest pores of
all bodies, and diffuses itself to the remotest limits
of the Mundane System : it is this which keeps the
planetary orbs, already impressed with motion,
equipoised upon their centres : it is this to which
we may attribute the pressure of the atmosphere :
it is this which causes the ocean to ebb and flow with
such wonderful regularity, and yet confines it within
proper bounds. These and other complicated ef-
fects

Lesson xm.J GRAVITY, WEIGHT, &c. 57

fects arise from one single cause. And what is
Gravity? We know there is such a power, and
we know how it acts; but that it is a primary qua-
lity essential to all bodies, is not universally ad-
mitted : those who inquire after the cause of Gra-
vity must be informed that the true cause is the
DEITY : for Gravity may not improperly be styled
the " Finger of GOD j the constant impression of
Divine power;" — in every other sense, the cause is
likely to continue to be unexplored by mortals.

But if the cause of Gravity have never yet been
discovered, shall Gravity itself for that reason be
called an occult quality, and rejected from philo-
sophy ? Those who draw such a conclusion should
take care lest they advance an absurdity, by which
the foundations of all philosophy may be over-
turned. For causes usually proceed in a continued
chain from compound to more simple ; and when
we have arrived at the most simple cause we can
proceed no farther. No mechanical explication
can be given of the most simple cause: for, if
there could, the cause would not yet be the most
simple. If these most simple causes, then, may
be called occult, and rejected ; for the same reason
we may reject those causes which immediately
depend upon them, and those also which depend
upon these last ; and so on until philosophy be
entirely divested of all causes whatever.

By the method of Analysis it is that we must

trace out the established laws of nature, or that

order in which instrumental causes are used in

producing natural effects. But, as we rise from

D 5 effects

'38 GRAVITY, WEIGHT, &C. [LesSOIl XIII.

effects to causes, the more general are those powers
which we discover. Effects apparently contra-
dictory are found to proceed from the same prin-
ciple. The ascent of light bodies, as well as the
descent of heavy ones, is the consequence of the
universal gravitation of matter. Cohesion, disso-
lution, and various phenomena in chemistry, are
derived from the attractions of minute particles at
very small distances. And, wherever we turn our
view, the whole course of nature evidently points
but to u>», that all the various appearances which
we behold flow from a few very general and subordi-
nate causes, which more immediately depend upon
the ascendant power of the INK SUPREME CAUSE,
the Author and Governor of the Universe ! whose
existence and influence are manifested by every
the most obvious effect ; and of whose power, wis-
dom, and goodness we acquire higher and more
enlarged conceptions in proportion as we obtain
a more complete knowledge of his works.

The laws of nature being discovered, as above-
mentioned, by analysis, particular phenomena
are explained synthetically, by shewing their con-
formity to these laws. Thus, to shewthat the Moon
is retained in its orbit by the force of gravity, is
to shew the agreement between that force and the
force by which a stone, or any heavy body, lends
lo the centre of the earth : that the Moon is con-
tinually bent from the tangent of its orbit, in the
same manner as a body near the surface of the
•earth is turned from its rectilinear motion into a
curve : that both these motions are directed to the

same

GRAVITY, WEIGHT, &C. $9

same point, and agree in quantity : that, if the
Moon were to approach to ihe surface of the
E th, the force, by which it is retained in its or-
bit, would make it descend « ,waids .he centre of
the Earth, through ihe same space which a heavy
body, falling by its gravity, would descend through
in the same time : and that if a stone or a bullet
could be carried to the distance of the Moon, and
there projected with a sufficient velocity, it would
revolve round the Earth like a Moon, for the same
reason by which it is bent into a curve, when pro-
jected near the surface of the earth. By pursuing
these methods Sir Isaac Newton demonstrated the
universal gravitation of matter ; and it is now
pretty generally allowed that the same principle of
gravity, by which we see all bodies tend towards
the centre of the Earth, is a general law of na-
ture, extended to all distances, and to every body
in the universe. Thus it is agreed, that the pri-
mary and secondary planets in our system, as also
the Sun, are mutually attracted by each other.
But since all attractions are mutual, it will follow,
that if one or more bodies revolve about another,
which is also attracted by them, that other body will
not be at rest ; but together with them will revolve
round the common centre of gravity of the whole
system. Hence, then, and from the proportions of
the quantities of matter of the Sun and the planets,
it is found that the common centre of gravity of •
{he solar system is never far removed from the body
of the Sun, and is generally within its surface.
Round this point the Sun itself is continually,

moved

6o GRAVITY, WEIGHT, &c. [Lesson xin.

moved in various directions, approaching or re-
ceding according to the different positions of the
planets.

Since, then, all bodies, terrestrial and celestial,
on which experiments or observations can be made,
arc found to gravitate towards each other, what
has been before said of the universal extension of
Gravity will be the more willingly acceded to j I
hope, therefore, I may now quit this part of the
subject, without giving any additional arguments
in support of the opinion.

Before I conclude this Lesson, I cannot avoid
adding a few words to explain the difference be-
tween Gravity, freight, and Heaviness ; which
appear to me the more necessary, because I am
aware that the notions commonly entertained are
not very correct.

In order to form an exact idea of the weight of
a body, it must be recollected, that Gravity im-
presses, or has a tendency to impress, on every
particle of bodies, in an instant, a certain velocity,
with which they would fall, if they were not sup-
ported ; and that, abstracting the influence of the
air, this velocity would be the same for each of
the particles of bodies, whatever be their substance.
This being observed, we must understand by the
weight of a body, the effort necessary to prevent
it from falling ; and, it is evident, that in order
to this, it is necessary to destroy the velocity which
gravity has impressed on every particle. This ef-
fort must, therefore, be equal to the sum of the velo-
cities of all the particles. Hence it may be naturally

con-

Lesson XIII.] GRAVITY, WEIGHT, Sec. 6l

concluded that bodies the most compact, and which
consequently contain a greater number of particles
in the same bulk, will weigh more than others; be-
cause the weight being the sum of the velocities
impressed on all the particles, that sum must be so
much the greater, as there are more material par-
ticles contained in the mass of the body.

From what is here said, I would observe with
M. de Condorcet, that we may see " the necessity
" of carefully distinguishing between the effect of
" Gravity, and that of Weight : the former is the
t( power of transmitting, or a tendency to trans-
" tnit, into every particle of matter a certain velo-
<c city which is absolutely independent on the
" number of material particles; and the second is
" the effort which must be exercised to prevent a
" given mass from obeying the law of Gravity.
*' Weight accordingly depends on the mass, lut
" Gravity has no dependence at all upon it."

Again, with respect to the difference between
Heaviness and Weight, taken in their literal sense,
heaviness is that quality in a body which we feel,
and distinguish by itself: weight is the measure
>nd degree of that quality which we cannot as-
certain but by comparison. We say absolutely,
and in an undetermined sense, that a thing is
heavy ; but relatively, and in a determined man-
ner, that it is of such a weight ; for example, of
two, three, or four pounds. A thousand circum-
stances prove the heaviness of the air, for instance;
but the mercury in the barometer determines its
exact weight*

LESSON

LESSON XIV.

ON ECLIPSES OF THE SUN AND MOON.

Give me the ways of wandering stars to know,
The depths of heav'n above and earth below ;
Teach me the various labours of the Moon,
And whence proceed th' eclipses of the Sun.

VIRG. GEORG. ir.

1 DOUBT not but that several of you, my young
friends, will heartily join in Virgil's petition above
cited : and though you, perhaps, may never have
either leisure or opportunity enough to acquire a
very great astronomical knowledge; yet I can as-
sure you it is no difficult mailer to attain such an
acquaintance with the science, as to understand
the reason of Eclipses of the Sun and Moon.

You will observe, then, that an Eclipse of the
Jfloon is a privation of the light of tht Moon, oc-
casioned by an interposition of the body of the
Earth (as she revolves in her orbit) directly be-
tween the Sun and Moon j by which mean, the
Sun's rays are so intercepted that they cannot
illuminate the Moon : then

- — The silver Moon is all o'er blood,

A settling crimson stains her beauteous face. LEE.

It is at the lime of full Moon that lunar eclipses

happen 5

Lesson xiv.] ECLIPSES. 63

happen ; because it is only then that the Earth is
between the Sun and Moon : neither do they hap-
pen every full Moon (as they would do if the
orbits of the Earth and Moon were coincident)
because of the obliquity of the Moon's path with
respect to the Earth's ; but only in such full Moons
as happen at the intersections of those two paths,
called the Moon's nodes; or at least on those full
Moons which happen but a little distance from
the nodes.

The chief circumstances in lunar eclipses, as
they are given by Dr. Hutlon in his Mathemati-
cal and Philosophical Dictionary, are as follow:
— 1. All lunar eclipses are universal, or visible in
all parts of the earth which have the Moon above
the horizon ; and are every where of the same
magnitude, with the Fame beginning and end. —
2. In all lunar eclipses, the eastern side is what
first immerges and emerges again; i.e. the left
side of the Moon as we look toward her from the
north ; for the proper motion of the Moon being
swifter than that of the Earth's shadow, the Moon
approaches it from the west, overtakes it and
passes through it with the Moon's east side fore-
most, leaving the shadow behind, or to the west-
ward.— 3, Total eclipses, and those of i he-longest
duration, happen in the very nodes of the eclip-
tic ; because the section of the Earth's shadow^
then falling on the Moon, is considerably larger
than her disc. There may, however, be total
eclipses within a small distance of the nodes ; but
their duration is the less as they are farther

from

64 ECLIPSE*. [Lesson xiv.

from them ; till they become only partial ones, and
at last not at all. — 4. The Moon, even in the
middle of an eclipse, has usually a faint appear-
ance of light, resembling tarnished copper; which
Gassendus, Ricciolus, and Kepler, attribute to the
light of the Sun, refracted by the Earth's atmos-
phere, and so transmitted thither. — Lastly, she
grows sensibly paler and dimmer before entering
into the real shadow; owing to a penumbra which
surrounds that shadow to some distance.

In addition to these circumstances, some astro-
nomers observe, and it is here added, that no
eclipse of the Moon can last above 5| hours, from'
the Moon's first touching the Earth's penumbra,
to its last leaving it : but an eclipse of the Moon,
by the Earth's shadow, perhaps never lasts above
3| hours; nor when total, above If hours.

An Eclipse oj the Sun is an occultation or
hiding of the Sun's body from our sight, occasion-
ed by an interposition of the Moon between the
Earth and Sun.

.• — Shorn of his beams, the Sun

In dim eclipse disastrous twilight sheds,

MILTON.

It is by several considered and called an Eclipse
of the Earth, since the light of the Sun is hid from
the Earth by the Moon, whose shadow involves a
part of the Earth. The manner of a solar eclipse
may be conceived by imagining a small part near
the vertex of the Moon's conical shadow, travel-
ling over a part of the earth's surface, and making

a com-

Lesson xiv.] ECLIPSES. 63

a complete eclipse to all the inhabitants residing
within that track; but no where else ; for in the
large space around, within the limits of the fainter
shade called the penumbra, the eclipse will only
be partial.

It will not be difficult to understand that solar
eclipses can only happen about the time of New
Moon, when the Moon is in conjunction with the
Sun, In the nodes, when the Moon has no visible
latitude, the eclipses are total : out cf the nodes,
but near them, the eclipses are partial : the limits
are about 17 degrees on each side the nodes:—
but much also depends upon the Moon's latitude,
for it must in these cases be always less than the
apparent semi- diameters of the Sun and Moon
added together.

Some circumstances of solar eclipses, as de-
scribed by the very ingenious author before-men-
tioned in this Lesson, are, 1. That none of them
are universal ; that is, none of them are seen
throughout the whole hemisphere which the Sim
is then above : the Moon's disc being much too
little, and much too near the Earth, to hide the
Sun from the whole disc of the Earth. Commonly
the Moon's dark shadow covers only a spot on the
Earth's surface, about 180 miles broad, when the
Sun's distance is greatest, and the Moon's least.
But her partial shadow or penumbra, may thea
cover a circular space of 4900 mites in diameter,
within which the Sun is more or less eclipsed as the
places are nearer to or farther from the centre of
the penumbra. In this case the axis of the shade

passe

06 ECLIPSES. [Lesson xiv.

passes through the centre of the Earth, or the New
Moon happens exactly in the node, and then it is
evident that the section of the shadow is circular j
but in every other case the conical shadow is cut
obliquely by the surface of the Earth, and the sec-
tion will be an oval, and very nearly a true ellipsis.
—2. Nor does the eclipse appear the same in all
parts of the Earth, where it is seen ; but when in
one place it is total, in another it is only partial.
Farther, when the Moon appears much less than
the Sun, as is chiefly the case when she is in
Apoge, and he in Perige *; the vertex of the lunar
shadow is then too short to reach the Earth, and
though she be in a central conjunction with the
Sun, is yet not large enough to cover his whole
disc, but lets his ring appear as a lucid ring or
bracelet, and so causes an annular eclipse. — 3. A
solar eclipse does not happen at the same time in
all places where it is seen j but appears more early
to the western parts, and later to the eastern j as the
motion of the Moon, and consequently of her
shadow, is from west to east. — 4. In most solar
eclipses the Moon's disc is covered with a faint
light, which is attributed to the reflection of the
light from the illuminated part of the Earth.—
Lastly, in total eclipses of the Sun, the Moon's
limb is seen surrounded by a pale circle of light j
which some astronomers consider as an indication
of an atmosphere of the Sun, because it has been

* Apoge is that place in which the Sun or a planet primary or
secondary, is at its greatest distance from the Karlh : Perige. is
when either of these is at Us neatest possible distance from us.

observed

f.esson xiv.] ECLIPSES. 67

observed to move equally with the Sun, and not
with the Moon.

In addition to these circumstances we may
observe, that though a solar eclipse may last from
beginning to end (at one place on the earth) more
than two hours ; yet the duration of total dark-
ness can never, in the greatest eclipse he more
than four minutes, and very commonly not more
than two.

We may also observe, with regard to eclipses of
both luminaries, that in general, as many eclipses
happen of the Sun as of the Moon : but in any
particular place there are more eclipses of the
Moon than of the Sun. Again, that though in
lunar eclipses the eastern side is first eclipsed, and
the eclipse ends on the western sidej yet in solar
eclipses, the western side is first eclipsed, and ends
on the eastern.

As to the number of eclipses both solar and
lunar, it may be observed that there cannot in
any year be less than two, nor more than seven :
the most usual number is four, and it is very sel-
dom that there are more than six.

The satellites of some of the superior planets
frequently undergo eclipses and occultations j Hut
as these are unobservable by the naked eye, it
would not agree with my design to say more
about them. Some of the fixed stars, Aldeba-
ran for instance, is frequently hidden behind the
Moon ; Jupiter also experiences occultations of
this kind: but of these the bare mention may-
suffice.

LESSON

LESSON XV.

ON THE FIXED STARS, WITH REFLECTIONS
ON THE IMMENSITY OF THE V*lllr£KSE.

——Who turns bis eye on Nature's midnight face
Rut must inquire — " What hand behind tin1. s cc-nv,
•' What arm Almighty, put these wheeling globes
" In motion, and wound up the vjxst machine ?
" Who rounded in his palm those spacious orb.1! ?
" Who bowl'd them flaming through the dark profound,
"And set the bosom of old night on lire?"
Nature's Controulcr, Author, Guide, mid End !

YOUNG.

V\HEN you, my young friends, consider the
unwieldy size of those celestial bodies on which we
have already descanted, and reflect upon the asto-
nishing rapidity of some of their motions j surely
you must entertain very high ideas of the GREAT
POWER which first launched them in the illimi-
table void, and causes their motions to continue
through the flux of so many thousand years ; none
having yet mistaken their way, or wandered from
their destined paths :— on the contrary, their ro-
tations still proceed in such exquisite regularity
and harmony as is best adapted to the perfection
of the whole. What awful power and adorable
goodness is here displayed ! But our reflections on

tke

Lesson xv.] FIXED STARS, Sec. 69

the heavens must be carried infinitely farther than
we have yet extended them.

The gems in the brilliant canopy which remain
to be contemplated, are the fixed stars; which
are chiefly distinguishable, as was suggested in
the Second Lesson, from their never changing
their relative situation with regard to each other.

The heavens are divided into three regions,
called the Northern and Southern Hemispheres,
and the Zodiac. The Fixed Stars were classed by
the ancients under the outlines of certain figures
of birds, beasts, fishes, and other animals j and
these were called Constellations. The number of
which is, in the Northern Hemisphere, 36 j in the
Southern, 32; and in theZodiac,12. Stars not com-
prehended in any of these ancient constellations,
are called Unformed Stars; and others, of a
cloudy appearance, are called Nebula:. Of this
number are the Magellanic clouds near the south
pole, which resemble two whitish spots in the
heavens, and are well known to sailors *.

The

• The Plate which is »;iven as a Frontispiece, is a projec-
tion of the northern and southern CELESTIAL HEMISPHERES
on the plans of the llqxator. The centre of the first projec-
tion is the North Pole of the Equator, aroand which are de-
scribed two circles ; the smaller is the Arctic circle, the larger,
the Tropic of Cancer: a little above the centre of the first pro-
jection is the North Poll of the Ecliptic, where all the Circles of
latitude drawn through every tenth degree of each Sign of the
Zodiac, meet and intersect each other. The centre of the
second projection is the South Pole of the Equator; the first
of the two circles, which are described about it, is the An-
tarctic circle, the other is the Tropic of Capricorn : a little below

the

70 FIXED STARS, &c. [Lesson XV.

The last star in the tail of Ursa Minor, or the
Less Bear, is called the Polar Star, and serves
for a guide to mariners ; because, on account of
its nearness to the north pole, its apparent situa-
tion, with regard to the Earth, varies but very
little throughout the period of the Earth's annual
revolution. Two of the stars in the constellation
of Ursa Major) or the Greater Bear, are called

the centre of the second projection is the South pole of the
Ecliptic, where all the Circles of Latitude meet and intersect,
as in the Southern Hemisphere. From the Poles of the
Ecliptic as centres, the Circles of Longitude are drawn at
every tenth degree: that circle which is described at 90*
from each pole of the Ecliptic, is the Ecliptic itself ; of
this, half appears in the one projection, and half in the
other; it interests the Equator in the fiist points of Arits(«¥»)
and Libra (•£:). The diameter of each projection which
crosses it from top to bottom, is called the Solstitial Colure,
because it passes through the solstitial points, Cancer (25)
and Capricorn (Vf} '• the diameter that crosses each projection
from right to left denotes the Equinoctial Colure, so called be-
cause it passes through the equinoctial points. Ariet and
Libra. These four points of the Ecliptic which are crossed
by the Colures are called Cardinal Points; and when the Sun
enters one or other of these points, one of the four Seasons
of the year commenc( s.

The Stars are given in this plate as they appear on the sur-
face of the Celestial Globe, with this difference, that the
figures of the Constellations are omitted, as they would only
tend to create confusion when the Hemispheres arc projected
on so small a scale. The Stars of different magnitudes are so
distinguished, that with little difficulty they may be reckoned
in many instances : Thus, in Ursa Minor, or the Less Hear, it is
easy to reckon two stars of the second, one of the third, three
of the fourth, one of the fifth, and three of the sixth magnitude.
Again, in Cunicula, or the Little Dog, you may discover ten
stars, whereof one, called Procyon, is of the first magnitude.

the

Lesson xv.J FIXED STARS, 8cc. 71

the Pointers, because they always point very
nearly to the polar star.

Those of the fixed stars which are nearest to us
seem largest, and are therefore said to be of the
first magnitude ; those of the second magnitude,
being at a greater distance, seem lessj and thus
they proceed by regular gradations unto the
sixth magnitude, which includes all the rest of the
fixed stars that are visible without a telescope.
With regard to their number, a common observer
might be led to suppose that even to the unas-
sisted eye they are innumerable : but this arises
from their being observed in a confused manner :
for it may be proved, that when they are divided
into proper classes, and reckoned up, those in the
visible hemisphere,seen without a telescope, amount
not to many more than a thousand.

Since the introduction of telescopes into astro-
nomical observations, the number of fixed stars
has been very justly considered as immense ; for,
to the greater perfection our glasses are carried,,
the more stars we discover. The astonishingly
immense distance of the fixed stars from one ano-
ther, and from the earth we inhabit, is one of the
most proper considerations for elevating our ideas
of the works of GOD. Astronomers have com-
puted from indubitable principles, that the distance
of Sirius or the Dog Star (which is the nearest fixed
star) from us, is considerably more than two mil-
lions of millions of miles ! A distance almost in-
conceivable ! A cannon-ball flying from thence

at

FIXED STARS. [Lesson xv.

at the rate of 400 miles in an hour, would not
reach us in 570,000 years.

The stars being at such great distances from the*
sun, cannot possibly receive from him so strong
a light as they shine with: hence, on mature re*
flection, it will appear that they shine with their
own native lustre, in like manner with the sun ;
and since each star is confined to a particular por-
tion of space, we must reasonably conclude that
each fixed star is in reality a sun *.

It is not at ail probable that the ALMIGHTY,
whose actions all evince infinite wisdom j and who
does nothing in vain, should create so many glo-
rious suns for no other purpose than to add to our
pleasure, and give us an additional glimmering
of light. Those who are so fond of arrogating
Divine favours to themselves have but a mean opi-
nion of Infinite Wisdom : since, by a considerably

• " That stars arc suns will scarcely admit of a doubt.
Their immense distance would perfectly exclude them from
our view, if the light they sent us were not of the solar kind.
Besides the analogy may be traced much farther. The sun
turns on its axis ; so does the star Algol ; so do the stars called
$ Lyra-, S Cephet, ij Antinoi, -e Ccti, and many more; most
probably all. From what other catise can we so probably
account for their periodical changes ? Again, our fun has
spots on its surface ; so has the star Algol: and- so have the
stars already named; and probably every star iu the heavens.
On our sun those spots are changeable ; so they are on the
star o Ceti ; as evidently appears from the irregularity of its
changeable lustre, which is often broken in upon by acciden-
tal changes, while the general period continues unaltered.
The same little deviations have been observed in other pe-
riodical stars, and ought to be ascribed to the same cause."

HERSCHEL.

less

XV.] FIXRD, STAHS, &C. f3

less degree of creating power, our earth would
have received much more light from only one ad^
ditional moon.

And canst then think, poor worm, these orbs of ligkt,

In size immense, in number infinite,

Were made for thee alone, to twinkle in thy sight?

Presumptuous mortal! can thy nerves descry,

How far from thee they roll, from thee how high?

With all thy boasted knowledge canst thon see

Their various beauty, order, harmony?

If not— then sure they were not made for thee.

BASER

Instead, then, of one sun and one world only
in the universe, as the unscientific suppose, our
contemplations induce us to acknowledge that
there must be an inconceivable number of suns
and of systems of planets revolving round them,
dispersed through the infinitely wide expanse of
boundless space; insomuch that were our sun,
with all the planets about it, annihilated, they
would be no more missed by an eye that could
take in the whole creation, than a drop of water
from the wide ocean-

M Our single system is asuougfct in estimate

" When balaoc'd with the heatr*ns : greater the specfc
M Which on the sun-beam dances, when compar'd
" With Taurus, or the Alps, or Caucasus ;
14 Or on the blade the dew-drop to the »ea."

These reBections tend to excite a deep con-
sciousness of our own inferiority. Who can help
exclaiming with David after a similar contempla-

JK t

74 FIXBD STARS, &c. [Lesson xv.

tion-— " Lord, what is man, lhat thou art mindful
"of him?"

As there is a. general analogy running through
and connecting every part of the creation, into
one grand whole : and as there is undoubtedly an
absolute similarity between the earth we inhabit
and the other planets in our system ; can it be un-
reasonable to suppose that they and the planets of
ether systems have plants, and trees, herbs, fruits,
&c. &c. as we have? Or is it repugnant to na-
ture to imagine that they are inhabited by animals
and rational creatures ? Among numberless argu-
ments which might be adduced, a very good one
to shew the great probability of the planets being
inhabited, is derived from the following conside-
ration. . There is no part of matter that we are ac-
quainted with, which lies waste and useless : seas,
lakrs,and rivers,teem with living creatures; moun-
tains and vallies; trees and herbs; grasses and the
animals which feed upon them; nay, even the
blood and:humours of the animals themselves, all
have their respective inhabitants. Surely, then,
t-he most numerous and large bodies in the uni-
verse, are furnished with beings adapted to their
several situations. What an august conception does
this give of the works of the CREATOR ! Almost
more than the human imagination is able to con-
ceive.

Millions of --suns at immense distances from
each other; attended by tens of millions of worlds
moving round them, all in rapid motion, yet re-
gular and calm: and these, we may safely infer,

are

Letion xv.] FIXED STARS, fcc.

are inhabited -by millions of millions of rational
creatures formed for endless felicity;

- Hail ! Source of being ! universal Son!
Of' heaven and earth ! essential Presence hail !
To THEE I bend the knee, to THEE my thoughts
Continual climb, who with a master-hand
Hast the great whole into perfection touch'd!

THOMSON,

When an innumerable multitude of bodies of
enormous bulk, are all set in motion, and keep
travelling through their extensive orbits with such
beauteous regularity and order, by means of the
attraction of the suns to which they respectively
belong; without having their motions either de-
stroyed or directed into other courses ; how can
we express our conceptions of the greatness, wis-
dom, and goodness of HIM who made and go-
verns the whole ?

" By the word of the LOHD were the heavens
" made, and ail the host of them by the Ireatk
" of his mouth." (DavidJ What an amazing in-
stance of Omnipotence ! How inconceivably great
do these his marvellous works evince him to be :
then

Since the great Sovereign sends ten thousand worlds,

To tell us he resides above them all,

In glory's unapproachable recess : YOUH&.

how can we forbear venting our adoration in

hymns of praise ? — Previous to my closing this

Lesson I shall therefore insert a hymn indited by

E £ inspiration,

7* FIXED STARS, See. [Lesson XT.

inspiration, and translated into our language by
no less a Christian and poet than Mr. Addison.

HYMN. PSALM XIX.

THE spacious firmament on high,
With all the blue ctlit rial sky,
And spangled heavens, a shining frame,
Their great Original proclaim.
Th' unwearied sun from day to day
Does his Creator's power display,
And publishes to every land
The work of an Almighty hand.

Soon as the evening shades prevail,
The moon takes up the wondrous tale,
And nightly, to the listening earth,
Repeats the story of her birth ;
While all the stars that round her bum,
And all th* planets, in their turn,
Confirm the tidings as they roll,
And spread the truth from pole to pole.

What though in solemn silence all
Move round the dark terrestrial ball ?
What though nor real voice, nor sound,
Amid their radiant orbs are found ?
In reason's ear they all rejoice,
And utter forth a glorious voice;
For ever singing, as they shine,
The HAND that made vs is divine!

END OF THE ASTRONOMICAL PART.

U36

ON

LESSON XVI.

ON THE ATMOSPHERE.

Diffusing gently its enlivening pow'r,
The genial Air we all around us feel
Cheering — though unexplor'd by human sight.

we have now finished our survey of the hea-
venly bodies, our inquiries may naturally descend
to the Earth we inhabit : and here the first thing
which attracts our attention is, that thin, transpa-
rent, and fluid body, called Air, which surrounds
this terraqueous globe, and covers it to a consider-
able height. Or, if we include in our definition
the whole of the fluid mass, consisting of air,
electric matter, aqueous and other vapours, which
surrounds the Earth, and partakes of all its motions;
we then make use of the word Atmosphere, as a
term comprising the whole. Beside the different
kinds of air, it is manifest that the whole mass of
the atmosphere contains a considerable quantity
of water, together with an heterogeneous collec-
tion of particles exhaled from all solid or fluid
bodies on the surface of the Earth. These, how-
ever, are transformed into a fluid mass called
Atmospheric Air, which is that transparent, colour-
less fluid which every where invests this elobe,
possessing permanent elasticity and gravity. It is
composed of four gases, but principally of 78 parts
of nitrogen and 22 of oxygen gas in bulk ; and in-
E 3 weigh U

78 , ATMOSPHERE, [LesSWl XVI.

':. I" —— '• - '.. I I ' P I

weight of about 74 nitrogen, and 26 oxygen ; and
is soluble in about 30 times its bulk of water :
10O cubic inches weigh 3 1 grains. On the surface
of the earth it is compressed by the weight of the
superincumbent atmosphere: its density, therefore,
diminishes according to its height above the earth.
It is dilatable by heat : at 60° of temperature, its
bulk is increased about its l-82d part. The con-
st^ituent principles of atmospheric air are rendered
evident by the following experiment: quicksilver
being enclosed in a proper vessel of atmospheric
air, on heat being applied the air will be diminish-
ed, and the quicksilver will lose its splendour, and
gradually change to a reddish powder ; acquiring,
at the same time, an augmentation of weight.
When neither the air nor the quicksilver suffers
any farther change, the separation of the princi-
ples has taken place : the one, the gas remaining
in the receivers, is now unfit for supporting flame,,
or maintaining respiration, and is nitrogen gas :
the other is absorbed by the quicksilver, while re-
ducing to the state of an oxide, and may be ex-
tricated from it on the application of heat ; when
the powder, to which the quicksilver is reduced,
will be restored to its metallic state> but will have
lost the weight it had gained during its oxidation }
this deficiency being exactly equal to the weight
of the evolved gas, which is oxygen gas. These
separated gases, thus differing in their properties
from each other, and, from atmospheric air being
again mix,ed, form atmospheric air of the or^i-
nary degree of purity.

The-

Lesson xvi.] ATMOSPHERE. 79

The following is Mr. Dalton's table of the
weights of the different gases constituting the at-
mosphere : —

Incites of Mercury •

Azotic 6as 23.36

Oxygenous Gas •• ' 6.18

Aqueous Vapour • -14

Carbonic Acid Gas «•• .02

30.00

Table of the proportional weights of the dif-
ferent gases in a given volume of atmospheric air,
taken at the surface of the earth :— •

Azotic Gas •

Oxygenous Gas • • • •
Aqueous Vapour • •
Carbonic Acid Gas

100.00

The uses of the Atmosphere are so many and
great, that it is absolutely necessary, not only to the
comfort and convenience of mankind, but even to
the existence of all animal and vegetable life. Ex.-
periments which have been frequently made with
an instrument called an air pump, place it beyond
doubt that without the air or atmosphere, no.
animal could exist, or even be produced : with-
out its aid all vegetation would cease, neither
would there be any great degree of either inflam-
mation or combustion. Sound could not be pro-
duced without it, nor would there be either rains
or dews to moisten the ground : in short, all our
S 4 reflections

*O ATMOSPHERE. [LeSWH XVf.

reflections on the atmosphere will tend more
clearly to convince us that we continually stand
in need of the superintendance of our allwisc
CREATOR.

Besides other innumerable conveniences which
we receive from the atmosphere, one great advan-
tage is, that while the Sun shines, it makes the
face of the heavens appear lucid and bright: but,
on> the contrary, if there were no atmosphere
surrounding the Earth, only that part of the sky
would appear light in which the Sun was placed:
if a person should turn his back to the Sun, he
•would directly perceive it as dark as night, and the
least stars would be seen to shine, as in th«
clearest night. For in that case there would be no
substance to reflect the rays of the sun to our eyes ;
and of course, those which did not fall upon the
Earth would be thrown out into infinite space, and
would never be reflected back to us. But since
there is an atmosphere covering the Earth, which
is strongly illuminated by the Sun, it, by its
power of reflection, turns the light towards us,
and makes the whole heavens to shine with such
splendour as to render the light of the stars invisi-
ble in ttie day-time.
*

By means of the atmosphere it happens, thai
though after the Sun has set, we receive no direct
Kcrht from the Sun, yet we enjoy its reflected and
refracted light for some time; so that the dark-
ness of the night docs not come on suddenly (as
it would otherwise do) but by degrees. For, after
the Earth "by revolving on its axis has withdrawn

us

Lesson xvj.] TWILIGHT. 8T,

us from seeing the Sun ; the atmosphere (whose
reflecting part reaches to the height of about sixty
miles) will still be illuminated by that luminary :
so that for a while the whole heaven will have
some of his light imparted to it. But as the
Earth pursues its revolution, the Sun retires
farther below the horrzon ; and so much the less
is the atmosphere illustrated by him : until trie
Sun is about eighteen degrees below the horizon^

w O

when he no longer enlightens our atmosphere,
and then all that part thereof which is over us be-
comes dark.

Likewise in the morning, as soon as the Sun
comes within eighteen degrees of the horizon, he
begins again to enlighten the atmosphere, and to
diffuse his light over the sky : so tbat its bright-
ness does still increase, till the Sun rises and makes -
full day. This kind of illumination between day
and night, which is observed' in the morning be-
fore the Sun's rising, and 'in the evening after his
settihg, is called Crespusculum or Twilight. It is -
longest in England, from May 24th to July 23d;
during which period there is " no real night;" and
shortest on March 2d and October 1 2th, when its
duration at London is about 1 hour 55 minutes.

The terrestrial atmosphere also refracts those
rays which fall upon it from the Sun and Stars,
and changes their directions, by propagating the
light in other lines, and thus making the apparent
places of the celestial bodies different from their
true places. This refraction causes the Sun to be
yisible before he has risen above the horizon., and i
E 5. io

ATMOSPHERE. [Lesson xvt.

to protract his stay with us after he is set in the
evening. This is an admirable contrivance to
shorten the long and dismal nights in the frigid
zones, and thus to add to the comfort of the in-
habitants of those forlorn regions. Varenius re-
lates in his geography, that " to those Hollanders
" who wintered in Nova Zemlla, the Sun was
" visible, in a clear sky, sixteen days before it ac-
(t tually rose above the horizon, being yet four de-
** grees below it." And Hook, speaking of the
same circumstance, says, — " The night in that
*' place shortened no less than a whole month j
^•which must needs be a very great comfort, to
*' all such people as live very far towards the
«* North and South poles, where length of night,
t( and want of seeing the Sun, cannot but be very
<l tedious and irksome."

Though it is rather foreign from the immediate
subject of this Lesson, yet I shall here relate a few
properties of refraction ; as it will somewhat tend
to elucidate what is above-mentioned with regard
to the twilight. By numerous experiments we
find that the rays of a luminous body or even of
any visible object, when they fall upon a medium
or diaphonous body of air or water of a different
.density from- that from whence they first proceeded,
do not afterwards go directly in the same straight
lines, but are- broken or bent, and proceed as
though they had been propagated from another
point. And if the medium on which they fall be
denser than the first, they are bent towards a line
perpendicular »o the, surface -whereon they fall

at

Lesson xvi.] REFRACTION. 83

at the point of incidence; but if it be a rarer me-
dium, in their bending they recede from the per-
pendicular.

We observe in nature many effects of refraction :
for instance — A staff, one part of .which is immers-
ed in water, and the other in air, appears broken ;
and that part which is. in water, appears higher
than it really is. Again — Take a tub, whose sides
are straight, and in the middle of the bottom lay
a shilling, or any other visible object, fixed so
that it cannot move, then go so far from the tub
that you can but just see the object, and stand
there till another person more than half fills the
tub with water, and the shilling will then appear
as though it were removed some distance farther
from you : this experiment may be varied several
ways. . t

Another remarkable instance of refraction is
the following : — A person standing by the side of
the river Thames at Greenwich, when it is high
water there, may see the cattle grazing on the
marshy meadow on the other side of the river
called the Isle of Dogs ; but when it is low water
there, he cannot see any thing of them, they
being hid from his view by the bank on the other
side the river. This curious effect is probabjy
owing to the moist and dense vapours just above
the surface of the water, being raised higher pr
lifted up with the surface of the water at the tim«
of high tide; the. rays ..passing through these
tapqurs are so much refracted as to render those

things

84 ATMOSPHERE. [Lesson XVI.

things risible, which arc not to be seen at the time
of low water.

But to return from this digression, and proceed
\vith our account of the air and atmosphere: lire
science Jvhich treats of the weight, pressure, and
elasticity of the air is called Pneumatics. And
'here it may be first observed, that the air is a fluid
body which surrounds and gravitates upon all parts
' of the earth's surface. But it differs from all other
fluids in the following particulars : 1. It can be
compressed into a much less space than what it
naturally " possesses, which no other fluid can.
£. It cannot be congealed as other fluids can. 3. It
is of a different density in every part upward from
the earth's surface, decreasing in its weight, bulk
> for bulk, the higher it rises : and therefore must
also decrease in density; and the law of diminu-
tion is such, that when the heights increase in
arithmetical progression, the densities decrease in
geometrical progression. 4. It is of an elastic or
springy nature : and the law it observes in this
respect is, that the force of the spring is equal to
its weight, or the density is alway§ proportional to
the force by which it is compressed. We may also
observe that heat increases and cold diminishes
the elasticity of the air : or heat expands and cold
condenses it.

The weight or pressure of the atmosphere upon
any base at the surface of the earth, is equal to the
weight of a column of quicksilver of the sarn« base,
and its height between twenty-eight and thirty-one

inches:

Lesson X.VL] PRESSURE OF AIR. 85

inches : or equal to the weight of a column of
water of the same base and height, betw.een thirty-
two and thirty-five feet. The first part of this is
proved by observations on the Barometer, an in-
strument which measures the pressure of the air:
tor the limit of barometrical variation is between
twenty-eight and thirty-one inches. And the latter
part is proved by the sucking pump, which will
never raise water higher than thirty. five feet, and
sometimes not higher than thirty-two. This va-
riation in the weight of the atmosphere depends
in great measure on the different degrees of heat
in the air near the surface of the earth ; but,
perhaps it depends in a much greater degree, on
the commotions and changes in the atmosphere
from wind, vapours, and other causes.

From the foregoing account of the weight of
the atmosphere, it will not be difficult to infer,
that, at a medium, there is a pressure equal to nearly
fifteen pounds avoirdupois upon every square inch :
this entirely, arises from its weight and fluidity.
By the combination of these two qualities, which
bind down all bodies on the earth with such great
force, many wonderful effects are produced: it is
this which prevents the arterial vessels of animals
and plants from being too much distended, by the
impetus of the circulating juices, or by the. elastic
foice of the air so copiously abounding in them :. it
is this also which hinders the fluids from transpir-
at. ing in. too great a degree through the pores of their
containing vessels, which would otherwise destroy

the

66 ATMOSPHERE. [Lesson xvi.

the animal by a debility gradually brought on : to
this are also owing many natural phenomena
by far too numerous to be mentioned in this
place.

Another property of air, and which indeed is
its chief criterion, is its elasticity or springiness ;
it is by virtue of this quality that it dilates itself,
after the removal of any pressure ; or contracts
itself into a less space when it has to sustain a
greater pressure. A familiar instance of this qua-
lity you may often have observed ; namely, by
'having a fresh bladder filled with air ; for when
squeezed in the hand the air makes a sensible
resistance, but when the hand is taken away, the
parts which were compressed, directly restore
themselves to their former state.

I have before observed that th« air presses on
a square inch with the weight of J5lbs. on a me-
dium. Now if we suppose the surface of a full-
sized human body to be ten square feet, which is
not too much, we shall find, (as it is the nature
of the air to press equally in all directions,) that a
mart who probably supposes he bears no weight,
sustains a pressure of no less than -21,601) Ibs.
When we consider that the greater part of us are
surrounded with such an astonishing pressure, and
that this pressure may in the course of a very few
hours be either increased or diminished by more
than a thousand pounds weight ; are we never led
to reflect upon that POWER who keeps us from
utler destruction! Let the Atheist consider what*

he

Lesson xvi.] PRESSURE OF AIR. 87'

he has to expect, for his blasphemous denial of so
wise and mighty a Being.

Another remarkable property of air, which ought
to fill our hearts with thankfulness to the adorable
CREATOR, is its transparency : let us recollect in
what a dreary and disconsolate situation we should
be if the air were visible. What would then be
the use of that noble instrument the eye? Or how
should we discern those diversified and variegated
prospects of distant towns, green woods, flowery
meado.ws, fields of corn, 8cc. which now so often
give us pleasure ? Alas ! how dismal and gloomy
would be the reverse ! Surely our hearts must
overflow with gratitude to the DIVINE AUTHOR of
our existence, for such unbounded goodness to us
his creatures.

Before we terminate this Lesson, we cannot for-
bear recurring to the use of the air in respiration ;
but shall point out one or two striking instances
which it furnishes of exquisite contrivance for the
most beneficent purposes. '

Animal heat is preserved enfirely by the in-
spiration of atmospheric air ! The lungs, which
imbibe the oxygen gas from the air, impart it to
the blood ; and the blood, in its circulation, gives
out the caloric to every part of the body. No-
thing can afford a more striking proof of creative
wisdom, than this provision for the preservation
of an equable animal temperature. By the de-
composition of atmospheric air, caloric is evolved,
and this caloric is taken up by the arterial blood,
without its temperature being at all raised by the

addition,

ATMOSPHERE. [Lesson xvi.

addition. When it passes to the veins, its capacity
for caloric is diminished, as much as it had been
before increased in the longs: the caloric, there-
fore, which had been absorbed, is again given out fc
and this slow and constant evolution of caloric in
the extreme vessels over the whole body, is the
source of that uniform temperature which we have
so much occasion to admire. Dr. Crawford asr
certained, that whenever an animal is placed in a
medium, the temperature of which is considerably
high, the usual change of arterial into venous
blood does not go on j consequently, no evolution
of caloric will take place, and the animal heat
will not rise much above the natural standard.
How pleasing it is to contemplate the arrange-
ments which the Deity has made for the preservat-
ion and felichy of his creatures, and to observe
.that he has provided for every possible exigency !

Lavoisier has shewn, that in respiration there is
a constant combination of the oxygen of the at-
mbsphere with the hydrogen and carbon of the
blood.

Thus Itfe discordant elements arrests,

Rejects the noxious and tire pure digests ;

Combines with heat the fluctuating mass,

And gives a while solidity to gas, DARTHH..

