140 Notices respecting New Books. 
tained by all bodies in the same manner and proportions, as 
caloric, what difference can we state as existing between them, 
except that motion, by which, whenever possessed by caloric, 
bodies are rendered visible ?”’ 
“ Bodies are luminous by light emitted: they are vistble by 
light reflected from them.’’—“ Ifa red-hot ball be placed in 
the focus of a concave mirror, both the light and the caloric will 
be reflected by the mirror, and may be collected by an opposite 
mirror and again reflected, in the same manner as caloric has 
been before described.” —* Bodies are seen by the light which 
they themselves attract.”’ In preof of this—‘‘ their colour arises 
from the nature of the light which impinges on them. Thus 
a coloured ray, separated by the prism, or other meaus, gives its 
own hue to every object on which it is thrown. If therefore 
bodies had no influence in regulating the nature of the ray of 
light which should approach them to be reflected to produce vi- 
sion, their colour would always depend upon, and vary with, 
their situation. This, however, i is shown by every moment’s ob- 
servation Hot to be the fact. The experiments last referred to, 
are directly adverse to the theory suggested by Sir Isaac Newton 
on thé subject. He supposed, that all the rays that fell upon any 
body might be absorbed, except that part which formed its co- 
lour ; and the reflection of that part of the ray, rather than any 
other, he suggested, might arise from the di fference in magnitude 
of the particles of light. If this hypothesis were just, a sepa- 
rated coloured ray ought to be wholly absorbed by every body 
not of the same colour, instead of giving them a tinge unnatural 
to them. Upon that theory too, no part of a ray of light ¢ould 
be reflected more than once between bodies of different colours ; 
and every kind of body, except that which absorbed the smallest 
particles, would reflect, on account of their magnitude, smaller 
particles than those which it received. The division of the solar 
ray, however, by that truly wonderful man, has been the chief 
discovery yet made respecting the nature of light, and the most 
probable guide to all others which may be made in future.” 
In the third section of Chap. II. the aim of the author is to 
show that light is a compound ethereal fluid composed of only 
two simple fluids, combined in different proportions according to 
circumstances : and that caloric is another modification of the 
same compound ethereal substance. We cannot convey an ade- 
quate idea of the arguments by which this is enforced, but by in- 
serting it entire, which we shall do as soon as we can make room 
for it. 
On Electricity, the conclusion of the author is, that the two 
kinds of electricity which are known by the names of negative 
and positive are, in their combined state, identically the same 
fluid 
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