Thomas Reid.

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it a priori ; because the necessary effect of
pressing one arm down, is the pressing the
other up with the same force : therefore,
each arm is pressed down by the weight in
its own scale, and equally pressed up by the
weight in the other scale ; and, being pressed
with equal force in contrary directions, it
remains at rest. Your Lordship will easily
apply this reasoning to a fluid, every part of
which is as moveable as the balance is about
its fulcrum ; and no one part can move, but
an equal part must be moved in a contrary
direction. And I think it is impossible we
should differ in this, but in words.

Next, as to the barometer. You say the
mercury is kept up by the expansive power
of the air : but you say further, that it is
not kept up by the weight of the air. I
agree to the first, but not to the last. The
expansive power of the air is owing to its
being compressed ; and it is compressed by
the weight of the incumbent atmosphere.
Its expansive force is exactly equal to the
force that presses and condenses it ; and
that force is the weight of the air above it,
to the top of the atmosphere — so that the ex-
pansive force of the air is the causa proximn,
the weight of the atmosphere the causa
remota of the suspension of the mercury.
Your Lordship knows the maxim, Causa
causes est causa causati. The barometer,
therefore, while it measures the expansive
force of the air which presses upon the
lower end of the tube, at the same time
measures the weight of the atmosphere,
which is the cause of that expansive force,
and exactly equal to it. If the air was not
pressed by the incumbent weight, it would
expand in boundless space, until it had no
more expansive force.

As to the observation in the postscript,
it is true, that the gravity of the air, while
it rests upon an unyielding bottom, will give
no motion to it ; but the mercury in the
lower end of the tube yields to the pressure
of the air upon it, until the weight of the
mercury is balanced by the prassure of the
air.

Opas Mar/man, goes on, but more slowly
than I wish — I am, most respectfully, my
Lord, yours,

Tho. Reid.

LETTERS TO LORD KAMES.

61

VIII.

ON THE ACCELERATED MOTION OF FALLING
BODIES.

Glasgow College, Nov. 11, 1782.

My Lord, — My hope that your Lordship
is in no worse state of health than when I
left you, and that the rest of the good family
are well, is confirmed by your continuing
your favourite speculations. I promised to
call upon you in the morning before I came
away. I sent in Samuel to see if you was
awake : he reported that you was sleeping
sound ; and I could not find it in my heart

When we say, that, in falling bodies, the
space gone through is as the square of the
velocity, it must be carefully observed that
the velocity meant in this proposition, is the
last velocity, which the body acquires only
the last moment of its fall : but the space
meant is the whole space gone through,
from the beginning of its fall to the end.

As this is the meaning of the proposition,
your Lordship will easily perceive, that the
velocity of the last moment must indeed
correspond to the space gone through in
that moment, but cannot correspond to the
space gone through in any preceding moment,
with a less velocity ; and, consequently, can-
not correspond to the whole space gone
through in the last and all preceding mo-
ments taken together. You say very justly,
that, whether the motion be equable or
accelerated, the space gone through in any
instant of time corresponds to the velocity
in that instant. But it does not follow from
this, that, in accelerated motion, the space
gone through in many succeeding instants
will correspond to the velocity of the last
instant.

If any writer in physics has pretended to
demonstrate mathematically this proposi-
tion — that a body falling by gravity in vacuo,
goes through a space which is as the square
of its last velocity ; he must be one who
writes without distinct conceptions, of which
kind we have not a few.

The proposition is not mathematical, but
physical. It admits not of demonstration,
as your Lordship justly observes, but of
proof by experiment, or reasoning grounded
on experiment. There is, however, a ma-
thematical proposition, which possibly an

inaccurate writer might confound with the
last mentioned. It is this — that a body
uniformly accelerated from a state of rest,
will go through a space which is as the
square of the last velocity. ' This is an ab-
stract proposition, and has been mathema-
tically demonstrated ; and it may be made
a step in the proof of the physical proposi-
tion. But the proof must be completed by
shewing, that, in fact, bodies descending by
gravitation are uniformly accelerated. This
is sometimes shewn by a machine invented
by S'Gravesande, to measure the velocities
of falling bodies ; sometimes it is proved
by the experiments upon pendulums ; and
sometimes we deduce it by reasoning from
the second law of motion, which we think
is grounded on universal experience. So
that the proof of the physical proposition
always rests ultimately upon experience, and
not solely upon mathematical demonstra-
tion. — I am, my Lord, respectfully yours,
Tho. Reid.