A postulatutn has been assumed by some atheists,
that the organs of the body have been formed by
•what they call appetency, i. e. endeavours per-
petuated, and imperceptibly working its effects
through a long series of generations : hut I. would

ask-,

PRESStfRE OF AIK.

ask any one, whether he would venture to assert
that he believes this to be the way in which the
lungs acquired the faculty of decomposing atmos-
pheric air; and that he believes that this hypothesis
is sufficient to account for the composition of this
air, which so exactly suits the operation of these
lungs, and which contains that exact portion of
caloric which the animal ceconomy requires ! It
is worthy of remark, that cold-blooded animals,
which are not furnished with this breathing ap-
paratus, are so constituted that their temperature
changes with every change of the temperature of
the surrounding medium. Frogs have been abso-
lutely frozen so as to chip like ice, and then when
carefully and gradually thawed, have been com-
pletely re-animated.

Lastly, it may be remarked, that the interval
which there is between every inspiration seems to
have been designed to allow time for the nitrogen
gas which is throwirout of the lungs to mount in
the air above the head, in order that a fresh por-
tion of air might be taken in, and that the same
air might not be repeatedly breathed.

During that remarkable interval that always
occurs in breathing, there is sufficient time al-
lowed for the noxious fluids to separate; the first
to ascend, while the other preponderates, leaving
a. space for a fresh current of uncontaminated
atmospheric air. Thus every thing is prepared by
Divine Goodness, without any care or forethought
,of purs, for a new inspiration.

" The

go ATMOSPHERE. [Lesson XVT.

The air inhaled is not the gas
That from a thousand lungs reek back to thine,
Sated with exhalations rank and fell,
Which, drunk, would poison the balsamic blood,
And rouse the heart to ev'ry fever's rape-
But air that trembling floats from hill to hill,
From vale to mountain, with inccstai.t change
Of purest element.

LESSON

LESSON XVII,

ON WINDS.

Trade-winds, observing well their stated course,'
To human good employ their powerful force :
The loaded ships across the ocean fann'd
By steady galen, spread commerce through the land.
These you observe— but have you no desire
The hidden Spring of such effects t'inqnire?
Or, when contending winds around you blow,
Do you ne'er wish the cause of them to know ?

XlITHERTO our reflections have carried us no
farther than to consider the air in a motionless
state ; but as this fluid mass is frequently in motion,
and that too sometimes in a violent degree, it
would be almost unpardonable to pass by such an
obvious effect without paying some attention to it,
Air in a current-like motion is known by the
nam« of wind. Though the winds in a temperate
zone of the earth are very inconstant and change-
able, yet this is not the case in every part of the
terrestrial globe j for in the torrid zone and some
other parts, the winds are generally very uniform
and constant in their directions, as will appear
from the following facts relative to them : —

1. Over the Atlantic and Pacific oceans, parli-

' ~

cularly between thirty degrees of North and thirty
degrees of South latitude, the Trade-winds, as they

are

0$ WINDS. [Lesson xvir.

are called, blow uniformly from east to west, all the
year round, with a small variation in the different
seasons. — 2. When the sun is on the equator, the
Trade-winds in sailing northward, veer more and
more from the east towards the north; so that about
their limit they become nearly north-east: and vice
versa in sailing southward, they become at last
nearly south-east. — 3. When the sun is near the
Tropic of Cancer, the Trade-winds north of the
equator, become more nearly east than at other
times, and those south of the equator more nearly
south ; and vice versa, when the sun is near the
Tropic of Capricorn.— 4. The Trade- winds are
not due east upon the equator, but about four de-
grees to the north of it.

To account for these facts relative to the winds is
a most curious and important, though mysterious
inquiry ; having employed the pens of several very
eminent philosophers : but amongst all the expla-
nations I have seen, there is none in my opinion
more agreeable to nature than one given by Mr.
John Dallon, of Manchester, in his " Meteoro-
logical Observations and Essays." The method of
reasoning applied to the subject in that work, I
shall here adopt.

The inequality of heat in the different climates
and places, and the earth's rotation on its axis,
appear to be the principal causes of all winds, re-
gular and irregular. It may be observed, that
whenever the heat is greatest, there the air will
ascend, and a supply of colder air will be received

from

Lessen xvn.] WINDS. 93

from the neighbouring parts : it will be willingly
allowed that the heat is at all times greatest in the
torrid zone, and decreases gradually in proceeding;
northward or southward ; also that the poles may
at all times be considered as the centres of cold.
Hence it manifestly results, that, abstracting from
accidental circumstances, there will be a constant
ascent of air over the torrid zone, which air will
afterwards fall northward and southward, whilst
the colder air below is determined by a continual
impulse towards the equator.

When the effects of the earth's rotation are takea
into consideration, our reasoning must be as fol-
lows :-— The air over any part of the earth's surface,
when apparently at rest or calm, will have the
same rotatory Telocity as that part ; but if a quan-
tity of air in the northern hemisphere receive an
impulse in the direction of the meridian, either
northward or southward, its rotatory velocity will
be greater in the former case, and less in the latter,
than that of the air into which it moves ; con-
sequently, if it move northward, it will have a
greater velocity eastward than the air, or surface
of the earth over which it moves, and will there-
fore become a south-west wind, or a wind be-
tween the south and west.' And vice versa, if it
move southward, it becomes a north-east wind.
From similar considerations it will appear, that in
the southward hemisphere the winds will be north-
west and south-east respectively.

The Trade-winds may therefore be explained
thns : The two general masses of air proceeding

from

Q4 TRA»E-wiNCi»__ [Lesson XVII.

from both hemispheres towards the equator, as they
advance, are constantly deflected more and more
towards the east, by reason of the earth's rotation j
that from the southern hemisphere originally a
south wind, is made to veer more and more towards
the east : in like manner, that from the northern
hemisphere is made to change its direction from the
north towards the east. These two masses meeting
near the equator, their velocities south and north
destroy each other, and they proceed afterwards
with their common velocity from east to west
round the torrid zone, excepting the irregularities
produced by the continents. The equator is not
in reality the place of concourse, but the northern,
parallel of four degrees : because the centre of heat
is thereabouts, the sun being no longer on the north
side of the equator than on the south side. More-
over, when the sun is near one of the tropics, the
centre of heat upon the earth's surface is then
nearer that tropic than usual, and therefore the
winds about the tropic are more nearly east at that
time, and those about the other tropic more nearly
north and south.

If all the terrestrial globe were covered with
water, or, if the variations of the earth's surface in
heat were regular and constant, so that the heat
was the same in every part of the same parallel of
latitude, the winds would then be very nearly re-
gular also. But this is not the case : for we find the
irregularities of heat, arising from the interspersion
of land and sea, are such, that though all the1 parts
of the atmosphere in some measure conspire to

produce

Lesson XVH.j TRADE-WIrfDS. 95

produce regular winds about the torrid zone, yet
very striking irregularities are often found to take
place. A remarkable instance we have in Mon-
soon$t which are winds that in the Indian ocean,
&c. blow for six months together one way, and
the next six months the contrary way : these with
sea and land breezes do not seem easily accounted
for on any other principle than that of rarefaction.
Perhaps some persons may be led to suppose that
the winds in the northern temperate zone should be
between the north and east towards the poles, and
between the south and west nearer the equator,
almost as regular as the Trade-winds: but when
the changes of seasons, the different capacities of
land and water for heat, the interference and op-
position of the two general currents are considered,
it might be concluded almost next to impossible
that the winds in the temperate zone should exhibit
any thing like regularity. However, notwithstand-
ing this, observations sufficiently evince, that the
winds therein are, for the most part, in the direc-
tion of one of the general currents : namely, some-
where between the south and west, or almost as
commonly between the north and east j and that
winds in other directions happen only as acci-
dental varieties, chiefly in unsettled weather.

We may have frequently taken notice, that
several winds, particularly stormy ones, are at-
tended with a cloudy sky. To this it may be added,
that we have more winds than usually occur in
rather less latitudes, where the atmosphere is gene-
rally more serene: these considered make it exceed-
ingly

WINDS,

ingly probable, that the aqueous vapours which
are sustained by the air, from whence come clouds
and rains may be one great cause of irregular
winds. It has been determined, from very accurate
experiments, that one inch of water when evapo-
rated, will fill more than 2000 inches of space :
from hence it appears that the water which falls in
drops of rain, &c. possessed more than 2000 times
the space when it floated in the atmosphere in
vapours j the condensation thereof must therefore
occasion vacuities of such a nature as will cause
winds of different kind and degrees, according to
the deficiency which is to be supplied.

The oeconomy of winds, an illustration of which
has been here attempted, is admirably adapted to
the various purposes of nature, and to the general
intercourse of mankind : — if the earth had been
fixed, and the sun had revolved about it, the air
over the torrid zone, and particularly about the.
equator would have been almost always stagnant :
and in the other zones the winds would have had
little variation either in direction or strength; in
this case navigation would have been greatly
impeded, and a communication between the two
hemispheres by sea rendered impracticable. Oil
the present system of things, however, the irregu-
larity of winds is of the happiest consequence, by
being subservient to navigation : and a general
circulation of air constantly takes place between
the eastern and western hemispheres, as well as
between the polar and equatorial regions ; by
reason of which, that diffusion and intermixture

of

Lesson xvn.] WINDS. 97

of the different aerial fluids, so necessary for the
life, health, and prosperity of the animal and vege-
table kingdoms, is accomplished : — such is the
transcendant wisdom and providential care of the
beneficent FATHER OF ALL !

LESSON

LESSON XVIII.

ON SOUNDS AND ECHOES.

• - • Sweet music breathe,
Above, about, or underneath,
Sent by some spirit to mortals good. MILTON.

ANOTHER peculiar motion of the air remains
yet to be considered, which is, that by means of
which sounds are rendered audible or sensible to
us, under all their different affections and circum-
stances. Of the philosophy of sounds, Music is un-
doubtedly the essential and most refined part ; and
we find that persons in general are exceedingly fond
of musical sounds, being thereby affected with the
most agreeable and ravishing sensations. It is my
province in this place to give no more of the science
of Music than what relates to the production of
musical sounds, and indeed of sounds in general,
to which I shall now proceed*.

Experiments

* Though it be somewhat foreign to the subject immedi-
ately under discussion, yet I cannot pass by an opportunity
of suggesting an obvious improvement in the practice of Mu-
sic ; the use of which has been frequently urged, though it be
not yet generally acceded to. This improvement is no other
than the substitution of proper characters to denote the dif-
ferent kinds and velocities of musical time, instead of those

vague,

Lesson xvm.J SOUND. 99

Experiments on the air-pump prove to us, that
without the assistance of air, sounds cannot be
produced : they also evince, that the nature of
sounds depends entirely upon a certain motion of
the aerial particles. This motion is a pulsive or
vibratory one, carrying these particles forward
and backward through the very same space : and
it results from, or depends upon, the spring or
elasticity of the air. It is by means of this power
that, when any one particle is by any cause urged
forward, it must necessarily propel the particle
next before it : this second particle, in the same

vague, indefinite ones, which are now in use. What is the in-
formation we can obtain from casting our eyes upon the cha-
racters f > T> T> ¥, &c. ? Why truly, no more than can be learn-
ed from reckoning up the Crotchets, Minims, Quavers, &c. in
the first complete bar in the tune. The characters for the
several rates of common time ; and the terms Adagio, Largo,
Allegro, Presto, &c. &c. are also of very little avail in ascer-
taining with precision the point the musician wishes to dis-
cover. Every composer of musical airs, &c. would be of real
iervice to the practitioner, if he would point out the absolute
rate at which his music is to be performed : this would be no
difficult task ; as he would only have to mention the length of
a pendulum which would make one complete vibration in the
time that part of a bar called a beat was performing. Thus,
for instance, suppose I set a tune in triple time, and wish to
have each bar performed in a second and a half, the cha-
racter I must make use of is iV for from this it might be con-
cluded that there were three beats in a bar, and each of these
beats must be performed in the time a pendulum 10 inches
long made one vibration.

To explain this method clearly, much more room is requisite;
but the present would not be a proper place for it : however,
Jthosc who understand what improvement i: intended, from
this short account, will, I hope, excuse me for exhorting
them to use their best endeavours to make it general.

F 2 manner,

100 SOUND. [Lesson •XVIIT.

manner, moves a third, and so on, successively:
and by these means the motion is propagated in
the several particles, through a certain space
in a direction forward : but, on the other hand,
when the force which was first impre>t upon the
elastic particles of air ceases to act, those particles
return again, by the action of the air's elasticity,
through the same space. It is evident, that if the
producing force be continued on these elastic par-
ticles, there must necessarily be produced in them
a mutual vibratory motion of each particle, so long
as the repercussive force continues to act : and this
motion of the aerial particles being continued
until it reaches the ear, the different parts, nerves,
&c. belonging to and contiguous to the organ of
hearing, being exquisitely adapted to the purpose,
convey the sensation to the Irain, and so produce
the idea or perception of sound.

The waves in water, and the pulses in aif which
produce sound, though brought about by two dif-
ferent causes, gravity and elasticity, are yet some-
what similar : if a stone be dropped into the water,
it will cause waves to be propagated in a circular
direction upon the water's surface all round the
point where the stone was thrown in ; in like
manner, the motion of a sounding body is propa-
gated around it in regular gradations : but the
aqueous waves differ from the aerial pulses in this,
that the former are circular, being generated on a
plane surface ; but the latter are of a spherical
form, because they are produced in the lody of an
elastic fluid.

The

Lesson xvin.] SOUND. 101

The kind of motion which produces sound must
be understood to be that which is brought about
by means of the elastic particles of which sonorous
bodies consist; for without such an elastic dispo-
sition of parts they could not by any means be ren-
dered sonorous, or capabje of emitting sounds ; be-
cause the stroke being made externally, affects the
particles of such a body but with one single act:
the particles of the body could therefore, in such a
case, be moved only through a certain small space,
and would there be made to stop by the resistance
of, the parts beyond : thus without an elastic force,
the particles would remain at rest, after the percu-
tient body was removed ; and therefore, from a
single stroke the parts of unelastic bodies could
emit but a kind of blunt, short sound : in such,
cases, it is common to say we hear the stroke, as
when we strike with a hammer on a piece of lead.

But when we consider the stroke impressed on
bodies whose parts are in any considerable degree
elastic, they not only yield to the stroke and go
forward through a small space, but, after the strik-
ing body is removed, those elastic parts, by their
renilent force, return again with a velocity equal
to that by which they were displaced ; and thus a
vibratory motion being produced, will continue a
perceptible time, and produce successive impulses
on the contiguous air; hence, the air being thus
agitated by the elastic particles of the body, trans-
mits its impulses successively to ^he ear, and there
produces a sensation of sound of some duration.
Thus amongst sonorous bodies, we notice a wire
F 3 when

102 SOUND. [Lesson xvur.

when stretched and properly struck : also a bell
and a glass, which are some of the fittest instru-
ments for musical modulations. Much more might
be said on the causes of sound in general j but for
a general notion, what has been already mention-
ed may suffice.

To determine the nature and effect of different
bodies in conducting sound, Mr. George Sounder s
made a variety of experiments : some of his con-
clusions and remarks are as follow : —

Earth may be supposed to have a two-fold pro-
perty with respect to sound. Being very porous,
it absorbs sound, which is counteracted by its
property of conducting it, and occasions it to
pass on a plane, in an equal proportion to its
progress in air, unencumbered by any body. If a
sound be sufficiently intense to impress the earth
in its tremulous quality, it will be carried to a con-
siderable distance, as when the earth is struck with
any thing hard, as by horses' feet, or the motion of
a carriage. Plaister is proportionally better than
loose earth for conducting sound, as it is more
compact.

Clothes of every kind, but particularly wool-
len ones, are very prejudicial to sound ; their
absorption of sound, may be compared to
their absorption of water, which they greedily
imbibe.

A number of people seated before others (as in
the gallery of a chapel or theatre) considerably pre-
vent the voice reaching those behind ; and hencs
it is that we hear so much better in the front of the

galleries,

Lesson xvin.] SOUND. 103

galleries, than behind others. Our seats, rising
so little above each other, occasion this defect j
which would be remedied, could we have the seats
to rise their whole height above each other, as iu
the ancient theatres.

Water has been little noticed with respect to
its conducting of sound ; but it has been lately-
found to conduct sound more than any other
body whatever. A conversation delivered- in no
very loud tone, has been distinctly heard, on
water, at the distance of a mile ; and a whisper
has been heard at the distance of more than two
hundred yards.

Stone is sonorous, but gives a harsh disa-
greeable tone, unfavourable to music. Brick, in
respect to sound, has nearly the same properties
as stone.

Wood is sonorous, conductive, and vibrative. Of
all materials, it produces a tone the most agreeable
and melodious; and it is, therefore, the fittest for
musical instruments, and for lining rooms and
theatres.

Paint has been generally thought unfavourable
to sound, from its being so to musical instruments,
whose effects it entirely destroys. Musical instru-
ments mostly depend on the vibrative or tremulous
property of the material, which a body of colour
hardened in oil must very much alter : but we
should distinguish that this regards information
of sound, which may not altogether be the case in
the progress of it.

A remarkable circumstance in the nature of
F 4 sounds,

104 SOUND. f Lesson xvm.

souuds, which well deserves the attention of my
young readers, is, that every substance whatever,
whose parts are so connected as to be capable of
an uniform vibration, may have that vibration pro-
duced in it by the sounding of a certain musical
note or tone, with which it is in unison. Thus
Kircher speaks of a large stone that would tremble
at the sound of one particular organ-pipe. Mr.
Eoyle states the fact of seats trembling at the sound
of organs ; he tells us also, that he has felt his
hat to shake under his hand at certain notes, both
of organs and other instruments ; and he was
told by an experienced builder, that any well-
built vault will answer some determinate note.
JEven liquids, when so suspended as to be capable
of vibration (for example, water in a glass), are
observed, not only to vibrate when a particular
note is struck or sounded, but actually sound
themselves in concord. That water suspended in
a glass becomes in reality a sonorous body, is
proved by the mode of tuning a set of musical
glasses, which become the graver in tone, the more
water is poured into them ; for, were it only the
empty part of the glass that sounded, the sound
would become more acute, as more water is pour-
ed in ; but, as the contrary is the fact, it is thence
evident that the water and glass together form one
compound sonorous substance, of which the
greater the quantity or volume, the deeper is its
musical tone.

From what has been already stated, it will ap-
pear manifest; that when the producing cause of

any

Lesson xvnf.] SOUND. 103

any sound is at a distance, there must be an inter,
val of time elapse before the sound itself can arrive
tt the ear j and, indeed, this may often have been
manifested to us by our own observations. Thus,
for instance, when a gun has been fired at a dis-
tance, we may have taken notice, that after we
have seen the flash, sometime has elapsed previous
to our hearing the report : or again, when a wood-
man, remote from us, has been felling trees, we
may have observed that an interval of time passes
away after we have seen the action performed
before we hear the stroke. The experiments which
have been made to determine the velocity of sound,
have neither been so numerous nor so accurate as
could be wished ; and on this account it is, that
opinions differ concerning the nature of its pro-
gressive motion. Because the intensity of sound
diminishes as the distance increases, some persons
suppose that the velocity does also : they therefore
imagine that the velocity is inversely as the dis-
tance, and consequently the time will be directly
as the distance : but an opinion which meets with
more advocates, and may now bt regarded as con-
firmed, is, that sound moves uniformly in common,
atmospheric air, at the rate of 1 142 feet in one se-
cond of lime, or about an English mile in 4f se-
conds ; and this rate of motion being allowed, it
will not be any way difficult to determine the time
for the passage of sound, the distance being given,
and vice versa, in a variety of cases.

A curious phaenomenon with regard to sounds,

is an echoy which is caused by the vibrating air

r 5 being

106 ECHO. [Lesson XVHI

being interrupted in its passage. For as the air
tmdulates forward like a wave, it often meets with
various objects, and by striking against them is
reflected back to us, and causes new vibrations,
xvhich, if the object lie in a proper situation, return
to us and repeat the same sound, tone, or word, as
was first given : and this, it sometimes happens,
not only once but several times.

From this short account of the nature of echoes,
it will not be difficult to conceive that they also
may be applied to the measuring of inaccessible
distances : thus, Dr. Derham, standing upon the
bank of the Thames opposite to Woolwich, ob-
served that the echo of a single sound was reflected
back from the houses on the opposite bank in 3
seconds ; consequently the sum of the direct and
reflex rays must have been 1142 multiplied into 3,
or 3126 feet, and the half of it, viz. 17 13 feet, the
breadth of the river in that place.

But to treat upon the nature of sounds in such a
manner as the importance of the subject demands

' would fill a volume : I must therefore now desist.
From what little has been here mentioned, the

•contemplative young reader will with pleasure
draw this inference : that even in the nature and
production of sounds the goodness of the CRE-
ATOR to his creatures is conspicuously shewn:
for, if bodies had no degree of elasticity, or if the
air were not so fluid as to be easily put in motion,
there would be an end of all the melody and har-
mony which now so much delight us. What
praise does that benevolent BEING require from

us,

Lesson xvin.] ECHO. 107

us, who not only administers to us what is neces-
sary for our welfare, but has contrived all around
us in so admirable a manner as to be subservient
to our pleasures !

" On the1 contrary, had God wished our misery,
or even had he been indifferent to our happiness,
he might have formed our senses to be so many
pains and sores to us, as they now are instruments
of gratification and enjoyment : or have placed
us amidst objects so ill surted to our perceptions
as to have continually offended us, instead of mi-
nistering to our refreshment and delight. He
might have made, for example, every thing we
tasted, bitter ; every thing we saw, loathsome ;
every thing we touched, a sting ; every smell, a
stench j and every sound, a discord."

LESSON

LESSON XIX.

ON ErAPORATION, RATN, HAIL, SNOW, MISTS,
AND DEW.

• Th' effusive south

Warms the wide air, and o'er the void of heav'A
Breathes the big clouds with vernal show'rs distent,
At first a dusky wreath they seem to rise,
Scarce staining aether; but by swift degrees,
In heaps on heaps, the doubling vapour sails
Along the clouded sky. THOMSON.

t\

OUR next business is to reflect upon the means
by which the most usual meteors, as Rain, Hail,
Snow, and the all-enlivening Dew, are produced :
and in order to this, the first thing we are to con-
sider is the process of Evaporation. To have a
precise idea of evaporation, some persons distin-
guish it from exha ation, and say that the former
is the act of dissipating the humidity of a body in
fumes or vapour ; while the latter, they say, is'
properly a dispersion of dry particles issuing from
a body. Others say there is no need of any such
distinction, exhalation (properly signifying a
Ireathing forth) being applicable to all bodies
"capable of being respired, whether moist or dry.
The term commonly used by chemists for the
wising of the minute panicles of bodies in a dry

form*

Lesson xix.] EVAPORATION, &c. 109

form, is sublimation. Evaporation is by them ge-
nerally applied to bodies in a state of humidity;
and precipitation is the falling down ot any body>
dry or humid, which has been held in solution ia
any other body.

There are, indeed, few subjects of philosophi-
cal investigation that have occasioned a greater
variety of opinions than the theory of Evapo-
ration : as such a diversity of opinions yet exist,
it is almost next to impossible to advance one,
but what may be contradicted, and, in some
respect, refuted : however, be this as it will,
among the various theories I shall make use of
the following.

Dr. Hamilton, late Professor of Philosophy in the
University of Dublin, supposes that Evaporation
is nothing more than a gradual solution of water
in air produced and promoted by attraction, heat,
and motion, just as other solutions are effected.
To account for the ascent of aqueous vapours
into the atmosphere, this ingenious author ob-
serves, that the lowest part of the air being
pressed by the weight of the upper against the
surface of the water, and continually nibbing
upon it by its motion, attracts and dissolves those
particles which it is in contact with, and separates
them from the rest of the water. And since the
cause of solution in this case is the stronger attrac-
tion of the particles of water towards the air, than
towards each other, those that are already dissolved
and taken up, will be still farther raised bv the at-
traction of the dry air that lice over them, and thus

will

110 EVAPORATION, 8cc. [Lesson xix.

will diffuse themselves, rising gradually higher and
higher, and so leave the lowest air not so much satu-
rated but that it will still be able to dissolve and take
up fresh particles of water; which process is greatly
promoted by the motion of the wind. When the
vapours are thus raised and carried by the winds into
the higher and colder regions of the atmosphere,
some of them will coalesce into small particles,
which slightly attracting each other, and being
intermixed with air, will form clouds; and these
clouds will float at different heights (varying from
less than half a mile to somewhat more than two
miles) according to the quantity of vapour borne
up, and the degree of heat in the upper part of the
atmosphere: and thus, clouds are generally higher
in summer than in winter.

When the clouds are much increased by a con-
tinual addition of vapours, and their particles are
driven close together, by winds, cold, and other
causes, then will they run into drops heavy enough
to fall down in Rain :

—The clouds consign their treasures to the fields,
And, softly shaking on the dimpled pool
Prelusive drops, let all the moisture flow
In large effusion o'er the fresLen'd world.

THOMSON.

In the winter, when the air is disposed for freez-
ing, it is not unlikely that the atoms of vapour
which are near the earth are congealed, whereby
they become more opaque, and form those ob-
scure fogs which constitute a hoar frost. At this

time

Lesson xix.] SNOW, HAIL, 8cc. 1 1 1

time the clouds are probably frozen before their
particles are gathered into drops : small pieces of
them being condensed and made heavier by the
cold, fall down in Snow :—

Then from aerial treasures downward pours
Sheets of unsullied snow in lucid showers ;
Flake after flake, through air, thick wav'ring flie»,
Till one vast shining waste all natnre lies.
Then the proud hills a virgin whiteness shed
A dazzling brightness glitters from the mead ;
The hoary trees reflect a silver show,
And groves beneath the lovely burden bow.

BROOME,

On a close examination, Snow is found to be
composed of icy darts or stars united to each
other, as crystals of water commonly are, whether
they compose ice, snow, or hoar frost, at angles
of 60 or 120 degrees. Its whiteness is owing to
the small particles, into which it is divided, re-
fracting and reflecting, instead of transmitting, all
the rays of light that fall upon it. Ice, when
pounded, becomes equally white.

If drops of rain in their falling pass through
a region of cold air, they become congealed in
their passage, and fall in Hailstones: but Signior
Beccana supposes that Hail is formed in the
higher regions of the air, where ihe cold is
intense, and where the electric matter is very
copious.

In the months of October and November, Fogs
or Mist 9 are more frequent and thicker than at any
other period of the year. If we consider the cause

of

llf EVAPORATION, Sec. [Lesson xix.

of Fogs, the reason of this will appear evident.
There is, besides the evaporation from the seas,
lakes, and rivers, a constant and very large exha-
lation from the surface of the earth, at all seasons,
of water in the form of vapour ; and the warmer
the ground the greater will be the evaporation.
When the air is waum-r, or even but a little colder
than the earth, the ascent of vapour is not per-
ceptible to the eye : but when the temperature of
the air is considerably lower, the vapour as soon
as it rises is deprived of part of its heat, the
watery particles are brought more into union, and
they become visible in the form of steam. It is
also essential to the formation of Fog, that there
should be little or no wind stirring, in order that
the rising exhalations may have full opportunity
to condense. The heat of the middle of the days
in autumn is stiil sufficient to warm the earth and
cause a large ascent of vapour, which .the chill-
ing frosty nights, which are also generally very
calm, condense into Fogs.

When vapour is condensed into small drops upon
the surface of bodies on the ground, it is called
Dew ; the most apparent difference between Dew
and Rain is, that the condensation of vapour, in
the one case, is made at or near the surface of the
body receiving it, and in the other the drops fall
a considerable space before thev reach the earth :
the cause is the same in both cases, namely, cold
operating upon vapoury air. At first view, 4t will
appear improbable that a condensation of vapour
should take place in the air resting upon the earth's

surface,

Lesson xrx.] FOGS, DEWS, &c. H3f

surface, which is generally supposed to be warmer
than that above; but it is an incontestible fact,
that after sun-set, and during the night, in serene
weather, the air is coldest at the earth's surface,
and grows warmer the higher we ascend, till a
certain moderate height, commonly between 2O
and 100 yards : accordingly we find, that Dews and
Hoar Frost are more copious in valleys than in
elevated situations. When we recollect that winds
in great measure prevent the accumulation of Dew,
it can scarcely be doubted but that it depends upon
the abovexircumstance.

It would be nearly inexcusable to conclude this
Lesson, without calling the attention of my young
readers, for a moment, to the beneficent and wise
laws established by the AUTHOR OF NATURE to
provide for the various exigencies of the sublunary
creation, and to make the several parts so depend-
ant upon each other, as to form one well-regulated
whole. In the torrid zone, and, it may be added,
in the temperate and frigid zones also, in summer,
the heat produced by the action of the solar rays
would be insupportable, were not a large portion
of it absorbed, in the process of Evaporation, into
the atmosphere, without increasing its tempe-
rature. This heat is again given out in winter,
when the vapour is condensed, and mitigates the
severity of the cold. The dry spring months are
favourable to agriculture, and the Evaporation,
which then begins to be considerable, absorbs a
portion of the heat imparted to the earth by the
sun, and thus renders the transition from cold to

heat

114 EVAPORATION, &C. [Lesson XIX.

heat slow and gradual. Jn autumn, the sun's in-
fluence fails apace, but ihe condensation of vapour
contributes to keep up the temperature and pre-
vent too rapid a transition to winter.

Thus have you another page of the volume of
nature opened to your view ; and though de-
scanted upon in a concise manner, I have no
doubt but that it will be an additional incentive
for you to increase in gratitude, reverence, and
love for the adorable AUTHOU of ail good.

LESSON

LESSON XX.

ON FROST.

What art thou, Frost! and whence are thy keen stores
Deriv'd, thou secret, all-invading power,

Whom even th' illusive fluid cannot fly?

THOMSON.

XlOW admirably wonderful and diversified are
the opejations of Frost ! The thronging mulii-
tudes of the stars with peculiar brilliancy glitter
through the fair expanse, while the Frost pours
its subtle and penetrating influence all around ;
and sharp and intensely severe throughout th^
long night continues its rigid operations.

Loud rings the frozen earth, and hard reflect*

A double noise : while at the evening watch

The village dog deters the nightly thief:

The heifer lows ; the distant water-fall

Swells in the breeze ; and with the hasty tread

Of traveller, the hollow sounding plain

Shakes from afar. THOMSON.

When, late and slowly, the morning opens her
pale eye, in what a curious and amusing disguise
is nature dressed ! The icicles, jagged and un-
even, hang pendant from the eves, and a whitish
film encrusts the windows, where mimic landscapes
rise, and fancied figures swell. The once fruitful
fields are hardened as iron, and the moistened mea-
dows

116 rnosr. [Leston xx.

dows are firmly congealed. The limpid stream is
arrested in its career, and its formerly flowing sur-
face chained to the banks. The fluid paths become
a solid road ; and where the finny shoals were wont
to rove, the sportive youths slide, or with rapid
/motion skate along the crystal pavement. When
these and other wonders brought about by freez-
ing, are considered, surely it is not unnatural to
ask — how are they occasioned ? This, perhaps,
cannot be answered with the wi?hed-for accuracy :
however, though the following observations do not
entirely determine the point under consideration,
they may yet be somewhat amusing.

The fixing of a fluid body into a firm or solid
mass by the action of cold, is called freezing, or
congelation ; in which sense the terms are applied
to water when it freezes into Ice. By what mean
it is that fluid bodies should thus be rendered solid
by cold, the learned have not yet been able to dis-
cover. It would seem, however, that it arises from
the air then abounding with nitrous and saline par-
ticles, which insinuate themselves into the pores of
water, &c.by which mean they become hard. This
is the more probable when it is considered that
zmongfreezing mixtures, all kinds of salts, whether
alkaline or acid, are the principal ingredients.

The process of congelation is always attended
with the emission of heat : it is also observed, that
water loses of its weight by freezing, being found
lighter after thawing again, than before it was
frozen. And indeed it evaporates almost as fast
when frozen, as when it is fluid : iiay, it has been

observed,

Lesson xx.] FROST. 117

observed, that, in Frost, the greater the cold the
greater the evaporation; and this, by the bye, fur-
nishes us with areason why there should generally
be more rain fall in February than in any other
month.

The manner in which congelation is effected, is
now generally thus explained. When water is
exposed to <tn atmosphere colder than itself, it
parts with some of its free heat, and is reduced in
temperature : but no part of it begins to freeze
until the mass is reduced somewhat be!ow the 32d
degree of Fahrenheit's thermometer * : some of the
water then becomes solid, which, by changing its
state, sets at liberty a quantity of its combined
heat, which restores the fluid in contact with it
to the temperature of 32 degrees, or rather above
it. The congelation is, therefore, rather at a stand,
till this sensible heat is abstracted by the atmos-
phere, and the mass reduced somewhat below tire
32d degree. Another portion of water then con-
geals, and the process is again stopped by the
emission of heat. In this manner congelation
proceeds, and is performed at intervals which are
very observable when the phenomenon of freez-
ing is accurately attended to.

Water which has been boiled freezes more rea-
dily than that which has not been boiled : it is also
observed, that a slight disturbance of the fiuid dis-
poses it to freeze more speedily. Water having

•* For a few remarks relative to this instrument, the Reader
is referred to the Appendix.

it*

HQ FIIOST. [Lesson xx.

its surface covered with oil of olives, does not
freeze so readily as without it : and nut-oil abso-
lutely preserves it under a strong frost, when olive
oil would not. The surface of water in freezing,

C7

appears, as it were, wrinkled ; the wrinkles being
sometimes in parallel lines; but more commonly
they make angles of about 60 degrees with each
other ; and sometimes they are like rays proceed-
ing from a centre to the circumference.

Another circumstance relative to the congela-
tion of water I cannot forbear mentioning, as it is
very remarkable. When water is cooled to within
eight or nine degrees of the freezing point, it not
only ceases to be farther condensed, but is actually
expandedby farther diminutions of its heat ; and
this expansion goes on as the heat is diminished,
so long as the water can be kept fluid : and when
it is converted into ice, it expands even still more,
and the ice floats on the surface of the uncongealed
part of the fluid. This is the more extraordinary,
as it is an exception to one of the more general
Jaws of nature with which we are acquainted. It
ie also worth while to remark, that though in tem-
peratures above blood-heat, the expansion of water
with heat is very considerable, yet in the neigh-
bourhood of the freezing point, it is exceedingly
small. Now it is evident, that when the specific
gravity of a liquid is but little changed by any given
change of temperature, the motions among the
particles of the liquid occasioned by this change
must be sluggish, and the communication of ht.at
of course very slow, and hence, from the preceding

account

Lesson xx.] FROST. 11$

account of congelation, its process must also be
slow.

The late Count Eumford (whose reasonings on
this point are very ingenious, and have been far
extended) draws from the circumstance an obser-
vation 'which I cannot forbear presenting to my
young readers. " Suppose," says he, " that in
'* the general arrangements of things it had been
" necessary to contrive matters so that water
" should not freeze in winter, — or that it should
" not freeze but with the greatest difficulty,
" very slowly, and in the smallest quantity pos-
ts sille ; — how could this have been most readily
« effected ?

" Those who are acquainted with the law of the
" condensation of water, on parting with its heat,
" have already anticipated me in these specula-
" tions ; and it does not appear to me that there
" is any thing which human sagacity can fathom,
" within the wide-extended bounds of the visible
" creation, which affords a more striking or more
" palpable proof of the wisdom of the CREATOR,
f{ and of the special care he has taken in the gene-
" ral arrangement of the universe to preserve ani-
" mal life, than this wonderful contrivance : for
** though the extensiveness and immutability of
** the general laws of Nature impress our minds
" with awe and reverence for the Creator of the
" universe, yet exceptions to those laws, or parti-
" cular modifications of them, from which we are
tl able to trace effects evidently salutary or advan-
" tageous to ourselves and our fellow-creatures,

« afford

120 TROST. [Lesson XX.

c* afford still more striking proofs of contrivance
<f and ought certainly to awaken in us the most
" lively sentiments of admiration, love, and gra-
•« tilude."

Though we cannot speak with confidence and
certainty as to the secondary causes by which
many or' the wondrous effects of congelation are
brought about, we cannot surely be at a loss to
ascribe these and every other effect which takes
place in the different seasons, to the great FIRST
CAUSE. With regard to the attendants of winter,
they ought, though -cold and dreary, to warm our
hearts with the fire of Charity. Ye that sit easy
and joyous in your commodious apartments, solac-
ing yourselves in the diffusive warmth of your fire ;
O ! remember, that many of your fellow-creatures,
amidst all the rigour of the inclement skies, are
emaciated with sickness, benumbed with age, and
pining with hunger. Think ! for Heaven's sake,
think

• How many drink the cup

Of baleful grief, or eat. the bitter bread

Of misery! Sore pierced by wintry wind*,

How many shrink into the sordid hut

Of cheerless poverty! THOMSON.

while a few faint and dying ambers on the squalid
hearth, rather mock their wishes than warm their
limbs. Methinks every piercing wind that blows,
and every addition Co the severity of the frost,
pleads for the poor indigents : may they breathy
pity into your breasts, and may you be thereby in-
duced

Lesson xx.] FROST. 121

cluced to succour them in their distresses, relieve
them from their calamities, clothe their naked bo-
dies, and mitigate the severities of their wants :
thus shall you obtain their prayers, and bring peace
and comfort to your own souls !*

* As the following sentences have an affinity to the per-
suasives above given, I hope an apology for inserting them
here is wholly unnecessary.

" Wheu the fatherless calls upon thee, when the widow's
heart is sunk, and she imploreth thy assistance with tears of
sorrow ; O pity her affliction, and extend thy hand to thosa
who have none to help them.

" When thon seest the naked wanderer of the street shiver-
ing with cold, and destitute of habitation, let bounty open
thine heart; let the wings of Charity shelter him from death
that thine own soul may live.

" Whilst the poer man groaneth on the bed of sickness*
whilst the unfortunate languish in the horrors of a dungeon,
or the hoary head of age lifts up a feeble eye to thee for pity;
O how canst thou riot in superfluous enjoyments, regardless
of their wants, unfeeling of their woes!"

ECONOMY OF HUMAN LIFF-

LESSON

LESSON XXT.

ON ELECTRICITY.

Electricity possesses much of what is admirably adapted U

discipline the mind Let your resolutions then be

formed to study it, as a science in all its tendencies favour-
able to the general interest of knowledge, and to your own
particular improvement. MORGAN.

JjEFORE I attempt to explain to you the nature
of Thunder-storms, which will be the business of
the next Lesson, it may be advantageous to appro-
priate a few pages to the subject of Electricity, as
it will tend to elucidate what may be said relative
o these phsenomena.

Electricity (derived from the Greek name for
amber) is that power or property, which was first
observed in amber, and which sealing-wax, glass,
and a variety of other substances, called Electrics,
are known to possess, of attracting light bodies,
such as chaff, fine thread, and bits of straw, when
«xcited by heat or friction : and which is also
capable of being communicated in particular cir-
cumstances to other bodies. The term is also,
often, more extensively applied to all other similar
powers or properties, and their various effects, in

whatever-

Lesson xxi.] ELECTRICITY. 123

whatever bodies they reside, or to whatever bodies
they may be communicated.

If a tube of glass, an inch and an half in diame-
ter and about three feet long, be rubbed, by re-
peatedly drawing the hand, or a piece of leather,
from one end to the other, it will become electric ;
so that small flashes of divergent flame, ramified
somewhat like trees bare of leaves, will dart into
the air ; from many parts of the surface of the tube,
to the distance of six or eight inches, attended with
a crackling noise ; and sometimes spafrks will fly
along the tube to the rubber at more than a foot
distant. This luminous matter is called the Elec-
tric Matter or Fluid, and all bodies that we are
acquainted with have more or less of it in them j
though it seems to lie dormant till it be put in
action by rubbing, and then (in a dark room) it
appears, like fire.

Some bodies freely admit this fluid, and let U
pass through th,eir pores ; others do not. The
former- of these are called, Non-electrtts, or Con-
ductors : of this sort are all metals, living-creatures,
water, and moist wood ; but metals. are found to
be the best conductors. The latter, which do not
allow the Electric Fluid to pass through their
pores, are called Electrics, or Non-conductors : of
this kind are glass, wax, rosin, dry glue, baked
wood, and silk. But if either of these be wetted
with water, the water that adheres to it will render
it a conductor ; consequently, when any body is to
be used as a non-conductor, it should be well wiped
G 2 with

ELECTRICITY. [Lesson xxi.

with a dry warm cloth, to clear it of damps, which
it may have contracted in a variety of ways. The
quantity of Electric Matter which every body has
lying dormant in it, is called its natural quantity;
and this would always remain motionless and in-
visible if nothing disturbed it. But when any
more is forced into it, as suppose at one end, the
whole is instantly put into motion thereby, and
begins to be driven out at the other end, if it can
find a passage.

The earth is the grand source of the Electric
Fluid, and no additional quantity can be forced
into any body but from the earlh. If the body
be a free conductor, and have a communication
with the earth by .means of any other conducting
substance, as metal, or by a table, to the floor and
walls of a room, and from thence to the earth, the
Electric Fluid will run as fast from the conductor
Jo the earth, as it is by any means driven into the
conductor. But if the communication between
the earth and the conducting body be cut off by
means of any non-conductor, some of the Electric
Matter may be forced into the conductor, by
which means it will have more than its natural
quantity; and the earth, from which that addi-
tional quantity comes, will have so much less :
which could never be, if the Electric Fluid were
not of an elastic nature, or could not be com-
pressed.

When any body has more than its natural quan-
tity of this fluid, it is said to be electrified positive-

ly,

1*559/1 XXI.] ELECTRIClTV. 125

ly, or plus ; and when it has less than its natural
quantity, it is said to be electrified negatively, or
'minus. When bodies are electrified either of these
ways, they repel each other ; but if some be elec-
trified plus, and others minus, they mutually at-
tract ; or if one body be electrified plus, and the
other no way at all, they also attract each other.

The following experiments will tend to shew
the reality of Electrical Attraction and Repulsion.
Cut two bits of cork into the shape and size of a
common pea. With a needle draw a thread
through each of the corks, so that they may be
made to hang at the ends of the threads with a
knot below them. Let the oilier ends of the
threads be inserted in the notch of a small
piece of wood, about a foot long, an inch broad,
and the thickness of a common match. Lay the
piece of wood over the mouths of two wine
glasses, a few inches asunder, so that the end
of it, in which the threads are, may project over
the edge of the glass nearest it, and the corks
may be in contact with one another. Take ano-
ther wine glass ; and having rubbed it heartily
with a piece of flannel, or upon the skirt, or
sleeve, of a woollen coat, hold its mouth to within
about an inch of the corks, and they will suddenly
start asunder and continue so for some time.

