52 On the Penetration of Heat across Layers of Gas. 
It is moreover shown that many observations which have been 
relied on as evidence that hydrogen possesses a Jarge conducting 
power for heat, in reality prove that a copious escape of heat by 
penetration takes place in this gas at higher tensions and to greater 
distances than in gases that are denser. This result has been 
confirmed by repeating in common atmospheric air Sir William 
Groves’ experiment upon the cooling effect of hydrogen on a 
platinum wire, previously rendered incandescent by electricity. 
This experiment when made in the open air further shows that 
the Crookes’s layer surrounding the incandescent wire has a thick- 
ness of much more than a millimetre. 
Finally it is shown that all parts of the phenomenon of a 
volatile liquid in the spheroidal state are the immediate con- 
sequences of the mechanical and thermal properties of the curtailed 
Crookes’s layer which exists between the liquid and the hot 
surface upon which it rests. 
It is also shown that the drops which are often seen running 
over the surface of a volatile liquid are globules in the spheroidal 
state supported upon Crookes’s layers; and that the extreme 
mobility of a very fine solid powder when placed in a hot metal 
dish is also due to the intervening Crookes’s layer. 