IX.

EXTRACT OF A LETTER TO MRS DRUMMOND,
AFTER THE DEATH OF HER HUSBAND,
LORD KAMES, IN 1782.

I accept, dear madam, the present you
sent me,*" as a testimony of your regard,
and as a precious relic of a man whose
talents I admired and whose virtues I
honoured ; a man who honoured me with
a share of his conversation, and of his cor-
respondence, which is my pride, and which
gave < me the best opportunity of knowing
his real worth.

I have lost in him one of the greatest
comforts of my life; but his remembrance
will always be dear to me, and demand my
best wishes and prayers for those whom he
has left behind him.

When time has abated your just grief
for the loss of such a husband, the recol-
lection of his eminent talents, and of his
public and domestic virtues, will pour balm
into the wound. Friends are not lost who
leave such a character behind them, and
such an example to those who come after
them.

A gold snuff boy.

62

CORRESPONDENCE OF DR REID.

C— LETTERS TO DR JAMES GREGORY.

I.

Glasqou Crl/cge, April 7, 1783.

Dear Smj— By favour of Mr Patrick
Wilson, our Assistant Frofessor of Astro-
nomy, I send you two more numbers of my
lucubrations.* I am not sure when I can
send more, as I am not sure whether my
scribe may soon leave the College.

I shall be much obliged to you if you will
continue to favour me with your observa-
tions, though I have put off examining those
you have sent until the MSS. be returned,
which I expect about the end of this month,
along with Dug. Stewart's observations. I
have also sent the Genealogy of the Gre-
gories, which your brother left with me :
I suspected that it was more particular than
the copy I had, but I find they agree per-
fectly.

You will please deliver it to him, with
my compliments. The few days he was
here he payed his respects to all the Pro-
fessors and all his acquaintance, and they
are all very much pleased with his appear-
ance. If it please God to spare his life, I
hope he will do honour to his Alma Mater.
and to his friends. -f*

I know not upon what authority the
Edinburgh and London news-writers have
given contradictory accounts of Dr Hun-
ter's settlements.^: There is nothing cer-
tainly known here. I know that, six or
seven years ago, he made a settlement very
favourable to this College. But whether
this is altered, or in what respect, I believe
nobody here knows. But we shall probably
know soon. He was surely a man that did
great honour to his country, and I doubt
not but his publick spirit, which I take to
have been great, will have disposed him to
leave his books, medals, and other literary
furniture — which he had collected at vast
expense, and with great industry — in such
a way as that it may be useful to the pub-
lick.

I beg you to make my best respects to
Mrs Gregory, and to all your family ; and
I am, dear Sir,

Tho. Ekid.

* His " Essays on 'he Intellectual Powers " — H.

t This was the Rev. William Gregory, A. M. of
Ralliol College, Oxford, afterwards Hector of St
Mary's, Bentham, and one of the Preachers of Can-
terbury Cathedral. He had studied at Glasgow pre-
viously to ei tcring at Oxford. — H„

X The celebrated Dr Win Hunter. He bequeathed
his anatomical preparations, library, and collection
of medals, to the University of Glasgow, and a sum
of money for the ereclion of a museum.— H.

II.

Glasgow College, June 8, 1783.

Dear Sir,

I cannot get
more copied of my papers till next winter,
and indeed have not much more ready.
This parcel goes to page 658. I believe
what you have got before may be one-half
or more of all I intend. The materials of
what is not yet ready for the copyer are
partly discourses read in our Literary So-
ciety, partly notes of my Lectures.

Your judgment of what you have seen
flatters me very much, and adds greatly to
my own opinion of it, though authors sel-
dom are deficient in a good opinion of their
own works.

I am at a loss to express my obligations
to you for the pains you have taken, and pro-
pose to take again upon it. I have carefully
laid up the observations you sent me, to be
considered when the copy they refer to is
returned, and I hope for the continuation of
them. The analogy between memory and
prescience is, I believe, a notion of my own.
But I shall be open to conviction on this
and every thing else we may differ about.

