FRICTION. 
Nences are the greater, and the fubftanee the harder : ae 
as the body, by tear ng » becomes more and m 
polifhed, the friétion dim 
Hence it follows, sine oF es of the parts of ma- 
chines that touch each other fhould be as {mooth and po- 
However, | itis ner d by ay that 
¢ bodies - may o far 
to increafe fri be caufe the attr. son of 
cohefion become ee as we ae ing the fue aces of bodies 
nearér affd nearer: nta&. But, as no bod n be fo 
much pelifhed, as ace to take away all eae 3 ee 
thofe numerous ridges difcovered by the microfcope on the 
fmoothell furfaces ;  hetice arifes the neceffity of anointing 
the ee that touch with oil, or fome other fatty matter. 
io} 
ox, Laws of. 1. As the weight-o of a body moving 
tICT 
on anode is increafed, fe: ue friction 
This we fee exper ver cntally in a ba lance e, which, when 
only charged with a {mall ise hoe eal ily turns ; but with a 
greater, a greater force 18 require 
ee if the line of diretion of a moving body ‘be ob- 
lique ‘to ite urface moved on, the friCtion i is the cee 
‘this having the fama ign as an increafe of weight. 
And h s a perpendicular flicks e or impreffion 
one, as the whole fine to the fine of the 
incidence; and the fine of a greater angle is 
greater, and that of a leffer lefs ; the fei is the ei 
lin 
the line of dire€tion approaches nearer to a pérpen- 
al 
This is eafily servecllaue and efpecially in the teeth of 
wheels, oe are frequently broke on this very account. 
The fri on, ne Ae is istaken away, if an line of seapaics 
ody that rolls than it would 
e to 6 fide. as is eafily demonftrated. 
For fuppofe a dented pine A B, Plate XXIX. 
fuppofea wheel D E to move along with it, wit 
: he 
were to flide, the tooth’ F, when it touched the ruler, would 
defcribe a right line on: its furface, and, asthe tooth of the 
shea H refifts the fame, it could not apc without re- 
ing or breaking either the oars H, or that at F. And 
a ae will hold in thé fliding any rough farface upon 
another, where the oie friction will take place that can 
any way arife from the roughnefs of the fu ee But if 
the wheel ED roll along the ruler, then the tooth H will 
no longer refift its motion, an as it is to des hoifted out of 
the cavity F over the eminence of the tooth H ; aid thie 
ame holds in oe rubbing a any rough “ere overt the fur- 
face of anot 
- Hence, in machines, left oe debate fhould e mploy a 
ow S ken, eh rio . et 
n be ed ; 
as is ufually done, ina fo or cotcavé matrix, but be- 
tween little a A ie fg. 2. moveable on .their re- 
contrivance, the friGtion: i is tranf. 
and rther, by a2 
the axles of thofe wheels reft upon other frigtion 
whe ele that turn round with them. This was long-ago re- 
conimended ‘by P. Cafatus ;. and. experiefice confirms, that 
we fave much power by it. Hence-alfo it is,, that-a: pulley 
aa on its axis refilts lefs than if it were fixed. An id 
re the fam may be epiens of the wheels of ‘coaches, and. 
-other carriages. 
From thee nike with a little farther help from the 
hi igher geometry, | Olaus Roemer determined the figure ’ of. 
the teeth of wheels, that fhould make the leaft refiftance 
poffible, and which fhould be epicycloidal. And the fame 
was balla ey lags by De la Hire. See WHEELS 
and WreeLt-Car 
Hei 
nee in ‘a wing » mills, the fides of the wooden rectangle: 
‘the faws are fitted - into ° fhould be furnifhed with rotule, or 
little wheels, which would greatly leffen the fri@tion; and. 
the like in other cafes. 
; eg Galculation of oe Quantity of. The fri€tion is 
a: point e -utmoft im mpo machines; and by all . 
means to be contidered in aut their force : yet it is. 
generally ov sce in fuch ealc ulation : but this is Dalen 
cipally becaufe its precife value t kn own. It i 
yet reduced to certain.and infallible rules ; fince it depends 
upon the ftru€ture.of bodies, the form o romitient 
parts and cavities, and upon their rigidity, their feeee le 
heir ee and other circumftances. c 
metho ely: to compute the rere Ww. 
moving ce ls from the: machine ; either on account of 
its diftance from a fixed point ; or of- the dir rectio 
it ats. And in all the demonttrations it is fu 
the furfaces of bodies are perfeGtly {mooth and’ ‘polled. 
Indeed the engineers expect, that: in the practice they fhould 
lofe part of the.advantage ‘of their force by the friction s: 
but how ~~ it is. fappofed, nothing: but = praétice can 
determin montons, indee ‘de PAcad.. 
h Royale ie Sciencés 1699), has ‘made an ene t to fettle, 
by experiment, a foundatiom for the precife. eee of. 
the quantity of a aes and OMe ore has onfirthed 1 it 
r the re elitacce oppofed to the motion of a 
el furface, Nepends on oe weight, 
which they bear on each other 
of y 
thick be oad and ther reby tea 
face of anc 
exaéily fit t 
other fixed piece of the fn wood, it. wil acqiiiré 
gale is paribus ), 
weight bearing on tho 
four t rae hee number. pliphed by = 
toto number multiplied by tour times the weight,. it 
is plain that the effect, that is, the refiftance, i8 ‘equal:ir in Botli, 
cafes,- and therefore requires the fame: force to a ats. 
Upon the firft propofal of this paraddx, M. de la- ‘Hite. 
had ae to experiments, wee fucceéded | awe j in fa-. 
vour of the new fyftem, He lat 
0 
pli ed’ to them by a little pulley, was anes to’ put each 
iin motion, notwithitanding: ‘all the: i equality of the fir. 
faces. The experiment fucceeded in oe fa sy “Manner it. 
pieces of marble, laid’ on'a’ marble table. U-pon this Ld | 
‘la Hire 
