ATTRACTION. 
equinoxes is defective in several respects. 
He has perfectly established the principle 
which he had discovered ; but left the com- 
plete development of its consequences to 
the geometers that should succeed him. 
The profound analysis also, of which he 
was the inventor, had not been sufficiently 
perfected, to enable him to give complete 
solutions to all the difficult problems which 
arise, in considering the theory of the sys- 
tem of the world ; so that he was oftentimes 
obliged to give only imperfect sketches or 
approximations, and leave them to be veri- 
lied by a more rigorous calculation. 
Attraction may be divided, with respect 
to the law it observes, into two kinds. 
1. That which extends to sensible distances, 
such is the attraction of gravity, of which 
we have been treating, which is found in all 
bodies, and the attraction of magnetism 
and of electricity found in some par ticular 
bodies; S. That which extends to very 
small, or insensible distances. 
The attractions belonging to the first 
class must be as numerous as there are bo- 
dies situated at sensible distances. It has 
been proved that their intensity varies with 
the mass and the distance of the attracting 
bodies ; it increases with the mass of 
those bodies, but diminishes as the distance 
between them increases. The rate of va- 
riation has been demonstrated .to be in- 
versely as the square of the distance in all 
cases of attraction belonging to the first 
class. 
The nature of the attraction of gravity 
has been already discussed. It is, as far as 
the experience of man can extend, univer- 
sal in all matter. The attractions of mag- 
netism and of electricity are partial, being 
confined to certain sets of bodies, while 
the rest of matter is destitute of them ; for 
it is well known that all bodies are not elec- 
tric, and that scarcely any bodies are mag- 
netic, except iron, cobalt, nickel, and chro- 
mium ; and there is good reason to suspect 
that the magnetism of the three latter sub- 
stances is caused by their containing some 
iron united to them. 
The intensity of these three attractions 
increases as the mass of the attracting bo- 
dies, and diminishes as the square of the 
distance. 
The first extends to the greatest distance 
at which bodies are known to be separated 
from each other. How far electricity ex- 
tends has not been ascertained ; but mag- 
netism extends at least so far as the semi- 
diameter of the earth. All bodies possess 
gravity ; but it has been supposed that the 
other two attractions are confined to two 
or three subtile fluids, which constitute a 
part of all those bodies that exhibit the 
attractions of magnetism or of electricity. 
If we compare the different bodies acted 
on by gravitation, we shall find that the ab- 
solute force of their gravitation is in all 
cases the same, provided their distances 
from each other, and their mass be the 
same ; but this is by no means the case with 
electrical and magnetic bodies : in them the 
forces by which they are attracted towards 
each other, called electricity and magne- 
tism, are exceedingly various, even when 
the mass and the distance are the same. 
Sometimes these forces disappear almost 
entirely ; at other times they are exceed- 
ingly intense. 
Gravity, therefore, is a force inherent in 
bodies ; electricity and magnetism not so ; 
a circumstance which renders the opinion of 
their depending on peculiar fluids extreme- 
ly probable. If we compare the absolute 
force of these three powers with each other, 
it would appear that the intensity of the 
two last, every thing else being equal, is 
greater than that of the first ; but their re- 
lative intensity cannot be compared, and is 
therefore unknown. Hence it follows that 
these different attractions, though they fol- 
low the same laws of variation, are not the 
same in kind. 
The attractions between bodies at insen- 
sible distances, have been distinguished by 
the name of affinity, while the term attrac- 
tion has been more commonly confined to 
cases of sensible distance. 
Affinity may be considered as operating on 
homogeneous or heterogeneous substances. 
Homogeneous affinity urges substances of 
the same nature together as iron to [iron, 
soda to soda. Heterogeneous affinity draws 
substances of different nature into union, as 
acid and alkalis. 
Homegeneous affinity is usually denomi- 
nated cohesion, and sometimes adhesion 
when the surfaces of bodies are only referred 
to ; it is nearly universal ; as far as is known, 
caloric and light alone are destitute of it. 
Heterogeneous affinity is the cause of the 
formation of compound substances; thus 
muriatic acid unites with soda, and forms 
sea-salt; and sea-salt in saturated solution is 
united into masses by homogeneous affinity. 
Heterogeneous affinity is universal as far as 
is known ; that is to say, there is no sub- 
stance which is not attracted by some other 
subs lance. It is generally taken for grant- 