Again, lay a pocket watch upon an horizontal
table, and take a common tobacco-pipe, and place
it on the face of the watch so that it may rest
thereon in equilibria : then, after rubbing a wine
glass (as described in the former experiment),
G 3 bring

126 ELECTRICITY. [LeSSOH XXI.

bring it to within an inch of the smaller end of the
tobacco pipe, and by moving the glass gently
round in an horizontal circular track, you will
cause the pipe to turn round on the watch-
glass as the needle turns on its centre in a mari-
ner's compass.

A great many experiments may be performed
with the help of an Electrical Machine ; which may
be bought, with the necessary apparatus, at the
shop of any philosophical-instrument maker in
London : but, as it is probable that several persons
may wish to try Electrical Experiments, who can-
not well afford to purchase a more complete appa-
ratus, I shall here give a description of a very sim-
ple machine, and one that may be made at but
little expense. It consists of two plates of a cir-
cular form ; the under plate may be of wood, glass,
or brass, five inches in diameter and covered on
the upper side with an even coat of melted sealing-
wax of the second quality. The upper plate may
be made of wood, coated entirely with tin-foil,
having a handle of baked wood, or glass, fixed in
the centre of its upper surface. Or it may be
made of tin, wired a^id soldered round the edges
on the upper side, with a small socket in the cen-
tre for fixing the handle. The socket and handle
may be coated with melted sealing-wax dissolved
in spirit of wine. If the under plate be made of
wood, glass, or sulphur, it may be coated on
the under side with tin-foil, fixed on with stiff
paste. /

To use this machine : First, with a dry, warm

piece

Lesson xxi.] ELECTRICITY. 127

piece of flannel, rub briskly that side of the under
plate which is covered with sealing-wax, place it on
a table with the excited side upward ; set the upper
plate exactly on the lower, touch the upper plate
with the finger, then raise the upper plate by the
handle, and it will give a spark of Electric Fire to
any conducting substance. By repeating the ope-
ration, another spark may be obtained, and s« on.
If the upper plate be not touched with the ringer,
or some conducting substance, no spark can be
obtained. If the sparks be given to the ball of,a
coated* phial, it will become charged, and the
Electric Shock may be given.

Having said thus much concerning an Electrical
Machine, I will proceed to describe a few more

experiments. If one body, as suppose a piece

of metal, be kept for some time in an electrified
state, by means of the machine, and an unelectri-
fied light body, as suppose the down of a feather,
be brought near the metal, the feather will be at-
tracted to it, and thence electrified: on which ijt
will be immediately repelled from it, and will not
return to it again, till after it has touched some un-

* Bottles may be easily coated in the following manner :—
Take bismuth two parts, lead and tin of each one part, melt
them together and carefnlly skim off the dross ; remove the
mixture from the fire, and, before, it grows cold add ten parts
of hot mercury ; stir the whole together, and the amalgam
when cold, is fit for use. Let the bottle, to be coated, be quit*
new and clean ; put into it a sufficient quantity of the amal-
gam, incline the bottle, and gently turn it round that the
composition may adhere to every part, ponr out the super-
fluous amalgam, and the bottle will be beautifully coated.

G 4 electrified

128 ELECTRICITY. [Lesson xxi.

electrified body that is of the conducting kind, and
deposited its fluid into it, and then if the distance
be but small, as about two or three inches, it will
return to the electrified metal as before, and be
repelled from it again.

If a round piece of metal be electrified, and any
pointed piece of metal be held near it, the point
will draw off the fire from the electrified metal, if
that which has the point be supported by any con-
ducting substance.

If the middle of a wire, that is pointed at both
ends, be fixed to a stick of wax, and either of the
points be held near the metal which is kept in
an electrified state by the machine, that point will
draw off the fire from the metal, and the fire will
run off from the other point into the air. From
this \v£ learn, what is very remarkable, that metal-
lic points throw off, as well as attract Electric Fire.
Should this experiment be made in a dark room,
the Electric Matter drawn from the metal would
appear like a round spark on the point that at-
tracts, and would be seen going off in the form of
a cone from the other point.

If a large globe of metal be electrified positively,
it will retain the Electric Fire for some considerable
time. For the surrounding air prevents the accu-
mulated fire from issuing so fast from the globe as

it otherwise would If two globes of metal

be hung by silk lines, or placed on wax, at about
two feet from each other, and one globe be then
electrified, and the other be hung, or placed, rather
nearer it j the .former will soon lose part of the

Electric

Lesson xxi.] ELECTRICITY. 129

Electric Matter, which will be drawn off by the
latter; but the point of a needle would draw it off
much sooner.

Writers on Electricity give accounts of a variety
of experiments in this entertaining science, from
which some of the properties of the Electric Matter
may be deduced ; but as to its real nature philoso-
phers have entertained very different sentiments.
Some have supposed that it is the same with the
ether of Sir Isaac Newton, to which the attraction
and repulsion are ascribed ; whilst the light, smell,
and other sensible qualities of the fluid, are referred
to the grosser particles of bodies driven from them
by the forcible action of this ether : and other ap-
pearances are explained by means of a subtile me-
dium diffused over the surfaces of all bodies, and
resisting the exit and entrance of the ether; which
medium, it is supposed, is the same with the Elec-
tric Fluid, and is more rare on the surfaces of con-
ductors, and more dense and resisting on those of
Electrics. But Dr. Priestley (whose abilities and
penetration, as a philosopher, are two well known
to need any encomium from me,) objects, in some
measure, to the hypothesis above recited, and gives
it as his opinion, founded on experiments, that the
Electric Matter either is phlogiston, or contains it •
since he found that both produced similar effects.
Mr. Henley also apprehends, that the Electric
Fluid is a modification of that element, which, in
its quiescent stale, is called phlogiston; in its first
active state, Electricity j and, when violently agi-
tated, Fire.

G 5 This

*
130 ELECTRICITY; [Lesson xxr.

This Electric Fluid, it is supposed, moves with
great ease in those bodies that are called conductors,
but with extreme difficulty and slowness in the
pores of Electrics ; whence it comes to pass, that
all Electrics are impermeable to it. Jt is farther
supposed, that Electrics contain always an equal
quantity of this fluid, so that there can be no sur-
charge or increase on one side, without a propor-
tionable decrease or loss on the other, and vice
versa ; and as the Electric does not admit the pas-
sage of the fluid through its pores, there will bean
accumulation on one side, and corresponding de-
ficiency on the other. Then when both sides are
connected together by proper conductors, the equi-
librium will be restored by the rushing of the re-
dundant fluid from the overcharged surface to the
exhausted one. Thus also, if an Electric be rub-
bed by a conducting substance, the Electricity is
only conveyed from one to the other, the one giving
what the other receives ; and, if one be electrified
positively, the other will be electrified negatively,.
unl< ss the loss be supplied by other bodies connect-
ed with it. This theory serves likewise to illustrate
the various phenomena and operations in the
science of Electricity : thus, bodies differently elec-
trified will naturally attract each other, till they
mutually give and receive an equal quanti'y of the
EKctric Fluid, and the equilibrium is restored be-
tween them. B.eccaria supposes that this effect is
prodncfd-by the Electric Matter making a vacuum
in its passage, and the contiguous air afterwards
collapsing, and so pushing the bodies together.

It

Lesson xxi.] ELECTKICITY. 131

It is natural to imagine, that a power of such ef-
ficacy as that of Electricity, might be applied with
advantage to medicinal purposes; especially since
it has been found invariably to increase the sensible
perspiration, to quicken the circulation of the
blood, and to promote the glandular secretion : ac-
cordingly, many instances occur in the history of
this science, in which it has been applied with con-
siderable advantage and success. In most disor-
ders in which it has been used with perseverance,
it has given at least a temporary and partial relief,
and in many it has effected a total cure. Electrical
shocks, properly applied, have frequently cured the
ague, tooth-ach, head-ach, rheumatism, pain in the
stomach, sore throat, and sometimes the gout ;
deafness of several years' continuance has been re-
moved; and in one case, a person who had been
deaf from his birth, was cured by Electricity : it
has cured chilblains, and removed hard swellings
in various parts of the body j it has been success-
fully applied in bad spasmodic and paralytic cas^s f
it has cured the St. Vitus's dance; and it has in
one ease, if not more, restored* sight to the blind.
Since the science of Ereolricrty has been applied
to the desirable purpose of restoring health to the
sick, the emaciated, and infirm, often with con-
siderable success, even by gentlemen who are not
physicians, and consequently cannot be supposed
to distinguish always between cases where it may,
and where it may not, be advantageously applied;
it is much to be lamented, that medical gentlemen
of skill and judgment do not, more generally than

they

ELECTRICITY. [/.mow xxi.

they have hitherto done, give directions for the
use of the Electrical Machine, and point out in
what cases we may have recourse to it with benefit
and safety, and in what cases it would be pre-
judicial. For I am convinced, that were such di-
rections laid down and properly disseminated, many
benevolent persons in different parts of the king-
dom would, with alacrity, embrace the many op-
portunities which would be then afforded them,
of removing the infirmities, and allaying the
excruciating pains of their indigent neighbours ;
thus alleviating distress, and restoring comfort and
joy to those who may have been long pressed
down with affliction.

From perusing the imperfect account which .1
have here given of the science of Electricity, I hope
you will be induced to labour after a more familiar
acquaintance with it. Be assured that it possesses
every property which can make knowledge interest-
ing to the human mind : the power whose laws,
whose relations, and whose effects it investigates,
has been proved to be one of the most extensive in
nature : there is scarcely any science, the light of
which may not be increased by it : many are the
arts in social life to which it will communicate new
powers, and many are the mysterious circumstances
in the history of nature and mankind, which by
it may properly be developed and explained.

It must be acknowledged, however, that this
science is, as yet, in its infantine state : the Ian"
guage by which it is taught is imperfect and ob-
scure : aud though various laudable attempts have

becu

Lesson xxi.] ELECTHICITIT. 133

been made by philosophers of eminence and cele-
briiy, to gain a respectable place among its sister
sciences, it is rarely made an object of eager and
complete attention, or of that persevering activity,
by which alone it can rise to its proper consequence
and maturity.

Before I conclude this lesson I must briefly
notice Galvanism or Voltaism, which embraces
the phaenome.na which result from different con-
ductors of Electricity being placed under different
circumstances of contacr. The conductors must
be either perfect or imperfect conductors of Elec-
tricity: and the Galvanic Phenomena may be pro-
duced by two conductors of one of these classes
placed in contact with each other, in one or more
points, and in other distinct points with a conduc-
tor of the other class : thus gold and zinc may be
made to touch each other, in some points, and may
be connected in other points, by a portion of
common water.

To produce the Galvanic phenomena with any
considerable effect, several series of conductors,
thus disposed, should be employed. Then, not
only may an acid taste, a flash of light, the con-
tractions of muscles just detached from a living
body, the oxidizement of metals, and the decom-
position of acids and of water, be produced ; but
shocks on the human body analogous to the
electric shock, and brilliant sparks, with the de-
flagration of even silver and gold, may also be oc-
casioned by this fluid, under certain circumstances.
Fabrtni, in Nicholson's Journal for 1800, noticing

the

134 ELECTRICITY. [Lesson XXI.

the ox idizement of metals while under Voltaic in-
fluence, concluded it to be a chemical phenomenon
merely. In this year, Volta announced his dis-
covery of the Galvanic pile, formed by plates of
two different metals, as zinc and silver, disposed
alternately with moistened pasteboard between
them. By connecting the ends of the pile by
the hands, he obtained a strong shock, and pro-
duced many curious experiments. Mr. Nicholson,
in the same year, employed much of his ingenuity
in examining these phaenomena, and devoted a
considerable portion of his Journal to their investi-
gation. By making a tube of water form part of
the line connecting the two ends of the pile, he.
found, from the wire passing into the water from
the silver end, hydrogen separated; whilst the
other, if an oxidable metal, became oxidized, but,
if platina, he found oxygen was evolved. Thug
was ascertained its cftemical action, and its powers
of decomposing water.

But the most important discoveries in Voltaism
have been made by Sir Humphrey Davy. They^
however, would of themselves fill a volume, and
therefore camioi be here detailed.

LESSON

LESSON XXII.

ON THUNDER AND LIGHTNING.

— By conflicting winds together dash'd,

The Thunder holds his black tremendous throne ;

From cloud to clond the rending Lightnings rage;

'Till, in the furious elemental war

Dissolv'd, the whole precipitated mass

Unbroken floods and solid torrents pours.

THOMSON..

AMONG the numerous phenomena which you
have observed, it is scarcely probable that there are
any which should more tend to raise in your mind
serious reflections, than that which we are now
about to consider. The more than usual gloomi-
ness of the sky, — the uncommon heat of the air, —
the astonishingly rapid descent of the rain or hail;,
which generally attend the Thunder's tremendous
clap, and the Lightning's forked flash, undoubt-
edly all contribute »o raise ideas of wonder and awe.
But when we reflect upon the terrible effects which
Thunder Storms sometimes produce, — buildings
set on fire, — huge trees split into shivers,- — steeples
rent, — animals and men destroyed, — and metals
melted like wax; — what emotions do we feel? The
guilty soul will in a manner shrink into itself
with terror : but the truly religious and philoso-
phic mind, whilst filled with admiration of the

- POWER

136 THUNDER Sc LIGHTNING. [Lesson XXII.

POWER which produces such stupendous effects,
will be naturally led to inquire by what natural
means they are occasioned.

An opinion very prevalent among philosophers
until late years, was, that this awful class of
phsenomena is produced by a variety of acetous,
bituminous, spirituous, nitrous, and sulphureous
particles, exhaled from various bodies, and raised
into the air; and there being driven to and fro by
the wind and other causes, are at length violently
agitated, and furiously striking against each other
force themselves through the clouds, attended with
an explosion which we call Thunder, and a flame
or flash which is called Lightning: the bituminous
and sulphureous particles causing the flash, and
the nitrous particles occasioning the explosion.

But it is now universally allowed, that Thun-
der-storms are produced by electricity : the proof
of this was reserved for Dr. Franklin, who is
so justly celebrated for his many discoveries
particularly in that branch of natural philosophy
which was the subject of the preceding Lesson.
This philosopher traced out with much accuracy
several particulars in which Lightning and the
Electric Spark agree : a few of these I shall here
mention.

Flashes of L'ghtning are generally seen crooked
and waving in the air: this is also the case with the
Electric Spark, when it is draun from an irregular
body at some distance. Lightning strikes the
highest and most pointed objects in its way, pre-
ferably to others: in like manner, all pointed con-
ductors

Lesson xxn.] THUNDER 8c LIGHTNING. ' 137

ductors receive or throw off the electric fluid more
readily than such as are terminated by flat surfaces.
Lightning takes the readiest and best conductor:
so does the electrical fluid. Lightning burns : so
does electricity. Lightning sometimes dissolves
metals : so does electricity. Lightning has been
often known to strike people blind : and pigeons
and other small birds have been struck blind by
electricity. Lightning sometimes destroys animal
life: animals have likewise been killed by elec-
tricity.

But what demonstrates in the clearest manner
possible the identity of electrical fire with the mat-
ter of Lightning, is, that the Doctor, astonishing
as it must have appeared, contrived actually to
bring Lightning from the heavens by means of an
electrical kite, which he raised when a storm of
thunder was coming on. The same experiment
has been frequently repeated by other philosophers;
and it is to be lamented, that it was once attended
with fatal consequences : for the Allc Richman
was killed by a flash of Lightning which he drew
down from the clouds, in an experiment he was
making at Petersburgh.

To know that Lightning and electric matter are
the same, is a great step in natural philosophy]
but so long as our acquaintance with the properties
of electricity continues so very imperfect as it yet
is, we must necessarily remain ignorant of the causes
of many of the appearances which accompany
Thunder-storms. However, we will now proceed
to give such an explanation of the phenomena, as

the

J38 THUNDER & LIGHTNING. [Lesson XXII.

the present state of knowledge will permit. Many
observations and experiments tend to prove that
some clouds are in a positive, and some in a nega-
tive state of electricity; and from other experiments
ithas been inferred that the quantity of electric mat-
ter in a common Thunder-storm, is inconceivably
great, considering how many pointed bodies, as
steeples and trees, are continually drawing it off,
and what a prodigious quantity is repeatedly dis-
charged to or from the earth. This matter is in
such abundance, that it is thought impossible for
any number of clouds to contain it all, so as either
to receive or discharge it. During the progress
and increase of a storm-, it has been observed, that
though the Lightning frequently struck to the
earth, the same clouds were ready the next mo-
ment to make a still greater discharge: whence it
is concluded, that the clouds serve as conductors
to convey the electric fluid from those parts of the
earth that are overloaded with it, to those that are
exhausted of it. The same cause by which a cloud
is first raised, from vapours in the atmosphere,
draws to it those which are already formed, and
still continues to form new ones, till the whole col-
lected mass extends sufficiently far to reach a part
of the earth where there is a deficiency of the elec-
tric fluid, at which place the electric matter will
discharge itsrlt on the earth. A channel of com-
munication being thus formed, a fresh supply of
electric matter is raided from the overloaded part,
which continues to be conveyed by the medium of
the clouds, till the equilibrium of the fluid is re-
stored

Lesson xxn.] THUNDER 8c LIGHTNING. 139

f —

stored between the two places of the earth. The
Lightning throws before it the narts of conducting
bodies, and distributes them along the resisting
medium through which it must force its passage ;
the longest flashes seem to be made, by forcing
in the way of the electric matter, part of the va-
pours of the air.

The claps of Thunder which accompany the
flashes of Lightning, seem to be occasioned by the
filling of the vast vacuum made by the passage of
the electric matter: for, although the air collapses
the moment after the matter has passed, and the
vibration on which the sound depends commences
at the same moment : yet when the flash is di-
rected towards the person who hears the report, the
vibrations excited at the nearer end of the track
will reach his ear much sooner than those from the
remote end ; and the sound will, without any echo
or repercussion, continue, till all the vibrations
have successively reached him.

It must be confessed, however, that the question,
how it happens that particular parts of the earth or
the clouds come into the opposite states of positive
and negative electricity, is not absolutely deter-
mined: among the numerous conjectures, the one
which supposes the electric matter then in the
clouds to be generated by the fermentation of sul-
phureous vapours with mineral or acid ones, seems
to have a great share of probability, especially
when it is recollected that Thunder-storms generally
happen when the air is in a sultry state.

With

140 THUNDER Sc LIGHTNING. [Lesson XXIf.

With regard to the degree of danger in storms
of Thunder and Lightning, it is not easy to speak
with precision : though it may be noticed, that it
seems to depend chiefly on the distance from the
track of the electric fluid: which distance is greater
or less in proportion as a greater or less interval of
time elapses, between seeing the flash and hearing
the explosion. If a person can count five pulsa-
tions between the flash and the succeeding clap of
Thunder, he may infer that the cloud is a mile dis-
tant. For ten pulsations the distance is two
miles, and so on.

As to places of safety from the danger of these
storms, the general opinion is that the open fields
are more safe than under cover of a house : those
who are in the fields at such times, would do well
to place themselves within 50 yards of a tree, but
by no means quite near it. It is generally thought
safer to have one's clothes wet than dry, as the
Lightning might then in a great measure be trans-
mitted to the ground, by the water on the outside
of the body. — Under cover, people are advised to
sit near the middle of a room on one chair, and
lay the feet on another, observing that no metals,
as candlesticks, iron chains, &c. are near. A
still better method is, to place the chairs upon
mattresses or feather-beds : a safer way yet is,
to be in a hammock hung on silken cords at
an equal distance from all the sides of the room.
But the place of greatest safety must be in a
deep cellar, and especially the middle of it: for

when

Lesson xxii.] THUNDER Sc LIGHTNING. 141

when a person is lower than the surface of the
earth^ the Lightning must s rike it and spend
itself, having a great probability of not reaching
him.

A building may be secured, to a considerable
degree, from the dreadful effects which Lightning
sometimes produces; and this by fixing a pointed
iron rod higher than any parts of the building,
and joining to the lower end of it a wire which
must communicate with the earth, or, rather, the
nearest water. This rod the Lightning will seize
upon, sooner than any part of the building : it will
therefore descend along it, and the annexed wire,
till it reaches the earth or water, when it will be
dissipated without doing any harm. It would be
advisable to have that part of the wire which is
within five or six feet of the ground, surrounded
by an open frame, of such a kind as will prevent
men or animals from coming so near the wire, as
to be injured by the Lightning, which it is designed
to convey to the earth.

Several of the British poets have given us sub-
lime descriptions of Thunder-storms, with admira-
ble reflections suggested by them : as a specimen,
my young readers are requested to peruse the
following.

In gloomy pomp, whilst awful midnight reigns,
Aud wide o'er earth her mournful mantle spreads,
Whilst deep-voic'd Thunders threaten guilty heads,

And rushing torrents drown the frighted plains,
And quirk-glanc'd Lightnings, to my dazzled sight,
Betray the double horrors of the night.

A solerum

14« THUNDER & LIGHTNING. [Lesson XXIf.

A solemn stillness creeps upon my soul,
And all its powers in deep attention die;
My heart forgets to beat ; my stedfast eye

Catches the flying gleam; the distant toll,
Advancing gradual, swells upon my ear
With louder peals, more dreadful as more near.

Awake, my soul, from thy forgetful trance ,J

The storm calls loud, and meditation wakes;

How at the sound pale superstition shakes,
Whilst all her train of frantic fears advance !

Children of darkness, hence ! fly far from me !

And dwell with guilt and infidelity !

But come, with look compos'd and sober pace,
Calm contemplation, come ! and hither lead
Devotion, that on earth disdains to tread ;

Her inward flame illumes her glowing face,
Her upcast eye, and spreading wings, prepare *
Her flight for heav'n, to find her treasure there.

She sees, enraptur'd, through the thickest gloom,
Celestial beauty beam, and 'midst the howl
Of warring winds, sweet music charms her soul;

She sees, while rifted oaks in flames consume,
A FATHER GOD, that o'er the storm presides,
Threatens, to gave, — and loves, when most he eludes.

s. CHAPONE.

LESSON

LESSON XXIII.

ON THE IGNIS FATUUS.

-A wand'ring fire

"Compact of unctuous vapour, which the night
Condenses, and the cold environs round,
Kindled through agitation to a flame,
(Which oft, they sa>, some evil spirit attends,)
Hovering, aud blazing with delusive light,
Misleads th' amaz'd night-wanderer from his way
Through bogs and mire. MILTOV

1 OO numerous by far are the stones of ghosts
and apparitions, hobgoblins and spectres, which
are handed down from one generation to another,
by the great vvtakness and folly of some parents
and nurses, who?e whole in'ention, one would
imagine, is to make tueir children chiefly suscepti-
ble of the impn sions of fear. When we consider
how difficult it is to eradicate prejt.d cts which
were imbibed in th Idhood, we shall not be greatly
surprized at the avidity with which tales of the
mischievous feats performed by Jack o' Lanterns,
and Will u 1th a Wisps, are swallowed, even by up-
grown people, of mature judgment in otb. r con-
cerns. For instance, a child njay have been told
by his father, that once, when he was going over a
piece of marihy land in a dark night, he was sud-
denly

144 IGNIS PATUUS. [Lesson xxm.

denly startled with the appearance of a spirit wrap-
ped up in fire, which kept dancing round him,
and dazzled his eyes to such a degree, that he
became dismally frightened, and so the fiery spirit
led him out of his road, and then left him. This
misfortune of the father would be remembered by
the child when he arrived at years of maturity,
when he would, perhaps, hear several similar
tales from other persons, which the credulous
youth would look upon as so many corroborating
testimonies of the reality of such ghostly appear-
ances ; and, of course, the prejudice would be
the more rooted in his mind.

Should any persons who have been thus mise-
rably misinformed, peruse these Lessons, I hope
they will be quickly convinced that these horrible
Jack 61 Lanterns are far from having any thing
supernatural about them : on the contrary, their
cause, and the effects they produce, may be ac-
counted for in a very natural and easy manner.

The meleor vulgarly known by the names before
mentioned, is among philosophers called Ignis Fa-
tuus : it is chiefly seen about marshes, meadows,
and other moist places, also in burying grounds
that lie flat and low, and sometimes near dunghills.
The appearances of it usually observed, sufficiently
evince that it is an ignited vapour: for inflam-
mable air has been found to be the most common
of all the factitious airs in nature; and as it is
known to be frequently produced from the putre-
faction and decomposition of vegetable substances
in water, with which marshes, bogs, 8cc. abound,

it

Lesson XXIIK] IGNIS FATUUS.

it may be reasonably inferred that when this in-
flammable air arises, it will be speedily kindled,
and, being wafted about near the surface of the
earth, will cause the appearances which create so
much unnecessary alarm.

Dr. Skaiv has described a singular Ignis Fatuus
which he saw in the Holy Land, when the atmos-
phere had been thick and hazy, insomuch that
the dew on the horses' bridles was remarkably
clammy and unctuous. This meteor was sometimes
globular, then in the form of a flame of a candle;
presently afterwards it spread itself so much as to
involve the whole company in a pale harmless
light, and then it would contract itself and suddenly
disappear. But in less than a minute it would be-
come visible as before, or, running along from one
place to another, with a swift, progressive motion,
would expand itself at certain intervals over niote
than two or three acres of the adjacent mountains.

In the plains in the territory of Bologna, these
meteors are very often seen : sometimes they vary.
in figure and situation in a very uncertain manner;
but commonly they are very large, and give light
equal to a torch.

Even in England they are frequently seen in dif-
ferent numbers, from two or three to upwards of
twenty together in one field, running here and
there with great rapidity; sometimes mixed to-
gether and crossing each other's paths, as though '
they were danciig: then all at once several of
them disappear, which may, perhaps, be occasioned
by their striking against each other, or some cori-
H tisruoii*

146 IGNIS FATUUS. [LeSSOH XXIH.

tiguous object. In many places, one may be
almost sure of seeing them every dark night.

That persons should be ltd out of the way by
these meteors is more to be attributed to their own
unreasonable fears, raised by prejudices instilled
into their minds in their infantile years, than any
other cause. For when the Ignis Fatuus happens
to overtake or approach them, ihcy are struck with
fear and surprize at so shining a light, and dismal
a spectre, as they imagine it to be; whence they, in
their fright, immediately run out of the direct
pathway, and by such deviation very probably
lose their road entirely : more especially, if (as
will most frequently be the case) the meteor be
attracted after them in iheir flight.

From a consideration of what has been here ad-
vanced, the great importance of being educated
without having any superstitious or childish pre-
judices engrafted in the mind, is exceedingly ob-
vious : to the elder part of my readers I would
therefore take the liberty of recommending a pe-
culiar attention that no idle trash be insinuated
into the minds of their children j for in this, as
well as other cases,

Children, like tender osiers, take the bow,
And as they first are fashiou'd always grow.

To those who have, unfortunately, been badly
educated in this respect, a friendly act would be,
to endeavour with sound reasoning to convince
them of their error, and dissuade them from giving
hoed, in future,-to idle, superstitious, or inconsistent

stories

Lesson xxm.} IGNIS FATUUS. 147

stories of any kind ; advising them to furnish
themselves with such knowledge, as may have a
tendency to produce true pleasur.|e and happiness
through life, and which when dying they can re-
flect upon without uneasiness*.

* " The natural offspring of prevailing superstition is infi-
delity. Of the truth of this, the present times afford as a
lamentable example. Where ignorance and fear once ruled
supreme, there has rash philosophy but too successfully
planted presumption and atheism. Tis the diffusion of pure
and solid knowledge, which alone can preserve us from the
dominion of these opposite tyrants. How should this consi-
deration increase our zeal and stimulate our endeavours!
The immediate sphere of our action may be circumscribed,
but our exertions trill not on that account be entirely lost.
In that circumscribed sphere let us labour to root out every
superstitious lying vanity, and plant pure religion and unso-
phisticated truth in its stead.

" How charming, how enlivening to the soul, to gaze upon
the dawning beams of opening light, to behold them irradiate
that dismal gloom of intellectual darkness which long over-
whelmed the millions of mankind! How supremely pleasing,
to view them wider and wider spreading their invigorating
influence ! How rapturously transporting, to contemplate
the spleadescent prospect of pure and perfect day !

" Power supreme !

" O everlasting King! to thee we kneel,
" To thee we lift our voice ;"

" () spread thy benign, thy vivifying light over the iJvrefl;-
iiiit> of the sons of men; dispel the yet impending mists of
ignorance and superstition: and, O preserve us from the
dismal gulph of infidelity and atheism; let thy truth run
and prevail gloriously, let pure, celestial wisdom over-
spread thp earth as the waters cover the sea! — Then
shall millions kneel before thee with grateful and enrap-
tured hearts; then shall they rejoice to sing the praises
of thee, their Benefactor, their Father, and their Gad: then
H 2 >uall

148 1SN1S FATUUS. [f.fSKOn XXHI.

shall this val« of tears be filled with the mansions of joy and
gladness, and become a blissful foretaste of those regions,
where the saints, crowned with unfading glory and felicity,
surround thy throne with never-ceasing hallelujahs !"

See Sermons on " The Iwmty and Mischitf of Vitlgar
Superstitions," by the Kev, M..J. Naylor.

LESSON

LESSON XXIV.

ON THE AURORA BOREALIS.

Silent from the north,

A blaze of meteors shoots : cnsweeping first

The lower skies, they all at once converge

High to the crown of heav'n, nnd all at once

Relapsing quick, as quickly reascend,

And mix «ml thwart, extinguish and renew,

All aether emu sing in a maze of light. THOMSON.

1 HERE are, perhaps, but few appearances in*
nature which are more curious than those known
by the appellations, Aurora B&realis, Northern-
lights, or Streamers. The radiant streams, )ikfi
legions rushing to the engagement, meet and
mingle, insomuch that the air seems to be con-
flicting fire; — presently they start from one ano-
ther, and, like armies in precipitate flight, each
marching a different way, they are thrown into a
quivering motion : — the whole horizon is illumi-
nated with the glancing flames j and, with an
aspect partly awful, and partly ludicrous, they re-
present extravagant and antic vagaries,

The villagers, assembled together, gaze at the

spectacle, first with astonishment, then with horror,

H 3

150 NORTHERN LIGHTS. [Lesson XXIV.

From look to look, contagious through the crowd

The panic runs, and into woudroas shapes

Th' appearance throws; armies in meet array,

Throng'd with aerial spears and steeds office,

Till the long lines of full extended war,

In bleeding fight commixt, the sanguine flood

Rolls a broad slaughter o'er the plains of heav'u.

As thus they scaii the visionary scene,

On all sides swell the superstitious diii,

Incontinent; and bnsy frenzy talks

Of blood and battle, cities overturn'd,

And late at night in swallowing earthquakes sunk,

Or hideous wrapt in fierce ascending flame ;

Of sallow famine, inundation, storm ;

Of pestilence, and very great distress;

Empires subvers'd, when ruling fate has struck

Th' unalterable hour: ev'n Nature's self

Is deem'd to totter on the brink of time.

THOMSON.

Though this waving brightness, which plays so
innocently over our heads, causes such astonish-
ment in ihe gazing throng, it has a very different
effect upon the philosopher: he feels stimulated to
inquire how so curious, and in great measure
pleasing, an appearance may be occasioned. In
order to arrive at the result of such inquiry, it will
be necessary to consider with attention the various
phenomena of this meteor, as they have been ac-
curately observed.

It may be remarked, then, that the appearances
of the Aurora come under four different descrip-
tions : — First, a horizontal light, like the morning
Aurora, or break of day; which horizontal light
tends to the magnetic east and west, and is bisected
by the magnetic meridian. — Secondly, fine, splen-
did,

Lesson xxtv.] NORTHERS LIGHTS* 751

did, luminous beams, well defined, and of dense
light; these continue i, £, or 1 minute, sometimes
apparently at rest, but more frequently with a quick
•lateral motion. These beams appear at all places
alike, to be arches of great circles of the sphere,
with the eye in the centre ; and these arches, it*
prolonged upwards, would all meet in one point.
This converging point is the same as that to which
the south pole of the dipping needle points, at the
place where the observation is made. — Thirdly,
flashes pointing upward, or in the same direction
as the beams, which they always succeed. These arc
only momentary, and have no lateral motion, but
they are generally repeated many times in a mi-
nute : they appear much broader, more diffuse, and
of a weaker light than the beams: they become
gradually fainter till they disappear ; but they
sometimes continue for hours, flashing at inter-
vals.— Fourthly, arches nearly in the form of rain-
bows. These, when complete, go quite across the
heavens, tending to the magnetic east and west,
and crossing the magnetic meridian at right angles.

When an Aurora takes place, the appearances
above described generally succeed one another in
the following order:— first, the faint, rainbow-like
arches; second, the beams; third, the flashes. As
for the horizontal light, it is found to consist of au
abundance of flashes or beams, blended together,
owing to the situation of the observer relative to
them.

These phenomena have been accounted for on

various suppositions, i. It has been supposed to

H 4 he

152 NORTHERN LIGHTS. [LffSSOn XXIV.

be a fianie arising from a chemical effervescence of
combustible exhalations from the earth. 2. It has
been thought lo be inflammable air, fired by elec-
tricity. 3. It has been imagined to be occasioned
by the zodiacal light. 4. It has been conjectured,
that it is caused by the reflection of the sun's
•beams on large bodies of ice floating near the po-
lar regions. But all these suppositions will admit
t)f objections, being utterly inadequate to account
.for the appearances. Lastly, it has been supposed
electric light itself; and this opinion has met with
many advocates since the identity of lightning and
the electric matter has been determined : for we
know that discharges of the electric fluid in the
atmosphere do exhibit light; and for this, and other
reasons which might be advanced, it is considered
almost beyond a doubt, that the light of the Au-
rora Borealisas-we]] as \hatof falling stars, and the
large meteors, is electric light solely, and that there
is nothing of combustion in any of these phae-
nomena.

M. Libes has lately proposed a new theory of the
Aurora Borealis, which has already been adopted
by most of the northern philosophers, and may be
concisely stated thus : the production of hydro-
genous gas is next to nothing at the poles ; there-
tore, so often as the electricity is put into an equi-
librated state in the atmosphere, the spark, instead
of passing through a mixture of hydrogenous and
oxygenous gas, as in our climates, passes through
a mixture of oxygenous and azotic gas : it must
therefore cause a production of nitrous gas, nitrous

acid,

Lesson xx i v.] NORTHBR-N LIGHTS.. 153

acid, and nitric acid, which give birlh to ruddy
vapours, whose red colour will vary according to
ihe quantity and proportion of those different sub-
stances, which are generated. These vapours are
carried towards the south, where the air is most
dilated, so that they approach more and more to-
wards the spectator; and it is probable their mo-
tion may be assisted by a north wind. Sometimes
they rise as if to the zenith of the spectator, and
then descend again towards the south; and a great
number of causes may carry the vapour towards
the different points of the heavens, whence origi-
nate the different motions taken by the Aurora
Borealis, or its several parts. Lastly, the slight
detonations which are sometimes heard, depend
upon the small quantity of hydrogenous gas,
which is found in the upper regions of the atmos-
phere, and .which combines with the oxygen to
form water.

These principles, at the same time that they ac-
count in. M. L'bcs's estimation, for all thephaeno-
mena accompanying the Aurora Borealis, explain
also why it is so common towards the poles^ and
so rare in the temperate regions; while thunder,
which is frequent in the torrid zone, is scarcely eve.*1
heard in the polar. regions. The disengagement
of hydrogenous gas is considerable near the equa-
tor, and very little towards the poles: and svhea
we excite the electric spark in a mixture of hydro-
gen, oxygen, and azote, it combines in preference
the bases of the two former gases;, the electric
spark ought, therefore, to occasion thunder solely
H .•> in

134 NORTHERN XIGHTS. [LeSSOn XXIV.

r.— .. — ^f^ft^ff^tt - • -_. ^.- . ^. ^ — _-~ —

in hot countries, and to produce Aurora Boreales
alone in cold countries.

This theory, though plausible, is not, however,
entirely free from objections. Mr John Dalton,
whose name I mentioned in the Seventeenth
Lesson, has advanced a new theory of the Aurora
Borealis, in which he has endeavoured to shew,
that the luminous beams of this phenomenon are
cylindrical, and parallel to each other at least
over a moderate extent of country, — that these
cylindrical beams are all magnetic, and parallel to
the dipping-needle at ihe places over which they
appear, — that the distance of these beams from
the earth is nearly equal to their len<nh, — that the
rainbow-like arches are about i50 English miles
above ihe earth's surface, — and that the Aurora
Borealis is a magnetic phenomenon whose beams
are governed by the earth's magnetism.

LESSON

LESSON XXV.

ON LIGHT AND COLOURS.

Behold the Light emitted from the sun ;
What more familiar, and what more unknown?
While by its spreading radiance it reveals
All nature » face, it still itself conceals.

BLACKMORE*

God said, — Let there be Light:— and there was Light.

MOSES.

1 HE famous Longinus, in his treatise on the
Sublime in Writing, produces the above passage of
ihe inspired historian, as one of the most striking
he had ever met with. Its chief sublimity seems
to consist in a forcible declaration of the al-
mighty power of GOD. From this passage alone
we might inter, that to will, to sp^ak, and to ac-
complish, is all one with the DIITY; being an
essential part of his attribuies, without which he
would be imperfect. In the sacred record it is next
said, that " GOD saw the Ligli' that it was goodi"
and indeed we have the greatest reasons for think-
ing so. How good must that Light be, which en-
ables us to behold the heavens beautified with stars ;
and by means of which we can look around us,
and trace the numero.us wonders of the earth we

inhabit,.

156 LIGHT AND COLOUR?. [Lesson xxv.

inhabit, raising in our minds the most exalted
ideas of the Divine perfections ! We may also here
observe, that the all -wise CREATOR has so divided
our time into day and night, light and darkness,
that we may never forget that all things in human
life are mixtures of good and evil. Heaven is said
to be all light, and hell is as frequently represented
to be utter darkness : wherever the favour of GOD
shines, there is light ;

" His presence gives eternal day,

And makes eternal rest ;"

ljut his absence and anger create darkness.

By Light, I would wish to have understood, that
principle by which objects are made perceptible to
our sense of seeing; or the sensation occasioned in
the mind by the view of luminous objects. The
nature of Light has very long been a subject of
philosophical speculation: the earliest philosophers
doubted whether objects became visible by means
of any thing proceeding from them, or from the
eye of the spectator. On this subject, opinions
are still afloat. It is thought by some, that Light
may be a fluid (per se) equally diffused through the
universe; the action of the solar, or other rays, is
necessary, according to this hypothesis, to give it
motion, and make its effects perceptible. Others
are of opinion, that Light is a quality , which can-
not exist independently of matter, and which re-
quires the assistance of the solar and other rays, to
bring it into action. But as the hypothesis of New-
ton is the most generally received, what I shall say

on

Lesson xxv.l LIGHT AND COLOCRS. 157

on the subject will be agreeable thereto ; though it
must be allowed that some rather formidable ob-
jections have been advanced against it.

The Newtonians maintain, that Light consists of
a great number of exceedingly small particles,
thrown off from the luminous body by a repulsive
power with an immense velocity, and in all direc-
tions ; hence, Light is produced from motion : but
then as all motion will not produce Light, there-
fore much manifestly depends on the quality of
certain bodies which are of themselves luminous,
and have the constant and invariable property of
emitting or sending forth these very minute parti-
cles : such is the property of the sun, a star, a can-
dle alighted, and all sorts of flame, &c. The velo-
city of the particles of Light is truly astonishing,
amounting to near two hundred thousand miles in
a second of time, which is almost a million times
greater than the velocity of a cannon-ball. This
may be easily proved by observations on the
eclipses of Jupiter's satellites ; for when the earth
is between the sun and this planet those eclipses
will happen about 81 minutes sooner, than accord-
ing to the tables ; but when tke earth is in the con-
trary position, the eclipses happen about 8J mi-
nutes later than they are predicted by the tables.
Hence, therefore, light takes up about 8\ minutes
in passing from the sun to the earth, a distance of
95 millions of miles : whence what was mentioned
just above may be deduced.

Since Light diffuses itself every way with such
incredible velocity, it is evident that if its particles

were

158 LIGHT AND COLOURS. [LeiSOn XXV.

were not surprisingly small, it woul i strike against
bodies with great force : this would be very inju-
rious to those tender organs the eyes, and would
probablv soon causcvhlindness : but it is found that
these particles are small, almost beyond concep-
tion; for it has b« en computed that there fly out
of the end of a flame of a burning candle in a se-
cond or time, ten thousand nrnlliuns of timer- more
such panicles than there are visible grains of sand
in the whole earth : it they were not inconceivably
small, it is cer'ain, therefore, that the flame would
be entire!) dissipated and lost.

It is also asserted, that the panicles of Light are
emitted in right lines : preserving their rectili-
near motion till they are turned out of their path
by some of the following causes, viz. either by the
attraction of some other body near which they pass,
which is called inflection} or, by passing obliquely
through a body of different density, which is called
refraction ; or, by being turned aside by the op-
position of some intervening body, \vhi( h is called
reflection; or, lastly, by b- ing totally stopped by
some body into which they penetrate, and this is
called their extinction. A succession of these par-
ticles following one another, in an exact right line,
is called a ray of Light ; and this ray, in whatever
manner its direction mav be changed, whether by
reflection, refraction, or inflection, always preserves
a rectilinear course, till it be again changed. It is
to be observed, that bodies, as they respect the rays
of light, are divided into three kinds : K Those
which emit the rays of Light; as the sun and fixed

stars :

Lesson xxv.] LIGHT AND cotouus. 159

stars : 2. Those which transmit the rays, as the
air, and glass : and 3. Those which rt fleet them,
as the moon, the earth, polished iron, &c. The
first are called luminous, the second p llucid, and
the third opaque bodies. Ii is also to be observed,
that the rays of Light themselves are not seen ; but
by their means we see the luminous bodies, from
which thi-y originally came, and the opaque bodies,
from which they are reflected thus, for instance,
when the moon shines, we cannot see the rays
which pass from the sun to the moon ; but, by their
means, we see the moon, from whence they are
reflected. If the eye be placed directly in the me-
dium, through which the rays pass to it, the me-
dium is notseen ; thus, we never see the air through
which the rays come to our eyes. But if a pellucid
bodv, through which the rays are to pass, be placed
at a distance from our eyes, that body will be
seen, as well as those bodies from whence the rays
come which pass through it to our eyes. For in-
stance, he who looks through a pair of spectacles,
not only sees bodies through them, but -also sees
the spectacle glasses; because the glass, being a
solid body, reflects some rays of light from its sur-
face; and being placed at a convenient distance
from the eye, may be seen by those reflected rays,
at the same time lhat bodies at a greater distance
are rendmd visible by the transmitted rays.