I have often thought of what you propose
— to give the History of the Ideal System ;
and what I have to say against it, by itself,
and I am far from being positive that it
stands in the most proper place. Perhaps
it will be easier to judge of this when the
work is concluded. I have endeavoured to
put it in separate chapters, whose titles may
direct those who have no taste for it to pass
over them. But I hope to have your opi-
nion upon this point at more length when
we meet- I observe that Boyle and others,
who, at the Reformation of Natural Philo-
sophy, gave new light, found it necessary to
contrast their discoveries with the Aristo-
telian notions which then prevailed. We
could now wish their works purged of the
controversial part ; but, perhaps, it was pro-
per and necessary at the time they wrote,
when men's minds were full of the old sys-
tems, and prepossessed in its favour. What
I take to be the genuine philosophy of the
human mind, is in so low a state, and has
so many enemies, that, I apprehend those
who would make any improvement in it
must, for some time at least, build with one
hand, and hold a weapon with the other.

I shall be very glad to see you heue, and
will take it as a favour if you acquaint me
when you have fixed your time, that I may
be sure to be at home. I beg you will

LETTERS TO DB JAMES GREGORY

63

make my best compliments to Mrs Gregory,
whom I should be happy to see along with
you in good health, and to Mr D. Gordon,
if he is still with you, and to all your fa-
mily ; and am, dear sir,

Yours most affectionately,
Tho. Reid.

III.

March 14, 1784.

Dear Sir, — I send you now the remainder
of what I propose to print with respect to
the Intellectual Powers of the Mind. It
may, perhaps, be a year before what relates
to the Active Powers be ready, and, there-
fore, I think the former might be published
by itself, as it is very uncertain whether I
shall live to publish the latter.

I have enclosed, in the first of the three
papers now sent, the contents of the whole,
which you was so good as to write out as
far as it was carried last year. I think the
title may be, Essays on the Intellectual Powers
of the Human Mind. It will easily divide
into eight essays, as you will see by the
contents ; but with regard to this, as well
as whether the two parts may be published
Mr Stuart's — (Sic.) Since you have been so
good as to take a concern in it, I apprehend
that the second Part — I mean what relates to
the Active Powers — will not be near so large
as the first. I wish to have the manuscript,
with your remarks and Mr Stuart's, (sic,)
about the end of April, if you can. Dr
Eose at Chiswick — who, you know, has all
along had a principal concern in The
Monthly Review — has made me a very kind
offer, that, if I please to send the MSS. to
him, he will both give me his remarks, and
treat with a bookseller about the sale of it.
I think this is an offer that I ought not to re-
fuse ; and I can have a good occasion of
sending it about the beginning of the month
of May, by his son, who is at this college.
I long to hear how Mrs Gregory has stood
this severe winter, and beg my most humble
respects to her, and to the Rev. Mr Wil-
liam, when you write him.

I send you on the other page an anecdote
respecting Sir I. Newton,* which I do not
remember whether I ever happened to men-
tion to you in conversation. If his descent
be not clearly ascertained, (as I think it is
not in the books I have seen,) might it not
be worth while for the antiquarian branch
of your R. Society, to inquire if they
can find evidence to confirm the account
which he is said to have given of himself.
Sheriff Cross was very zealous about it,

• See Brewster's " Life of Newton," and, ro/r.7,
Reicl's letter to Mr Robison, at the end of his Cor.
respondents. — H.

when death put a stop to his inquiries I

am, dear Sir, yours most respectfully,

Tho. Reid.

When I lived in Old Aberdeen, above
twenty years ago, I happened to be con-
versing over a pipe of tobacco, with a gen-
tleman of that country, who had been lately
at Edinburgh. He told me that he had
been often in company with Mr Hepburn
of Keith, with whom I had the honour of
some acquaintance. He said that, speaking
of Sir Tsaac Newton, Mr Hepburn men-
tioned an anecdote, which he had from Mr
James Gregory, Professor of Mathematics
at Edinburgh, which was to this purpose : —
Mr Gregory being at London for some time
after he resigned the mathematical chair,
was often with Sir I. Newton. One day
Sir Isaac said to him, " Gregory, I believe
you don't know that I am connected with
Scotland." " Pray, how, Sir Isaac ?" said
Gregory. Sir Isaac said — " He was told,
that his grandfather was a gentleman of
East Lothian ; that he came to London with
King James at his accession to the Crown
of England, and there spent his fortune, as
many more did at that time, by which his
son (Sir Isaac's father) was reduced to mean
circumstances." To this Gregory bluntly
replied — " Newton, a gentleman in East
Lothian ? — I never heard of a gentleman of
East Lothian of that name." Upon this
Sir Isaac said, that, being very young when
and it might be a mistake ; and imme-
diately turned the conversation to another
subject.

