Radiating and Absorbing Powers. 307 



middle between the two chambers as before, with its coated 

 side turned towards the bright side of the cylindrical chamber 

 and its bright side towards the coated surface of the other 

 chamber, fill it with hot water, and the liquid in the stem will 

 be found to remain perfectly stationary- The reason of this 

 beautiful result is equally obvious: From the coated surface of 

 the canister we have a copious flow of radiant heat, suppose 

 ten times as much as from the metallic surface, which falls 

 on a surface of feeble absorbing power, which we shall sup- 

 pose takes in only one part out of ten of the whole radiant 

 stream ; from the other side of the canister we have only a 

 very small portion of radiant heat, which we suppose equal to 

 one, which portion is absorbed by the coated surface of the 

 chamber, and rapidly conveyed to the included air ; and, since 

 the effect on both chambers is the same, we conclude the 

 radiating and absorbing powers are exactly equal to each other. 

 If the surfaces be scratched or coated with other substances, 

 the same law will be found uniformly to obtain. The instru- 

 ment which I have described is not only useful for the striking 

 illustration of this fact in the lecture-room, but, with slight 

 variations, may be successfully employed for illustrating the 

 whole theory of radiant heat. 



ON THE PENETRATIVENESS OF FLUIDS. 



By J. K. MITCHELL, M.D., Lecturer on Medical Chemistry in the 

 Philadelphia Medical Institute. 



[Continued from page 118.] 



HAVING completed ihejirst series of experiments on molecular infil- 

 tration, before entering upon an account of the second, reserved for 

 the next number of the Journal, it may be refreshing both to experi- 

 menter and reader, in a very toilsome investigation, to pass in cursory 

 review some of the almost infinite theoretic and practical sugges- 

 tions, which flow from the facts before us. 



The most striking generality, is that of the high power of penetra- 

 tiveness of gases for organic molecular tissue, long known to be in- 

 filtrable by liquids ? but until now not generally known to admit of 

 any permeation, by at least, insoluble aeriform substances. 



