418 A new Theory of Light. 
fluates, and of their being compounds of oxides, with an 
acid containing oxygen, that acid, according to the law of 
definite proportions, must contain more oxygen in pro- 
portion to its quantity of inflammable matter than water ; 
which is highly improbable, and contrary to all analogies. 
Dr. Wollaston has found, that the fluoric combinations 
have very low powers of refracting light, and particularly 
the pure fluoric acid ; so that the refracting powers of fluo- 
rine will probably be found lower than those of any other 
substance, and it appears to possess higher acidifying and 
aturating powers than either oxygen or chlorine. 
It is easy to perceive, in following the above theory, that 
all the ideas current in chemical authors respecting the 
fluoric combinations, must be changed. Fluor spar, and 
other analogous substances, for instance, must be regarded 
_ as binary compounds of metals and fluorine. 
Many objects of inquiry arise, likewise, from these new 
views: the topaz contains the fluoric principle ; but new 
experiments are required to show whether that gem is a 
true silicated-fluate of alumina, ora compound of the in- 
flammable bases of alumina and silica with fluorine. 
I have ascertained that the chryolite yields no silicated 
fluoric gas, when acted on by sulphuric acid; but merely 
pure fluoric acid: but I have not continued the research so 
far, as to determine whether it contains fluorine united to 
inflammable matter only, or fluorine and oxygen. 
LXIX. A new Theory of Light ; with Experiments to prove 
that Blackness arises from the Reflection of Indigo and 
Red-orange on the seven prismatic Rays of Light. By 
_JoespH READER, M.D. 
To Mr. Tilloch. 
srx,— On locking over my library, I find that Sir Isaac 
Newton took his ideas of blackness or darkness from Des 
Cartes, who observed * ‘‘that black suffocates or extin- 
guishes the rays that fall upon it; whereas white reflects 
them.” Mr. Boyle taking up this opinion says, ‘* Many 
learned men supposed that snow affects the eyes not by a 
borrowed light, but by a native one; but having placed a 
quantity of snow in a room, from which all foreign light 
was carefully excluded, neither be nor any other person 
could perceive it.”. To try whether white bodies reflect 
more light than others, he held a sheet of white paper in a 
* Dioptricks, p. 50, sae 
=F suns 673 