The properties, of reflection and refraction pro-
duce several curious effects, some of which have
been noticed in the Sixteenth Lesson ; and others
•will be spoken of as we proceed.

Amongst

LIGHT AND COLOURS. [LeSSOH XXV.

Amongst them we must not pass by ihe phae-
nomenon of the variety of Colourst which are ob-
servable all over the face of nature, seeming pe-
culiarly adapted to increase the pleasure of man-
kind. Colours are nothing else than different sen-
sations excited in us by the variously refracted rays
of light being carried to our eyes in a different
manner, according to the different size, or shape,
or situation of the particles of which the surfaces
of bodies are composed. Colours, then, are not
inherent in the bodies which appear to wear them;
but they seem to arise from a capability or dispo-
sition in those bodies to reflect back particular
rays, and these rays possessing different degrees of
refrangibility produce the effect : thus it is found
that the least refrangible rays produce the idea of
a red Colour j and as the refrangibility increases,
the ideas of the intermediate Colours are excited,
till at length we arrive at the opposite extreme of
refrangibility, and then the sensation of a violet
Colour is produced. The primary Colours are,
according to NEWTON, seven in number, of these
I here present you with a poetical account:

— First the flaming red

Sprung vivid forth ; the tawny orange next ;

And next delicious yellow; by whose side

Fell the kind beams of all-refreshing green;

Then the pure blue, that swells autumnal skies.

Etherial play'd; and then, of sadder hue,

Emerg'd the deepen'd indico, as when

The heavy-skirted evening droops with frost;.

While the last gleanings of refracted Light

Dj'd in the fainting violet away. THOMSON.

Thus

Lesson xxv.] LIGHT AND COLOURS. 161

Thus you have the regular gradations from one
Colour to another laid before you, agreeably to the
hypothesis which supposes the number of primary
Colours to be seven : but it is yet a matter of dis-
pute whether there are seven primary Colours,
or whether their number is greater or less than
s'even. Many persons assert that there are but
three primary Colours; but it is very evident that
they affix an idea to the term totally different from
that which is derived from Newton's definition.
He calls the Light whose rays are all alike refran-
gible, simple, homogeneal, and primary ; and he
shews that Colours may le produced by composi-
tion, which shall le light to the Colours of homo-
geneal Light, as to the appearance of Colour, but
not as to the immutability of Colour and constitu-
tion of Light. But the new opinion of the the-
orists above spoken of is, that the primary Co-
lours are red, yellow, and Hue, because, of pro-
per mixtures of these three Colours, all others
may be formed. It would be a needless multi-
plication of words to shew, that Newton and
they considered the subject in different points of
view.

To have a familiar notion of the production of
Colours, let the following experiment be tried :
any time when the sun shines, standing in the
open air, let the bowl of a tobacco pipe be filled
with a lather of soap and water; then, gently
blowing at the other end, a large bubble will arise,
which let remain suspended at the top of the bowl:
then let two or three persons carefully observe the

different

162 LIGHT AND COLOURS. [Lesson XXV.

different Colours, as ihey arise in the bubble; and
they will perceive first red, then perhaps blue, or
orange, green, indigo, violet, and in short, here
and there, all manner of Colours j even white and

perhaps at last a sort of black*.

It

* The following curious and useful remarks on the dif-
ferent degrees of heat imbibed from the sun's rays, &c. by
cloths of different Colours, were extracted from " Experi-
ments and Observations" by that famous American philo-
sopher and politician, Dr. B, Franklin.

" First, let me mention an experiment you may easily make
yourself. Walk but a quarter of an hour in your garden
•when the sun shines, with a part of your dress white, and a
part black ; then apply your hand to the,m alternately, and
you will find a very great difference in their warmth. The
black will be quite hot to the touch, the white still cool.

" Another. Try to fin paper with a burning glass. If it be
white, you will not easily burn it;— but if you bring the focus
to a black spot, or upon letters written or printed, the paper
will immediately be on fire under the letters.

" Thus Fullers and Dyers find black cloths of equal thick*
ness with white ones, and hung out equally wet, dry in the
sun much sooner than the white, being more readily heated
by the sun's rays. It is the same before, a fire; the heat of
which sooner penetrates black stockings thai) white ones, and
is so apt sooner to burn a man's shins. Also beer much
6 ooner warms in a black mug set before the fire, than in a
white one, or in a bright silver tankard.

" My experiment was this: 1 took a number of little square
pieces of broad cloth from a tailors pattern card, of various
colours. There were black, deep blue, lighter blue, green,
purple, rf d, yellow, white, and other Colours, or shades of
Colours. I laid them all out upon the snow in a bright sun-
shin v morning. In a few hours (I cannot now be exact as to
tin.- time; the black, being warmed most by the sun, was sunk so
low as to be below the stroke of the sun's rays ; the dark blue
almost as low, the lighter blue not quite so low a« the dark .

the

Lesson xxv.] LIGHT AND COLOURS. r63

It may be observed, that Hack and while are
never reckoned among the primary Colours ; for

the other colours less as they were lighter; and the quite
white remained on the surface of the snow, not having en-
tered it at all.

" What signifies philosophy that does not apply to some
nse ? May we not learn from hence, that black clothes arc
not so fit to wear in a hot snnny climate, or season, as white
ones } because, in such clothes the body is more heated by
the sun when we walk abroad, and are at the same time
heated by the exercise, which double heat is apt to bring on
putrid dangerous fevers ? That soldiers and seamen who
must march and labour in the sun, should, in the East or West
Indies, have an uniform of white ? That summer hats for
men or women, should be white, as repelling that heat which
gives head-achs to many, and to some the fatal stroke that
the French call the Coup tie Soleill That the ladies' summer
hats, however, should be lined with black, as not reverberat-
ing on their faces those rays which are reflected upwards
from the earth or water ? That the putting a white cap of
paper or linen, within the crown of a black hat, as some do,
will not keep out the heat, though it would if placed without ?
That fruit walls being blacked ma> receive so much heat
from the sun in the day time, as to continue warm, in some
degree, through the night, and thereby preserve the fruit
from frosts, or forward its growth ? With sundry other parti«
culars of less or greater importance, that will occur from time
to time to attentive mindsr"

Many other properties of bodies of different Colours may
be found in various parts of Sir Isaac Newton's Optics.

The subject of Light and Colours has been lately consider-
ed with much acuteness and attention by Mr. Delavel. From
a variety of well-conducted experiments this gentleman con-
cludes, that Colours are exhibited, not by reflected, but by
transmitted Light. For an ample investigation of this curious
and interesting subject, the reader must be referred to the
Memoirs of the Manchester Society, Vol. II.

Hack

164 LIGHT AND COLOURS. [Lesson XXV.

black cannot with propriety be called a Colour, it
being a deprivation of all Light, because the sub-
stance stifles all the rays : but white, on the con-
trary, is comprehended of all the primary Colours
in one, as may be proved experimentally, by tak-
ing a small wheel with a broad rim, which let be
divided into 360 equal parts; then let 45 of these
parts be painted red; 37, orange; 48, yellow; 5O,
green; 60, blue; 40, indico ; and 80 of violet ;
making in all 360 : if this wheel be whirled
swiftly round, the rim will appear as though it were
painted of the purest while. It is pretty generally
admitted, that the whiteness of the sun's Light is
owing to a mixture of all the original Colours in a
clue proportion; and hence it is naturally con-
cluded, that whiteness in other bodies is a dispo-
sition to reflect all the rays of Light in the same
proportion and order as they come from the sun.

My young readers will, I doubt not, after at-
tending to what has been advanced in this Lesson,
readily unite with me in acknowledging, with
gratitiule and joy, the great utility and benefit of
Light. For by the help of this admirable, this
first-made creature of the Deity ', we are enabled
(•as before suggested) to behold many other of his
glorious works : we can view with admiration
and pleasure the beauties of the flowery fields, the
gay attire of the feathered tribes, the exquisite and
well-adapted proportions of many insects, qua-
drupeds, and other creatures; we can dwell with
rapture in the coiUemplaiion of extensive land-
scapes

Lesson xxv.] LIGHT AND COLOURS. 165

scapes and diversified prospects j we can trace
enough to be convinced of the great harmony and
beauty of the lower part of creation j and we can
extend our views to the heavens, and thus survey
God's wonderful skill and contrivance, so clearly
manifested in every region of his glorious works.

LESSON XXVI.

ON THE RAINBOW.

•• " Refracted from yon eastern clout! ,
Bestriding earth the grand etheriel bow
Shoots up immense, and every hue unfolds,
In fair proportion running from the red,
To where the violet fades into the sky.

THOMSON.

DOUBTLESS you have frequently beheld thai
beautiful appearance known by the appellation
of the Rainbow, or Iris, bending gracefully and
majestically across the sky, painting the arched
vault with a pleasing variety of beautiful colours :
when this is viewed by the philosophic eye, it
immediately excites an inclination to explore the
cause of so curious and pleasing a phenomenon.

Not so the playful boy ;

He wondering views the bright enchantment bend,

Delightful, o'er the radiant fields, and runs

To catch the falling glory ; but, amazed,

Behold t h' amimve arch before him fly,

Then vanish quite away. THOMSON.

By a perusal of holy writ you will discover, that
the Rainbow was first placed, and is still at times

seen

Lesson xxvi.J RAINBOW. 167

«een in the clouds, as a pledge of inviolable- fidelity
and infinite mercy j assuring us, that, " while the
"earth remaineth, seed-time and harvest, and
" cold and heat, and summer and winter, and day
(t and nigh*, shall not cease." How gracious and
benevolent that BEING, who so often renews a
covenant of kindness and mercy to his creatures;
and that too, in such a manner as to raise pleas-
ing sensations in every heart, and charm every
beholder !

To account for the production of the Rainbotv,
we are in the first place (o consider, that it is never
seen but in the time of rain, or near it, and when
the sun shines. You will understand, then, that
when a ray from the sun falls upon a drop of rain
in a cloud, if it enter the^ upper part of the drop
in a proper situation, it will, by refraction, be
thrown upon the inner surface of the back part of
'the drop; from thence it will be reflected to the
lower part of the drop, at which place undergoing
a second refraction, it will be bent towards the
earth : and thus rays of the sun, after one re-
flection, and two refractions, may come to the
eye of a spectator, whose back is towards the sun,
and his face towards the drop. When rays which
are effectual, emerge from the drop after one re-
flection and two refractions, those which are most
refrangible, will, at their emersion, make angles
with the incident rays, different from. those which
are least refrangible; by which means the rays
that produce the sensations of different colours

will

168 IJAINBOW. [Lesson xxvi.

will be separated from one another. Hence it
may be easily perceived, that some of the falling
globules may be in that position which will cause
the rays that produce a red colour to fall upor the
eye, — others next to them below will send forth
orange-making rays, — the drops next to them will
cast the yellow-making rays, — and those suc-
cessively in order below them, will refract the
blue, indico, and violet-making rays to the eye;— •
and thus, in a certain space in the cloud, all the
colours will appear ; and since, under the same
angles, the same phcenomena will be produced,
therefore an arch of this various-coloured light
must necessarily be produced in the clouds.

The different sizes of the Rainbows depend en-
tirely upon the height of the sun at the time : for
when the sun is in the meridian, or at his highest
altitude, the bow will then be least to our sight,
being but a small segment of a circle; but as the
sun gets lower and lower, the bow will increase in
height; and when the sun is in the horizon, or just
setting, a bow at that time is as large as it can be,
being very nearly semi-circular. It may also be ob-
served that at all those places and times when the
altitude of the sun is more than 42° no primary
Rainbow can appear ; and when his altitude ex-
ceeds 54l° no secondary bow can appear.

With regard to the part of the sky in which a
Rainbow appears, when I say that it is always
opposite to the sun, I present you with an invariable
rule where to find it ; and this is anadditional reason

for

Lesson xxvi.] RAINBOW. 169

for concluding, that the appearance is occasioned
by the rays of the sun shining upon the falling
drops of rain.

There is also often seen a fainter coloured bow,
commonly called a water-gall, above the Rainbow;
and here it will be found, that the colours are in a
contrary position to what they are in the bow it-
self: hence it is evident that this is a kind of re-
flection from the Rainbow, or a double reflection
from the drops of rain ; and as a considerable
quantity of light is lost at each reflection, it
is plain that the colours in the superior bow
will be more dilute and faint than those in the
lower.

The nature of the Rainbow, as here explained,
may be illustrated and confirmed by experiment in
several different ways. Thus, for example, hang
up a glass globe, full of water, in the sun-shine,
and view it in such a posture, that the rays which
come from the globe to the eye may make an
angle of about 42- with the sun's direct rays, and
you will see a full red colour in that side of the
globe opposite to the sun : and by varying the
position so as to make that angle gradually less,
the other colours, yellow, green, and blue, will
appear very distinctly, in succession, on the same
side of the globe. But if, by raising the globe,
the angle be made about 50 , there will appear a
red colour in that side of the globe which is toward
the sun, though somewhat faint ; and if, by raising
the globe still higher, the angle be made greater,
x this

170 RAINBOW. [Lesson xxvi.

this red will change successively to the other co-
lours, yellow, green, ajid blue.

Or, the appearances of the Rainbow may be
exhibited, in a very natural and beautiful manner,
any day when the sun shine?, with the assistance
of an artificial fountain, or jet d'eau, which is an
instrument expressly intended to throw up streams
of water to a great height. These streams, spreading
very wide in their upper part, when falling, form
a delightful shower of artificial rain. When the
fountain is playing, move between it and the sun,
at a proper distance from the fountain, until your
shadow points directly towards it : then looking at
the shower, you will observe the colours of the
Rainbow, very vivid and strong — those of the
water-gall very languid and faint — the gradations
of the colours of each in an inverted order : and,
what forcibly shews the deceitfulness of vision, the
bows appear, notwithstanding the nearness of the
artificial shower, to be as far off, and as large, as
those which we really see in a natural shower of
rain.

A similar bow is often observed among the
waves of the sea, the upper parts of the waves
being blown about by the wind and so falling down
in drops : this is called the Marine Rainbow. This
appearance is also sometimes seen by moon-light,
though it is seldom vivid enough to render the
difFert-nt colours distinguishable: it is then called
the Lunar Rainbow. Rainbows are even sometimes
seen on the ground, when the sun shines on a very

thick

Lesson xxvi.] RAINBOW. . IJL

thick dew. All these are of the same nature, an<J
are produced by the same causes as the common
Rainbow *.

When we consider what a wonderful scenery of
nature is here displayed} and yet recollect, that
though these variegated beauties are the common
objects of vision, how few there are that under-
stand the reason of them, and how much fewer are
any way anxious about them : surely those who
think the doctrine of colours, 8cc. highly worthy of
contemplation, and who are aware that the know-
ledge of their causes is truly adorning to a reason-
able mind, ought to be thankful that their natural
genius enables them to understand such studies !

* I cannot forbear adding a note in thu place, to state a
fact which is not universally known : a piece of iron when
heated, assumes all the colours of the JJainfcetr, before it becomes red
hot. This extraordinary circumstance, I believe, has not yet
been satisfactorily account? d for.

i 2 LESSON

LESSON XXVII.

ON HAWS AND PARHELIA.

As when two suns appear in th' azure sky,
Mounted in Phcebus' chariot fierie brighte:
Both darting forth faire beams to each man's eye,
And both adorn'd with lamps of flaming light;
All that behold such strange prodigious sight,
Not knowing nature's work, nor what to weeue,
Are wrapt with wonder, and with rar« affrighte.

SPENSER.

1 HERE remain yet two appearances caused by
the reflection and refraction of light, to be de-
scribed and accounted for: the first, known by the
name of an Halo or Crown, is very frequently
seen without creating any degree of surprize ; the
other, called a Parhelion, Parheliam, or mock sun,
is but very seldom observed ; and as it is a curious
phenomenon, it is not at all extraordinary that it
is, among the common people, considered as por-
tentous. To a description of each of these I shall
now proceed.

And first ofHalos, or Coron<#,which are coloured
circles, or rather ovals, appearing round the face
of the sun and moon, as well as some of the larger
stars, particularly the planet Jupiter. Halos round
the sun or moon, generally appear oval and excen-

tric

Lesson xxvu.] HALOS AND PARHELIA. 173

trie to the luminary, having their longest diameter
perpendicular to the horizon and extending farther
below the luminary than above it : this probably is
a deception of vision, arising from the apparent
concave of the sky being less than a hemisphere.
Those about the moon are often very large, and
when seen by the country people, they will com-
monly observe, " We shall have a change of
weather soon, for there is a bur round the moon :"
perhaps their observation may not be altogether
void of a reasonable foundation.

Philosophers sometimes conceive Halos to arise
from a refraction of the rays of light in passing
through the fine rare vesiculae of a thin vapour to-
wards the upper parts of the atmosphere. But an
opinion more generally receivrd, is that which
supposes Halos to be formed by small round grains
of hail, composed of two different parts; the one
of which is transparent, inclosing the other which
is opaque, and the reflection from these producing
the appearances : this is the more probable when it
is recollected that they are only seen in frosty,
rhimy, or hazy weather.

There are several ways of exhibiting phaenomena
similar to those of Halos : thus, the flame of a can-
dle, placed in the midst of a steam in cold weaihrr,
or placed at the distance of some feet on the other
side of the window, in each of these circumstances
will appear to be encompassed by a coloured Halo.
Also, when the window of a room is encrusted
over with a thin plate of ice, the moon seen
1 3 through

174 HALOS AND PARHELIA. [Lesson XXVJI.

through it will seem surrounded with a large and
various coloured Halo.

Parhelia are far more rarely seen, but their ap-
pearance is singularly curious. Their apparent size
is generally the same as the true sun ; but they
are not always round, nor always so bright as the
sunj and, when several appear, some are brighter
than o'thers. They are tinged externally with
colours like the rainbow; and many of them have
a long fiery tail, opposite to the sun, becoming
paler towards the extremity. These tails mostly
appear in a* white horizontal circle, commonly
passing through all the Parhelia, and would go
through the centre of the sun, if it were entire.

We have on record, an account of Parhelia
seen at Rome, in March 1629 : at this time four
were observed, one of which was very much tinged
with various colours like the rainbow ; and the
others were faintly so. Some were also observed
by Cassiniy in 1C83. In England and Scotland,
two have frequently been seen at a time. In
North America they are often seen, and continue
for hours, nay sometimes for several days, being
visible from sun-rise to sun- set : when these dis-
appear, rain or snow is there generally expected.

M. Huygens, on applying his attention to these
appearances, was soon sensible that they could not
arise from such globules as formed the Halos : yet
since Parhelia are always attended with Halos, he
was satisfied that their causes must be much alike.
Considering, then, what other figures hail-stones

might

Lesson xxvn.] HALOS AND PARHELIA. if?

might possibly have, besides a spherical one, he
could find no other so simple as that of a cylinder:
and, indeed, he had often observed, that snow
consisted of several slender oblong particles, mixed
with those of other shapes : and seeing that small
globules were sufficient for the production of
Halos, he imagined that a great number of small
cylinders, floating in the air, might produce simi-
lar appearances. He also remembered that Da-
cartes had taken notice of certain small columns,
which he had seen lying on the ground, the ex-
tremities of which were bounded with flat star-like
figures, consisting of six rays.

The large white horizontal circle, observed in
some of these phaenomena, M.Huygens supposed
to be produced by the reflection of the sun's rays
from the outsides of the upright cylinders ; since,
when the sun shines upon a number of such cylin-
ders suspended in the air, a white circle must
necessarily appear to pass through the sun parallel
to the horizon. This he shews very distinctly by a
large figure of a cylinder, and by pointing out the
progress of the sun's rays reflected from it. For
every point of the sun's verticle diameter, as well
as his centre, will illuminate a circle of cylinders,
of the same apparent height as the illuminating
point. — It is observable that no thick clouds are
seen in the air when these circles appear; but only
such as are very thin, and scarcely visible. For in
most of these observations the sky is said to have
been very clear and serene ; which agrees quite
well with this hypothesis ; since these minute
1 4 cylinders

176 HALOS AND PARHELIA. [LeSSOn XXVIT.

cylinders must constitute a very thin cloud uni-
formly extended : through which the sun, and
even the colour of the sky may be seen.

The whole of Huygens's dissertation,from which
the above hypothesis is deduced, is much too long
to be given in this place. Those of my young
readers who wish to peruse it, are referred to
chap. xi. book I. Dr. Smith's Optics,

LESSON

LESSON XXVIII.

ON FIRE.

Fire, thou swift herald of His face,
Whose glorious rage, at his command,
Levels a palace with the sand,
Blending the loft; spires in r»in with the base!
Ye heavenly flumes that singe the air,

Artillery of a jealous God;
Bright arrows that his sounding quivers bear,

To scatter deaths abroad :

Lightnings, adore the Sovereign Arm that flings
His vengeance, and your fires upon the heads of kings.

WATTS.

IN our contemplations, we will now make a
transition, to consider the advantages, nature, and
effects, of that wonderful agent of nature called
Fire : and here we shall find numerous reasons fc*
increasing in gratitude and love to the beneficent
POWER who produced so astonishing an element
chiefly for our use. If there were no such thing as
fire, in what would the earth we inhabit, after the
setting of the sun, covered with cloudy and noc-
turnal vapours, differ from the most dismal sub-
terraneous caverns and dungeons j since, during
such time, no man would be able to dispatch any
I & kind

178 FIRE. [Lesson xxviu.

kind of business, neither would he have the teme-
rity to move one foot forwards ? Without fire,
which, by the means of candles, lamps, torches,
and the like, affords us light in the greatest dark-
ness, what difference would there be between our
condition, and that of men who should be blind
half their life-time ? Without fire, greater part of
the productions of the earth which serve mankind
for food, for refreshment, or for dainties, would be
absolutely unfit for those purposes ; as several of
them could neither be chewed by the teeth, nor
digested by the stomach. Nay, we may be easily
convinced, that neither corn, nor flesh, nor several
of the fruits of the ground, nor of trees, would,
without the help of fire, be of any service ; but
would turn to a crude, unwholesome nourishment.

Again, — would not the dreadful cold of winter,
if not moderated by fire, be the mean of dis-
peopling whole countries, and of freezing to death
myriads of men, women, and children ? And,
again, — if there were no fire, though the mines of
iron, &c. were more numerous than they are, of
what utility would they be ; since, without its aid>
they could not separate the metal from the ore, nor
by any means make those instruments- for agricul-
ture, arts, and manufactures, which we now have
in such abundance ?

For the sake of a supposition, let us imagine,
that we were in a state, continually without light>
without warmth, without any method of preparing
raw food for sustenance, without all the conve-
niencies, which metals (and principally iron) now

afford

Lesson xxvm.] F'RE* 179

afford us : let us suppose, I say, that in such a
situation we received information that a person had
invented something by the help of which all these
defects and wants might be supplied : I would only
ask, if we should not, under such circumstances,
entertain very high ideas of the wisdom of the
inventor ?

The ingenious young reader will know how to
apply this conjecture and question, without any
farther comment upon them.

By Fire is here to be understood, that subtile in-
visible cause by which bodies are made hot to the
touch, and expanded or enlarged in bulk ; by which
fluids are rarefied into vapour; or solid bodies be-
come fluid, and at last either dissipated and carried
off in vapour, or else melted into glass. It seems
also to be the chief agent in nature, on which
animal and vegetable life have an immediate de-
pendence.

Among philosophers, Fire is now usually de-
nominated CALOKIC, which appears to be a highly
elastic and imponderable substance ; and it is so
very subtile, that neither has its gravity been yet
ascertained, nor its existence, in a simple and
uncombined state, been shewn. There can be very1
little doubt that it radiates with light from the
sun : and experiments shew, that, like light, its
absorption is affected by the difference of colour
and of surface possessed by different bodies. It
combines chemically with all bodies, in a quantity
proportioned to their affinity with it. By its elastic
power, or power of repulsion, it constantly tends

to

180 FIRE. [Lesson xxvnr.

to separate the particles of matter ; in which it is
opposed by the attraction of cohesion : hence at-
traction of cohesion predominating, the body ex-
ists in a solid form : caloric existing in such a pro-
portion as to weaken the attraction of cohesion to
a certain degree, the body assumes a liquid form j
and when the quantity of caloric is increased still
farther, the body takes a gaseous form.

That heat moves, like light, with vast velocity,
is inferred from caloric being always found to ac-
company the rays of light. Dr. Herscheli has dis-
covered that the coloured rays of light are pos-
sessed of a heating power, and that the least re-
frangible rays possess this power in the highest
degree : this power diminishing as the refrangi-
bility increases j the red rays possessing, therefore,
the greatest, and the violet the smallest power.
This property is directly opposite, in this respect,
to the property which the rays of light possess, of
deoxidizing substances exposed to their action 5
this property existing in the rays of light, in pro-
portion to their degrees of refrangibility. It i*
likewise remarkable, that as the deoxidizing power
exists, in the highest degree of all, at a certain
distance beyond the violet ray, and out of the
spectrum, so the calorific power is found to exist,
at its maximum, at about half an inch beyond the
termination of the spectrum, by the red rays.

These calorific rays, and which are even regarded
as rays of caloric itself, suffer refraction and reflec-
tion, similar to the rays of light ; possessing ge-
nerally, however, less refrangibility than the rays

of

-Lesson XXVIIK] FIRE. 181

of light j and having the angle of their reflection
equal to the angle of their incidence. This is
supposed to be the case, not merely with the
caloric immediately derived from the sun, but
with that which proceeds from our common fires,
candles, and even hot water, and iron heated not
so much as to become lucid. It appears, by the
experiments of Professor Pictet, that ihe radiation
of heat, and even its reflection, takes place inde-
pendent of light : thus a piece of iron heated,
but not so high as to emit any light, being
placed in the focus of a concave mirror, will very
sensibly affect a thermometer, placed in the focus
of another mirror opposed to the former. On the
same principle, if ice be employed instead of
heated iron, the thermometer will be affected in
a contrary direction. From this latter experiment
it has been conjectured that cold, as a body, is
emitted from the ice, and reflected by the mirror.
This opinion, however, appears to be entirely un-
founded. On a lighted candle being thus em-
ployed, and a plate of clear glass being placed be-
tween the mirrors, the caloric appeared to be in-
tercepted, although the light passed with its usual
facility ; the thermometer sinking 14°, in nine
minutes, and rising 12°, in seven minutes after its
removal. Caloric is transmitted through some
bodies with unabated rapidity, whilst its passage
through others is very considerably retarded ; and
hence bodies have been named either good or lad
cojiductors. The cause of this difference has never
yet been satisfactorily ascertained, All bodies

appear

18« FIRE. [Lesson xxvin.

appear to be capable of conducting caloric, and
fluids also possess the property of conducting it
slowly.

Heat constantly tends to form an equilibrium,
by passing from bodies of an higher and diffusing
itself through bodies of a lower temperature.

Two bodies of the same nature, unequally
heated, on being brought into contact, soon arrive
at an equal temperature, the caloric becoming
equally divided between them. But when two
bodies, differing in their nature, aad differing in

* ^ w

the quantity of caloric they possess, are thus al-
lowed to form one common temperature, by com-
munication, this will not be found to be an arith-
metical mean between the two original tempera-
tures ; but the one will be found to have required
a greater or less quantity of caloric than the other,
to render it of the common temperature.

In this way it is found that the quantity of ca-
loric which raises mercury 38', raises water only
12°; consequently the caloric which raises the
temperature of water 1°, will raise that of the same
weight of mercury 3.16°. The quantity of caloric
which a body thus requires to heat it to a given
temperature, is called the specific caloric of that
body. Thus the quantity of caloric which heats
water 1°, heats the same quantity of mercury
3.16' ; the specific caloric of water is, therefore,
3.16 times greater than that of mercury ; and, con-
sequently, if the specific caloric of water be = 1,
that of mercury must be = 0.31. It is fully
established that the specific caloric is different in*

different

Tesson xxvin.] FIRE. 18*

different bodies : as when bodies manifest the
same temperature by the test of the thermometer*
the relative quantity of caloric which they contain
is, we discover, very different. Much ingenuity
and acute investigation have been employed toj
ascertain the absolute quantity of caloric which*
they contain. These endeavours have not, per-
haps, been as yet completely successful.

Dr. Black discovered, that whenever a solid le-
romes a fluid, a great portion of heat enters into it,
which does not affect the thermometer j and that,
on its again becoming solid, this portion of heat
quits it, without a diminution of its temperature
taking place. Snow at 32°, being mixed with an
equal quantity of water at 172°, the snow melts,
and the mixture is only 32"> j so that the water has
parted with 14O1, which has disappeared, and has
combined with the snow, shewing that snow or
ice, during its change into water, absorbs, and, in-
deed, combines with 140°, of caloric. It also ap-
pears that water, though cooled down to 32", does
not freeze until it has given out 140° of caloric :
on the absorption, or the parting with this dose of
caloric, depends therefore the fluidity or solidity of
water. Not only the fluidity of such bodies as
liquify, but the softness of such bodies as acquire
this state by heat, depends also on the quantity of
heat which thus combines with them> The mal»
leability and ductility of metals likewise depends
on the same cause. The quantity of heat thus im-
bibed, Dr. Black calls latent heat ; since it does
not manifest itself by its effects on the thermo-
meter.

184 FIRE. [Lesson xxvm.

meter. It has been called by others the caloric of
fluidity.

At the moment of the chemical union of two
different substances, the new compound, not, per-
haps, having the same capacity for caloric as its
constituents, must either yield a part to neigh-
bouring bodies, or receive it from them: pro-
ducing thereby a change in their temperature,
which is increased in the former, and diminished
in the latter case.

Ice, we have seen, imbibes the caloric of sur-
rounding bodies, until it has imbibed sufficient to
render it fluid j the temperature of those bodies
descending proportionally. On this principle may
be explained the effects of freezing mixtures, of
snow and different salts, but particularly muriate
of lime. During the liquefaction of these mix-
tures, so rapidly and so considerably is the caloric
absorbed, as to produce a most extraordinary de-
gree of cold, such as even to solidify quicksilver.

Another change in bodies is effected by the
presence of heat. All liquids, and many solids,,
assume a gaseous form, when heated to a certain
temperature : thus water is made to assume the
form of vapour, and become 1800 times more
bulky than water itself. This change Dr. Black
discovered also to depend on a certain portion of
heat combining with the liquid, without producing
any increase of temperature. The latent heat of
steam was ascertained to be at least 940°. The
Doctor proved that all liquids, during their change
into vapour, combine with a portion of heat, with-
out

Lesson xxviii.] FIRE. 185

out undergoing a change of temperature ; and
that on their reduction to a liquid state, a portion
of heat is givtn out, and likewise without mani-
festing any change of temperature.

Thus it appears, that by a certain dose of caloric
solid bodies become liquid, and that by a farther
dose they acquire a gaseous form. Hence the ge-
neral law discovered by Dr. Black ; Whenever a
lody changes its state, it either combines with
caloric, rr separates from caloric.

Dr. Irvine admitted the importance of the facts
discovered by Dr. Black ; but supposed, that the
quantity of heat absorbed by different substances
depended on the capacities which those sub-
stances possessed for heat: and which he ascer-
tained was different, in different substances ; and,
in the same substances, under different forms. He
also believed that the heat thus absorbed does not
exist in any peculiar state : he therefore objected
to the term latent heat, when intended to imply
such a circumstance.

It has been likewise ascertained, that on salts,
which contain much water in their composition, as
muriate of lime, &c. being dissolved in waier, the
temperature sinks considerably ; but if previously
deprived of their water, the temperature rises. This
is to be explained by this law — that when the
compound, formed by the union of two bodies, is
more dense or fluid than the mean density or
fluidity of the two bodies before mixture, then the
temperature is diminished : but when the fluidity

or

186 FIUF. [Lesson xxvm.

or density becomes less, then the temperature is
increased. Thus when the solution of a mixture
of salt and snow is completed, the temperature
rises. The whole of these phaenomena, as Dr.
Thomson observes, as well as the evolution of
heat during putrefaction or fermentation, are
readily explained by Dr. Black's theory of latent
heat.

Setting aside certain particularities of a very
few bodies, it may be assumed, that every addition
of caloric to a body is succeeded by the expansion
of that body : and every abstraction of caloric by
a diminution of bulk. Gaseous bodies in general
expand most : common air expands eight times
more than water, and liquids expand more than
solids : thus the expansion of water is about forty-
five times greater than that of iron.

Mr. Dalton, of Manchester, has ascertained, by
a simple apparatus ; consisting of a graduated glass
tube, open at one end, at which end mercury is in-
troduced to a given point, the rest of the tube
being filled by gaseous matter, the dilation of
which is measur-ed by the quantity of mercury,
which is forced out by the application of heat to
the gas j that all gaseous bodies suffer the same
degree of expansion from the same addition of
caloric, under the same circumstances : and the
increase of bulk it J- part, for 1° elevation of the
mercury in the thermometer. M.GayLausac also
made a series of experiments, the result of which
coincided with that of Mr. Dal ton's. From these

experiments

Lesion xxvin.] FIRE. )&7

experiments it appears, that the expansion of all
elastic fluids, including steam of water, vapour
of ether, Jcc. is equal and uniform, and nearly
equable.

Fire, in a sensible or collective state, is well
known to be one of the grandest agents of nature ;
and for this very reason, perhaps, was regarded
amongst most nations, in an early period of the
world, cither as the creator and productive cause
of all things, or, at least, as the substance from
which the Creator produced all things. Hence the
Persians, Ethiopians, Scythians, andCarthaginians,
in the Old World, and the Mexicans and Peruvians
in the New, paid divine honours to fire itself, or
to the sun, which was esteemed the sublimest re-
presentation of this element. Zoroaster ordained
the erection of pyrea, or temples dedicated to fire,
throughout all Persia. And even the Hebrews
imagined fire to be the grandest proof of the pre-
sence of the Deity. Under this symbol, He ap-
peared to Moses on Mount Horeb ; and to the
Hebrews at large on Mount Sinai, on the promul-
gation of the sacred law ; and under this symbol
He evinced his protective presence every night, by
assuming the form of a fiery pillar. And, im-
pressed with this idea, the Jews were ever anxious
to preserve it in a pure and active flame, upon the
national altar. When, therefore, the Jews were
borne away in captivity to Persia, the priests took
the sacred fire of the altar and concealed it in a
dry cave, with which none but themselves were
acquainted, and where, on their restoration to li-
berty,

188 FIRE. [Lesson xxvnr.

berty, the posterity of those priests found it on
their return 10 Judea. (2 Mac-cab, i. 18.) Fire
was regarded wiih an equal degree of veneration
throughout Greece and Rome. Temples in every
city were erected to the goddess Vesta — a name
importing fire, whether derived from the Grecian
grrja, or the Hebrew : and in every temple a lam-
bent flame was perpettially burning over the
altar. And even so late as in the third century of
the Christian sera, when Heliogabalus anticipated
his own apotheosis, and instituted the worship
of himself over all the Roman empire, having
erected a magnificent temple to his own divinity,
he supplied its altar \\ith sacred fire from the
temple of Vesta, which he plundered for this
purpose.

The frequent reference to fire in the Holy
Scriptures, as emblematical and typical, and its
frequent introduction either to add dignity or so-
lemnity to occurrences, suggests important re-
flections. Sacrifices were consumed by fire, to
signify that wrath from Heaven is due to sin,
and would fall upon the sinful offerer himself,
if the victim did not receive it for him by sub-
stitution. When the law was given on Mount
Sinai, the heavens flamed with fire, and the moun-
tain burned below, to give the people a sense of
the terrors of Divine judgment. With allusion to
which exhibition, and other examples of the ac-
tual effects of his wrath, God is said to be " a con-
suming fire " to his enemies, while he is as " «
wall ef fire" about those who trust in him, to de-
fend

Lesson xxvni.] FIRE. 189

fend them. Elijah was taken up to heaven " in a
chariot of fire ;" and the destruction of the world
by fire, is a positive doctrine of Scripture. This
doctrine, indeed, is perfectly consistent with the
most correct philosophy. All bodies contain ca-
loric, and this substance, by its expansive forre,
tends constantly to ex1 end its energy to surround-
ing substances. The matter which produces light-
ning also, whatever it may be, is now found to be
universally diffused through the system of nature :
so that the heavens which, according to the lan-
guage of Peter, are to " melt with fervent heat,"
want no foreign matter to convert them into fire.
So, likewise, " the earth and the works that are
therein," carry with them the seeds of their own
destruction, and will, in the appointed time, be
burnt up by that element which now r sides within
them, and is only waiting for the word from its
Creator.

LESSON XXIX.

ON WATER.

Ye, whose vital moisture yields

Life's pwrple stream, and fresh supply
Sweet waters, wand'ring through the flow'ry fields,

Or dropping from the sky ;
Confess the Power whose all-snfficient name,
Nor needs your aid to build, nor to support our frame.

WATTS.

IF any such person as an Atheist should peruse
these Lessons, if he be not yet convinced of the
existence of a DEITY, let him pass on with me to
the contemplation of Water : and here I may ven-
ture to say, that he will at least agree with me
when I assert, that if there had been no such thing
as water in the world, all mankind, and almost
all living creatures, even in the midst of a super-
fluity of air and other food, would certainly perish
in a very short time ; since thirst, if it be not ex-
tinguished, is soon fatal, all men and the greater
part of the animal kingdom being unable to exist
without drink.

But it may be also observed, that even if it were
possible that men and other creatures could exist
without drinking, their condition would still be

very

XXIX.] WATER. 191

very miserable deprived of Water : for without its
nourishment, neither grass, nor plants, nor trees,
would be able to spring out of the earth ; the con-
sequence of which would be, that animals, and
consequently mankind would be deprived of food,
as well as drink, whence death must speedily fol-
low. From these passages I would not wish to
have it inferred, that it is not in the power of the
ALMIGHTY to furnish us with a substitute for
Water: this the reader may easily judge is not my
intention : my only design is, to ask, if these
things be produced by chance, as Atheists assert,
how it comes about that this same chance is always
en our side ? For it must appear very strange,
that it is owing to mere chance, that creatures in
general have the faculty of supporting their lives
by Water, and likewise that Water has, by a very
lucky hit, acquired the properties which are neces-
sary for that purpose !

From the Mosaic account of the creation of the
world, we learn, that the division and partition of
the Water into proper channels and courses, was
part of the workmanship of the second and third
days: we there also learn, that the business of the
creation was completed in six days. GOD could
certainly have spoken the whole world into exist-
ence in an instant ; but his love for his creatures
led him to consult their happiness, to make their
felicity flow from their duty : for the regular man-
ner in which HE has pleased to create all things,
points out to us a lesson which should never be
forgotten, namely, that we should so regulate the

manner

WATER. [Lesson xxix.

manner of spending our time in this world, that
the performance of one duty may not interfere
with or obstruct another.

Water is an uninflammable fluid, and, when
pure, is transparent, colourless, and void both of
tas<e and smell. Mr. Cavendish made the dis-
covery that it i<* formed by the union of hydrogen
and oxygen. It may, therefore, be considered as
an oxide oj hydrogen : oxygen and hydrogen ap-
pearing to unite, only in that certain proportion
of which water is the result. The proof of its
composition is thus obtained : water, in a slate of
vapour, being made to pass over iron wire twisted
a.nd made red hot, the iron is oxidized, a consi-
derable portion of the water disappears, and hy-
drogen gas is produced; the iron depriving the
wat^r of its oxygen, by which it becomes an oxide,
while the hydrogen, combining with caloric, forms
the hydrogen gas. Again : 15 parts of hydrogen
gas being burnt in a close vessel, with 85 parts of
oxygen, water is formed nearly of the same weight
as the gases employed : it appearing that, at a
temperature lower than that of ignition, the at-
traction of the respective bases of the two gases to
caloric, is stronger than their attraction to each
other, which prevents their decomposition ; but
that at the degree of ignition the attraction of the
bases are stronger to each other than to caloric ;
hence they unite and form water, the caloric and
light, their imponderable parts, being disengaged
with flame.

The composition of water by the ponderable

parts

Lesson xxix.] WATER. 19S

parts of the gases is beautifully evinced, by the ex,-
periments of Dr. Pearson, by means of the electric
spark. Water may be decomposed also by the in-
fluence of the galvanic pile. Fresh leaves also
being immersed in water, and exposed to the sun,
the Water will be decomposed : the oxygen will
rise in bubbles, and the hydrogen will enter into
combination in the plant.

The ingenious Mrs. Fulhame teaches, that
Water is essential to the oxygenizement of com-
bustible bodies. Thus, in the reduction of me-
tals, she supposes theWater suffers decomposition ;
the reducing substance attracting the oxygen of
the water, whilst its hydrogen, uniting in its na-
scent state, with the oxygen of the metal, effects
its reduction by a double affinity. Hence, and from
a series of well-adapted experiments, she infers,
that, first, the hydrogen of Water is the only sub-
stance that restores bodies to their combustible
state. Secondly, Water is the only source of the
oxygen, which oxygenizes combustible bodies.
Thirdly, No case of combustion is effected by a
single affinity.

At the temperature, marked 32" F., Water parts
with caloric, has its volume increased by a con-
fused crystallization, formed by crystallized needle:,
crossing each other at 60°, or 120°, and assumes a
solid form, when it is termed ICE. The tempera-
ture being increased, it re- assumes the liquid form
of Water, in which a considerable quantity of ca-
loric becomes fixed, and is prevented from passing
into a state of vapour, by the pressure of the at-
K Biosphere.