I confess I suspected that the gentleman
who was my author had given some colour-
ing to this story ; and, therefore, I never
mentioned it for a good many years.

After I removed to Glasgow, I came to
be very intimately acquainted with Mr
Cross, the Sheriff of Lanerick, and one day
at his own house mentioned this story with-
out naming my author, of whom I expressed
some diffidence. The Sheriff immediately
took it up as a matter worth being inquired
into. He said he was well acquainted with
Mr Hepburn of Keith, (who was then
alive,) and that he would write him, to
know whether he ever heard Mr Gregory
say that he had such it conversation with
Sir Isaac Newton. He said, he knew that
Mr Keith, the ambassador, was also inti-
mate with Mr Gregory, and that he would
write him to the same purpose. Some time
after, Mr Cross told me, -that he had
answers from both the gentlemen above-
mentioned, and that both remembered to
have heard Mr Gregory mention the con-
versation between him and Sir Isaac New-
ton to the purpose above narrated ; and at
the same time acknowledged that thev had

64

CORRESPONDENCE OF DR RKID.

ter.

Mr Cross, however, continued in the
inquiry ; and, a short time before his death,
told me, that all he had learned was, that
there is, or was lately, a baronet's family
of the name of Newton in West-Lothian,
or Mid-Lothian, (I have forgot which;)
that there is a tradition in that family that
Sir Isaac Newton wrote a letter to the old
knight that was, (I think Sir John New-
ton ' of Newton was his name,) desiring
to know what children, and particularly what
sons he had ; their age, and what profes-
sions they intended. That the old baronet
never deigned to return an answer to this
letter, which his family was sorry for, as
they thought Sir Isaac might have intended
to do something for them.

IV.

Dear Sib, — Happening to have gone into
the country a little way, your letter of 5th
June did not reach me in time to write you
before you set out upon your journey, which
I wish to be attended with much happiness
to the parties, and comfort to their friends. •

I was so stupid at first as to misunder-
stand the direction you gave me how to
write you. Now I see it is plain enough,
and I hope have taken it right. I send you
the enclosed to Dr Rose, as you desire.

I have by me our friend D. Stewart's
" Discourse on the Ideas of Cause and
Effect," &c. ; and I have this day sent him
my remarks upon it. I am happy to find
his sentiments on that subject agree so
much with my own. I think it well wrote,
and hope it will be very useful.

Dr Rose will shew you the letter I wrote
to him along with the MSS., and one from
Mr Bell+ to me, which I enclosed in it :
these contain all the information I have to
give, and all the instructions I thought
necessary. I expect an answer from one
quarter, at least, before the work be cold from
the press. But the only answer that shall
ever have any reply from me must be one.
who keeps good temper, and who observes
good manners, in the first place ; and next
one who, in my opinion, gives new light to
the subject.

I wish you happy success in your own
affairs, and a safe return. If nothing hap-
pens of which you wish to acquaint me
sooner, I shall be glad to hear from you on
your return ; being, dear sir,

Most affectionately yours,

Tho. Reid.

Glasgow Coll 1784.

• This alludes to the marriage of Dr Gregory's
eldest sister to the Kev. Archibald Alison.— H.
J Ihc publisher — 11.

[ The letter quotr.il above by Mr Stewart,
(/>. 34) " to one of Dr Jleid's most intimate
friends,* 1 was addressed toDrJame.-t Gregory
on the death of his first wife, and should
properly here find its place. — H. ]

V.

ON THE MEANING OF NOTION.

Glasgow College, December 31, 1784.

Dear Sir, — I had the favour of yours by
Mr Tower, and take the opportunity of his
this season.

I believe you and I cannot differ about
right or wrong notions, but in words.

The notions we have of real existences,
may with good reason be said to be right or
wrong, true or false ; but I think every
notion of this kind has a standard to which
I believe my notion to agree ; and as that
belief is true or false, so my notion of the
thing is true or false. For instance, if my
notion of the Devil includes horns and cloven
feet, I must believe these to be attributes
of the Devil, otherwise they would not be
included in my notion of him. If this be-
lief be wrong, I have a wrong notion of him ;
and, as soon as I am convinced that this
belief is wrong, I leave out these attributes
in my notion of him.

