Physics. 267 
SCIENTIFIC INTELLIGENCE. 
I, PHYSICS. 
1. On the passage of radiant heat through polished, rough, and smoked 
rock-salt, and on the diffusion of rays of heat—H. Knosiavcn has con- 
tributed a very elaborate and valuable investigation of the transmission 
of radiant heat through rock-salt. e give the results in the author’s 
own words, referring the reader for details of apparatus and methods to 
the original memoir. 
I. (1.) Clear chemically pure rock-salt permits rays of heat of all 
kinds to pass through it in equal proportion, whether the difference be- 
lasses. 
henomena can not be referred (with Forbes) to an absorp- 
; nor (with 
Melloni) to an unequal dispersion in the rough and cloudy media de- 
pending on the heat-color, by which the rays are more or less deviated 
from the thermoscope. Neither is the roughness of the surface in itself, 
nor the direction of the rays proceeding from a single point the deter- 
mining condition. 
(4.) The diffuse heat arising from radiation through rough or cloudy 
Screens or reflection from rough surfaces radiates more abundantly through 
diffusing screens according as (a) the rays are more diffuse, (6) in com- 
Parison with parallel rays, as the screens are more diltusive. 
Yariously radiated from a greater or less number of points. 
(6.) Hence, for one and the same source of heat, the ratio of trans- 
Mission in question (in spite of a constant quantity of heat falling directly 
ia the plates) diminishes with the distance of the source, and the more 
: m ; 
(7.) It is ible, by a proper ‘arrangement of the experiments, to 
Cause the wee abansadt Saal of rays of heat from a source at 
100° ©, in comparison with those from the lamp, cited in (1.), to disap- 