194 WATER. [Lesson xxix.

mosphere. But if, in the most common state of
ihe atmosphere, the Water be heated to the tem-
perature of 21 2 « F. it then boils, and is converted
into an elastic fluid, or AQUEOUS VAPOUKS, or
ST2AM, which occupies about 1 800 times thcspace
that Water does, and is an invisible fluid, lighter
than common air, as 10 to 12, according to Kir"
waiiy and as 10 to 14, according to Saussure. The
degree of heat necessary to make Water boil in an
open vessel is, however, variable, according to the
purity of the Water and the weight of the atmos-
phere. The requisite degree of heat is generally
between 205* and 214° of Fahrenheit's thermo-
meter. When the pressure of the air is removed,
Water will boil with 90° of h.eat. Water, when
confined in the strong metallic vessel, called Pa-
pin's Digester, may be heated so intensely as to dis-
solve most earths, and to fuse metallic bodies.

Next to fire, Water is found to be the most pe-
netrative of all bodies, and the most difficult to be
confined. It will pass through leather, bladders,
and other substances which will confine air : it will
make its way gradually through wood ; and is
only retainable in glass and some metals. Nay, it
was found by experiment at Florence, that when
shut up in a spherical vessel of gold, which was
pressed with a great force, it made its way through
the pores of the gold.

Water, by this penetrative quality alone, may
be inferred to enter the composition of all bodies,
vegetable, animal, fossil, and even mineral : with
this particular circumstance, that it is easily, and

with

Lesson xxix.] WATER. 195

with a gentle heat, separable again from bodies it
had united with. And yet the same Water, as
little cohesive as it is, and as easily separated from
nu>st bodies, will cohere firmly with some others^
and bind them together in the most solid masses :
as in the tempering of earth or ashes, clay or pow-
dered bones, with water, and then causing them to
be dried and burnt, when the masses become hard
as stones; though, without the Water, they would
have become mere dust or powder. Indeed, it
appears wonderful, that Water, which is an almost
universal dissolvent, should nevertheless be, in
many instances, a great coagulator.

It has been imagined by some that Water is In-
compressible, and therefore non-elastic : but Mr.
Canton has proved, by accurate experiments, that
Water is actually compressed, even by the weight
of the atmosphere. Besides, the diminution of
size which Water suffers when it passes to a less
degree of heat, sufficiently shews that the par-
ticles of this fluid are, like those of all other
known substances, capable of approaching nearer
together.

But the most remarkable property of Water is,
that which has been already spoken of in the
Twentieth Lesson : the discovery o£ which, as it ap-
pears to be one of the most curious and important
which modern times can boast of, I must again
recur to. For this discovery we are indebted to
Count Rumford; and it is given in his Essays. After
proving, in a very satisfactory way, that the par-
ticles of fluids are incapable of imparting heat to
K. 2 e&ch

196 WATER. [Lesson xxix.

each other, and that when their temperature is
undergoing any change, an intestine faction is
kept up in them, by a successive alteration taking
place in the specific gravity of their particles, he
proceeds to shew, that " all bodies are condensed
(f by cold without limitation, Water only excep led,"
and describes the wonderful effects produced in
consequence of this particular fact*.

" Though in temperatures above blood-heat
(says the Count), " the expansion of Water with
" heat is very considerable, yet in ihe neighbour-
" hood of the freezing point it is almost nothing.
tl And what is still more remarkable, as it is an ex-
tl ception to one of the most general laws of nature
t( with which we are acquainted, when in cooling
" it comes within eight or nine degrees of Fahren-

* The circnmstances of this remarkable anomaly have been
for some time believed to be the following: —

When heat is applied to water, ice cold, or at a tempera-
ture not far distant, it causes a diminution of the fluid. The
water contracts, and continues to contract, with the tempe-
rature, till it reaches the 10th or 41st degree. Between this
point and the 42d or 43d, it suffers scarcely any perceptible
change ; but when heated beyond the last-mentioned degree,
it begins to expand, and increases in volume with every sub-
sequent rise of temperature.

During the abstraction of heat, the peculiarity in the con-
stitution of water equally appears. Warm water, as it cools,
shrinks, as other bodies do, till it arrives at the temperature
of 43r or 42°. It then suffers a loss of two degrees without
any alteration of density. But when farther cooled, it begins
to dilate, and continues to dilate, as the temperature falls, till
congelation actually commences, whether this occurs as soon
as the water reaches the 32°, or after it has descended auy
number of degrees'below it.

« belt's

Lesson xxix.] WATER. 197

" heit's scale of the freezing point, instead of going
« on to he farther condensed, as it loses more of its
" heat, it actually expands, as it grows colder,
" and continues to expand more and more as it is
" more cooled."

After enlarging upon this subject, he proceeds
thus : — " As nourishment and life are conveyed
" to all living creatures through the medium of
"Water; liquid, living Water; to preserve life,
" it was absolutely necessary to preserve a great
" quantity of Water in a fluid state, in winter as
" well as in summer. But in cold climates the
«'• temperature of the atmosphere, during many
" months in the year, is so much below the
" freezing point, that had not measures been taken
" to prevent so fatal an accident, all the water
" must inevitably have been changed to ice, which
" would infallibly have caused the destruction of
•" every living thing/'

Count Rumford then shews how very powerfully
this wonderful contrivance tends to retard the
cooling of 'Water, when it is exposed in a cold
atmosphere, and its consequent tendency to pre-
vent all those dreadful evils which must have ne-
cessarily ensued, had it not been for this remark-
able property : but instead of making farther ex-
tracts, which, as they must be short, would be in.
adequate to the purpose, I must refer my young
reader to the Essays themselves, for the time be-
stowed on the perusal of which he will find him-
self amply repaid.

K. 3 Water,

198 WATER. [Lesson xxix.

Water, as a fluid, is governed by several laws
peculiarto itself, to notice all of which would require
a volume : one of its most curious properties is,
that its pressure, or force, varies in the proportion,
of its depth, without any regard to its breadth : if
it were not for this remarkable property, it would
be impossible for ships, or any other vessels, to put
out to sea, — for if the lateral pressure varied with
the breadth, it is evident that every sailing vessel
would be forced against the nearest shore with
great violence, and, of course, there would be an
insuperable bar in the way of navigation.

As it would be absolutely impossible to mnke a
calculation of the quantity of subterraneousWaters,
I shall not attempi it ; but as it is a much easier
matter to have an idea of the enormous quantity
of Water on the earth's surface contained in seas,
we will here set about it. It is a reasonable sup-
position that of the earth's surface two-thirds are
seas : now if we suppose one common depth to
be the tenth part of a mile, we shall find that there
is Water sufficient to cover the whole globe to the
height of six hundred feet ; and if this Water were
reduced into one mass, it would form a globe of
more than sixty miles diameter.

In reflecting upon the various changes of Water,
we have a curious kind of perpetual motion placed
in view : — Vapours are raised from the ocean, by
means of the sun and other agents in the process
of evaporation ; and these are transported by the
winds,. 8cc. through every climate. The progress of

these

Lesson xxix.] WATER. 199

these vapours is interrupted by the tops of moun-
tains, and other causes, whence they accumulate
into clouds, and descend in the form of rain, snow,
&c. as explained in the Nineteenth Lesson: after
having refreshed the surface of the earth, the sur-
plus proceeds, by virtue of its intrinsic gravity, to
steer its course through rivulets, &c. to the lower
parts, where it meets with rivers, which conduct it
to the sea; from whence it again undergoes a si-
milar process, and so on continually. Here I
cannot help adverting to the great utility and ad-
vantage of the distribution of the Waters and the

D

dry land; which, although it may seem rude and
undesigned to a careless view, yet is admirably
adapted to our benefit and convenience. The
Earth and Waters are so placed about the globe,
as to minister to one another's uses. The great
oceans, with the seas and the lakes, are so exten-
sive, and so situated as to produce sufficient va-
pours for clouds and rains, to mitigate the heats,
and to refresh the earth with fertile showers. The
mountains and the smaller hills are distributed in
such a manner as to afford proper situations for
fountains, and the sources of rivers; and this,
whether they are supplied from the condensation
of vapours, or from subterraneous channels. Nay,
so abundant is this great blessing which the most
indulgent Creator hath bestowed upon us, by
means of the distribution of the Earth and
Waters, that there is more than a scanty, bare
sufficiency, even a surplus and plenty, of this most
K 4 necessary

20O

WATER.

[Lesson xxix.

necessary article afforded to the world : this, too,
is so well ordered, by means of the hills and vales
on the surface of the earth, as not to suffer a
sufficient quantity to remain stagnant at one time,
to be of any material injury to mankind. How
ought our hearts to overflow with gratitude and
praise, for 'such beneficence and wisdom as ar«
here made manifest \

LESSON

LESSON XXX.

FOUNTAINS OR SPRINGS.

Tell by what paths, what subterranean ways,
Back to the fountain's head the sea conveys
The r,efluent rivei's, and the land repays :
Tell what superior, what controuling cause,
Makes waters, in contempt of Nature's law#,
Climb up, and gain the aspiring mountain's height,
Swift and forgetful of their native weight.

BLACKMORE.

1 KE conjectures of philosophers, concerning the
origin of Fountains, have been various : and though
the subject has been discussed frequently for more
than two thousand years, it is to be lamented that
it is yet attended with considerable difficulty.

Aristotle, whose thoughts on the matter have
reached us, was of opinion, that the air contained
in the caverns of the earth, being condensed by
cold near its surface, was thereby changed into
water, and, making its way through, formed foun-
tains or springs. Most of the ancient philosophers
after him, embraced this opinion j- but the mo-
derns have entirely rejected it, as they have no ex-
perience of any such transmutation of air into water.
Among the hypotheses which have lately been
proposed to account for the formation of Springs,
K 5 I

802 FOUNTAINS. [Lesson xxx.

I shall describe to you only three, they being the
only ones which in my opinion carry with them
any degree of probability.

The first hypothesis is, that Springs are owing
to rain and melted snow. The water penetrates the
earth till it meets with a soil, or stratum of earth,
of a nature sufficiently solid to sustain it, and pre-
vent it from descending lower in such minute
quantities. It then glides gently along in that
way which the stratum declines, and in its passage
meets with fresh quantities which have been fil-
tered through in the same manner : these gradually
descend together till they arrive at an aperture in the
surface, through which they escape and form a
spring, and perhaps the source of a brook or rivulet.

Another hypothesis, so nearly allied to that just
mentioned that it is almost unnecessary to dis-
tinguish them in a work of this kind, is that of the
ingenious Dr. Halley. When this gentleman made
his celestial observations upon the tops of the
mountains at St. Helena, he found that the quan-
tity of vapour which fell there (even when the sky
was clear) was so great, that his observations were
thereby much impeded: his glasses were so covered
with water through the condensation of the Vapours,
that he was obliged to wipe them every ten minutes.
In reflecting upon this, he was led to suppose that
the water raised by evaporation from the seas and
large rivers might afford a sufficient supply for the
water discharged by Fountains. In order to deter-
mine, with some degree of accuracy, how much
water would be raised in vapour in any space of

time,

Lesson xxx.j SPRINGS, f03

time, he took a vessel of water salted to the same
degree with that of sea-water, in which he placed
a thermometer, and by means of a pan of coals
brought the water to the same degree of heat as
would be produced by the sun in summer : he
then affixed the vessel of water with the thermo-
meter in it, to one end of a pair of scales, and
exactly counterpoised it with weights on the other.
Then, at the end of two hours, he found by the
alteration in the weight of the vessel, that a six-
tieth part of an inch in the depth of the water was
gone off in vapour; and therefore, in twelve hours,
one tenth of an inch would have gone off.

From this experiment the Doctor calculates (in
as accurate a manner as the subject will admit)
the quantity of water raised by evaporation from
the Mediterranean Sea, to be at least five thousand
two hundred and eighty millions of tuns of water
in a day ; and from the River Thames twenty mil-
lions three hundred thousand tuns per day, on the
average. If, as it appeared reasonable to conclude,
other seas and rivers should afford vapour in the
same proportion, when they are acted upon by the
sun in a similar degree; or in greater or less pro-
portions as they are acted upon in a greater or less
degree; this was thought, by the Doctor, a source
abundantly sufficient for the supply of Fountains.

The waters thus raised by evaporation, he ima-
gined would keep rising, and float in extremely
fcmall and light bubbles, till, being condensed by the
cold, they become specifially heavier than the air
when they would descend, or being driven by the

wind*

SPRINGS. [Lesson xxx.

winds against the sides of mountains (some of
which surpass the usual height to which the va-
pours would of themselves ascend) are compelled
by the stream of air to mount up with it to their
tops; and, being presently precipitated, enter the
crannies of the mountains, and glide down, as
described in the former hypothesis.

Jn the third hypothesis it is imagined, that the
water is conveyed from the sea to the places where
there are Fountains, by some subterranean passage;
either by ascending in very small portions in capil-
lary tubes, or by being conveyed in larger portions
by means of Charyldes. Charybdis is a name
given to an opening which is supposed to be in the
bottom of the sea. The Fluxus moschonicus or
MaalstromCf on the coast of Norway, is supposed
to be owing to some such subterranean indraught;
and it is asserted also, by several, that the Mediter-
ranean Sea could not be emptied of the vast quan-
tities of water which it receives, but would over-
flow its boundaries, unless part were taken off by
such a charybdis, which is either in some part of
the bason of that sea, or near the mouth of it.
In support of this supposition may be mentioned
that strong under-current, described by all those
who have treated of this sea. A large charybdis,
placed near the strait's mouth, may be hid under
the immensity of waters therej and as it would con-
tinually draw in the lower waters in large quantities,
it would necessarily cause such an under-current.
If it be admitted, that there are such orifices
as these eharybdes at the bottoms of some seas,

it

Lesson xxx.] SPRINGS.

it is natural to inquire of what use they are. A«d
perhaps none will offer a more probable answer to
this inquiry, than those who say the waters of the
sea are by such means conveyed through subterra-
nean channels to the sides of mountains and hills,
whence they gush out at convenient apertures, and
form springs.

Each of the hypotheses here advanced admits of
objections. To the first two it is objected that they
are not the only ways in which Springs are pro-
duced: for as causes may always be measured by
their effects, it is unphilosophical to conclude, that
an inconstant cause will produce a constant effect—
and therefore Springs which constantly send forth
the same, or nearly the same quantities of water,
cannot be supplied in the manner pointed out
under the two first hypotheses, where the causes, as
pain, snow, or vapours, are inconstant or variable.

Suppose the truth of this remark be allowed, it
does not follow from this, that all Springs are pro-
duced in some other way. Perhaps, if the nature
of Springs, and the nature of the hypothesis be
compared, we shall, by such comparison, be
brought to a very different conclusion.

Let us consider the first hypothesis. Neither rain
nor snow continues without intermission : but
there are intervals between the showers, during
which neither rain nor snow descends. Is it not
probable, that those Springs which flow and stop
alternately, and are therefore called intermitting
Springs, are caused by these showers ? It may,
perhaps, be objected, that in such Springs, the-

time

J00 SPRINGS. [Lesson xxx.

time of flowing does not seem at all connected
with the time of the shower. But in answer to this,
I would observe, that it is not an easy matter to
judge of this, as it cannot be determined which was
the shower that caused the flowing of the Spring.
Those showers which cause the Spring to flow may
perhaps fall at a great distance from it j while those
which fall near it may have an effect upon some
Spring at a distance. Or there may be four or five
showers fall in the interval, between the flowing o£
the Spring and that shower which caused it to flow.

But perhaps it may be said, that this hypothesis
will not satisfactorily account for those Springs
which ebb and flow every six hours, or some such
short period. It will not: we must therefore have
recourse to the third hypothesis, and suppose that
Springs which ebb and flow thus regularly are sup-
plied by charybdes, placed in some parts of the sea
of such a depth as to cause their discharges to be
effected by the tide, and when the tide ebbs and
flows at periods similar to those of the Spring.

The second hypothesis will assist us in account-
ing for reciprocating Springs, or those which flow
constantly with a stream subject to increase and de^
crease. If these are supplied by condensed vapours,
their streams will increase or decrease in propor-
tion as the vapour which supplied them was pro-
duced in a greater or less degree by the union of
heat, wind, and other causes.

As to those Springs which are constant and
regular in their discharge, we may suppose, that
they are supplied from ckaryldes) situated at such a

depth

Lesson xxx.] SPRINGS. 207

depth as to be not at all affected by the ebbing and
flowing of the sea ; but convey the water always
in equal portions in equal times, and, of course,
supply the Springs with regularity.

Against this hypothesis of charybdes, T imagine
two objections will be opposed ; but I think neither
of them will overset it. And first, it may be said,
that if many of the Springs are supplied in this way,
the charybdes must be numerous, and therefore it
js surprising that not more of them are discovered.
Here I would reply, that if there are many, suppose
a charybdis to a Spring, it follows that they must,
comparatively speaking, be very small, and of
course, their effects may not be perceptible upon so
large and deep a body of water. A hole a quarter
of an inch in diameter, would let out much liquor
from a full hogshead, though it would not disturb
the tranquillity of the liquor at the surface.

But, in the second place, it may be said, that I
cannot explain the way in which water is con-
ducted so high above its source. I cannot j. but
this is no proof that it is not so conducted — no
more than it would be a proof that a man was
lifeless, because he could not account for his own
existence. The properties of various kinds of
matter have been determined j but only in such
circumstances as would admit of experiments being
tried : in those cases wheje we can only form a
judgment by analogy, we are always liable to fall
into error, though we may sometimes escape it.

Since the late discoveries in Electricity and Mag-
netism, matter has been found to possess qualities

which

208 SPRINGS. [Lesson xxx.

which philosophers of an earlier period were not
aware of: and in all probability, matter differently
modified, or under different circumstances, may
possess properties which, are yet undiscovered.
Let this stimulate us to fresh exertions in the cause
of philosophy ; and if, after all, we are obliged to
confess ourselves purblind and ignorant in a great
degree, let us not despair ; for Religion points out
a cheering prospect : she directs us to a period
when all our faculties shall be expanded, and all
our inquiries satisfied :

" When GOD'S almighty hand shall lift the curtain high,
And all creation's wonders open to our eye."

LESSON

LESSON XXXI.

ON THE TIDES.

Now the mighty mass of water swells

Resistless, heaving on the broken rocks,
And the full river turning, till again
The tide revertive, unattracted leaves
A yellow waste of idle sands behind.

THOMSON.

'PHILOSOPHERS in every age of the world have
been greatly puzzled to explain and account for
the Tides of the sea, which ebb and flow twice in
twenty-four hours ; but in despite of every attempt,
the doctrine of them remained in obscurity, until
the great Sir Isaac Newton developed the mystery.
This eminent philosopher having demonstrated
that there is a principle in all bodies, by which they
mutually draw or attract each other in certain pro-
portions according as their distances or size vary,
proved that as fluids are very easily put in motion
by any force acting upon them, those parts of the
sea which are immediately below the moon, must
be attracted towards it, and consequently wherevec
the moon is nearly vertical, the sea will be raised,
which occasions the flowing of the Tide there. A
similar reason occasions the flowing of the Tide
likewise in those places where the moon is in the

nadir,

CIO TIDES. [Lesson xxxi.

nadir, and which must be diametrically opposite to
the former : for in the hemisphere farthest from the
moon, the parts in the nadir being less attracted by
her than the other parts which are nearer to her,
gravitate less towards the earth's centre, and con-
sequently must be higher than the rest. Those
parts of the earth, on the contrary, where the moon
appears on the horizon, will have low water: for as
the waters in the zenith and nadir rise at the same
time, the waters in their neighbourhood will press
towards those places to maintain the equilibrium ;
to supply the place of these, others will move the
same way, and so on, to the places ninety degrees
distant from the zenith and nadir, where the water
will be the lowest.

Let the diurnal rotation of the earth be now taken
into the consideration, and it is evident, that every
portion will pass twice through the elevated, and
twice through the depressed parts, so as to produce
two Tides in the day. But the places of high and
low water are now altered ; for the impressed
motions of rising and falling are retained for some
time after the forces which produce them are
greatest: and the greatest elevation happens about
three hours after the meridian of the place has
passed under the luminary, when it points about
half a quadrant to the east of it : and the water
continues to descend for 90 degrees hence, or till
the meridian points about half a quadrant to the
east of the next quarter. But in shallow seas, and
in the mouths of rivers, the Tides are retarded till
the fourth, fifth, or perhaps, sixth hour, after the

meridian

Lesson xxxi.] TIDES. 211

meridian of the place has passed under the lumi-
nary.

The force of the sun to raise the Tides, is about
a third that of the moon : but it is evident, that
when the forces of both conspire,"so as to elevate
and depress the water in the same places, then the
Tides are greatest, and are called Spring Tides,
which happen about the new and full moon.

When the moon is in her quarters, she elevates
the water most where it is most depressed by the
sun, and the contrary ; and the Tides, being
raised by the difference of their forces, are least,
or Neap Tides. But because of the continuation
of motion, these effects are greatest and least,
some time after the forces are : so .that the
greatest Spring Tides commonly happen three
days after the new and full moons; and the least
Neap Tides three days after the first and third
quarters.

By the action of the sun the time of high water
is also changed, being sometimes sooner, and
sometimes later than it would happen by the action
of the moon alone. For in the transit of the moon
from new or full to a quarter, when the tide raised
by the sun alone would precede that raised by
the moon alone, the high water which is produced
by their united actions, will happen at an interme-
diate time, nearer to, but yet before, the time at
which it would be raised by the action of the moon.
But when the moon is passing from her quarters to
the new or full moon, since the sun alone would

produce

TIDES. [Lesson xxxi.

produce a greater tide, the time of high water is
retarded.

The greatest Spring Tide will happen when the
moon is in perige, if other things are the same :
and the succeeding Spring Tide, when the moon is
in apogc, will be least. But because the. earth is
nearer the sun in winter than in summer ; and the
effect of a luminary is also greater, the nearer it ap-
proaches to the plane of the equator ; the greatest
Spring Tides, and the least Neap Tides, will gene-
rally happen immediately after the autumnal and
before the vernal equinox.

In places remote from the equator, the two im-
mediately succeeding Tides are unequal, whenever
the luminary declines from the equator. Thus it is
observed, that the evening tides in summer exceed
the morning Tides ; and the contrary, in winter.
For, if the greatest elevation immediatelyunder the
luminary points to one side of the equator, the op-
posite greatesfelevation points as much to the other
side. And those places, which are on the same
side of the equator with the luminary, approach
nearer to the greatest elevation, when the luminary
is above the horizon, than to the greatest opposite
elevation, when the luminary is below the horizon.

This inequality is greatest, when the sun and
moon have the greatest declination. It is also
greatest in places most remote from the equator.
The nearer the place approaches to the poles, the
farther it is removed from the greatest elevation on
the opposite side of the equator. Thus the less

Tide

Lesson xxxi.] TIDES.

Tide is continually diminished, til! at last it en-
tirely vanishes, and leaves only one Tide in the day.
Hence it is found by observation, that, when the
moon has declination, there is only one Tide in
twenty-four hours in all places in the polar regions,
in which the moon is either always above or al-
ways below the horizon, during a whole rotation
of the earth about its axis.

These things would happen uniformly in the
manner above described, if the whole surface of the
earth were covered with water ; but since there is a
multitude of islands, continents, &c. which inter-
rupt the natural course of the water, varieties of
appearances are to be met with in different places,
which cannot be explained without regarding the
situation of shores, straits, and other objects :
and as this would lead me too great a length, with-
out oeing of much utility, I shall here take my
leave of the subject, with remarking, that the most
correct popular view of it with which I am ac-
quainted is given by Laplace in his Exposition du
Systems du Monde.

LESSON

LESSON XXXIT.

ON DAYS AND NIGHTS.

My God, all nature owns thy sway :
Thou giv'st the Night, and Thou the Day !
When all thy lov'd creation wakes,
When Morning, rich in lustre, breaks,
And bathes in dew the opening llow'r,
To Thee we owe her fragrant hour;
And when she pours her choral song,
Ker melodies to Thee belong !
Or when, in paler tints array'd,
The Evening slowly spreads her shade ;
That soothing shade, that grateful gloom,
Can more than Day's enliv'ning bloom,
Still ev'ry fond and vain desire,
And calmer, purer thoughts inspire;
From eartli the pensive spirit free,
And lead the soften'd heart to Thee

Miss WILLIAMS.

PjlEVIOUSLYto the dawn of thetruepbilosnphy,
when several erroneous opinions were entertained
by philosophers, the principal one with regard to
the form of the earth was, that it was a vastly
wide extended plain ; lhat the visible horizon
bounded the earth, and the ocean bounded the
horizon. To account for Day and Night, it was
then imagined that thesun in the morning emerged
from the eastern ocean, and, after pursuing his

daily

Lesson XXKII.] DAYS AND NIGHTS. 215

daily track, was immerged inio the western ocean,
whence, in the course of the Night, he travelled on
to the eastern in order to perform his next di-
urnal journey : an absurd doctrine, which is now
entirely laid aside ; except, indeed, by the most
illiterate.

But as my young readers will readily admit the
near approach of the earth to a spherical form, I
must endeavour to explain to them the occasion of
Day and Night in a more rational manner. — On
account of the immense distance of the earth from
the sun, and the earth's minute size when compared
with him, it is evident that the rays of light emitted
from that luminary (setting aside the effects of the
atmosphere) will fall upon the earth in parallel
directions, and will always illuminate a hemisphere
of the earth, whilst the other hemisphere remains
in darkness. Hence then, so long as any parti-
cular place on the earth continues in the darkened
hemisphere, it will be night at that place : but, as
soon as that place, by the diurnal rotation of the
earth from west to east, is brought to the verge
of the enlightened hemisphere, then \sDay-lreak;
and

The morn, in russet mantle clad,

Walks o'er the dew of you high eastern hill.

SHAKESPEARE.

When the meridian of that place is, by the
rotatory motion, brought directly beneath the sun,
it is then Noon there, and at every place in
the enlightened part of the same meridian : but
in the darkened part of the same meridian it

is

21() ' DAYS AND NIGHTS. [LesSOH XXJ

is then midnight. As the place is carried for-
ward, the afterhoon hours keep wasting, until it
arrive at the edge of the darkened hemisphere, and
then approaches sober Evening, shedding her
dusky influence round : that part of the globe
which is directly opposite., is, at the same moment,
just emerged from darkness into Day-light : and
thus, by the earth's rotation, the whole is obviously
accounted for.

When to the western main the Sun descends,

To other lands a rising day he lends ;
The spreading dawn another region spies,
And e'er the Antipodes* begins to rise:
While we in Sleep's embraces waste the night,
The climes oppos'd enjoy meridian light ;
And when those lands the busy sun forsakes,
With us again the rosy Morning wakes.

GAY.

To explain the reason of the different lengths
of Days and Nights will be part of the subject
of the next Lesson : but I shall first present you
with an agreeable method of shewing all those
places of the earth which are enlightened by the
sun at any time. In order to this, let a terrestrial
globe be taken from its several appendages, and
placed upon a pedestal in the sun-shine, in such a
manner that its north pole may point directly
towards the north pole of the heavens, and that
the meridian of the place where you are may be
directly toward the south. Then the sun will

* Those people are called Antipodes, who, living on the
other side of the earth, have their feet directly opposite to

ours.

shine

XXXII.] DAYS AND NIOHYS.

shine upon ail the like places or the globe, as
4ie does really on the earth, rising to some when
he is setting to others: as you may perceive by
noticing where the enlightened hair" of the globe
is divided from the half in the shade ; all those
places, on which the sun shines at any time,
having day, — and all those on which he dues not
shine, having night : also, when any pL.ce is near
the middle of the enlightened part, it is then
nearly noon there ; and those places which ar$
about the middle of the darkened part, have then,
midnight.

The vicissitudes of Days and Nights have raised
in the minds of several prose and poetical writers
very serious and excellent reflections concerning
the sublunary state : with one of which this Lesson
day be concluded.

For ever running an enchanted ronnd,

Passe* the Day, deceitful, vain, and void ;

Af* fleets the vision o'er the formful brain,

This moment hurrying wild th* impassion'd soul,

The next in nothing lost. Tis so to Itim

The dreamer of this earth, an idle blank;

A tight of horror to the cruel wretch,

Who all day long in sordid pleasure roli'd,

Himself an useless load, has squauder'd vilsj

Upon his scoundrel train, what might have chcer'd

A drooping family of modest worth :

But to the generous still-improving mind,

That gives the hopeless heart to sing for joy,

Diffusing kind beneficence around,

Boastlcss as now descends the silent dew;

To him the long review of order'd life

la inward rapture only to be felt.

LfcSSON

LESSON XXXIII.

ON THE SEASONS.

Observe the circling year; how unperceiv'd
H«r Seasons change! behold, by slow degrees,
Stern Winter tam'd into a ruder Spring ;
The ripeii'd Spring a milder Summer glows;
Departing Summer sheds Pomona's store;
And aged Autumn brews the Winter's storm.

ARMSTRONG.

1 THINK there is scarcely one of the youthful
perusers of these pages, but must have an inclina-
tion (if he be not already acquainted with it) to be
made sensible in some measure of the reason and
cause of that agreeable succession of the Seasons
which constitute the year. 'Here we meet with a
variety, the limits of which are not ascertainable.
With pleasure we behold the varied appearances of
nature : whether Spring arrays herself in her
spotted robe; or Summer scorches with his sultry
beams j or Autumn pours forth her exuberant
stores j or Winter with his howling tempest drives
us to our habitations; — still we are admirers of na-
ture, and disposed

-" To mark the mighty Hand

That, ever busy, wheels the silent spheres;

Works in the secret deep ; shoots streaming thence

The fair profusion that o'erspreads the Spring ;

Flings

Lest on xxxm.] SEASONS.

Flings from the sun direct the flaming day;
Feeds ev'ry creature ; hurls the tempest forth :
And as on earth this grateful change revolves,
With transport touches all the springs of life."

It may have been observed that, when explain-
ing the nature of the tides, I said, " The earth is
nearer the sun in Winter than in Summer." This
may to many persons appear improbable, but it is
absolutely fact : for the apparent diameter of the
sun is about 32' 48" on the shortest day, and only
31 30" on the longest : whence it is manifest that
his distance from us must be less in the former
case than in the latter. But the effects occa-
sioned by the difference of distance are more than
counterbalanced to the inhabitants of the earth's
northern hemisphere : for, though the sun in
Summer be farther from us ; yet, on account .
of his being more nearly in a vertical position,
his rays fall more directly on any part, and
of course are denser and thicker; and this, not
•nly because the same quantity of rays fell on
a less space of the earth, but because they are
not so much refracted and attenuated by the at-
mosphere, as when they fall upon it more ob-
liquely.

The diversity of seasons is occasioned by the
earth's annual motion in her orbit ; and in this
motion two peculiar circumstances must be well
understood, because on their combination the
whole phaenomena depend. " 1. The earth's axis
does not always keep the same relative situation
with regard to the sun as the centre of its orbit ;
L 2 but.

220 SEASONS. [Lesson

t>ut, on the contrary, it always keeps very nearly
in a parallel position, or points always towards
the same part of the heavens. 2. The axis of the
earth is inclined to the plane of the earth's orbit,
which may be conceived by supposing a spindle
put 'through a ball, with one end of it touching
the ground, oj table; then by moving the ball
directly forwards whilst the one end of the «,pindl<e
continues to touch the ground, or table, and
the other points towards ihe heavens, a tolerable
conception of the inclination of the earth's axis to
her orbit may be obtained.

The most easy method of acquiring a right idea
of the varieties of the Seasons, and the different
lengths of days and nights will be by an experi-
ment xwhioh I shall now endeavour >to describe.
Let two large circular hoops nearly of «q<ual
size be procured : let one of these be fixed in an
horizontal position, and let the other be fixed
within it in such a manner as to cross it in an
angle of 23k. degrees, having one half above the
horizontal hoop, and the other half below.
When night is arrived, the flame of a candle must
be fixed -exactly >in the centre of the hoops, and a
small terrestrial globe must be taken from its ap-
pendages, having a string tied to its north pole,
from which string the globe may be suspended.
In this experiment, the candle flame must be sup-
posed to represent the sun, and the inclined hoop
the earth's orbit: just on the inside of this hoop,
the globe suspended from the string must be car-
tied gently round in a direction from west to east ;

then

JLesson xxxni.] SEASONS.

then its axis will always be parallel to itself, and
the various seasons will be represented in the
different parts of the path. Thus, when the globe
is at one of the places where the hoops intersect,
its poles are equally illuminated, and the days are
every where of the same length : then Spring
commences to the inhabitants of the northern
hemisphere; being about the 9Oth of March.
As the globe is carried onrthe days keep increas-
ing, until it has arrived at the lowest part of thft
hoops ; when the north pole will appear a con-
siderable way in the illuminated hemisphere, and
the south pole as much in the darkened one ; then
is our beginning of Summer and their beginning
of Winter ; and here it may be perceived that any
parallel of latitude toward the north pole is
considerably more in the enlightened hemisphere
than in the darkened one; while, on the con-
trary, in the southern hemisphere, a far greater
part of the parallel of latitude is darkened than
enlightened: hence, our days are then longest*
and theirs shortest; which happens about the
21st of June. The globe being carried on until it
arrive at the intersection of the hoops on the other
side; each. of. its poles is again illuminated, and
the days every, where of equal length^ because
each parallel of latitude is half in the enlightened
and half in- the darkened part^ then 'Commence*
Autumn with us, being about the 22el. of Sep-
tember. As the globe is- carried oa> the days
with us shorten, until it has-arrived at the highest
part of the hoop : then the north pok is in th«
fc.-3 darkened

222 SEASONS. [Lessen xxxw.

darkened hemisphere, and the southern one in
the enlightened part; our day is at the shortest,
while in the southern hemisphere the clay is lon-
gest; our Winter commences and their Summer;

. being about the 21st of December. As the mo-
tion of the globe is continued, our days lengthen ;.
and when it has again arrived at the intersection
of the hoops, we have Spring, and the inhabitants
of the southern hemisphere have Autumn. In
the course of this experiment it will be found, that
•ach of thepoles continues enlightened half through
the annual revolution, and darkened through the
other half: consequently, at the poles of the
earth, there is but one day and one night through
the year.

At the equator the sun's rays fall perpendicu-
larly on the earth, and therefore act more
powerfully; whence arises the great heat* of the
torrid zone. On advancing towards both poles,,
the rays fall more and more obliquely, and
therefore act with less force and less; whence
this -space is occupied, first by the temperate

.zones extending on each side the tropics, and then
by the frigid zones extending from these to the
poles. So weak is the sun's power in these last
owing to the great obliq-uity with which its rays
strike the earth, that they are buried in almost
•perpetual snow and ice. But these are merely
the differences of climate: the differences of
Season depend not upon these causes merely,
but also upon the length of time that any por-
iion of the earth is exposed to the solar rays.

During

Lesson xxxin.] SEASONS. 223

During the short days, the sun's influence it
less, both with respect to the intensity of its rays
and the time of their continuance, which there-
fore produces \yinter: during the long days, it is
greater in both respects, and therefore causes
Summer. The middle seasons of Spring and Au-
tumn correspond with the equality of nights and
days. It is to be remarked, however, that this
correspondence is not perfectly exact ; for the
severest frosts usually take place afier the days
hare begun to lengthen, and the most oppres-
sive heats are found to happen when the days
are decreasing : the reason of which is, that the
earth, having imbibed more heat than it gave out
during the summer months, is not exhausted of
its superabundant warmth till about the close of
the year: in like manner, because the waste
of the earth's heat is greater in Winter than
its supply, it continues to imbibe heat during
the Spring, and is not saturated till after the
Summer Solstice. Hence also arises the differ-
ence between the Spring and Autumn, though
the position of the sun,, in respect to the earth, is
in both the same. The heat, "of- the Spring is
inferior to that of Autumn, both in point of
regularity and degree; for, on account of the
deficiency of warmth in the earth, it is con-
stantly imbibing heat from the lower part of
the atmosphere; hence originates a large collec-
tion of cloud.-?, which, intercepting the solar
rays, combines, together with the absorption of
the earth, to .deprive the air of much of its heat:
• L.4 whereas

224 REASONS. [Lesson xxxu:>

•whereas in Autumn, the earth being holier thaiu '
the air, gives out regularly a large portion of
•warmth, which, naturally tending to disperse the
clouds, affords a free passage to the solar rays. Thus
Autumn ought in general to be hotter than Spring,
far these two reasons : first, that the earth itself-
gives out a considerable quantity of heat ^and, se-
condly, that the rays of the sun meet with fewer
interruptions in passing thence to the earth. At
the equator there is no proper difference of Sea-
sons except as occasioned by rainy or windy pe-
riods, which proceed from other causes ; and the.
case is much the same on each side of it for some,
distance.

Several of the British poets have presented us
•with a variety of descriptions of the Seasons ; some
Serious, some humorous and comic. As an in-
stance of thff latter, we have a droll account of
Winter's effects, in a song in Shakespeare's play
of (< Love's labour lost" But the obvious simi-
larity between infancy, youth, manhood, and old
age of human life, and the Spring, Summer,.
Autumn,.and Winter of the year, suggests a subject
for the most sublime reflections. The excellence o£
those which Mr. Thomson has made on this heady
will supersede the necessity of my apologizing for
giving them insertion here.

-Behold, fond roan !

See here ihy pictur'd life: pass some few years,
Thy flowering Spring, thy Summer's ardent strength,
Tliy sober Autumn fading into age,
And pale concluding Winter conaf t sit last

And-

JE«SOH XXXI11.] SEASONS. 225

And shuts the scene. Ah! whither now are fled

Those dreams of greatness ; those unsolid hepes

Of happiness ; those" longings after fame;

Those restless cares ; those busy bustling days ;

Tliose gay-spent festive'nights ; those veering thoughts,

Lost between good and ill, that shar'd thy life ?

All now are vanished! Virtue sole survives,

Immortal never-failing friend of man ;

His guide to happiness on high.' Ami set !

'Tis come, the glorious morn ! the second birth

Of heav'n and earth! Awakening nature hears

The new-creating word, and starts to life,

In every heighten'd form, from paift and death

For ever free*. The great eternal scheme,

Involving all, and in a perfect whole

Uniting, as the prospect wider spreads,

To reason's eye refin'd clears up apace.

Ye vainly wise! ye blind presumptuous! now,

Confounded in the dust, adore that POWER

And WISDOM oft arpaign'd : see now the cans*

"Why unassuming worth in secret liv'd,

And died neglected'; why tfte good man's sbarfe

In life, was gall and bitterness of soul ;

Why the lone widow and her orphans pin'd

In starving solitude ; while luxury,

In palaces, lay straining her low thought, •

To form unreal wants ; why heav'h-born truth,

And moderation fair, wore the red m;trks

Of superstition's scourge; why liceu&'d paiuy

That cntel spoiler, that embosora'd'foe,

Imbitter'd all our-blissr. Ye good distrest !

Ye noble few! who-here imbelidirrg stand

Bt-ueath life's pressure, yet bear up a while,

And what your bounded view, which only sa-w

A little part, deem'd evil, is no more :

The storms of wintry time will quickly pass,

Aiul ou« unbounded spring encircle all!

THOMSON'S WiNftn.

LESSON XXXIV.

VEGETABLES OR PLANTS.

Your contemplations farther yet pursue;
The wondrous world of Vegetables view:
Observe the forest oak, the mountain pine,
The tow'ring cedar, and the humble vine,
The bending willow that o'ershades th« flood,
And each spontaneous offspring of the wood.

BLACKMOHEV

IVlY young readers having undoubtedly expe-
rienced delight in viewing the beauties of the Ve-
getable Creation, I am in hopes of contributing to
their satisfaction, while I endeavour to explain the
nature of Vegetables and Vegetation.

A Vegetable or Plant is an organized body, con-
sisting of various parts, taking in its nourishment
usually by a root, and increasing its dimensions by
growth. Vegetables may be divided into three
classes; namely, herbs, shrubs, and trees. Herbs
are those sorts of Vegetables whose stalks are soft,
and have no wood in them ; as parsley, lettuce,
violets, grass, thistles, and an infinite number of
others. Shrubs are those Plants which, though
woody, never grow into trees, but bow down their

branches

Lesson xxxiv-.J VEGETATION. 827

branches near the earth's surface: such are those
Planrs which produce roses/honeysuckles, goose-
berries', raspbcrres, and the like. But trees shoot
up in one great stem or body, and rise to a consi-
derable distance from the ground before they
spread their branches : as the oak, the ash, the
dm, the beach, the fir, the walnut tree, the pear
tree, and many others.

The most considerable parts of Plants are the
root, the stalk or stem, the kaves, the flowers, and
the seed. Most Plants have these several parts;
though there are some that have not all of them :
the alot, for instance, has no htalk ; the savine
has no leaves ; the fern has no flowers.

The uses of most of the parts of Plants are very
obvious: thus, the root evidently serves as a ba-
lance or counterpoise to the head, and by that
means enables the Plant to stand firmly in the
ground. In what other way could enormous oaks
be kept upright and fixed, but by the counter-
balance of their extensive, turgid roots? The
fibrous par's of the roots of Plants, like so many
mouths, absorb nutritious juices from the earth,
and thus convey to the Plants the chief of their
nourishment. The root also discharges the office
of a parent, by preserving the embryo Plants jn her
bosom, during the severity of the winter, in form
of bulbs or buds.

The trunk, or stem of plants, consists of various
parts, as bark, wood, pith, sap vessels, &c. The
bark of Plants performs the same offices to them
that the skin does to animals : it clothes and de-

fendi

VBGETATioy. [Lemn xxxiv.

jfrnds them from injuries, inhales the moisture of
the air and conveys from the Plant the superfluous
humid particles. The bark (as well as the
wood) is supplied with innumerable vessels, which.
convey the fluids to and from every part of the
Plant: the wood aUo is furnished with others,.
which contain air,, ami are distributed through its-
substance. The stability of trees and shrubs con-
sists in the wood, which corresponds with the
bones of animals. The pith, which is a fine tissue
of vessels originating in the centre of the stem, is
supposed to be the seat of life. The fluids of
Plants are : the sap, analogous to the blood of
animals, — and the proper juice, which is of various
colours and consistence, in different individuals ;
as white or milky in the dandelion, resinous in
the fir, and producing gum in cherry or plum
trees »

The leaves contribute both to the benefit and
the ornament of the plant : they are supposed to
answer the purpose of lungs ; and by their readi-
ness to be moved by the wind, they may in some
measure act the part of muscles. They are very
porous on both their surfaces, and inhale and ex-
hale freely. In some Plants (as Venus's Fly-trap),
the leaves are armed with long teeth, like the an*
tenna of insects : they are so irritable, that when
an insect creeps up them, they fold1 up, and
crush or pierce it to death.

