211 
487. But if it were granted that the refraction and 
extinction of certain rays depended on some power 
which resembled electro-chemical attraction, yet the 
admission of such a power would not explain the 
phenomena of reflexion. Hence, should we admit, 
says M. Haliy, the existence of an affinity between 
light and the particles of matter, we should still be 
embarrassed in reconciling the repulsive force, which 
reflexion indicates, with affinity, which is an attrac- 
tive force *. 
488. If, however, we call to mind the motions 
that arise in bodies submitted to electrization, in 
which we observe attractions and repulsions not only 
to succeed each other with great rapidity, but fre- 
quently to exist together, we can have no difficulty 
in conceiving that certain rays may be refracted and 
extinguished in bodies, at the same time that others 
are reflected. Sir Isaac Newton himself, indeed, 
considered reflexion to be caused, not by the solid 
parts of bodies, but by some subtile matter which in- 
tercedes their pores f ; and surely all the phenome- 
na of electricity and of magnetism lead us to believe, 
that, where repulsion is ascribed to -such a power, 
the corresponding attraction must be attributed to 
the exertion of a similar force. " Do not bodies 
and light," says Newton, " act mutually upon one 
another, that is to say, bodies upon light, in emitting, 
reflecting, refracting, and inflecting it, and light upon 
bodies in heating them ?" &c. " And do not the rays 
* Traite dc Phys. torn. ii. p. 26-*. 2d edit. 
f Optics, B. ii. part 3. prop. 8. 
o 
