Chemistry and Physics. 133 
radiation of its own equal in all directions and haga regard to the dis- 
tance of the particle from the surface of the gti - The radiation of 
3. The flow of heat from within upon the piss surface of a polished 
plate of indefinite thickness is proportional to the index of refraction of 
tion was then attempted to be traced. as shown that unless bodies 
from simply eg sae Ast their pobiad ni: for the same de- 
scription of hea there is no reason to su , the radiation of 
thin plates or ah at a high temperature will bear a less proportion 
to the total radiation of that temperature than at a low,—the conse- 
quence will be, that the wenn of single particles will i increase with the 
temperature in a less degree than Dulong and Petit’s law would indicate. 
It may even be that the radistioh of a particle or very thin plate may be 
Proportional to the absolute temperature of that particle. Taking a 
piece of glass or mica, therefore, at a low temperature, as it is very 
opaque with regard to the heat radiated by itself, we may suppose that 
the total radiation consists of that of the outer layer of particles onlys 
that from the inner layers being all stopped by the outer. At high te 
peratures, however, we may suppose that there is not only the md essa 
of the outer layer, but also part of that of the inner bb which has 
able to pass, swelling up the total radiation to what it appears in 
Dulong and Petit’s experiments. This way of looking at radiation may 
possibly bring the radiative gate of particles to obey the same laws 
with the conducti ting power o which Prof. Forbes has sete 
decreases with an increase of te temperature. The yee of this commu- 
nication is ans to Prof. Forbes for the use of th caennnenta and 
ces employed, and also for many valuable picpectictia with re- 
unded. some 
vacuum tubes I had obtained from Mr. Geir of Bon, I observed that 
the phosphorescence was no longer blue, but was of a slight ain color, 
To test whether this difference was due to the gaseo r remai 
in Geissler’s tubes, or to the character of the glass +e he uses, I h 
orricellian vacuums prepared in German glass tu bes, and in this manner 
ed the difference in the color was entirely due to the char- 
acter of the glass: that of Germany is, I believe, made with potash, and 
uced to some extent. a have rec ecently o ee ined a vacuum tube from 
Bonn, Ww 
ends of the tube are composed of German glass, the centre of the tube 
is of bias eh sense by this arrangement a gi th between the two is 
very manif 
