i 
40 British Association for the Advancement of Science. 
pared, in other respects, before we can estimate the effects really 
due to the state of the surface, he must, of course, be understood 
to speak under the qualification acutely whawed to by Prof. Bache, 
dependent on the fact noticed by Leslie, that radiation takes place 
not only from the surface, but from a certain minute, though sen- 
sible depth, which differs in different substances. 
aking this into account, the general meaning, as well as im- 
portance of the caution, will be manifest. In the sequel, Mr. 
Bache gives some very precise experimental proofs of the truth 
of the law just noticed, and shows, by successively adding fresh 
coats of the pigment, the precise limit beyond which such addi- 
tion ceases to increase the radiating power,—which, in fact, there 
comes to a maximum, and with greater thicknesses decreases. 
When this point had been ascertained carefully for each pig- 
ment, their effects were observed with great accuracy, and com- 
pared with a standard surface under similar circumstances; the 
observations include a considerable range of substances, diflering 
both in color and other properties. The results exhibit no cor- 
respondence of the greatness of effect with the color. he source 
of heat was hot water:—the author allows fully the distinction 
between properties of heat of this kind, and that connected with 
light ; in the latter case it is evident that color is an essential ele- 
ment ; a wide field is yet open for tracing on what the effect does 
: and again, since Melloni has pointed out the existence 
of many kinds of heat, differing in their relations to screens, to 
trace also their different relations to surfaces. 
Uric Acid and Urea, by Prof. Liebig—The important part 
which uric acid performs in the animal economy, has for a long 
time attracted the attention of the most distinguished physicians 
and chemists. Uric acid forms in one class of animals the whole 
of the excrement, and in another class it is its principal constitu- 
ent, and it is accompanied by urea, a never-failing constituent of 
the human urine. Its extraordinary production in that morbid 
state of the body, which we call a predisposition to gout, is well 
own to give origin to one of the most painful diseases to which 
is liable. It may be affirmed with the utmost certainty, 
that urea and uric acid are products of the organization. We 
ann t discover their existence in any part of our food, nor do 
hey itute a part of any organ, as fibrine does of the blassls 
nis a oh a 