The uses of th« flowers and seed, are too evident
to need enumeration.

The most general method of propagating Plants

is

XXXIV.] VEGETATIONS

is by seed : some, however, are raised by a part of
the root of the old plant set in the ground, as po-
tatoes f otheFS-, by new roots propagated from the
old one», as hyacinths and tulips; others by
cutting off branches and putting them into the
ground which will there take root and grow, as
vines; and others are propagated by grafting,
and budding, or inoculation*

What is most difficult with respect to Plants (and
what has been the subject of much controversy,
though yet undetermined), is to explain the man-
ner in which they receive tlieir nourishment. The
earth has not so much to do in this business as has
been commonly supposed. This is known from
the experiments of Mr. Boyle and Dr. Woodward.
These gentlemen raised several Plants in earth-
watered with rain or spring water, and even distil-
led water; and upon weighing the dry earth, both
before and after the product! an of the Plants, they
found that very little of it was diminished or takem
up by the Plant-

Jf the earth contributes so little towards the
production and nourishment of Plants, it seems
natural to apprehend that water must be much
concerned; and that this is the case in great mea-
sure is evident, from the quantity of water which-
most plants require to keep them in a state of
health and vigour. But there is some other agent
besides water; else, how can the growth of Plants
in sandy desarts where it seldom rains be account-
ed for, and these Plants such as cuntain juices i»
great abundance ?

Dr. Hunter^

ISO VEGETATION. [LesSOH XXXIV.

Dr. Hunter, so well known and so justly cele-
brated both as an anatomist and a naturalist, is in-
duced, by a number of experiments accurately con*
ducted, to believe, ttfat all Vegetables receive their
principal nourishment from oily particles incor-
porated with water by means of an alkaline salt$
or absorbent earth. Till oil is made miscibk-, it
cannot enter the radical vessels of Vegetables!
and on that account, Providence has bountifully
supplied all natural soils with chalkv or other ab->
sorbent particles : and those soils which are as-
sistfd by art are full of materials for that purpose;.
as lime, marl, and the volatile alkaline salt of pu-
trid dunghills.

The argument in favour of oil being the prin-
cipal food of Plants is confirmed by the observa-
tion, that all Vegetables, whose seeds are of an
oily nature, are found to be remarkable impoverish-
ers of the soil ; as hemp, rape, and flax : and the
best manures for lands worn out by these crops
are such as have a good deal of oil in their com-
position, provided that they are laid on with lime,
chalk, marl, or soap-ashes, so as to render the oily
part f les miscible with water.

But Plants not only receive nourishment by.
their roots, but also by their leaves. Vegetables-
that have a succulent leaf, such as peas, beans, and
buck wheat, draw much of their nourishment from
the air; and on that account impoverish the soil
less than wheat, oats, barley, or rye, the leaves of
which are of a firmer texture. The leaves of al]
kinds of grain are succulent for a time, during

which .

Lesson xxxiv.] VEGETATION. 231

which the Plants lake little from the earth ; but
as soon as the ear begins to be formed, thty lose
their softness, and diminish in thtir attractive
power. The radical fibres are then more vigorously
employed in extracting the oily particles from the
tarth, for the nourishment of the plant.

The leaves of Plants serve not only to imbibe
the dew and rain, which contain salt, sulphur, &c.
but they serve also as excretory ducts to separate
and carry off ihe redundant watery fluid, which
by being long detained in the Plants, would turn
rancid and prejudicial to them. The annual sun-
flower is an extraordinary instance of this fact : it
is said to perspire nineteen times as much as a
man in twenty-four hours. Fine weather encou-
rages the perspiration of Vegetables; but in htavy,
moist, and wet weather the inhalation is greatest.
The effluvia of Plants is thought unwholesome to
persons of delicate constitutions; but particularly
so at night, and in a dull state of the atmosphere :
the matter perspired by the yew tree, in particular,
is said to be very noxious.

Let us now endeavour to illustrate the subject of
Vegttation, by taking a view of what happens to a
bean after it has been committed to the earth. In
a few days, sooner or later, according to the tem-
perature of the weather and disposition of the soil,
the external coverings open at one end, and dis-
close to -.he naked eye part of the body of the grain.
This substance consists of two lobes, between
which the seminal Plaut is securely lodged. Soon

after

VEGETATION. [Lesson xxxir.

after the opening of the membranes, a sharp
pointed body appears, which is the root. By a
kind of instinctive principle (if the expression may
be allowed), it seeks a passage downward, and
fixes itself into the soil. At this period the root is
a smooth and polished- body, and has, perhaps, bub-
little power to absorb any thing from the earth for
the nutriment of the germ. The two lobes next
begin to separate; and the germ, with its leaves,
may be plainly discorered. As the germ increases-
insize, the lobes are farther separated, and the ten-
der leaves, being closely joined, push themselves-
forward in the form of a wedge* These leaves*
take a contrary direction tcrthat of th* root: they
seek a passage upward; which having obtained,
they lay aside their wedge-like form, and spread-
themselves in an horizontal direction, as being the
best adapted for receiving the rains and dew. The
radicle, every hour increasing in size and vigour,
pushes itself deeper into the earth, from- which it
now draws some nutritive particles. At the same-
time the leaves of the germ, being of a succulent-
nature, assist the Plant by attracting from the at-
mosphere such particles as the tender vessels are*
fit to convey. These particles, however, are of a
watery kind, and have not in their own nature a*-
sufficiency of nutriment for the increasing Plant.
Vegetables, a& well as animals, during their tender
state, require a large share of balmy nourishment.
As soon as an animal is brought to life, the milk of
its mother is supplied i& a liberal stream : but, at

LlSM-Jl XXXIV.] VFCETAT10N.

this period, the tender germ seems only to have the
crude and watery juices of the earth for its support*
This, however, is not the case ; for the Vegetable
lives upon a similar fluid, though differently sup-
plied. For its use the farinaceous lobes are melted
down into a milky juice, which, as long as it lasts, i&
conveyed to the tender Plant, by means of innu-
merable small vessels which are spread through the
substance of the lobes ; and which, uniting into one
common trunk, enter the body of the germ, and
thus supply that balmy liquor, without which the
Plant must inevitably ha\ e perished, its root being
then too small to absorb a sufficiency of food, and
its body too weak to assimilate it into nourishment,
Thus admirable and well contrived is the method of
Providence, in supporting the Plant in its earliest
and tenderest stages ! As the plant increases in
size, the almy juice diminishesrtill at last itisq^uite
exhausted. The trunk of small vessels then dries
up, and the external covering of the seed appear*
connected with the root in the form of a shrivelled
bag. In the process of vegetation there is no mor«
lalityt from the moment that the seed is lodged in
its parent eapth, the vegetative soul begins its-
operations, and,, in the whole successive gradation
of them-, illustrates the wisdom, power, and bounty
of Him who created and rules the UNIVERSE.

These attributes of the ALMIGHTY are also
strikingly manifested, in the provision which he has
afforded them against the winter season to secure
them from the effects of cold. Those called her-
I'aceous, which die down to the root every autumn,

are

234 VEGETATION. [Lesson xxxiv.

are now safely concealed under ground, preparing
their new shoots to burst forth when the earth is
softened in spring. Shrubs and trees which are ex-
posed to the open air have all their soft and ten-
der parts closely wrapt up in buds, which by their
firmness resist all the power of frosts ; the larger
kind of buds, and those which are almost ready to
expand, are farther guarded by a covering of resin
or gum, such as the horse-chesnut, the sycamore,
and the lime. Their external covering, however,
and the closeness of their internal texture, are of
themselves, as some say, not adequate to resist the
intense cold of a winter's night : a bud detached
from its stem, enclosed in glass, and thus protected
from all access of internal air, if suspended from a
tree during a sharp frost, will be entirely penetrated
and its parts deranged by the cold, while the buds
on the same tree will not have sustained the slight-
est injury: either the detached bud must have been
injured by reason of the cold entering it at the
part where it was broken from the stalk; or we
must attribute to the living principle in Vegetables,
the power of resisting cold to a very considerable
degree ; — probably each of these is true in »ome
measure; but how Vegetables require this latter-
mentioned property, must be left for future obser-
vations to determine.

After the frost is moderated, and the earth suffi-
ciently thawed, the first vital function in trees is
the ascent of the sap, which is taken up by the ab-
sorbent vessels composing the inner bark of the
tree, and reaching to the extremity of the fibres of

the

Lesson xxxiv.j VEGETATION. 23 "i

the roots. The water and oil, thus imbibed by the
roots, is there mfxed with a quantity of saccharine
matter, and formed into sap, whence it is distri-
buted in great abundance to every individual bud.
The amazing quantity of sweet liquid sap provided
for the nourishment of some trees, is evident from
a prevalent custom in this country, of tapping the
birch in the early part of spring; thus obtaining
from each tree more than a quart of liquor, which
is fermented into a species of wine. This great
accession of nourishment, by means of the ascent
of the sap, causes the bud to swell, to break through
its covering, and to spread into blossoms, or length-
en into a shoot bearing leaves. This is the first
process, and, properly speaking, is all that belongs
to the springing or elongation of trees j and, in
many Plants, namely, all those which are annual
or deciduous, there is no other process. The Plant
absorbsjuices from the earth, and, in proportion to
the quantity of these juices, increases in size; it ex-
pands its blossoms, perfects its fruit; and when the
ground is incapable, by drought or frost, of yield-
ing any more moisture, or when the vessels are not
able to draw it up, the Plant perishes. But in trees
though the beginning and end of the first process is
exactly similar to what takes place in annuals, yet
there is a second process, which at the same time
that it adds to their bulk, enables them to go on
increasing through a long series of years.

This second process begins soon after the first, in
this way. At the base of the foot-stalk of each leaf
a small bud is gradually formed; but the absorbent

vessels

936 VESETATION. [Lesson xxxtv.

vessels of the leaf, having exhausted themselves in
the formation of the bud, are unable to bring it
nearer to maturity. In this state it exactly resem-
bles a seed, containing within itself the rudiments
of vegetation, but destitute of absorbent vessels to
nourish and evolve the embryo. Being surround*-
ed, however, by sap, like a seed in moist earth, it is
in a proper situation for growing ; the influence
of the sun sets in motion the juices of the bud,,
and of the seed ; and the first operation in both of.
them, is to send forth the roots downwards a cer*
tain depth, cor the purpose of obtaining the. neces-
sary moisture. The bud, accordingly, shoots down-
its root-? upon the inner bark of the tree, till they
reach the part covered by the earth. Winter now
arriving, the cold and defect of moisture, owing t»-
the clogged condition of the absorbent vessels,.
cause the fruit and leaves to fall ; so that, except, the.
provision of buds with; roots, the remainder of the
tree, like an annual plant, i« entirely dead : the.
leaves, the flowers, and fruit, are gone ;. and what
was the inner bark is no longer organized, while
the roots of the buds form a new inner bark ; and
thus the buds with their roots contain all that re-
mains alive of the whole tree. It is owing to this
annual renovation- of. the inner bark, that the tree
increase.? in bulk j and a new coating being added
every year, we are iience furnished with an easy
and exact method qf ascertaining the age of a tree,,
by counting the number of concentric circles of
which the trunk is composed. A tree, therefore,
properly speaking, is rather a congeries of a mul-
titude.

Lesson xxx!v.] VEGETATION.

titiule of annual Plants, than a perennial indi-
vidual. The sap in trees always rises as soon as
the frost is abated, that when the stimulus of the
warm weather in the spring acts upon the bud,
there should be at hand a supply of food for its
nourishment; and if, by any means, the sap is
prevented from ascending in proper time, the tree
inevitably perishes, as has been very frequently
observed.

Before I conclude this Lesson, I cannot forbear
paying a few words on the different manners in
which Plants disseminate their seed. Having gone
through the progressive stages of springing, flower-
ing, and seeding, fhey liave at length brought to
maturity the rudiments of a future progeny, which
are>now to be deposited in thefostering bosom of the
earth. Seeds are scattered by the hand of nature
in various ways. Those of them which are furnish-
ed with plumes, or wings, are dispersed about by
the high winds which blow soon after the Autumnal
Equinox, the time of dissemination. Hence Plants
with such seeds are, of ail others, the most generally
to be met wkh: as dandelion, groundsel, thistles,
&c. Others by means of hooks, with which
they are furnished, lay hold of passing animals,
and are thus carried to distant places •: the common
burs are examples of this contrivance, Several
when ripe are thrown out with considerable force,
from their receptacle, by means of a strong spiral
elastic spring; of this the impatiens,or touch-me-
not, and all the species of cardamine, or cuckoo-
flower, are instances. Many are co; tamed in

berries,

238 VEGETATION. [Lesson

berries, which being eaten by birds, the seeds are
discharged again uninjured, and grow wherever
they happen to fall. In these, and in many other
ways, is the distribution of various kinds of Vege-
tables provided for. The shedding of the seed .
being finished, the parent Vegetable, if of the
herbaceous kind, either totally perishes or withers
down to the root; if a shrul, or tree, it casts all
those tender leaves that in the Spring and Summer
it had put forth. Thus it continues until the fol-
lowing Spring, when

These naked shoots,

Barren as lances, among which the wind

Makes wintry music, sighing as it goes,

Shall put their graceful foliage on again,

And more aspiring, a*nd with ampler spread,

Shall boast new charms, and more than they have lost.

LESSON

LESSON XXXV.

EARTHQUAKES.

The earth shook and trembled; the foundations also oftht
hills moved, and were shaken, because He was wroth.

DAVID.

HISTORIANS relate innumerable instances of
the dreadful and various effects of those tremend-
ous phenomena called Earthquakes : from which
I shall select two only. The first is the description
of the Earthquake at Calabria, in the year 1638 :.
it happened whilst the celebrated Father Kircher
was on his journey to visit Mount JEtna; and I
shall present it in the language of that great pro-
digy of learning.

<f Having hired a boat (says he), in company
with four more (two friars of the order of St.
Francis, and two seculars), we launched from
the harbour of Messina, in Sicily j and arrived,
the same day, at the promontory of Pelorus.
Our destination was for the city of Euphaemia,
irt Calabrfa; where we had some business to
transact ; and where we designed to tarry for some
time. However, Providence seemed willing to
cross our design ; for we were obliged to continue
three days at Pelorus, on account of the weather;

and

440 "EARTHQUAKES. [LeSSOH XX XT.

And though we ofien put out to sea, yet we were
as often driven tack. At length, wearied with the
delay, we resolved to prosecute our voyage ; and,
although the sea seemed more than usually agi-
tated, we ventured forward. The gulph of
Charybdis, which we approached, seemed wh.rled
•round in such a manner, as to form a vast hollow,
verging to a point in the centre. Proceeding on-
ward, and turning my eyes to ./Etna-, I saw it
cast forth Jarge volumes of smoke, of mountainous
sizes, which entirely covered the island, and blot*
ted out the very shores from iny view. This, to-
gether with the dreadful noise and the sulphurous
stench which was strongly perceived, filled me with
apprehensions that some more dreadful calamity
was impending. The sea itself seemed to wear a
very unusual appearances they who have seen a
lake in a violent s'hower of rain, covered all over
with bubbles, will conceive some idea of its agita*
tions. My surprise was increased by the calm-
ness and serenity of the weather; not a breeze,
not a cloud, which might be supposed to put all
Nature thus into -motion. I therefore warned my
companions, that an earthquake was approaching;
arnd after some time, making for the shore with
all possible diligence, we landed at Tropaea, happy
and thankful for having escaped the threatening
dangers of the sea.

" But our triumphs at land were of short dura-
tion ; for we had scarcely arrived at the Jesuits'
College, in that city, when our ears were stunned
with a horrid sound, resembling that of au infinite

number

ZesSfWXXXV.] rEARTHQUAKES. 241

number of chariots, driven fiercely forward ; the
wheels rattling, and the thongs cracking. Soon
after this, a most dreadful earthquake ensued; so
that the whole tract upon which we stood, seemed
to vibrate, as if we were in the scale of a balance,
that continued wavering. This motion, however,
' soon grew more violent ; and being no longer able
to keep my legs, I was thrown prostrate upon the
ground. In the mean time, the universal ruin
round me redoubled my amazement. The crash
of falling houses, the tottering of towers, and the
groans of the dying, ail contributed to raise my
terror and despair. On every side of me, I saw
nothing but a scene of ruin ; and danger threaten-
ing wherever I should fly. I commended myself
to God, as my last great refuge. At that hour, O
how vain was every sublunary happiness ! Wealth,
honour, empire, wisdom, all mere useless sounds,
.and as empty as the bubbles in the deep ! Just
standing on the threshold of eternity, nothing but
God was my pleasure ; and the nearer I approach-
ed, I only loved him the more. After some time,
however, finding that I remained unhurt, amidst
the general concussion, I resolved to venture for
safety ; and running as fast as I could, I reached
the shore, but almost terrified out of my reason. I
did not search long here, till I found the boat in
which I had landed: and my companions also,
whose terrors were even greater than mine. Our
meeting was not of that kind, where every one is
desirous of telling his own happy escape: it was
M ail

242 EARTHQUAKES. [Lesson xxxV.

all silence, and a gloomy dread of impending
terrors.

" Leaving this seat of desolation, we prosecuted
our voyage along the coast ; and the next day
came to Rochetta, where we landed, although the
earth still continued in violent agitations. But
^ve had scarcely arrived at our inn, when we were
once more obliged to return to the boat; and, in
about half an hour, we saw the greater part of the
town, and the inn at which we had set up, dashed
to the ground, and burying the inhabitants be-
neath the ruins."

" In this manner, proceeding onward in our
little ves"sel, finding no safety at land, and yet,
from the smallness of our boat, having but a very
dangerous continuance at sea, we at length landed
at Lopizium, a castle midway between Tropaea and
Euphaemia, the city to which, as I said before, we
were bound. Here, \\herever I turned my eyes,
nothing but scenes of ruin and horror appeared
towns and castles levelled to the ground ; Strom-
balo, though at sixty miles distance belching forth
flames in an unusual manner, and with a noise
which I could distinctly hear. But my attention
was quickly turned from moreremote,to contiguous
danger. The rumbling sound of an approaching
earthquake, which we by this time were grown ac-
quainted with, alarmed us for the consequence: it
every moment seemed to grow louder, and to ap-
proach nearer. The place on which we stood now
,l>egan to shake most dreadfully, so that, being un-
able

Less«n XXXV.} EARTHftUAKES. 242

able to stand, my companions and I caught hold
of whatever shrub grew next to us, and supported
ourselves in that manner."

" After some time, this violent paroxysm ceas-
ing, we again stood up, in order to prosecute our
voyage to Euphasmia, which lay within sight. In.
the mean time, while we were preparing for this
purpose, I turned my eyes towards the city, but
could see only a frightful dark cloud, that seemed
to rest upon the place. This the more surprised
us, as the weather was so very serene. We waited,
therefore, till the cloud had passed away : then
turning to look for the city, it was totally sunk.
Wonderful to tsll ! nothing but a dismal and pu-
trid lake was seen where it stood. We looked
about to find some one that could tell us of its sad
catastrophe, but could see no person. All was be-
come a melancholy solitude; a scene of hideous
desolation. Thus proceeding pensively along, in
quest of some human being that could give us a
little information, we at length saw a boy sitting
by the shore, and appearing stupified with terror.
Of him, therefore, we inquired concerning the fate
of the city ; but he could not be prevailed on to
give us an answer. We entreated him, with every
expression of tenderness and pity, to tell us ; but
his senses were quite wrapt up in the contempla-
tion of the danger he had escaped. We offered
him some victuals; but he seemtd to loath the sight.
We still persisted in our offices of kindness ; but
he only pointed to the place of the city, like one
out of his senses, and then, running up into the
M 2 woods

244 EARTHQUAKES. [LesSOJl XXXV.

woods, was never heard of after. Such was the
fate of the city of Euphsemia: and as we conti-
nued our melancholy course along the short, the
whole coast, for the space of two hundred miles,
presented nothing but the remains of cities; and
men scattered, without a habitation, over the
fields. Proceeding; thus along, we at length

C7 O * C1

ended our distressful voyage, by arriving at Na-
ples, after having escaped a thousand dangers both
at sea and land."

The great and almost universal Earthquake
which happened on the 1st of November, 1755,
affords a dreadful example of the chief attendants
of these striking phaenomena, on which account
the young reader shall be presented with the fol-
lowing description of it. '

At Lisbon its effects were most severe. In
1750, there had been a sensible trembling of the
earth felt in that city : for four years afterwards,
there had been an excessive drought ; insomuch
that some springs, formerly very plentiful of
water, were dried and totally lost. The predomi-
nant winds were north and north-east, accompa-
nied with various, though very small, tremors
of the earth. The year 1755 proved very wet and
rainy; the summer cooler than usual; and for
forty days before the earthquake, the weather was
clear, but not remarkably so. The last day of
October, the Bun was obscured, with a a singular
gloominess in the atmosphere. The-lst of Novem-
ber, early in the morning, ;i thick fog arose, which
was soon dissipated by the heat of the sun; no

wind

Lesson xxxv.] EARTHQUAKES.

wind was stirring ; the sea was calm, and the
weather as warm as in June or July in this coun-
try. At 35 minutes after nine, without the least
warning, except a rumbling noise not unlike the
artificial thunder in our theatres, a most dreadful
earthquake shook, by short but quick vibrations,
the foundations of all the city, so that many build-
ings instantly fell. Then, with a scarce precepti-
b!e pause, the nature of the motion was changed,
and the houses were tossed from side to side, with
a motion like that of a waggon violently driven
over rough stones. The second shock laid almost
the whole city in ruins, with prodigious slaughter
of the people. The earthquake lasted in all about
six minutes. At the moment of its beginning,
some persons on the river, near a mile from the
city, heard their boat make a noise as if it had run
aground, though they were then in deep water;
and at the same time they saw the houses falling
on both sides of ihe river. .The bed of the river
Tag us was in many places raised to its surface.
Ships were driven from their anchors, and jostled
together with great violence ; nor did their masters
know whether they were afloat or aground. A
large new quay sunk to an unfathomable depth,
with several hundreds of people who were upon it ;
nor was one of the dead bodies ever found. The
bjr was at fmt seen dry from shore : but suddenly
the sea came ruling in like a mountain; anci dboi.t
fielem Castle the water rose 50 feet aim -t u <<ii
insiant. About noon, there was another shock !
when the walls of several houses that ytt remained
M 3 were

846 EARTHQUAKES. [Lesson XXXV,

were seen to open from top to bottom more than a
quarter of a yard, and afterwards closed again so
exactly that scarcely any mark of the injury was left.
At Colares, about 20 miles from Lisbon, and two
miles from the sea, on the last day of October, the
weather was clear, and uncommonly warm for the
season. About four o'clock in the afternoon there
arose a fog, which came from the sea, and covered
the valleys ; a thing unusual at that season of the
year. Soon after, the wind changing to the east,
the fog returned to the sea, collecting itself, and
becoming exceeding thick. As the fog retired, the
sea rose with a prodigious roaring. The first of
November, the day broke with a serene sky, the
wind continuing at east; but about nine o'clock
the sun began to grow dim ; and about half an
hour after was heard a rumbling noise like that of
chariots, which increased to such a degree that it
became equal to the explosions of the largest can-
non. Immediately a shock of an earthquake was
felt, which was quickly succeeded by a second and
third; and at the same time several light flames of
jfire issued from the mountains resembling the kind-
ling of charcoal. In these three shocks, the walls of
the buildings moved from east to west. In another
situation, from whence the sea coast could he dis-
covered, there issued from one of the hills called
the Fojo a great quantity of smoke, very thick, but
not very black. This still increased with the
fourth shock, and afterwards continued to issue in
a greater or less degree. Just as the subterraneous
rumblings were heard, the smoke was always ob-
served

Lesson xxxv.] EARTHCIUAKES. £47

served to burst forth at the Fojo ; and the quantity
of smoke was always proportioned to the noise.
On visiting the place from whence the smoke was
seen to arise, no signs of fire could be perceived
near it.

At Oporto (near the mouth of the river Douro),
the earthquake began about 40 minutes past nine.
The sky was very serene j when a dreadful hollow
noise like thunder, or the rattling of coaches at a
distance, was heard, and almost at the same instant
the earth began to shake, fn the space of a minute
or two, the river rose and fell five or six feet, and
continued to do so for four hours. It ran up at
first with so much violence, that it broke a ship's
hawser. In some parts the river opened, and
seemed to discharge vast quantities of air; and the
agitation in the sea was so great about a league
beyond the bar, that air was supposed to have been
discharged there also.

St. Ube's, a sea-port town about £0 miles south
of Lisbon, was entirely swallowed up by the re-
peated shocks and the vast surf of the sea. Huge
pieces of rock were detached at the same time from
ihe promontory at the west end of the town, which
consists of a chain of mountains containing fine
jasper of different colours.

The same earthquake was felt all over Spain,
except in Catalonia, Arragon, and Valencia. At
Ayamonte (near where the Guadiana falls into the
Bay of Cadiz), a little before 10 o'clock on the 1st
of November, the earthquake was felt ; having
been immediately preceded by a hollow rushing
M 4 noise.

248 EABTHQUAKF.S. [Lesson xx?

noise. Here the shocks continued for 14 or 15
minutes, damaged almost all the buildings, throw-
ing down some, and leaving others irreparably
shattered. In little mote than half an hour after,
the sea and river, with all the canals, overflowed
their banks with great violence, laying underwater
all ihe coasts of the islands adjacent to the city
and its neighbourhood, and flowing 'into the very
streets. The water came en in vast black moun-
tains, white with foam at the top, and demolished
more tha.i one half of a tower at the bar named
De Canala. In the adjacent strands, every thing
was irrecoverably lost; for all that was overflowed
sunk, and the beach became a sea, without the least
resemblance of what it was before. Many per-
sons perished ; for although they got aboard some
vessels, yet part of these foundered ; and others
btin<i forced out to sea, the unhappy passengers
•were so terrified that they threw themselves over-
board. The day was serene, and not a breaih of
wind slirring.

At Cadiz, some minutes after nine in the morn-
ing, the, earthquake began, and lasted about five
minutes. The water of the cisterns under ground
washed backwards and forwards, so that a great
froth arose. Al ten minutes after eleven, a wave
was seen coming from the sea, at eight miles dis-
tance, at least 60 feet higher than usual. It dashed
against the west part of the town, which is very
rocky. Though the^e rocks broke a great deal of
its force, it at last came upon the city walls, beat
in the breast-work, and carried pieces of the build-
ing*

Lesson xxxv.] EARTHQUAKES. 24Q

ing, of eight or ten tons weight, to the distance of
40 or 50 yards. When the wave was gone, some
parts that are deep at low water, were left quite
dry ; for the water returned with the same violence
with which it came. At half an hour after 11
came a second wave, and after that four other re-
markable ones; the first at ten minutes before 12;
the second, half an hour b fore l ; the third; ten
minutes after 1 ; and the fourth, ten minutes be-
fore 2. Similar waves, but smaller, and gradually
lessening, continued with uncertain intervals till
the evening.

At Gibraltar, the earthquake was not felt ^till
after ten. It began with a tremulous motion of
the earth, which lasted about half a minute. Then
followed a violent shock : after that, a trembling
of the earth, for five or six seconds; then another
shock was not so violent as the first, which gradu-
ally went off as it began. The whole lasted about
two minutes. Some of the guns on the battery
were seen to rise, others to sink, the earth having
an undulating motion.. Most people were seized
with giddiness and sickness, and some fell down;
others were stupified ; and many that were walk-
ing or riding felt no motion in the earth, but were
sick. The sea rose six feet every 15 minutes;
and then fell so low, that boats and all the small
craft near the shore were left aground, as were
also numbers of small fish. The flux and reflux
lasted till next morning, having decreased gradu-
ally from two in the afternoon. At Madrid, the
earthquake came on the same time as at Gibraltar,
and lasted about six minutes,

M 5 la

250 EARTHQUAKES. [LeSSOH XXXV.

In Africa, the earthquake was felt almost as
severely as it had been in Europe. Great part of
the town of Algiers was destroyed. At Arzilla (a
town in the kingdom of Fez), about ten in the
morning, the sea suddenly rose with such impetuo-
sity, that it lifted up a vessel in the bay, and drop-
ped it with such force on the land, that it was
broken to pieces ; and a boat was found two musket-
shots wiihin land from the sea. At Fez and Me-
quinez, great numbers of houses fell down, and
a multitude of people were buried in the rums.
At Morocco, by the falling down of a great num-
ber of houses, many people lost their lives : and at
Salle, a great deal of damage also was done. At
Tangier, the earthquake began at ten in the morn-
ing, and lasted ten or twelve minutes. At Tetuan,
the earthquake began at the same time, but lasted
only seven or eight minutes. There were three
shocks so extremely violent, that it was feared the
whole city would be destroyed.

In the city of Funchal, in the island of Madeira,
a shock of this earthquake was first perceived at
thirty- eight minutes past nine in the morning. It
-was preceded by a rumbling noise in the air, like
that of empty carriages passing hastily over a stone
pavement. The observer felt the floor immediately
to move with a tremulous motion, vibrating very
quickly. The shock continued more than a mi-
nute ; during which interval, the vibrations, though
continual, were weakened and increased in force
twice very sensibly. The increase after the first
remission of the shock was the most intense. The
noise in the air accompanied the shock during the

whole

Lesson xxxv.} EARTHQUAKES. 251

whole of its continuance, and lasted some seconds
after the motion of the earth had ceased ; dying
away like a peal of distant thunder rolling through
the air. At three quarters past eleven, the sea,
which was quite calm, it being a fine day, and no
wind stirring, retired suddenly some paces; then
rising with a great swell without the least noise, and
as suddenly advancing, overflowed the shore, and
entered the city. It rose fifteen feet perpendicularly
above the high-water mark, although the tide,
which flows there seven feet, was then at half ebb.
The water immediately receded ; and after having
fluctuated four or five times between high and low
water-mark, it subsided, the sea remaining calm
as before. In the northern part of the island the
inundation was more violent, and the sea there
retiring above one hundred paces at first, and sud-
denly returning, overflowed the shore, forcing open
doors, breaking down the •;& alls of several maga-
zines and storehouses, leaving great quantities of
fish ashore and in the streets of the village of Ma-
chico. All this was the effect of one rising of the
sea, for it never afterwards flowed high enough to
reach the high-water mark. It continued, however,
to fluctuate here much longer before it subsided
than at Funchal ; and in some places farther to the
westward, it was hardly, if at all, perceptible.

These were the phaenomena with which this re-
markable earthquake was attended in those places
where it was violent. The effects of it, however,
reached to an immense distance; and were per-
ceived chiefly by the agitations of the waters, or

by

•52 EARTHQUAKES. ['LeSSOH XXXV.

by some slight motion of the earth. The m most
boundaries of this earthquake to the south are un-
known j the barbarity of the African nations ren-
dering it impossible to procure any intelligence
from them, except where the effects were dreadful.
O1. the north, however, we are assured, that it
reached as far as Norway and Sweden. In the
former, the waters of several rivers and lakes were
violently agitated. In the latter, shocks were felt in
several provinces, and all the rivers and lakes were
strongly agitated especially in Dalecarlia. The
river Ddia suddenly overflowed its banks, and as
suddenly retired. At the same time a lake at the
distance of a league from it, and which had no
manner of communication with it, bubbled up
with great violence.- At rahkin, a town in Dale-
carlia, several strong shocks were felt.

In many places of Germany, the tflfe cts of the
earthquake were very perceptible; but in Holland,,
the asritations were still more remarkable. At

O

Alphen on the Rhine, between Leydeii and Woer-
den, in the afternoon of the first of November, the
waters were agitated to such a violent degree that
buoys were broken from their chains, large vessel*
snapped their cables, smaller ones were thrown out
of the water upon the land, and others lying on
land were set afloat. At Amsterdam,' about » 1 in
the forenoon, the air being perfectly calm, the.
•waters were suddenly agitated in tht ir canals, so that
several boats broke loose; chandeliers were observ-
ed to vibrate in the churches ; but no motion of
the earth, or concussion of any building, was ob-
served.

Lesson xxxv.] EARTHQUAKES. 253

served. At Haerlem, in the forenoon, tor nearly
four minutes together, not only the water in the
rivers, canals, &c. but also all kinds of fluids in
smaller quantities, as in coolers, tubs, backs, 8cc.
were surprisingly agitated, and dashed over the
sides, though no moton was percepnble in the
vessels themselves. In these small quantities also
the fluid apparently ascended prior to its turbulent
motion; and in many places, even the rivers and
canals rose tv\elve inches perpendicularly.

The agitation of the waters was also perceived
in various parts of Great Britain and Ireland. At
Barlborough in Derbyshire, be i ween 11 and 12 in
the forenoon, in a boat-house on the west side of
a large body of water called Pibley Dam, sup-
posed to cover at least thirty acres of land, was
heard a surprising and terrible noise; a large swell
of water came in a current from (he south, and
rose two feet on the sloped dain-head at the north
end of the water. It then subsided; but returned
again immediately, though with less violence. The
water was thus agitated for three quarters of an
hour; but the current grew every time weaker and
weaker, till at last it entirely ceased.

At Busbridge in Surrey, at half an hour after
10 in the morning, the weather being remarkably
still, without the least wind, in a canal near 70O
feet long and 58 reet broad, with a small spring
constantly running through it, a very unusual
noise was heard at the east end, and the water
there observed to be in great agitation. It raised
itselt in a heap or ridge in the middle 5 and this

heap

251 EARTHQUAKES. [LeSSOU XXXV.

heap extended lengthwise about 30 yards, rising
between two or three feet above the usual level.
After this, the ridge heeled or vibrated towards the
north side of the canal with great force, and flowed
above eight feet over the grass walk on that side.
On its return back into the canal, it again ridged in
the middle, and then heeled with yet greater force
to the souih side, and flowed over its grass walk.
During this latter motion, the bottom on the north
side was left dry for several feet. This appearance
lasted for about a quarter of an hour, after which
the water became smooth and quiet as before.
During the whole time, the sand at the bottom was
thrown up and mixed with water; and there was
a continual noise like that of water turning a mill.
At Cobham in Surrey, Dunslall in Suffolk, Earsy
Court in Berkshire, Eatonbridge in Kent, and m any
other places, the waters were variously agitated.

At Eyam-bridge, Derbyshire (in the Peak), the
overseer of the lead mines sittins; in his writing-
room about 1 1 o'clock, felt a sudden shock, which
very sensibly raised him up in his chair, and caused
several pieces of plaisier io drop from the sides of
the room. The roof was so violently shaken, that
he imagined the engine shaft had been falling in.
Upon this he immediately ran to see what was the
matter, but found every thing in perfect safety.
At this time two miners were employed in carting,
or drawing along the drifts of the mines, the ore
and other materials to be raised up at the shafts.
The drift in which they were working was about
120 yards deep, and the space from one end to the '

other

Lesson xxxv.] EARTH QUAKES. 255

other 50 yards or upwards. The miner at the end
of the drift had just loaded his cart, and was draw-
ing it along ; but he was suddenly surprised by a
shock, which so terrified him that he immediately
quitted his employment, and ran to the west end of
the drift to his partner, who was no less terrified
than himself. They durst not attempt to climb the
shaft, lest that should be running in upon them :
but while they were consulting what means they
should take for their safety, they were surprized by
a second shock more violent than the first $ which
frightened them so much, that they both ran pre-
cipitately to the other end of the drift. They then
went down to another miner who worked about 12
yards below them. He told them that the violence
*of the second shock had been so great, that it
caused the rocks to grind upon one another. His
account was interrupted by a third shock, which
after an interval of four or five minutes, was suc-
ceeded by a fourth ; and, about the same space of
time after, by a fifth ; none of which were so vio-
lent as the second. They heard, after every shock,
a loud rumbling in the bowels of the earth, which
continued about half a minu;e, gradually decreas-
ing, or seeming to remove to a greater distance.

At Shireburn Castle, Oxfordshire, a little after
ten in the morning, a very strange motion was
observed in the water of a moat which encom-
passes the house. There was a pretty thick fog,
not a breath of air, and the surface of the water
all over the moat as smooth as a looking-glass,
except at one corner, where it flowed iulo the shore,

and

956 EAKTUaUAKES'. [LeSSOH XXXV,

and retired again successively, in a surprising
manner. In what manner it began to move is un-
certain, as nobody observed the beginning of its
motion. The flux and reflux, when seen, were
quite regular. Every flood began gently; its ve-
locity increased by degrees, when at last it rushed
in with great impetuosity, till it had attained its full
height. Having remained for a little time station-
ary, it then retired, ebbing gently at first, but
afterwards sinking away with great swiftness. At
every flux, the whole body of water seemed to be
violently thrown against the bank ; but neither
during the time of the flux nor that of reflux
did there appear even the least wrinkle of a wave
on the other pans of the moat. Lord Parker, who
had observed this motion, being desirous to know
whether it was universal over the moat, sent a per-
son to the other corner of it, at the same time that
he himself stood about £5 yards from him, to ex-
amine whether the waier moved there or not. He
could perceive no motion there, or hardly any ;
but another, who went to the north-east corner of
the moat, diagonally opposite to his lordship,
found it as considerable there as where he was.
His lordship imagining, that in all probability the
water at the corner diagonally opposite to where he
was would sink as that by him rose, he ordered the
person to signify, by calling out, when the water by
him began to sink, and. when to rise. This he did ;
but, to his lordship's great surprize, immediately
after the water began to rise at his own end, he
beard his voice culling that it began to rise with him

also ;

Lesson XXXV.] EARTHaUAKES. 257

also ; and in the same manner he heard that it \va3
sinking'at his end : soon after he perceived it to
sink by himself. A pond just below was agitated
in a similar manner; but the risings and sinkings
of it happened at different times from those at the
pond where Lord Parker stood.

At White Rock, in Glamorganshire, about two
hours ebb of the tide, and near three quaneis after
six in the evening, a vast quantity of water rushed
up with a prodigious noise; floated two large ves-
sels, the least of them above 20O tons ; broke their
moorings, drove them across the river, and had
like to have overset them. The whole rise and fall
of this extraordinary body of water, did not last
above ten minutes ; nor was it felt in any other
part of the river, so that it seemed to have gushed
out of the earth at that place.

Similar instances occurred at Loch Lomond and
L K h Ness in Scotland. — At Kinsale in Ireland,
and all along the coast to the westward, many si-
milar phenomena were observed.

Shocks were also perceived in several parts of
France; as at Biyonne, Bourdeaux, and Lyons j
and commotions of the wa'ers were observed at
Anoou'eme, Bleville, Havre de Grace, 8cc. but
not attended with the remarkable circumstances
above mentioned.

These are the most striking phenomena with
which the earthquake of November 1, 1755. was
attended on the surface of the earth. Those which
happened 1x1 .w ground cannot be knoiui but !,y
the changes observed in springs, &cc. which were

258 EARTHQUAKES. [Lesson XXXV,

in many places very remarkable. — At Colares, on
the afternoon of the 3 1 st of October, the water of a
fountain was greatly decreased : on the morning
of the first of November, it ran very muddy; and,
after the earthquake, returned to its usual state
both as to quantity and clearness. On the hills,
numbers of rocks were split : and there were
several rents in the ground, but none considerable.
In some places where formerly there had been no
water, springs burst forth, which continued to run.
— Some of the largest mountains in Portugal were
impetuously shaken as it were from their founda-
tion; most of them opened at their summit, split
and rent in a wonderful manner, and huge masses
of them were thrown down into the subjacent
valleys. — From the rock called Pedra de Alvidar,
near the hill Fojo, a kind of parapet was broken
off, which was thrown up from its foundation in
the sea. — At Varge, on the river Macaas, at the
time of the earthquake, many springs of water
burst forth ; some spouted to the height of 18
or 20 feet, throwing up sand of various colours,
which remained on the ground. A mountainous
point, seven or eight leagues from St. Ube's, cleft
asunder, and threw off several vast masses of rock,
—In Barbary, a large hill was rent in two : the two
halves fell different ways, and buried two large
towns. In another place, a mountain burst open,
and a stream issued from it as red as blood. At
Tangier, all the fountains were dried up, so that
there was no water to be had till night. — A very
remarkable change was observed on the medicinal

waters

Lesson xxxv.] EARTHQUAKES. 259

waters of Toplitz, a village in Bohemia famous for
its baths. These waters were discovered in the
year 762 j from which time the principal spring of
them had constantly thrown out hot water in the
same quantity, and of the same quality. On the
morning of the earthquake, between 1 I and 12 in.
the forenoon, the principal spring cast forth such
* quantity of water, that in the space of half an
hour all the baths ran over. About half an hour
before this great increase of the water, the spring
flowed turbid and muddy j then having stopped
entirely for a minute, it broke forth again with
prodigious violence, driving before it a consider-
able quantity of reddish ochre. After this it be-
came clear, and flowed as pure as before. It still
continues to do so ; but the water is in greater
quantity, and hotter, than before the earthquake.
At Angouleine in France, a subterraneous noise
like thunder was heard ; andPpresently after the
earth opened, and discharged a torrent of water
mixed with red sand. Most of the springs in the
neighbourhood sunk in such a manner, that for
some time they were thought to be quite dry. In
Britain, no considerable alteration was observed in
the earth, except that, near the lead mine above-
mentioned in Derbyshire, a cleft was observed
about a foot deep, six inches wide, and 150 yards
in length.