I may have an abstract notion of a being
with horns and cloven feet, without apply-
ing it to any individual — then it is a simple
apprehension, and neither true nor false ;
but it cannot be my notion of any indivi-
dual that exists, unless I believe that being
to have these attributes. I am therefore
still apt to think that true and false can only
with propriety be applied to notions which
include some belief; but whether my re-
mark on your use of the word notion be just
or not, I cannot presently say : you will
judge for yourself.

I thought to have seen D. Stewart here
acquaint him that I have made my remarks
upon the performance he left with me. I
am extremely obliged to you and him for
correcting the sheets of my performance.
You leave me very little to do.

By the slowness of printing, I conjecture
that the book cannot be published next
spring, and can only be ready for the spring
1786. I desired long ago to know of Mr
Bell whether he proposed to publish it in
one vol. or two ; but I have not had an
answer. I suspect it will be too thick for
one vol. and too thin for two. Perhaps if
the publication is delayed to 1786, 1 might
have my Essays on the Active Powers
ready, of which Mr Bell shall have the first
offer; and I apprehend that, with this

LETTERS TO DR JAMES GREGORY.

( ; 5

(Edition, there may be two sizeable 4tos in
the whole. — I am, dear Sir,

Yours most affectionately,

Tho. Reid.

VI.

Dear Sir, — I send you enclosed what I
propose as the title-page of my essays, with
an epistle, which, I hope, you and Mr
Stewart will please to allow me to prefix to
them.

Whether your name should go first, on
account of your doctor's degree, or Mr
Stewart's, on account of his seniority as a
professor, I leave you to adjust between
yourselves. *

As to the title-page, you and he may
alter what you think fit,t and deliver it to
Mr Bell without farther communication
with me, as he intends immediately to ad-
vertise the book.

If you find anything in the epistle that
you would have altered or corrected, you
may please write me; but you need not
send back the copy, as I have a copy by me.

I know not how to express my obliga-
tions to you and Mr Stewart for the aid

you have given me I am, dear Sir, your

most obliged servant,

Tho. Reid.
May 2d, 1785,

Glasgow College.

You will give the epistle to the printers
when it is wanted. I send with this the
last part of the MS.

VII.

MEANINGS OP CAUSE — MOTIVE — LAW OF
NATURE.

June 14, 1785.
Dear Sir, — I am extremely obliged to
health. For two days past, I have had
almost nothing of my ailment, which I
ascribe to some exercise I have taken, and
to a comfortable warmness in the air. I
resolve to try some short excursions, which
I can make either on foot or in a chaise.
If that do not produce the effect, I shall
fall to your prescriptions, which I think
very rational. I very probably may be at
home when you propose to be in Glasgow.

* In the MS. dedication of the " Essays on the
Intellectual Powers," Dr Gregory's name 6tands
before that of Mr Stewart. This order was, probably
by Dr Gregory himself, reversed. There are ,also
some verbal improvements in the style of the dedica-
tion, as it stands printed, which, it is likely, were
introduced hy Dr Gregory or Mr Stewart.— H.

t The title sent was, " Essays on the Intellectual
Powers of the Human Mind," or, " Essays on the
Intellectual Powers of Man." The latter was pre-
ferred.— H.

matically, the difference between the rela-
tion of motive and action, and the relation of
cause and effect," is, indeed, so new to me,
I shall offer some of my thoughts on the sub-
ject of those two relations. Whether they be
favourable to your speculation, or unfavour-
able, I cannot immediately determine.

The word cause, is very ambiguous in all
languages. I have wrote a chapter lately
upon the causes of this ambiguity. The
words power, agent, effect, have a like am-
biguity ; each different meaning of the first
mentioned word leading to a corresponding
meaning of the three last. A reason, an
end, an instrument, and even a motive, is
often called a cause. You certainly exclude
the last from what you call a cause.
Whether you exclude all the other meanings
which I think improper meanings, I am not
so sure.

In the strict and proper sense, I take an
efficient cause to be a being who had power
to produce the effect, and exerted that power
for that purpose.

Active power is a quality which can only
be in a substance that really exists, and is
endowed with that power. Power to pro-

Online LibraryThomas ReidThe works of Thomas Reid, D.D.; now fully collected, with selections from his umpublished letters → online text (page 16 of 114)