628 Proceedings of the Royal Society 
5. Farther Researches in very perfect Vacua. By 
Professors Dewar and Tait. 
(. Abstract .) 
The paper commences with an account of various methods of 
producing very perfect exhaustion of a receiver, especially that 
recently devised by the authors, in which the absorbent power of 
charcoal is made use of. An attempt is made to calculate the 
amount of exhaustion thus producible. 
Certain experiments described long ago by Bennett, Mark Watt, 
and others, and very recently much extended and improved by 
Crookes, are next referred to ; with the results obtained by the 
authors when repeating them in their charcoal vacua. 
By operating with discs of rock-salt and other materials under 
various circumstances of absorption, the observed phenomena are 
traced to the unequal heating of the movable parts of the appa- 
ratus; and their full explanation is given from the kinetic theory 
of gaseous pressure. 
To confirm this explanation various additional experiments are 
described — some, in particular, with amorphous sulphur. The 
amount of radiation from a magnesium lamp, as measured by the 
pyrheliometer, is shown to be quite consistent with the explanation 
offered. 