At sea, the shocks of this earthquake were felt
most violently. Off St. Lucar, the captain of the
Nancy frigate felt his ship so violently shaken, that
he thought she had struck the ground : but on

heaving

f 60 EARTHQUAKES. \LeSSOU XXXV,

heaving the lead, found she was in a great depth of
water. Captain Clarke from Denina, in N. lat 36.
24. between nine and ten in the morning, had his
ship shaken and strained as if she had struck upon
a rock, so that the seams of the deck opened, and
thv compass was overturned in the binnacle. The
master of a vessel bound to the American islands,
being in N. lat. 23", W. long. 40 . and writing in
his cabin, heard a violent noise, as he imagined,
in the steerage; and while he was asking what the
matter was, the ship was put into a strange agita-
tion, and seemed as if she had been suddenly jerked
up and suspended by a rope fastened to the mast-
head. He immediately started up with great terror
and astonishment: and looking out of the cabin
window, saw land, as he took it to be, at the distance
of about a mile. But, coming upon the deck, the
land was no more to be seen, but he perceived a
violent current cross' the ship's way to the leeward.
In about a minute, this current returned with great
impetuosity, and at a league's distance he saw
three craggy-pointed rocks throwing up waters of
various colours resembling fire. This phenomenon,
in about two minutes ended in a black cloud, which
ascended very heavily. After it had risen above
the horizon, no rocks were to .be seen ; though
the cloud, still ascending, was long visible, the
weather being extremely clear. — Between nine and
ten in the morning, another ship, 40 leagues west
of St. Vincent, was so strongly agitated, that the
anchors, which were lashed, bounced up, and the
jnen were thrown a foot and a half perpendicularly

u

Lesson xxxv.] EARTHQUAKES. 261

up from the deck. Immediately after this, the
ship sunk in the water as low as the main chains.
The lead shewed a great d^pth of water, and the
line was tinned of a yellow colour, and smelt of
sulphur. The sh >ck las't-d about ten minutes, but
they felt^maller ones for the space of 24 hours.

Such were the phaenomena of this very remark-
able and destructive earthquake, which extended
over a tract of at least four millions of square miles.

There have been various hypotheses entertained
"with regard to the production of Earthquakes ; nor
does it appear an easy task to account for them
with great precision. Those which are only felt at
small distances are probably occasioned by the
action of subterraneous fires, and the explosion
of volcanoes. But there have been Earthquakes
which are felt at great distances, and have shaken
an extensive tract of country : this kind of Earth-
quakes is by some persons accounted for in the
following manner.

To understand properly what .may be the cause
of these ; hoeuomcua, it must be remembered, that
all inflammable matters capable of explosion pro-
duce, like gunpowder, by inflammation, a great
quantity of air j that this air produced by fire is in
a state of very great rarefaction j and that, by a
state of compression in which 'it is found in the
bowels of the earth, it must produce very violent
"fetTects. It is then conjectured, that at a consider-
able depth, as at about one or two hundred fa-
thoms, pyrites and other sulphureous matters are
to be met with ; and that by the fermentation pro-
duced

£6-2 EARTHQUAKES. [Lesson xx xv.

<luced by the filtration of water, and other causes,
they inflame : the inflaming will produce a great
quantity of vapourizcd air,the spring of which, com-
pressed in a small space, like that of a cavern, will
not only shake the earth immediately above, but
will search for passages, in order to make its escape.
It will therefore naturally force its way through
those parts where it meets least obstruction, and
will proceed through any channels or caverns
where it can find a passage. This subterraneous
.air or vapour will also produce in its passage a
noise and motion proportioned to its force and
the resistance it meets with : and these effects will
be continued till it finds a vent, perhaps in the sea,
or till its force be diminished by being greatly ex-
panded. This explanation corresponds entirely
with all the phenomena that are observed respect-
ing Earthquakes : for they proceed with a wave-
like motion, and are felt at different places, not at
the same instant, but at different times in propor-
tion to the distance.

Yet plausible as the above hypothesis may ap-
pear, it is objected against by several of the modern
philosophers, who, in opposition thereto, assert,
that Earthquakes are produced by an accumulation
of the electric fluid in the bowels of the earth.

Mr. Nicholson, in his Introduction to Natural
Philosophy, says, t( It is extremely probable, that
" Earthquakes owe their original to the discharge
" between a cloud and the earth, in a hie;hly elec-
" trie state, or even between two clouds." In
.support of this opinion, he advances the following

arguments :

Lesson xxxv.] EARTHQUAKES. 2(53

arguments: — "They happen most frequently in dry
tf and hot countries, which are most subject to
" lightning and other electrical phaenomena ; and
" are even foretold by the electric coruscations and
et other appearances in the air, for some days pre-
fc ceding the event. Earthquakes are attended by
(f no fire, vapour, or smell, which, however could
tc hardly fail to appear, if the common opinion, of
t( their being occasioned by a subterraneous ex-
" plosion, were true. The effect of an explosion
<c of this nature would be a gradual lifting of the
" earth, after which it would fall -again, and, no
" doubt, destroy or change the course of springs,
11 and considerably alter the face of the country :
*' the contrary to which is true; for, as far as ob-
" servation can determine, the shock of an Earth-
" quake is instantaneous to the greatest distances,
" and seldom does more mischief than overthrow-
" ing buildings. Earthquakes are usually accom-
" panied by rain, and sometimes by the most dread-
" ful thunder-storms. All these, and many more
" circumstances, but especially the almost instan-
" taneous motion of the shock, induce us to look
" for their cause in electricity, the only power in
tf nature that acknowledges no sensible transition
" of time in its operations." — Against this reason-
ing, it has been objected,that if the accounts which
historians have transmitted us of Earthquakes in the
last century, be correct, the circumstances attend-
ing these awful events are frequently widely dif-
ferent from what Mr. Nicholson supposes them to
be. At present, each of these disagreeing hypo-
theses

264 EAKTHQUAKF.S. [Lesson xxxv.

theses has many advocates, though that which Mi
Nich<.lson supports stem* to be gaining ground :-
however, whether Earthquakes be produced by the
explosion of sulphureous matters, or by the power
of ihe electric fluid, we may safely infer, that the
natural cause of their production is inherent in the
earth. Hence the contemplative young reader will
conclude, that we migf-t be continually in expec-
tation of the whole earth being destroyed by this
invisible agent of nature ; if we were not certain
that it is always controlled by a wise and good, as
\ve!l as powerful, BILING, who keeps it safely
curbed, or gives it liberty to range, as it may by
HIM be thought most suitable to his Divine pur-
poses.

LESSON

LESSON XXXVI.

ON rOLCANOS.

The dread Volcano ministers to good :

Its smother'*! flames might undermine the world.

Loud ;Etnas fulminate in love to man.

YOUNC.

A WONDERFUL appearance on the face of
nature, which we have not yet reflected upon, is a
burning mountain, or Volcano; to describe which,
in the manner it deserves, would almost surpass the
power of words. A Volcano contains in its bowels
sulphur, bitumen, pumice stones, and other mate-
rials which serve as food to a subterraneous fire,
the effects of which are more violent than those of
gunpowder, or even of thunder : hence a Volcano
has been sometimes compared to a cannon of a very
large size. The orifice or mouth of a Volcano is,
in some cases, more than a mile across : and from
this mouth are emitted torrents of smoke and
flame; rivers of bitumen, sulphur, and melted
metal, the mixture bearing the name of lava;
clouds of cinders and stones, and sometimes it
ejects enormous rocks to many leagues distance,
when merely to stir them would baffle the utmost
efforts of human strength. The combustion is
N se

266 VOLCANOS. [Lesson xxxvf.

so terrible, and the quantity of burnt, fused,
calcined, and vitrified materials which is thrown
out at the orifice, is so plentiful, that they enter
towns and forests, cover the fields to more than an
hundred feet in thickness, and sometimes form
hills and mountains. The action of this fire is
so great, and the force of explosion so violent, that
its reaction has been known to shake the earth,
agitate the sea, overthrow mountains, and raise
the most solid edifices and towns, even to very
considerable distances.

A mixture of sulphur, filings of iron, and of
water, buried at a certain depth below the earth's
surface, will exhibit in miniature, all the appear-
ances of a Volcan'o : hence some are induced to
conclude, that in the bowels of burning moun-
tains, there are different kinds of inflammable
substances, which ferment when acted upon by
peculiar means (probably by moisture), and pro-
duce eruptions and explosions, of different de-
grees of strength, according to the quantity of in-
flammable matters accumulated.

The number of Volcanos now known is very
considerable; not less, I believe, than 400. In
Europe there are Jitna, Vesuvius, Hecla, Strmn-
boli, Volcano ; in Asia, one in Mount Taurus,
three in Kamschatka, -five in Japan, two in the
Philippines, and a great number more in the
different South Sea Islands; in Africa, one in
Fez, one in the island Bourbon, one in Fut-go,
one of the Cape Verd Islands: and in America,
several in the Andes, Morne Garou, in St. Vin-
cent,

Lesson xxxvi.J VOLCANOS. 667

cent, and two discovered by Captain Cook on the
western coast of North America.

Nearly all the Volcanos yet known are situated
at a small distance from the sea: and most of
them have been burning from time immemorial ;
though some few have burst out during late years.
Volcanos seem all to occupy the tops of'moun-
tains-c some of them which are situated in the
ocean, do not rise much above the surface ; but
even these seem to he the apices of mountains,
the greater part of which are covered by the sea.

Of each of the Volcanos in Europe, I shall
here present you wiih a short account. From
Mount JEtna the eruptions of flame and smoke
are discovered at a great distance, by those who
sail on the Mediterranean, even as far as the har-
bour of Malta, which is more than 40 leagues
from the shore of Sicily. Though fire and smoke
are continually vomited up by it, yet at some par-
ticular times it rages with greater violence. In
the year 1536, it shook all Sicily from the first to
the twelfth of May; after that there was heard a
most-horrible bellowing and cracking, as if great
guns had been fired : there were a great many
houses overthrown throughout the whole island.
When this storm had continued about eleven days,
the earth opened in several places, and dreadful
gapings appeared here and there, from which
issued fire and flame with great violence, which
in four days consumed and burnt up every
thing that was within five leages of JEtna. A
little after, the funnel, which is on the top of the
N £ mountain,

268 VOLCANOS. [Lesson XXXVT.

mountain, disgorged a great quantity of hot em-
bers and ashes, for three whole days together,
which were not only dispersed throughout the
•whole island, but also carried beyond sea to Italy ;
and several ships that were sailing to Venice, at
two hundred leagues distance, suffered damage.
Facellus, who has given an historical account of
the eruptions of this mountain, says, that the bot-
tom of it is one hundred leagues in circuit.

Mount Hecla rages sometimes with as great
violence as w*Etna, and casts out large stones. The
imprisoned fire often, for want of vent, produces
horrible sounds like lamentations and bowlings;
which make the credulous and superstitious think
it the place of hell, where the souls of the wicked
are tormented. The country in the vicinity of
Hecla abounds with boiling springs ; of which
many travellers present interesting accounts.

The declivity of Mount Vesuvius towards the
sea, is every where planted with vines and fruit
trees, and it is e iiially fertile towards the bottom.
The circumjacent plain affords a delightful pro-
spect, and the air is clear and wholesome. The
south and west sides of the mountain form very
different views; being, like the top, covered with
black cinders aud stones. Thehe'ght of this moun-
tain has been computed to be about 3QOO feet
above the surface of the sea. Vesuvius has been
a volcano beyond the reach of history and tradi-
tion : but there are on record more than 30 erup-
tions which have taken place since the one that
destro; ed the city of Herculaneum, in the tin.e of

Titus.

Lesson xxxvi.] VOLCANOS. 269

..-._. i. - - , • ' • •

Titus. Some of these have been very furious and
violent, desolating the country for miles around ;
and ships at sea, at the distance of sixty miles,
have, in some of these eruptions, been covered
with cinders, to the astonishment of the sailors.

A great eruption of Vesuvius happened on the
12th of August, 1805: the following account of
it is given in an extract of a letter from Naples,
dated August 13th : —

" Yesterday, at ten o'clock at night, the erup-
tion of Vesuvius, of which the earthquake seemed
to be the forerunner, took place. We were going
to visit the crater when the cries of the people
and a volume of flame informed us that the vol-
cano had opened. The lava precipitated itself in
three seconds from the last peak of the mountain,
and took a direction towards the valley, situated
between Torre del Greco and Torre del 1'Annun-
ziata, two towns on the sea coast, beyond Portici,
and seven or eight miles from Naples.

" We set off immediately to see this wonderful
and tremendous phenomenon nearer. From the
place of our departure, we saw the whole course
of the lava, which extended nearly two miles,
from the crater to the houses that join the two
towns. The sight was the most magnificently
frightful that could be seen. I contemplated the
cascades of flame pouring from the top of the
mountain, and shuddered at seeing an immense
torrent -of fire ravage the finest fields, overthrow
houses, and destroy in a few minutes the hopes
and resources of a hundred families.

H 3 "A line

VOLCANOS. [Lesson xxxv*.

" A line of fire marked the profile of the moun-
tain : a cloud of smoke, which seemed to «em
forth from time to time flashes of lightning, hun<
over the scene, and the moon appeared to be pale.
Nothing can adequately describe the grandeur of
the scene, or give an accurate idea of the horror
of it. As we approached the spot ravaged by this
.river of hell, ruined inhabitants having quitted
their houses — desolated families trying to save
their furniture and provisions, last and feeble re-
source — an immense crowd of curious spectators,
retreating step by step from the advancing lava,
and testifying by extraordinary cries their wonder,
fear, and pity — the frightful bellowing of the
mountain, the frequent explosions which burst
from the bottom of the torrent, the crackling of
the trees devoured by the flames, the noise of the
walls falling, and the lugubrious sound of a bell
.which the religious of the Camaldules, isolated
on a little hill and surrounded by two torrents of
fire, rang in their distress ! — Such are the details
of the frightful scene to which I was witness.

" The moment we arrived, the lava was crossing
the great road below Torre del Greco. To see it
better, we got into a beautiful house on the road
side : — from the terrace we saw the fire at no more
than fifteen paces from us : — in a minute we de-
scended, and twenty minutes afterwards there re-
mained of the house but three large walls. I ap-
proached as near as the heat and flow of the cur-
rent would permit me : I attempted at different
times to burn the end of my handkerchief in it —

I could

Lesson xxxvi.] VOLCANOS. 271

I could only do it by lying it to my cane. The
lava does not run in liquid waves : it resembles an
immense quantity of coals on fire, which an in-
vincible strength had heaped up and pushed on.
with violence. When it met with a wall, it col-
lected to the height of seven or ten feet, burnt it,
and overthrew it at once. I saw some walls get
rod hot, like iron, and melt, if I may use the ex-
pression, into the lava. In its greatest speed and
on an horizontal road, I reckoned that the torrent
travelled at the rate of eighteen inches a minute.
Its smell resembled that of iron red hot."

A still more recent eruption will make the year
J810 an epoch in the annals of Vesuvius, on ac-
count of the manner in which it began, and the
disasters it has produced. It is considered as a
very extraordinary circumstance, that this eruption
was not preceded by the usual indications ; every
convulsion of Vesuvius being previously announ-
ced by the drying up of the wells of Naples. This
phenomenon did not take place on this occasion,
and, to the great surprise of the inhabitants, V esu-
vius began to emit flames on the night of the 10th
of September.

On the morning of the llth, the flames became
more intense, and the lava began to flow from the
east and south-east sides of the mountain. To-
wards evening the conflagration increased, and
about twilight two grand streams of fire were seen
to flow down the ridge of the Volcano ; night pro-
duced no change in this state of things.

On the morning of the 1 2th, a hollow sound was
v 4 heard,

f 72 VOLCAKOS. [Lesson xxxrr.

heard, which continued increasing; the fire and
smoke also augmented in intensity, and towards
evening the horizon was obscured. Thebree,e,
usual in these parts, having blown from the south-
east, dissipated the accumulated clouds. The
mountain continued to vomit lava and a dense
smoke, which even at a distance was strongly sul-
phureous : the hollow noise in the sides of the
mountain continued to increase.

" Curious to witness as near as possible one of
the most astonishing phenomena of Nature, and
forgetting the misfortune of Pliny, I set out" (says
an English traveller) " from Naples, and at eight
in the evening I reached Portici. From thence to
the summit of the mountain, the road is long and
difficult. About half way there is a hermitage,
which has long served for refuge and shelter to the
traveller: — a good hermit has there fixed his resi-
dence, and takes care to furnish, for a moderate
sum, refreshments, which to the fatigued traveller
are worth their weight in gold. The environs of
this hermitage produce the famous wine called
Lachryma Christi.— - From the hermitage to the
foot of the cave there is a long quarter of a league
of road, tolerably good; but in order to reach from
thence the crater, it is necessary to climb a moun-
tain of cinders, where at every step you sink up to
the mid-leg. It took my companions, myself, and
our guides, two hours to make this ascent j and it
was already midnight when we reached the crater.

"The fire of the Volcano served us for a torch
the noise had totally ceased for two hours: the

flame

Lesson xxxvi.] VOLCASOS. 27 3

flame had also considerably decreased. These cir-
cumstances augmented our security, and supplied
us with the necessary confidence in traversing such
dangerous ground. We approached as near as ther
heat would permit, and we set fire to the sticks of
our guides in the lava, which slowly ran through
the hollows from the crater. The surface of this
inflamed matter nearly resembles metal in a state
of fusion j but as it flows, it carries a kind of scum,
which hardens as it cools, and then forms masses
of scoria, which dash against each other, and roll
all on fire, with noise, to the foot of the mountain.
Strong fumes of sulphuric acid gas arise in abun-
dance from these scoria, and by their caustic and
penetrating qualities render respiration difficult.

" We seemed to be pretty secure in this situa-
tion, and were far from thinking of retiring, when
a frightful explosion, which launched into the air
fragments of burning rocks to the distance of
more than IOO toises, reminded us of the danger
to which we were exposed. None of us hesitated
a moment in embracing a retreat ; and in five mi-
nutes we cleared, in our descent, a space of grouud
which we had taken two hours to clim by

" We had not reached the hermitage before a
noise more frightful than ever was heard; and the
Volcano, in all its fury, began to launch a mass
equal to some thousand can-loads of stones and
fragments of burning rocks, with a projectile forcQ
which it would be difficult to calculate. As the
projection was vertical, almost the whole of this
H 5 burning

271 VOLCANOS. [Lesson xxxvi.

burning mass fell back again into the mouth of
the Volcano, which vonrted it forth anew to re-
ceive it again, with the exception of some frag-
ments which flew off, to fall at a distance, and
alarm the inquisitive spectator.

" The 13th commenced with nearly the same
appearances as those of the preceding day. The
Volcano was tranquil, and the lava ran slowly in
the channels which it had formed during the night ;
but at four in the afternoon a frightful and conti-
nued noise, accompanied with frequent explosions,
announced a new eruption : the shocks of the
Volcano were so violent that at Fort de L'CEuf,
built upon a rock, where I then was, at the dis-
tance of nearly four leagues, I felt oscillations
similar to those produced by an earthquake.

*' About five o'clock the eruption commenced,
and continued during the greater part of the niuht.
This time the burning ir.atter flowed down all the
sides of the mountain, \vitH a force hitherto unpre-
cedented ; all Vesuvius seemed on fire. — The lava
has caused the greatest losses : houses and whole
estates have been overwhelmed ; and at this day
families in tears, and reduced to despair, search in
vain for the inheritance of theif ancestors, buried
under the destroying lava.

" At ten at night, the hermitage was no longer
accessible : a river of fire had obstructed the road.
The districts situated on the south-east quarter of
the mountain had still more to suffer. Mount
Vesuvius presented the appearance of one vast

flame,

Lesson \xxvi.] VOLCANOS. 275

flame, and the seaman at a great distance might
contemplate at his leisure this terrific illumination
of nature."

Among the great number of curious facts which
M. Humboldt has collected in his travels, one of
the most extraordinary is the following, which he
communicated to the French National Institute.
Many of the Volcanos of the Cordilliers of ihe
Andes throw up at intervals eruptions of mud
mixed with vast quantities of fresh water, and.,
what is extremely remarkable, an infinite multi-
tude of fahes. The Volcano of Imbaburu, for
example, once threw up such a vast number of
them near the village of Iborra, that their putrer
faction caused a sickness. This phenomenon, as-
tonishing as it is, is not, however, unfrequent : on
the contrary, it very often takes place; and pub-
lic authority has preserved accounts of the periods
at which this has happened, in an authentic man-
ner, along with those of the earthquakes. What
is very singular is, that the fish are not broken in
the least, although their bodies are very soft ;
they d > not even appear to have been exposed to
a great heat. The Indians, indeed, assert that
they sometimes arrive alive at the foot of the
mountain.

Sometimes these animals are ejected from the
mouth of the crater, sometimes they are vomited
forth at the lateral cavities; but always at from
24 to 26OO yards above the neighbouring plains.
M. HumL'olilt thinks that they live in the lakes
situated at this height in the inside of the crater :

and

S76 VOLCANOS. [Lesson xxxvr.

and what confirms this opinion is, that the same
species is found in the rivulets which run at the
foot of these mountains. It is the only species
of fish which lives at the height of 2800 yards in
the realm of Quito. This species is new to our
naturalists. M. Humloldt has delineated it on
the spot, and given it the name of Pimelodrus
Cyclopum, which signifies thrown up ly the
Cyclops — a name in some respects analogous to
their origin.

Dr. Woodward mentions the existence of Vol-
canos as a special favour of Providence, and says—
" There are scarcely any countries that are much
" annoyed with earthquakes that have not one of
" these fiery vents. And these are constantly all
*' in flames whenever any earthquake happens ;
tf they disgorging that fire which, whilst under-
" neath, was the cause of the disaster. Indeed,"
says he, " were it not for these diverticula
(t whereby it thus gaineth an exit, it would rage
" in the bowels of the earth much more furiously,
" and make greater havoc than it doth now. So>
t( that though those countries, where there are
" such xolcanos, are usually more or less trou-
** bled with earthquakes; yet, were these Volca-
" nos wanting, they would be much more annoyed
" with them than they now are j yea, in all proba-
" bility to that degree, as to render the earth, for
" a vast space around them, perfectly uninhabit-
" able, In one word, so beneficial are these to»
" the territories where they are, that there do not
(f want instances of some which have been res-

" cued

Lesson XXXYI.] VOI.CANOS. 277

" cued from earthquakes by the breaking forth of
" a new Volcano there j this continually discharg-
" ing that matter, which being till then barricaded
" up, and imprisoned in the bowels of the earth,
<{ was the occasion of very great and frequent ca-
" lamities."

Let me then be permitted to observe in this
place, that though we cannot, in every case, see
the beneficent tendency of particular creatures and
things in the universe, we ought to attribute this
to our limited capacities ; and not arraign AL-
MIGHTY SOVEREIGNTY, as is the custom with too
many carping sciolists of the present day. How-
ever dreadful and destructive subterraneous fires
may appear : on proper reflection it may be in-
ferred, that they are as necessary in promoting and
sustaining the operations of this part of the uni-
verse, as the natural heat in men's bodies is to the
preservation and support of their being.

As every body possesses inherently the princi-
ples of its own dissolution, it is by many wise and
learned men imagined that the general conflagra-
tion may at last be brought about by means of
these fires. Amongst the natural means of causing
it we are acquainted with, some persons embrace
the opinion here mentioned, whilst others are in-
clined to think the effect will be produced by co-
mets : but though finite creatures may conjecturfc
on this subject, it is most probable that it will ne-
ver be ascertained by mortals-. Such knowledge is

J D

not necessary for us ; and may be withheld for the
wisest and most beneficent reasons.

LESSON

LESSON XXXVII.

ON THE EYE.

In the materials of the human frame,

What num'rous wonders might we quickly name :

Let it suffice that I describe a few,

And treat my readers with a short review.

VvE will now direct our contemplations to the
human jabric : and here the science of Anatomy
discovers to us ten thousand beauties which the
narrow limits I have prescribed mystlf preclude
my mentioning : indeed it would not be possible,
in a performance of this kind, to explain adequate-
ly the geometrical and mechanical accuracy with
which the AUTHOR OF NATURK has constructed
every part of the body, to carry on the animal
economy, and answer the various purposes of life.
All I propose to perform in this and the two fol-
lowing Lessons is, by touching upon the nature
and wonders of the Eye, of Concoction, and of
the Circulation of the Blood, to give my young
readers some little insight into these matters, as an,
inducement for them to set apart a portion of their
leisure time for the purpose of acquiring a farther
acquaintance with Anatomy.

And

Lesson xxxvu/J THE EYE. 279

And first, for a short description of the organ of
Sight, that noble instrument which

O '

Takes in at once the landscape of the world,

At a small inlet which a grain might close,
And half creates the woudrous world we see.

YOUNG.

The Eye is in form nearly globular: it consists
of three coats and -hree humours. The part of the
outward coat hid from our sight is called the Sole"
rotica : the front part, which rather projects out,
the Cornea : the next within this coat is that called
the Choroides, which serves, as it were, for a
lining to the- other; in the front it joins with that
part known by the name of the Iris, because it is
in different persons of different colours, as blue,
brown, green, &c. The iris is composed of two
sets of muscular fibres ; the one, of a circular form,
which contracts the hole in the middle called the
Pupi1, when the light would otherwise be too strong
for the E\e; and the other, of radial fibres, tend-
ing every where from the circumference of the iris
towards the middle of the pupil: these, by their
contraction, dilate and enlarge the pupil, when the
Irght is wi-ak, in order to admit more rays. The
third coat is only a fine expansion of the optic
nerve, which spreads like net work all over the in-
side of the~choroides, and is therefore called the
Retina : upon it are in a manner painted the images
of all visible objects, by the rays of light which
cither flow or are reflected from them.

Immediately under the cornea is a fine transpa-
rent

S80 THE EYE. [Lesson xxxvn.

rent fluid, like water, which is therefore called the
aqueous humour : it gives a protuberant figure to
the cernea, and has the same limpidity and refrac-
tive power as water. At the back of this lies a
humour transparent like crystal, and much of the
consistenca of hard jelly : it is shaped like a
double convex glass, and is a little more convex
on the back than on the fore part : it is named the
crystalline humour) and is of service in converging
the rays which pass through it, to its focus at the
bottom of the Eye. This humour is enclosed in a
fine transparent membrane from which proceed ra-
dial fibres, called the ligamentum ciliare^ all around
its edge, joining to the circumference of the im.
These fibres have a power of dilating and contract-
ing occasionally, by which means the convexity
of the crystalline humour is altered ; and it is also
thereby shifted a little backward or forward in the
Eye, so as to adapt its focal distance at the bottom
of the Eye to the different distances of objects : .a
provision without which we could only see objects
distinctly at one particular distance from the Eye..
At the back of the crystalline, lies the vitreous
humoitr, which is transparent like glass, as its name
denotes, and is largest of all in quantity ; filling
the rest of the Eye, and giving it a globular shape :
h is much of the consistence of the white of an
egg, its refractive power very little exceeding that
of water.

As rays are emitted or reflected from every point
of an object; some of these from the side next ihe
Eye will fait upon ihe cornea, and, by passing on

through

Lesson xxxvn.] THE EYE. f Si

through thep*pzV and different humours, will be
converged to various points on the retina at the
bottom or' the Eye, and will form upon it an in-
VTted picture of the object J or, if this inverted
image be not formed, the object cannot be seen :
when, unfortunately, any of the parts of the Eye
are so injured as to lose their transparency, the
person becomes blind.

But it is not sufficient, in order to our seeing
objects, that their images should be painted on the
retina : some persons, it is said, are blind, though
this takes place. Hence it should seem, that
images painted on the retina are not the immediate
object of vision, and that the perception of the
soul is communicated some other way. The small
nerves of the retina (it is now generally admitted)
are agitated by the rays of light which form the
image at the bottom of the Eye j and this agita-.
tion is transmitted by the optic nerve to the brain.
It is there the mental perception is formed ; but the
nu»t dextrous anatomist is unable to pursue these
nerves 10 their source: the union of the soul with
the body will probably for ever remain a mystery.

There is an astonishing apparatus of muscles,
with which the Eye is furnished, to produce all the
necessary and convenient motions : among these I
cannot help alluding to that admirable contrivance
by which the pupil is contracted or dilated, ac-
cor.-iing as vision requires. This variability of the
pupil is essentially necessary to vision : for, if an
involuntary contraction were not to take place
when the Eye was brought into a very enlight-
ened

362 THF. EYE. [LfSSOJl XXXVlf.

ened situation, the great number of rays which
would enter, would probably much injure the fine
contexture of nerves at the bottom of the Eye, or*
which the image* of objects are pourtrayed; and
if the pupil did not expand when ihe eye was in a
dark place, the few feeble rays which would enter
the Eye, would not form any impression on the
retina. Hence it is a very remarkable and pro-
vidential circumstance, that the change in ihe pu-
pil should take place almost spontaneously and
independent of any act of the will.

The five following associated circumstances

w

seem to have some influence on our judgment con-
cerning distance : the number of objects which
intervene, the degree of distinctness in which the
minute parts are seen, the degree of brightness,
the inclination of the optic axes, and the confor-
mation of the Eye. Thus, distance is chiefly con-
ceived from experience j and the more distant an,
object is, the less it appears : when therefore, from
certain circumstances, we cannot form a just con-
ception of distance, and when we cannot judge of
objects but by the image which is pourtrayed in
our Eyes, we are then necessarily deceived as to
their size. Thus every person must be aware how
liable we are, in travelling by night, to mistake a
distant tree for a bush that is near, or a bush near
at hand for a tree at a distance. In the same
manner if we do not distinguish objects by their
shape, and by it also judge of distance, the fallacy
is likely to continue: in this case, a fly, which may
pass before us slowly, will seem to be a bird

at

Lesson xxxvn.] THE EYE. 283

at a considerable distance j and a horse, which
may be in the middle of a plain, not moving,
and in an attitude similar, for instance, to that of
a sheep, may in the dusk appear in every sense like
a sheep.

If, therefore, we are benighted in a strange place,
where no judgment of distance can be formed, we
are every moment liable to deceptions of vision.
Hence originate niost of the dreadful stories of
spectres, and of those wonderful, hideous and
gigantic figures, which many persons speak of hav-
ing seen. Though it is commonly asserted, that
such figures exist solely in the imagination ; yet it
is highly probable, that they might appear to the
Eye in every respect as described. This remark
will be allowed to have the greater force, when it
is considered, that if the size of an object be in
grekt measure estimated by the angle which it
forms in the Eye, it is magnified according to its
propinquity : of course, if it seemed at first to the
spectator (who is equally incapable of distinguish-
ing what he sees, and of judging at what distance
it is,) a few feet high, when at the distance of thirty
or forty yards from him : it must look to him, when,
he is within a. few feet of it, of a size stupendously
increased. At this he will naturally be terrified,
unless he touch and 'hus distinguish the seemingly
enormous object j for in* the instant he has an
actual perception of what it is, the enormity will
diminish, and the object will appear in its real
state: if, on the other hand, he be afraid to ap-
proach it, and flee from the spot with precipita-

lion,

f 84 THE ETE. [LeSSOH XXXVlf.

tion, the only idea remaining of what was present-
ed to his view, will be that of an image, gigantic
in its size, and horrible in its form. The preju-
dice about spectres and hobgoblins, therefore, in
some degree originates from nature, and such vi-
sionary objects depend not entirely on the imagi-
nation alone, as has been frequent!) supposed.

If room would permit, it would be a pleasing
employment to point out many advantages which
arise from the form, the size, ihe motion, and the
situation of the Eye, each of which haa a tendency
to evince the wisdom and goodness of the Omnipo-
tent Creator. But this has been well done by Dr.
Derham and Dr. Paley; to whose works I must
refer you. The celebrated Euler, in his " Letters
to a German Princtss," points out an astonishing
difference between tht human Eye, and any arti-
ficial eye which can be constructed : he then makes
some admirable reflections, part of which I now
lay before you. " The Eye which the Creator has
*l formed, is subject to no one of all the imperfec-
" tions under which the imaginary construction of
61 the free thinker labours. In this we discover the
.*' true reason, why Infinite Wissdom has employed
" several transparent substances in the formation
" of the Eye : it is thereby secured against all the
f( defects which characterize every work of man.
«* What a noble subject of contemplation ' He who
" formed the Eye, shall he not see ? and he who
"planted the ear, shall he not hear? The Eye
" alone being a master-piece that far transcends
•ts the human understanding, what an exalted idea

" must

Lesson xxxvii.] THE EYE. 285

" must we form of Him, who has bestowed this
" wonderful gift, and in the highest perfection, not
" on man only, but on the brute creation, nay,
" on the vilest of insects !"

Indeed, if we do but reflect upon the many diver-
sified and beautiful scenes which are made visible
to us by means of the organ of Sight, and consider
the deplorable state, and the many inconveniences
those persons lie under, who are deprived of this
blessing, our hearts ought to overflow with thank-
fulness to that kind BEING who has bestowed so
useful an instrument as the Eye upon us, to add to
our convenience and delight j and whose superin-
tendency protects it from those injuries to which
ii is continually exposed.

LESSON

LESSON XXXVIII.

ON CONCOCTION.
-The concoctivc powers, with various ait,

Subdue the cruder aliments to chyle ;

The chyle to blood ; the foamy purple tide

To liquors, which thro' finer arteries

To different parts their winding course pursue.

AKMSTKONG.

AMONG all the wise contrivances observed in
the human fabric, none can excite our attention
and admiration more than the disposition and me-
chanism of those parts, by which our aliment is
concocted, or fitted for our daily support and nou-
rishment.

To have a clear idea of the manner in which
Concoction is performed, we must distinguish it
into three stages : the first of which is performed
in the progress of the aliment from the mouth
down to the lacteals; which are vessels that receive
the chyle from the intestines ; the second is per-
formed in the passage of the milky liquor called
chyle, through the lacteal vessels to the loins, and
then up under the collar bone, where it mingles
with the blood : the third, or ultimate stage of
Concoction, is performed by the. circulation of
the blood and chyle together through the lungs,
and the whole arterial system. In all these stages

the

Lesson xxxvin.j CONCOCTION; 287

the design of the SUPREME CONTRIVER has
evidently been to grind and dissolve the aliment,
and to incorporate it with a large quantity of
animal juices already prepared, in such a manner
as to reduce it at last to the very same substance
with our blood and humours. • How wonderfully
and completely this design has been executed, my
young readers will presently be able to judge.

In the first stage of Concoction, by a curious
configuration of parts, and action of muscles,
adapted to their respective functions, our food is
ground small by the teeth, and moistened by a
copious saliva in the mouth. It is in the next
place swallowed, and conveyed down the gullet,
where it is farther mollified and lubricated by a
viscid unctuous humour, distilled from the glands
of that canal. From thence it slips into the
stomach, where several causes concur towards its
complete dissolution. It is diluted by the juices,
swelled and subtilized by the internal air, and it is
macerated and dissolved by iheheat which it meets
with in the cavity, ft is also agitated and attenu-
ated by the perpetual friction of the coats of the
stomach, and the pulsation of the arteries there;
by the alternate -elevation and depression of the
diaphragm or midriff in breathing; and hy the
compression of the strong muscles of the belly.
After a proper stay, it is gradually propelled into
the intestines, in- the form pf a thick, smooth,
uniform, ash-coloured fluid.

When our aliment, thus prepared, arrives at the
intestines,, it is there mixed with three different

sorts

•288 CONCOCTION. [Lesson xxxvn

T- ' ' ' — =f=

sorts of liquors. It receives two kinds of bile
the one, thick, yellow, and extremely bitter, from
the gall-bladder; the other, scarcely bitter, or yel-
low, but in a much larger quantity, from the liver.
The third liquor that falls here upon the food,
issues plentifully from a large glandular substance,
called the Pancreas or sweet-bread, and is a limpid
mild fluid, like the saliva, which serves to dilute
and sweeten what may be too thick and acrimo-
nious. The two saponaceous biles resolve and
attenuate viscid substances; incorporate oily fluids
with aqueous ones, making the whole mixture
homogeneous ; and by their penetrating and deter-
gent qualities render the chyle fit to enter the
lacteal veins, into which it is conveyed, partly by
their absorbent nature, and partly by the peristaltic
motion of the intestines.

If we now consider the change which our ali-
ment has undergone, in the mouth, gullet, and
stomach, together with the large quantity of bile,
and pancreatic juice poured upon it in the intes-
tines : and if we reflect also on the incessant ac-
tion of the muscles, blending, churning, and
incorporating the whole, we shall readily perceive
that their united agency must alter the flavours
and properties of the different kinds of food, in
such a manner as to bring the chyle nearer in its
nature to our animal juices, than to the original
substances from which it was formed. Our food,
thus changed into chyle, constitutes the first stage
of Concoction; and we shsll find the same assi-
milation carried on through the second.

Th«

Wesson xxxvin.] CONCOCTIOX. 23f

The next stage begins with the slender lacteat
veins, where they arise from the intestines by an
innumerable multitude of invisible pores, through
which the fine, while, fluid part of the chyle is
strained or absorbed; while, at the same time, the
gross, yellow,, fibrous part, conveyed slowly for-
ward, and further attenuated in the long intestinal
tube, 15 perpetually pressed and drained of its re-
maining chyle, until the dregs, becoming at last
useless, are ejected out of the body.

These lacteal veins issue from the intestines in
various directions, now. straight and then oblique,
often uniting and growing larger, but presently
separating again. They frequently meet at acute
•angles, and enter into soft glands dispersed through
the mesentery, from which they proceed larger
than before, and more turgid, with a fine lymph-
atic fluid : in most places also they run contiguous
•to the mesenteric arteries, by whose pulsation
their load is pushed forward. And thus, after
various communications, separations, and protru-
sions, the lacteal veins pour their chyle into a sort
of cistern or reservoir formed for that purpose,
between the lowest portion of the diaphaygm and
highest vertebre of the loins. It is very remark-
able, that these veins are furnished with proper
valves, which permit the chyle to move forward,
but effectually stop its return j and that a great
number of veins purely lymphatic, as well as the
lacteal ones, empty themselves into the same
cistern.

In all this contrivance it is evident^ that the
<» chyle

CONCOCTION. [Lesson xxxvm.(

cnyle, being more and more diluted and blended
\viih abundance of lymph from the glands through
which it passes, and from other sources, approaches
still nearer to the nature of our animal juices, and
consequently becomes more fit for nutrition.

The chyle is pushed from its reservoir into a
narrow transparent pipe, called the thoracic duct,
which climbs in a perpendicular direction by the
side of the back-bone, from the loins up to the
collar-bone, and opens into the subclavian vein :
where, by the peculiar arrangement of several
small valves, the chyle mingles gently with the
blood after it has been thoroughly elaborated ; and
attenuated with lymph from every part of the
thorax, or great cavity of the breast, and is from
thence soon conveyed to the heart.

Thus we may perceive, that by a wonderful me-
chanism, a large quantity of chyle and lymph is
forced upwards, in a perpendicular course, through
a thin slender pipe ; but lo render this more plain,
the following pariiculars must be attended to: —
First, to the progress of the chyle, urged forward
and continued from the ante edent action of the
intestines, and the beating of the mesenteric arte-
ries. Secondly, to the motion of the diaphragm
and lungs, in respiration, pressing the thoracic
duct that lies under them, whilst the thorax, rising
and falling:, resists their action, whereby the duct
is squeezed between two contrary forces, and the
liquor which it contains pushed upwards. Thirdly,
this duct runs close by the side of the great artery
(called by anatomists, the superior portion of the

descending

Lesson xxxvm.] CONCOCTION. 291

descending aorta) whose strong pulsation presses
its yielding sides, and compels the chyle and lymph
to mount in an upright ascent. Fourthly, it must
be observed, that this duct is accommodated with
valves, which permit its contents to move upwards
by every compression, hut never to fall back again.
Thus terminates the second stage of Concoc-
tion, when the chyle falls into the heart. And it
may be seen that in the progress through these
two stages, our aliment has been mixed accurately
with all the nourishing juices and with all the sub-
stances or principles which compose the blood,
viz. saliva, mucus, lymph, bile, water, salts, oil,
and spirits.

But here it will be proper to take notice, that
.he most fluid and subtile parts of our aliment,
before and after it is elaborated into chyle, pass
into the blood by certain absorbent veins dispersed
all over the mouth, gullet, stomach, and intestines:
when we consider how quickly refreshment and
strength are communicated to weary, faint, and
hungry people, immediately upon drinking a glass
of good wine, or eating any cordial spoon-meat,
this remark will appear ihe more obvious.

The thiid stage begins where ihe chyle mingles
with the blood, and, falling soon in;o the right ven-
tricle of the heart, is from thence propelled into
the lungs. It will appear that the lungs are the
principal instruments of converting the chyle into
the blood ; especially if we consider their struc-
ture, first with regard to the air-vessels of which
they are composed, and secondly with regard to
o 3 their

CONCOCTION. [Lesson xxrvni.

their blood-vessels : for we shall then clearly per-
ceive the change which their fabric and actjon.
must produce on the chyle.

The windpipe is composed of segments of car-
tilaginous rings on the fore part, to giv.e a free
passage to the air in respiration j and of a strong
membrane on its back part, to bend with the
neck, and give way to the gullet in deglutition.
This pipe is lined throughout with an infinity of
glands, which perpetually distil an unctuous dense
humour to lubricate and anoint the passages of
the air. Soon after the windpipe has descendecl
into the cavity of the breast, it is divided into
two great branches ; and these two are subdivided
into innumerable ramifications called bronchia,
which become smaller in their progress (not much
unlike a bushy tree inverted), until at last they ter-
minate in millions of Jittle bladders which hang
in clusters at their extremities, and are inflated
by their admission of air, and subside at its ex-
pulsion. The plusters constitute the lobes of the
lungs,

The blood-vessels of the lungs next deserve^ur
attention. The branches of the pulmonary artery
run along with those of the windpipe, and are ul-
timately subdivided into an endle.ss number of
capillary ramifications, which are spread, like a fine
net work, over the surface of every individual air-
bladder ; and the pulmonary vein, whose extreme
branches receive the blood and chyle from those of
the arteries, run likewise in form of a net over all
the air-bladders of the brpnchia.

From

Lesson xxxvm.] CONCOCTION.

