COHESION. 
bodies, which touch one another, cohere 
with a great force ; to account for which, 
some philosophers have recourse to a kind 
of hooked atoms, which in etfect is nothing 
else but to beg the thing in question. 
Others miagine that the particles of bodies 
are connected by rest, i. e. in effect by no- 
thing at all ; and others by conspiring mo- 
tions, i. e. by a relative rest among them- 
selves. For, myself, it rather appears to 
me that the particles of bodies cohere by 
an attractive force, whereby they tend 
rautuqlly toward each other ; which force, 
iti the very point of contact, is very great ; 
at little distances is less, and at farther 
distances is quite insensible.” 
But whatever the cause of cohesion may 
be, its effects are evident and certain. The 
different degrees of it constitute bodies of 
different forms and properties. Thus, New- 
ton observes, the particles of fluids which 
do not cohere too strongly, arid are small 
enough to render them susceptible of those 
agitations which keep liquors in a fluid state, 
are most easily separated apd rarefied into 
vapour, and make vyhat the chemists call 
volatile bodies ; being rarefied with an easy 
heat, and again condensed with a moderate 
cold. Those that have grosser particles, 
and so are less susceptible of agitation, or 
cohere by a stronger attraction, are not 
separable without a greater degree of heat ; 
and some of them not without decompo- 
^ition. 
Moderp chemi^s have agreed to consider 
the attraction of cohesion as the instrument 
of aggregation, or the union of similar com- 
pounds, and are careful not to confound it 
with the elective attractions, though there 
may, in strictness, be no difference betvyeen 
tliem. See CpEiqiSTRY. 
This kiqd of attraction is evinced by 
a variety of familiar experiments ; as, by 
the union of two contiguous drops of mer- 
cury ; by the mutual approach of two pieces 
of cork floating near each other in a bason 
of water; by the adhesion of two leaden 
balls whose surfaces are spraped apd joined 
together with a gentle twist, which is so 
considerable, that if the surfapes are about 
a quarter of an inch in diameter, they will 
not be separated by a weight of 10016.; by 
the ascent of oil or water between two 
glass planes, so as to form the hyperbolic 
curve, when they are made to tquch on 
one side and kept separate at a small dis- 
tance on the other ; by the depression of 
mercury, and by the rise of water in capil- 
lary tubes, and on the sides of glass vessels i 
also in sugar, sponge, and all porous sub- 
stances. And where this cohesive attrac- 
tion ends, a power of repulsion begins. 
It is uncertain in what proportion this 
force decreases as the distance increases: 
Desagulieis conjectures, from some pheno- 
mena, that it decreases as the biquadratic 
or 4t!i power of the distance, so that at 
twice the distance it acts 16 times more 
weakly, &c. 
To determine the force of cohesion, in a 
variety of different substances, many expe- 
riments have been made, and particularly 
by professor Muschenbroek. The adliesion 
of polished planes, about two inches in 
diameter, heated in boiling water, and 
smeared with grease, required the following 
vy'eights to separate them ; 
ColdGrease. IIotGrease. 
lb. lb. 
PlanesofGlass ,.130...., 300 
Brass 150 800 
Copper 200 850 
Marble 225 600 
Silver 150 250 
Iron... 300 950 
But when the brass planes were made to 
adhere by other sorts of matter, the results 
were as in the following table : 
"-.x 
With Water 12 
Oil 18 
Venice Turpentine 24 
Tallovv Candle 800 
Rosin 8,50, 
Pitch 1400 
In estimating the absolute cohesion of 
solid pieces of bodies, he applied weights to 
separate them according to their length : 
his pieces of wood vvere long square paral- 
lelopipedons, each side of which was .26 of 
an inch, and they were drawn asunder by 
the following weights ; 
lb. 
Fir 600 
Elm 950 
Alder 1000 
Linden tree 1000 
Oak 1150 
Beech - 1250 
Ash 1250 
He tried also wires of metal, l-lOtli of a 
Rhinland inch in diameter : fhe metals and 
weights are as follovy : 
lb. 
Of Lead 29Jr 
Tin 40i 
Copper 299i 
