= 
Poh ‘aes two kinds, t 
being dragged over another, and that which is occafioned 
by one body rolling over another. The refiftance in the 
firft eafe is greater than that in the fecond; and it appears 
from the experiments of Mufchenbroek nd others, that 
ody is carried along w 
conirme 
rubbing bo body, t to an quantit 
it increafed cs an faeeale of lea, bes was not 
portioned to the augmentation of celerity. He found alfo 
that the friction of -{mooth foft wood, moving upon fmooth 
foft wood, was aes to § of the weight ; of rough wood 
% of the weight ; of foft woo 
3 
fteel upon copper, 4, a 
the wei nae 
abou 
it. be rough, the friction is Titde 
lefs than half the w aes on the fame fuppofition, _ 
both the pieces of w are very {mooth, the friction 
about uae of the weight ; the friétion of foft ocd 
f hard wood upon foft, is one-fifth or one 
third of the v weight ; 
0 
e obiee rves in general, that metals of the 
fame fort have more friction than thofe of different forts ; 
that lead makes much refiftance; that iron or fteel running 
in brafs makes the leaft fri€tion cf any ; and that metals oiled 
make the friction lefs than w yhen polifhed, and twice as little 
onf, 
exhibiting the friction between various ee formed 
from his experimentsin Def. Exp. Phil. vol. i. p. 193. See 
alle his seas : the ee oF a Caring &e. 
8—46 
tion by the foregoing principles ; aes P 
rubbing part, the friétion ther 
re is fare jet or ena with regard 
to-which different perfons have formed fuch various -eenclun 
TO ance thana bis: : but a 
. have been rai 
CTION. 
fions, {6 that the nature and laws’ of frigtion are not yet 
ane clear and eee It is granted that the preflion 
has a effect, and is many cafes, the only thing te 
be va see in aon 3 eae it will be hard to ileal 
us ran to exclude the confideration of: the fur 
If two bodies; with plain furfaces, ieenees fey 
hard, ‘and = be moved along each o e .fric- 
tion will be none, or infinitely {mall ; but if, a vhs eu of 
fuch fappofton, which has no place in in nature, we fup- 
pole two ae ies, with rough, uneven furfaces, the diffi- 
ng one o ve 
at the parts muft be broken, and worn off ; or 
In the firft — rato ( of. raifing one of the bodies: 
makes that of the motion ; and of confequence the friGion 
arifes wholly fr om the weight,.or preffion ;. and the furface 
has nothing to do: in,it.- 
In the fecond cafe, the magnitude of the furface would’ 
be all; were it poffible this fecond cafe could ae ae lut oy 
abftracted from the firft, 2 e& could t of on 
body be rubbed and worn againft ge ae ne other,. 
without raifing one of them ;: it ie ene that a greater: 
mber of parts to be broken wou ea greater refiit- 
sin pra never rub, or grind,. 
without raifing the body, the reliance arifing from the: 
greatnefs of the furface in the fec cafe, is always com- 
bined with that from the preffion ; ae in the former 
aie arifing from the preffion | may be alone and uncom-- 
d 
Add, that what is — sale eae oe is ordinarily very~ 
little, with regard to the great number mes the body mutt’ 
ed durin the fridtion, nd al the little heights 
one ' together, which the body mut. have been-rarfe 
ince as the refiftance from preffion may be fingle ; and. 
as the fame a always accompanies. that arifing from the mags - 
the more con- 
e twos when it does accompa ay: 36 ; = arn 
are mad ey it is 
eae moft 
one perceived, at the ‘only one. that. needs to - ve onth 
dered.. 
But then, as-it is poffible, in certain cafes, for the pref- 
to be very pace and the number of parts to be rub-.- 
ery great;. it muft be owned there are cafes wherein ad 
fition| follows, zee fenfibly, the proportion of the 
"The fubje& of friction is of fuch importance in its rela- 
tion to the conftruétion and ufe of various machines, that 
we think it needlefs to make any Pople for extending this~ 
icle,. fo as e more recent facts and ‘ob-~ 
fervations, which may oie thofe w me-- 
diate 
r 
d communicated to the Royal ee an elabo- 
rate paper, containing a great number of experiments and of © 
oe that are deduced from them,.which merit ita : 
A. minute detail ‘would far exceed our = Sy: 
of the whole 
oun 
friétion of hard bodies in motion is an: unifor ormly ret 
- force ;_and that the any of ‘it is .confidered as suis . 