From this admirable structure of the lungs, it is
obvious, that the crude mixture of the blood and
chyle, passing through the minute ramifications o£
the pulmonary artery and vein, is compressed and
ground by two contrary forces, viz. by that of the
heart^ driving the mixture forward against the
sides of the bronchia and air-bladders; and by
the elastic force of the air equally repelling this
mixture from the contrary side.

By these two opposite forces the chyle and blood
are more intimately blended and incorporated 5
and by the admission and expulsion of the air in
respiration, the vessels are alternately inflated and
compressed (and probably some subtile air of
aether is received into the blood) by which means
the mixture is still farther attenuated and dis-
solved; and after various circulations through the
lungs and heart, and the whole arterial system, is
at last perfectly assimilated with the blood, being
fitted to nourish the body, and answer the different
purposes of animal life.

When the blood thus prepared from the aliment,
is, by repeated circulations, gradually drained of all
its bland and useful parts, and begins to acquire
too great a degree of acrimony, it is carried oft' by
both sensible and insensible evacuations, through
the several channels and distributions of nature.
By these evacuations the body is made languid,
and requires a fresh supply of aliment; while at
the same time the saliva, and juices of the sto-
mach and intestines, becoming thin and acrid by
multiplied circulations, vellicate the nerves of
© 3 thos

29* CONCOCTION'. [Lesson xxxvin

those passages, and excite hunger, as a faithfi
monitor, to remind us of that refreshment which
is now become necessary. And here I close my
account of the process of Concoction ; in the
consideration of which the young reader will
find abundant cause for astonishment and ad-
miration.

LESSON

LESSON XXXIX.

ON THE CIRCULATION OF THE BLOOD.

The Blood, the fountain whence the spirits flow ;
The pen'rous stream that waters ev'ry part,
And motion, vigour, and warm life conveys
To tv'ry particle that moves or lives.

ARMSTRONG.

1 HOUGH it be common to talk familiarly of
the Circulation of the Bloody yet perhaps very few
of my young readers are well acquainted with it :
I shall therefore appropriate this Lesson to the
purpose of giving them a brief, though I hope in-
.telligible, description of the manner in which the
Circulation is performed. This important secret
was brought to light by William Harvey, an Eng-
lish physician, a little before the year 1600: and
when it is considered thoroughly, it will appear to
be one of the most stupendous works of matchless

To form a distinct judgment of the mechanism
and importance of the Circulation, it will be
necessary to describe the structure of the arteries,
veins, and nerves ; and take notice of some expe-
riments made upon them; and then must be con-
o 4 sidered

CIRCULATION [Lesson xxxix.

sidered the cavities of the heart, by means of
which the Blood is propelled through the body.
To these I now proceed.

The arteries are blood-vessels consisting of a
close texture of strong elastic fibres, woven in
rarious webs, laid in different directions, and inter-
spersed with an infinity of delicate nerves, veins,
and minuter arteries. They are divided and sub-
divi^jd into numberless branches and ramifica-
tions, that become smaller and smaller as they
recede from the heart, until at last their extremi-
ties are found much more slender than the hairs
of our heads, (and are therefore called capillary
arteries), which either unite in continued pipes
with the beginnings of the veins, or terminate in
•mall receptacles, from which the veins derive
their origin. The arteries have ,no valves, but
only have their trunks spring from the heart : they
throb and beat perpetually whilst life remains j
their extremities differing in the thickness of their
coats and some other particulars, according to the
nature of the part which they pervade. All the
arteries in the lungs (except the small ones that
convey nourishment to them) are derived from
the great pulmonary artery, which issues from the
right ventricle of the heart. And all the arteries
in the rest of the body proceed from the aorta,
(which obtained this name, because the ancients
thought it contained air only), whose trunk springs
from the left ventricle of the heart.

The veins resemble the arteries in their figure
and distribution $ but their cavities are larger, and

thier

Lesson xxxix.] OF THE BLOOD. 29-7

their bnmches, perhaps, more numerous. Their
coats are much weaker and more slender than
those of the arteries. They are furnished with
several vdlves, contrived in such a manner as to
permit the Blood 10 pass freely from the smaller
into the larger branches, but to stop its retrogres-
sion. They neither throb nor beat. Their begin-
nings form continued pipes with the extremities of
the arteries, or arise horn some gland or recep-
tacle where the arteries terminate. All the veins
in the lungs, from their capillary beginnings grow-
ing still larger, unite at last and dischaige their
Blood into the left auricle of the heart: and all
those in the rest of the body empty themselves in
like manner, into the vena cava, which opens into
the right auricle of the heart.

The nerves deduce their origin from the brain,
or its appendages, in several pairs, ofacylindric
form, (like so many skeins of thread with their
respective sheaths;, which in their progress de-
crease by endless divisions and subdivisions, until
at last they spread themselves into a texture of
filaments, so slender, and so closely interwoven
with each other over the whole body, that the point
of a needle can hardly be put upon any part of it,
without touching the delicate branch of some
nerve.

It has been found by many trials, that when an
artery is laid bare, and a ligature made upon it, if
it be opened with a lancet between the ligature
and the heart, the Blood will rush out with great
•violence j and a rapid, jerking stream will coa-
O 5

298 CIRCULATION. [Lesson xxxix.

tinue (if it be not stopped by art) until, through
loss of Blood, the animal faints or dies. But if
the same artery be opened between the ligature and
extremities, a few drops only will ooze out from
the wounded coats.

On the other hand, when a vein is laid bare,
and a ligature made upon it, if it be opened be-
tween the ligature and the extremities, the Blood
will gush out, as we see in common venesection.
But if the same vein be opened between the bind-
ing and the heart, no Blood will appear. From
these experiments it is obvious to the slightest
attention, that the Blood flows from the heart,
through the arteries, to the extreme parts of the
body; and returns again through the veins to the
heart.'

For the regular performance and continuation
of this motion of the Blood through all the dif-
ferent parts of the body, the heart, which is the
primitm mobile, giving the first impulse, is fur-
nished with four distinct muscular cavities, that
is, with an auricle and a ventricle on the right
side, and an auricle and a ventricle on the left.
Through these cavities, curiously adapted to their
* respective offices, the Blood circulates in the fol-
lowing order : — it is received from the veins, first
into the right auricle, which, contracting itself,
pushes the Blood into the right ventricle at that
instant dilated. The moment this ventricle is
filled, it contracts itself with great force, and im-
pels the Blood into the pulmonary artery, which
passing through the lungs, and returning by the

pulmonary

Lesson xxxix.] OF THE BLOOD. 299

pulmonary veins, is received into the left auricle
of the heart, and from thence it is pushed into
the left ventricle 5 which, being thus filled, con-
tracts itself, and drives the Blood with great rapi-
dity to all the parts of the body, and from them
it returns again through the veins into the right
auricle of the heart, as before.

It is very remarkable, that we have here a dou-
ble Circulation : one, from the right ventricle,
through the lungs, to the left auricle of the heart,
in order to convert the chyle into Blood, and
finally prepare it for the nourishment of the ani-
mal ; the other, from the left ventricle, through
the whole body, to the right auricle of the heart,
which serves to apply that nourishment to every
part, besides various other purposes.

But to proceed — Of these four muscular cavi-
ties, the two auricles are contracted at the same
instant, while the two ventricles are dilated j the
ventricles, in their turn, are contracting them-
selves at the very instant that the auricles are di-
lating. The arteries, in like .manner, beat in
alternate time with the ventricles of the heart.

The nerves, as well as the veins and arteries,
act their part in this rotation of the Blood; for
if the eighth pair of nerves which proceeds from
the brain to the heart be bound up, the motion of
the heart immediately languishes, and soon ceases
entirely.

Thus we have a species of perpetual motion,
•which none but a Being of infinite wisdom and

power

300 CIRCULATION [Lesson xx xix

power could produce j yet whose continuation
requires the constant aid of the same hand that
first gave it existence. The brain transmits ani-
mal spirits to the heart, to give it a vigorous con-
traction. The heart, at the same time, pushes
the Blood into the brain to supply it with new
spirits; by which means the head and the heart
give continual mutual support to each other. But
this is not all ; the action of the heart sends the
Blood and other vital humours over the whole body
by the arteries, and distributes nourishment and
rigour to every part (while perhaps the animal
spirits, from the extremities of the nerves, return
again into the Blood), and the whole refluent mass
is conveyed back through the veins into the heart,
which enables it, without intermission, to persi&t
in rolling this tide of li/e.

But here it must not be supposed, that the arte-
ries pass on to the extremities of the limbs, before
they communicate wivh the returning veins : for
upon this supposition, after an amputation has
been performed, whatever Blood might be brought
to the stump by the arteries, it is certain, none of
it could be carried back again to ihe heart; be-
cause the intercourse between the heart and the
limbs would, in this case, be entirely cut off. But
the all-wise AUTHOR of our being has provided for
this exigency, by forming a great number of less
branches from the larger arteries, which constantly
communicate with corresponding branches of
the r«turning veins. And hence, it is easy to

conceive

Lesson xxxix.] OF THE BLOOD. 30-1

conceive how the Circulation is carried on after
amputation has been performed*.

From what little has been advanced in this and
the two preceding Lessons, the unprejudiced young
reader will rind a striking di-play of the wisdom
and goodness of our CKEATOR. To those who
still hold to the negation of such a Being, I scarce-
ly know what to say: for thev who live, move,
think, and act, must be left without excuse, if they
deny or forget GOD, or refuse to honour or be
thankful to "him. Those who withstand the evi-
dence of the works of nature, when properly ob-
served, are not likely to be convinced by rational
deductions ; but will probably continue infidels
(unless their hearts be changed by Divine Grace)
untH they are convinced of their fatal mistake, by
experiencing the indignation of that ALMIGHTY
B. ING, whose existence they have so impiously
denied. *

But this, I sincerely hope, will not be the case
with any of the youthful perusers of these Lessons.
However, in this sceptical age, when every part of
Divine Truth is questioned, opposed, and, alas ! too
frequently holden in derision, it becomes us to be

* With respect to the velocity of the circulating Blood, and
the time in which the whole quantity thereof has undergone a
complete circulation; although several computations have
been made, the matter is not decisively settled. Dr. Jurin
and Dr. Keill have most distinguished themselves in inquiries
of this nature; but they are far from agreeing in their con-
clusions. The substance of their calculations and experi-
ments may be seen in Dr. Reel's improved edition of CHAM-
CYCLOPAEDIA, under the articles Blood and Heart.

wary j

•302 CIRCULATION, &.c, [Lesson xxxix.

wary j and not only so, but to join in a general
endeavour to persuade those who are deflating
from the true path, speedily to return thereto.

Come! all ye nations ! bless the LORD,

To him your grateful homage pay :
Your voices raise with one accord,

JEHOVAH'S praises to display.

From clay our complex frames he moulds.

And succours us in time of need :
Like sheep when wandering from their folds

He calls us back, and does us feed.

Then through the world let's shout his praise,
Ten thousand million tongues sliould join,

To Heaven their thankful incense raise,
And sound their MAKER'S love divine.

When rolling years have ceas'd their rounds,

Yet shall his goodness onward tend :
For his great mercy has no bounds;

His truth and love shall never end !

LESSON

LESSON XL.

CONCLUDING REMARKS AND ADVICE.

Ye guardian Powers! who make mankind your care,
Give me to know wise Nature's hidden depths,
Trace each mysterious cause, with judgment read
Th' expanded Volume, and submiss adore
That great creative. VV ill, who at a word
Spoke forth this wondrous scene.

SOMERVILLE.

WHEN we consider the contracted and confined
nature of human knowledge, even in its present
improved state, we must not anticipate to our-
selves the pleasure of obtaining such a degree of
philosophic skill, as is described in the above- cited
lines of the poet : for it may be recollected that,
when endeavouring to elucidate the causes of some
of the grand phenomena of nature, we more fre-
quently proceeded upon conjecture ami hypotheses
than upon any real and permanent foundation.
However, though this be admitted, it need not be
thence concluded that we should be entirely inat-
tentive to philosophic speculations: for contempla-
tions of this kind, when properly regulated, have

a

304 CONCLUDING ADVICE. [LeSSQH XL.

a tendency to correct wrong ppinions, which we
might otherwise entertain of the wisdom and
goodness of that BEING who created the uni-
verse.

It is in conformity to this sentiment, that I have,
in the foregoing Lessons, attempted to describe to
you the nature and supposed causes of some few
of the numerous objects and appearances in crea-
tion: and I hope that, even from the descriptions
which I have given, faint and imperfect as they
must be acknowledged to be, I shall be justified in
adopting the language of Mr. Cotes, when he says,
" That man must be blind, who from the most
*' wise and excellent disposal of things, cannot
" immediately perceive tke infinite wisdom and
" goodness of tbf Almighty Creator; and he
" must be mad, svho refuses to acknowledge
« them."

I have, in the course of these Lessons, fre-
quently referred you to such works of eminent
writers, as may be consulted with advantage : I
shall now, previous to drawing a conclusion, men-
tion some other authors in whose works you may
meet with more information; not only on the
subjects treated upon in this performance, but oa
several,, which the narrow limits I am confined to
have hindered me from even mentioning.

On Anatomy, I would recommend 'he works of
Borellif Harvey, Hunter., Jurin, Keill, Motherby,
Monro, and Nieuuuentyt. On Astronomical sub-
jects, Bonny castle 3 Bryan^ Emerson, Fergusvn

Gregory

Lessen XL.]' CONCLUDING ADVICE. 305

Gregory, Ktill, Long, Maskelyne, Vince, and
Wales, are writers of distinguished reputation.
The best writers on Electricity, are Brooks, Caval-
lo, Ferguson, Frank in, Morgan, and Priestley.
On Optics, the performances of Harris, Martin,
NKWTON, Smith, and Wood, will particularly
merit your attention. Various other parts of
Philosophy, or Natural Philosophy in general,
may be found treated on, either in a popular or
scientific way, in the works of Adams, Cavallb*
Desaguliers, Emerson, Enfield, Ferguson, Gregory,
Keill, Martin, Mariotte, NEWTON, Nicfiolsont
Nieuiuentyt, Rowning, Rutherforth, and Ryland.
There has also been lately issued into the world,
a Dictionary, by my highly esteemed friend, Dr.
Charles Hutton, in which abundant information;
on astronomical, mathematical, and philosophical
subjects may be met with. I would also recom-
mend to your notice the periodical publications in
which philosophical and mathematical questions
are discussed: the principal of these are, the Ladies'
Diary and Supplement, Gentleman's Diary, and
Mathematical Repository $ besides monthly pro-
ductions, several of which are worth notice. Nor
tan I here omit pointing out, Maclaurins Piew
oj Sir Isaac Newton's Phiosophical Discoveries;
and, to those who are acquainted with th<^ French
lannuage, the Traitc Elcmentaire de Physique, par
M. R. J. Hauy, as works which will amply repay
tlie student for any attention he ma\ pay them.
And, since the author of a book commonly wishes

it

306 CONCLUDING ADVICE. [Lesson XL.

it to be read, and generally thinks it will be found
worthy a perusal, it would be a mere affectation
of modesty, were I not to recommend to the
notice of my readers, the treatises on Astronomy
and Mechanics advertised at the end of this
volume.

Finally, I must entreat my young readers early
to imbibe correct religious principles*; for it is
religion only that can regulate the heart, — it causes
it to melt in sympathy at another's distress, or to
glow with pleasure at another's happiness, — it is
this alone that can harmonize the mind,
" Attuning all its passions into peace."

The astronomer, if enlightened by it, must con-
template, with wonder and admiration, those lumi-
naries on which his eye so often gazes with plea-
sure. The philosopher too, when the wonders of
nature are open to his view, with what adoration

and gratitude must he look to that great Source

. .

from whence they flow ! Nay, in all professions

how imperfect is man, unless illumined by the
bright rays of Religion, which, like that glorious
fountain of light, the sun, will enlighten all our
paths.

Let me beg of you, therefore, to study, with par-

* " With the talents of an angel, a man may be a fool; if
" he judge amiss in the supreme point, judging aright in all
« else but aggravates his folly— as it shews him wrong, though
" Llest with the best capacity of being right."

DR. YOLIVG.
ticular

Lesson XL.] CONCLUDING ADVICF. 307

ticular attention, that much-negiected book the
BIBLE; where energy of language, sublimity of
sentiment, and the most exquisite beauties of
oriental poetry, are among the least of its perfec-
tions* ; from reading this book, and from con-
templating the works of nature, we may learn
that GOD is a supreme, eternal, self-existent, ne-
cessary, and independent Being: that he is also
invisible, immortal, incomprehensible, omnipotent,
omniscient, omnipresent, ami supremely good. We
may also thence deduce, that He manages the
world in wisdom and goodness, and governs it in
justice, truth, and holiness; that " not a sparrow
" falls to the ground without HIM;" that " even

* The Bible, on account of the precepts it contains, and
the consolations which may be derived from it, is above all
praise. But before it can be of advantage to a reader, he
ought to be convinced of the truth of Revelation. Young
persons should assent to the doctrines in this Divine Book ;
not because they were born in a country where they have
been told that they were true ; nor merely because they have
been assented to, and defended, by very eminent men ; but
because the evidences, accompanying the various parts of
the volume, have CONVINCED them, that it has GOD for its
author, TRUTH for its matter, and SALVATION for its end. I
cannot help adding, that when youth make these evidences
the subject of their pursuit, they should bear in mind a pre-
cept, which ought always to accompany them when pursuing
truth : namely, " As far as possible get rid of old prejudices,
and watch continually against new ones."

For more on this most interesting of all subjects, I trust
the reader may advantageously consult my " Letters on the
Evidences, Doctrines, and Duties of the Christian Reli.
gion."

"the

308 CONCLUDING ADVICE. [LeSSOH XL,

" the hairs of our head are all numbered j" and
that all second causes derive their origin, perma-
nency, and efficacy from HIM alone.

Since, then, THE LOKD GOD is himself the
Source and Perfection of all beauty and excellency
the Author of our existence, and the bountiful
Giver of all good g'fts ; we undoubtedly ought to
love him with our whole heart, and to serve him
with all our powers ; we ought to reverence his
majesty and authority, and endeavour above all
things to obtain his favour} we ought to devote
ourselves entirely to his service, and make all out
actions tend to the advancement of his glory.
And as his mercy.and goodness are unbounded, so
, should be our gratitude and praise.

JEHOVAH reigns : let ev'ry nation hear,

And at his footstool bow with holy fear ;
. Let heav n'^ high arches echo with his name,

And the wide peopled earth his praise proclaim ;
Then send it down to hell's deep gloom wsoundmg,
Through all her caves in dreadful murmurs sounding.

He rules with wide and absolute command,
O'er the broad orean and the stedfast land :
JEHOVAH reigns unbounded and alone,
And all creation hangs beneath his throne :

He reigus alone ; let no inferior nature

Usurp or share the throne of the Creator.

He saw the struggling beams of infant light
Shoot lhron«h the massy gloom of ancient night j
His Spirit hush'd the elemental strife,
And brooded o'er the kindling seeds of life ;
Seasons and months began the long procession,
And ineasur'd o'«r the year IK bright succesnion.

ThV

coNctuDiNct ADVICE.

The joyful sun sprung up th' ethereal way.

Strong as a giant, as a bridegroom gay :

And the pale moon diffus'd her shadowy light

Superior o'er the dusky brow -of night ;
Ten thousand glittering lamps the skies adorning,
Numerous as dew-drop» from the wemb of morning.

Earth's blooming face with rising flow'rs he dress'd,
And spread a verdant mantle o'er her breast ;
Then from the hollow of his hand he pours
The circling waters round her winding shores,—
The new-born world in their cool arms embracing,
And with soft murmurs still her banks caressing.

At lengthshe rose complete in finish'd pride,

All fair and spotless like a vkgin bride ;

Fresh with untai uish'd lustre as she stood,

Her MAKER bless'd his work, and call'd it good ;
The morning stars, with joyful acclamation,
Exulting sung, and hail'd the new creation.

Yet this fair world, the creature of a day,
Though built by God's right hand, must pass away <
And long oblivion creep o'er mortal things,
The fate of empires, and the pride of kings .:

Eternal night shall veil their proudest story,

And drop the curtain o'er all human glory.

The sun himself, with weary clouds opprest,
Shall in his silent, dark pavilion rest;
His golden urn shall broke and useless lie,
Amidst the common ruins of the sky !
The stars rush headlong in the wild commotion,

And bathe their glittering foreheads in the ocean.

/

But fix'd, O COD ! for .ever stands thy throne ;

JEHOVAH reigns, a universe alone;

Th' eternal fire that feeds each vital flame,

Collected or diffused is still the same,
He dwells within his own nnfathom'd essence,
Aujl fills all space with his unbounded presence.
, But

CONCLUDING ADVICE. [LtiSSIM Xf..

But oh ! our highest notes the theme debase,

Ari'd silence is our least injurious praise :

Cease, cease your songs, the daring flight controul, —

Revere him in the stillness of the soul j
With silent duty meekly bend before him,
And deep within your inmost hearts — adore him.

MRS. BA.RBAULU,

APPENDIX

APPENDIX

CONTAINING

SOME ADDITIONAL REMARKS

ON

HEAT, COLD, AND LIGHT.

J HERE is but little probability of our arriving at
any great degree of accuracy in our opinions con-
cerning these subjects, if in our reasonings upon
them we only consider them separately j for there
are several cases in which they have a dependence
upon each other, which can only be tracrd out by
considering them together. To answer this pur-
pose, the following pages are written.

As in the course of our discussion, the degrees
of heat and cold will be spoken of, it appears ne-
cessary to premise a little with regard to the instru-
ment by which they are. usually (though not always)
measured. This instrument is called a thermo-
meter : to describe it with a nice particularity is not
requisite, since more may be learnt from five
minutes' examination of one, than could be ga-
thered from a description which micht fill half a
dozen pages. In order that thermometers of dif-
ferent sizes may produce exactly the same conr
chmon in determining the heat or cold of bodies

applied

• 12 APPENDIX.

applied thereto, it is necessary to fix upon two
certain points at some distance, of each of which
we can judge by unvarying criteria. These ii
Fahrenheit's Tliermometer (the one most generally
used in England) are the boiling and freezing
points of water. With regard to the former of
these, it should be recollected as observed in the
Twenty-ninth Lesson, that the degree of heat at
which water bolls, is varied by the difference4 of
the pressure of the atmosphere. The boiling heat
is therefore taken at some certain degree of pres-
sure : the degree now used is such as makes the
mercury in a barometer stand at 29| inches. As to
the latter of these points, it does not appear to be
a proper criterion ; or at least, if it be, it has a
wrong name affixed to it ; for it is well known
that,' though fluids always thaw at the same de-
gree of heat, yet the degree at which they freeze
is liable to be varied with circumstances. It would
therefore be better, if in future this latter point
wene :laid aside^ and instead thereof the thawing
point made use of.

The different degrees of heat and cold are gene-
rally estimated by their distance either above or
below the, freezing point. Those above may be
denoted by the affirmative sign : those below by
the negative one ; though sometimes the words at
length are used ; and at others, the expressions
alove or below nothing are made use of j but this
latter method seems somewhat absurd.

Those who purchase thermometers ready made
should pay particular attention to the tube and

corresponding

HEAT, COLD, AND LIGHT. 313

corresponding divisions : it is frequently found
that the tubes, instead of being cylindrical, are
smallest in the middle, and widen gradually to-
wards each end, like two conic frustrums joined
at their less bases. When this is the case, it is
proper that the divisions, instead of being equal,
should be longest in the middle, and decrease by
regular gradations toward each end, so that the
cavity in the tube shall contain the same quantity
of fluid between every two division!.

We now proceed to the more immediate objects
of this Appendix, namely, Heat, Cold, and Light:
The two latter of these will not be considered very
attentively; only as they are connected with the
former, which will be handled more at large.

Heat and Cold are to be considered either as
particular sensations, or as the causes of powers
which bodies possess of exciting those sensations.
Thus, we say that we ourselves are hot or cold,
and that the fire or ice which heats or cools us is
likewise hot or cold : though the sensations we
experience are certainly very different things from
that which enables those bodies to excite them.
It must be observed that the sensations of Heat
and Cold are very fallacious ones, in so far as
they are effected by the temperature of the body
in which they are excited : for we may feel a sub-
stance hot when it is in the same circumstances in
which we should feel it cool at another time. To
elucidate this, we may observe that when we have
been accustomed to live in an atmosphere of be-
twixt 4- 60? and + 70°, if the Heat fall to + 60?
p \vc

314 APPENDIX.

we feel it cold : but, on the contrary, if we have
lived in an atmosphere of between. + 40" and -}-
5O°, if the Heat rise to -f- 6()u we feel it very hot.
Again, let two basons of water be taken, one
heated only to -f- 35°. the other to -f- no°, and
put one hand into the one, the other into the
other bason, for some time: if we then immerse
both hands in water 'heated to + 60Q} we shall
with one hand feel this Cold, with the other Hot.
Hence it may be reasonably inferred, that we can-
not judge with precision of Heat or Cold by the
Sensations they excite in us.

In the next place, we are to consider Heat and
Cold as the cause of powers which bodies possess
of exciting particular sensations. As to Cold, it
Is seldom supposed to be either matter itself or a
quality: it is more commonly looked upon as a
deprivation of Heat ; for the less the heat, found
in a body, the greater the Cold, and vice versa. —
There are particular cases in which Cold may be
produced. i. When some particular chemical
attraction takes place, Cold is produced. 2. The
conversion of solids into liquids, and of liquids into
vapour, produces Cold, as is shewn by chemists.
And 3. Cold may be produced by animal powers.
It is not intended to relate experiments by which
these may be proved : but the grand question
which we most wish to determine, is, with respect
to Heat, whether it be matter under some parti-
cular form, or only a quality. That our reason-
ings on this important subject may have the better
*ffect, we must first reflect upon the various means

of

HEAT, COLD, AND LIGHT. 315

of producing Heat. There are several ways by which
Heat may be generated. 1. By means of the sun's
rays. 2. By exciting vibrations in solids. 3. By the
taking place of certain chemical attractions. 4. By
conversion of vapours into fluids, and of fluids into
solids. 5. By animal powers. 6. In volcanos.

And first, if a cold body be exposed to the rays
of the sun, it will be heated.

It has been frequently conjectured that the sun
is fire, burning and heating ocher bodies in like
manner as a culinary fire: but the celebrated Dr.
Fordyce has asserted, that the sun is probably not
at all hot in itself; neither are the solar rays hot,
but have only a power of producing Heat on being
applied to other bodies. An opinion very little
different from this is also entertained by Dr. tVil-
liam Herschel, and supported with the authority
of demonstration. As a farther consideration of
this subject may tend to correct our notions con-
cerning Light, it is here attempted.

It is a constant rule, with regard to hot bodies
that they heat ail colder bodies which are brought
near them. Though it must be allowed (as will b«
hereafter seen) that some bodies will receive Heat
with more readiness than others: however, thi*
will not easily form an objection to what imme-
diately follows.

Now, if we take a 'large burning glass, and hold
a piece of iron in its focus, such Heat will be pro-
duced as to melt the iron. But the glass through
which all the rays passed is scarcely heated at all :
and when they fell on the iron they were n.Q hotter

pg than

31$ APPENDIX.

than water when it is poured on vitriolic acid*
But if we place water j which is perfectly transpa-
rent, in the focus, no heat will be produced : nay,
if spirits of wine were placed in the focus, they
would scarcely be heaied. But the same Heat
which melts iron, would more than suffice to make
water boil. From this experiment, then, without
advancing farther arguments, it appears that the
rays in themselves have no Heat ; and there is no
reason to suppose that the sun is hotter than the
earth we inhabit.

It is a question that has been much agitated,
whether the solar rays be matter, or only an ar-
rangement of matter; but their materiality is now
pretty generally admitted: but a question which
has not yet been answered satisfactorily, is, " If
f* Light be matter, what becomes of it ? " Perhaps
there is a distinction between Light and the solar
rays, which has not yet been properly attended to.
The sun's rays heat bodies only when they are
lent or destroyed. (The term absorbed does«not in
our opinion exactly answer the purpose.) Hence
they do not heat water if perfectly transparent ;
neither do they heat the air above the clouds: at
least, as very little bending takes place in these
cases, the heat is so trifling as to be scarcely worth
mentioning. The upper regions of the air, then,
are extremely cold, though exposed to the direct
action of the sun.

When a ray of Light is reflected, it does not
touch the body reflecting it; but is thrown back
before it arrives at the surface : therefore the more

white

HEAT, COLD, AND LIGHT. 317

white bodies are, or the more highly they are
polished, the less they are heated, because they
reflect more of the rays : and when a body is per-
fectly white it reflects all the light, and is not
heated at all.

Bodies, in proportion as they deviate from whitea
destroy the more solar rays, and a perfectly black
?Jody would destroy them all : hence bodies are
more heated, ccet. par. as they are darker coloured,
by this cause of Heat.

When a body is rough, asi f we make a piece of
glass so (which may have no colour) it destroys
part of the rays, or, at least, suffers them to ap-
proach' so near its surface before it reflects thein
that they cause it to be heated.

Thus far our reasonings induce us to suppose
that Heat i8 a quality: but Heat, as a quality,
cannot exist without a substance to exist in. So
that, if it were possible to produce a perfect va-
cuum, there could be no Heat therein. This also
leads us to conclude, that tiie denser a body is,
the more Heat may be therein produced ; other
circumstances being: the same.

Heai, it is affirmed, can only be produced by
the solar rays at the surfaces of bodies : conse-
quently the interior parts can only be heated by
communication. And if we ketp in mind that
Heat is more rtadily transmitted, communicated,
and received, by some bodies than others ; it will
then appear that, as a' body receives Heat with.
more facility, it will be the mere heated by the

sun's

318

APPENDIX.

sun's rays ; as a piece of iron will be more heated
than a piece of wood.

We have seen, then, — that the solar rays are not
hot in themselves, — that they produce Heat only
when they are bent or destroyed, — that therefore
they do not heat transparent bodies, nor do they
heat in passing through them, but only at tha»
entrance and passing out again.

It is evident^ since the rays of the sun have a
power of producing Heat, that they will heat a
.body more, the greater the quantity is that falls
on it. From this principle, combined with some
particular circumstances, arises the different Heat
and Cold of the seasons, and of the different parts
of the earth. For instance, the Heat about the
equator has been known to arise to -f- 1 10° : and
it is said, that the Cold in Siberia has been as low
as + 160°; but the accuracy of this may be
doubted, for I do not see how so great a degree of
Cold can be precisely measured.

The Heat produced by the solar rays is increased
also by reflection of them : if they be frequently
reflected, a greater Heat is produced than even if
they be all destroyed. Thus we find that, if we re-
ceive them into a box so constructed as to reflect
them frequently from side to side, more Heat will
be produced than in a box made black, so as to
destroy them almost all. Hence, in vallies, even
in temperate climates, where the rays are reflected
frequently, very great Heal is also produced.

The different distances of the planets from the

sun.

MEAT, COLD, AND LIGHT.

sun, it is imagined, makes a great difference in the
number of the rays and in the momentum with
which they fall on them. So that it has been.
thought that Mercury is exceedingly hot, and
Georgium Sidus cold beyond conception : but
since the Heat produced in- bodies depends on
their disposition to receive it, the several planets
may be so composed as to- have but a very trifling
difference in the Heat produced by the solar rays.
Hence, then, what has been hitherto said concern-
ing the Heat of the planets as calculated on the
-supposition of the sun being the source of Heat,
may be called in question : and, perhaps the New-
tonian opinion concerning comets (recited in the
astronomical part of this work) may in time be
entirely abandoned, and some later hypothesis
become generally received.

Thus much for the first method of producing
Heat.

The next method of producing Heat is by ex-
citing vibration in solids. Whether fluids can be
thus heated, we do not know : there is no clear
instance of Heat being produced by their vibration.
We may excite vibration in solids, by friction or
by collision. If we rub together or strike two
bodies, if they have any elasticity they will vibrate.
The rougher bodies are which are rubbed together,
the greater vibration is produced, and therefore the
greater heat. The vibration is also, cat. par. in
proportion to the elasticity of bodies.

Li Count Rumford's ninth Essay, which is an

inquiry

3*0 APPENDIX.

inquiry into the source of the Heat that is excited
by friction, many interesting experiments are re-
lated. From these experiments it appears, that
sufficient Heat was produced by the friction of two
metallic surfaces (when the access of atmosphe-
rical air was entirely prevented) to make water
actually boil. It appeared that a very considerable
.quantity of Heat was excited by the friction, and
given off in a constant stream in all directions^
without interruption or intermission, and without
any signs of diminution or exhaustion.

This ingenious philosopher, when reasoning on
these experiments, gives satisfactory reasons to
prove that the Heat could not be furnished either
by the air, or by the water which surrounded the
machinery. And, considering that the source of
the Heat generated in these experiments, appeared
evidently to be inexhaustible, he naturally con-
cluded, that Heal could not be matter: for, says
he, " It is hardly necessary to add, that any thing
«* which any insulated body, or system of bodies,
ft can continue to furnish without limitation, can-
"-not possibly le a material substance."

Another method of producing Heat is by the
taking place of chemical attractions. Every che-
mical attraction, as far as we know, in taking
place, produces either Heat or Cold : whether it be
simple combination, elective attraction, or com-
pound elective attraction. Some of the chemical
attractions are attended, besides the production
of Heat, with another striking phenomenon,

namely,

HEAT, COLD, AND LIGHT. 321

namely, the producing of Light. For instance,
this is produced by the combination of resp. air
with phlogiston; and other instances might be
adduced. This strikes out an interesting subject of
philosophical inquiry.

The fourth and fifth methods of producing
Ileat might be descanted upon very copiously j
but perhaps this would have but little tendency to-
wards determining what Heat is.

Lastly, Heat is produced in volcanos. This has
commonly been supposed to be by burning of
fuel. But it is evident that it cannot be produced
by this cause, or by any other known means of the
production of Heat. The burning of fuel, it is
known, destroys a proportionate quantity of air :
to produce a very great degree of Heat requires
(till more to be applied than is naturally combined
with phlogiston. Now the whole island Santalina
is a mass of iron ore very difficult of fusion,
which was fused and thrown up from the bottorn,
of the sea in the midst betwixt two shore?, by this
Heat ; where no air could therefore possibly come.
And if it could, it would have required more in
quantity than would have exhausted the whole
atmosphere, to animate fuel enough to have pro-
duced the Heat. In Friesland, some time ago,
there was a tract of country 100 miles across, the
whole of which (wiih men, animals, trees, and
whatever was on it) was melted into one common
mass. This Heat then cannot be produced by
the burning of fuel ; much less can it be by the
decomposition of pyrites, which is indeed the

burning

322 APPENDIX.

burning of sulphur. And by what means such
intense Heat is produced, we are at a loss to de-
termine.

Having spoken of the various methods of pro-
ducing Heat, we must next observe, that bodies
may be heated by communication. And several
experiments might be described to shew, that some
bodies will both communicate and receive Heat
more readily than, others. It is the same with re-
spect to Cold as to heat : for those bodies which
receive Heat most readily, most readily part with
it ; and if they do this, they must also suffer it to
pass through them (speaking of it as though it
were a body) from one substance to another, or
•onduct it most readily, and vice versa.

Iron is a good conductor of Heat : on the con-
trary, wood is one of the best non-conductors of
Heat known. That the former is a conductor, and'
the lattera non-conductor, of Heat, is evident from
the following simple experiment; if you take a
nail or a small piece of iron, and hold in the flame
of a fire or candle,, it will speedily become so hot
all over, as to oblige you to relinquish your hold ;
but if you take a small piece of wood and hold in
the flame, you may keep hold of it till it is nearly all
consumed by the fire, without being incommoded
by the heat of the wood. Hence heat passes with
case in iron, and with difficulty in wood.

From the results of various experiments, Count
Rumjord * concludes that water , oil, mercury,

and

* In the Essays of this philosopher, very ingenious princi-
ples are applied to practical uses in the great art qf living. That

my

HEAT, COLD, AN7D LIGHT. 32.T

and air, are non-conductors of Heat : indeed, he
thinks it essential to all fluids, that they should be

non- conductors

my young readers may have an idea of the advantages which
aiay arise, from applying philosophical- principles to s«eh
purposes, I present them with the following extracts :—

In Essay VI. the Count says, " Among all the various
" substances of which coverings may be formed for confining"
" Heat none can be applied with greater advantage than at-
" mospheric air. It is what Nature employs for that purpose ;
" and we cannot do better than imitate her.

" The warmth of tke wool and fur of beasts, and of the fea-
" thers of birds, is undoubtedly owing to the air in their in-
" terstices ; which air, being strongly attracted by these
" substances, is confined, and forms a barrier, which not only
" prevents the cold winds from approaching the body of th«
" animal, but which opposes an almost insurmountable ob-
" stacle to the escape of the Heat of the animalinto the at-
" mosphere. And in the same manner, the air in snow serves
u to preserve the Heat of the earth in wioter. The warmth,
44 of all kinds of artificial clothing may be shewn to depend
" on the same cause ; and were this circumstance more ge-
" nerally known, and more attended to, very important im-
" provemeuts in the management of Heat could not fail to
" result from it. A great part of our lives is spent in guard-
" ing against the extremes of Heat and of Cold, and in ope-
" rations in which the use of Fire is indispensable ; and yet
" how little progress has been made in that most useful and
" most important of the Arts — the management of Heat!

" Double windows have been in use many years in most of
" the northern parts of Europe, and their great utility, in
* rendering the houses furnished with them warm and com-
" fortable in winter, is universally acknowledged, — but I
" have never heard that any body has thought of employing
l< them in hot countries to keep their apartments cool in sum-
" mer;— yet how easy and natural is this application of so
"simple and so useful an invention! — If a double window
" can prevent the Heat which is in a room from passing out.

334 APPENDIX.

non-conductors of Heat ; or that all interchange
and communication of Heat among their particles,
as from one of them to the other, is absolutely
impossible. Glass, when rendered of a loose tex-
ture, conducts Heat with very great difficulty j
insomuch that the lava of a volcano has, sixteen
years after an eruption, been found red hat a foot
under the surface of such glass, though this was
quite cool. This circumstance might very pro-
bably give the hint for the assertion (paradoxical
as it may seem without proper deliberation) that it,
would be no difficult matter to convey an iron ball
red hot from London to Lincoln: to perform this,
it must be inclosed in pumice stone, which is very
porous glass, formed by volcanos, and then co-
vered over with fur, It is also easy, by covering
a room with (he to preserve the air in it of the

same

14 of it, one would imagine it would require no great effort of
" genius to discover that it would be equally efficacious for
" preventing the Heat without from coming in. But natural
" as this conclusion may appear, I believe it has never yet
" occurred to any body ; at least I am quite certain that I
" have never seen a double window, either in Italy, or in any
" other hot country, I have had occasion to visit."
A little farther on, he says, — " There is no communication
of Heat between one particle of air and anotiter particle of air*
From hence it follows, that though air may, and undoubt-
edly does, curry off Heat, and transport it from one place, or
from one body to another, yet a mass of air in a quiescent
state, or with all its particles at rest, could it remain in that
state, would be totally impervious to Heat; or such a mass
(l of air would be a perfect non-conductor,"

Much curious and valuable information on this subject may
be found in Professor LESLIE'S Experimental Inquiry init (lie
Naiun and Propagation qf Heat, lately published.

HEAT, COLD, AND LIGHT. 325

same temperature, without bringing any thing
into it eiiher hot or cold, fora very great length of
time.

As to the effects produced by Heat, it is known
to expand bodies ; and some late chemists affirm,
that it tends to diminish every attraction we are
acquainted with: they produce experiments to
evince that Heat diminishes the attraction — of
gravitation, — of cohesion, — of magnetism, — of
electricity, and chemical attractions. But though
it may be the case in particular instances, it will
be better not to be too sanguine in imagining that
such effects will take place universally. The asser-
tion may be disputed with regard to the attraction
of gravitation, and that of electricity. However,
those who allow that Heat universally diminishes
the electrical attraction, will strongly contend in.
support of their opinion, because they may thereby
explain with facility the reason of the frequency
of thunder-storms in summer.

From a review of what has been here advanced,
we shall find that there are few, or, perhaps, we
may confidently say, no appearances, but what
will admit of as easy an explanation, by conjec-
turing that Heat is a quality, as by supposing that
it is a substance. Nay, some of the phenomena,
particularly those which attend the production of
Heat by friction, or vibration in solids, will (as
must appear from what has been previously ob-
served) induce us to incline mose to the former
hypothesis than to the latter. Besides, whether
Heat be a substance, or a quality, it is manifest,

thai

326 APPENDIX.

that it may be created and annihilated. Now, we
have no idea of matter being created and anni
hilated by any natural cause, (for under all its
variety of forms, matter is matter still) ; then what
kind of a substance must Heat be, to be produced
and destroyed by so many causes ? Why, truly,
nobody can tell : for it must have a property which
matter has not. Heat is, then, probably a quality:
for qualities we know can easily be created and
annihilated. And, if Heat be a quality, it must
have matter to exist in ; so that, if we apply any
of the causes producing Heat, no Heat is produced
unless there be some matter to receive it. This,
therefore, is the result of our inquiries into the
-nature of Heat.

We have also seen, that Light may be produced
by particular means, the solar rays for instance : it
may likewise be destroyed, as has been previously
shewn. The method of reasoning just applied to
Heat, may with equal propriety be used here : and
this will induce us to conclude that Light, instead
of being a fluid per sr, as has been sometimes
conjectured, is a quality, and can no more exist
independently of matter than Heat can.

Whether these conclusions may be safely relied
on, is not for us to determine : the great myste-
rious BEING who made and governs the universe,
has set a part only of the chain of causes in our
view ; and we find that as HK himself is too high
for our comprehension, so His more immediate
instruments are also involved in an obscurity that
©ur feeble endeavours are not able to dissipate.

However,

MEAT, COLD, AND LIGHT. 39f

However, as Mr. Maclaurin has observed,—
" From what we are able to understand of nature,
" we may entertain the greater expectations of
t( what will be discovered to us, if ever we shall
" be allowed to penetrate to the FIRST CAUSE
" himself, and see the whole scheme of his works
•" as they are really derived from HIM, when our
4( imperfect philosophy shall bejcompleted."

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