[BOYLE] TEMPERATURE AND VELOCITY OF GAS CURRENT 87 
determining directly the amount of emanation existing in any parti- 
cular gas. Mr. Eve, of this laboratory, is now utilizing the method 
to determine the amount of radium emanation existing in the free 
atmosphere. 
It may be noted that since the emanation must be mixed with 
some gas, there is special interest in studying the information contained 
in the papers of Dewar and Ramsay concerning the absorption of the 
inert gases of the argon family which exist in the atmosphere. The 
cases are analogous in that the emanations are believed to be chemically 
inert gases and are mixed with the containing gas in extremely small 
proportions, but there is the distinctive difference that the emanations 
decay with time while the gases of the argon family do not. 
It is important to determine the laws which govern the absorption 
of the radio-active emanations, to know how far it depends on the speed 
of the containing gas through the absorbent, the temperature of the 
absorbent, and other conditions. An investigation of these points is 
the main object of this paper. 
Preliminary work has been carried out with the emanations of 
radium and thorium, and it appears probable that these differ in the 
manner and degree of their absorption. 
In consequence of the delicacy of electrical tests for determining 
the presence of minute quantities of emanations from radio-active sub- 
stances, it is possible to carry out experiments with quantities of eman- 
ation far too small for examination by chemical or other known physical 
methods; yet the measurements are capable of a high degree of accuracy. 
Radium Emanation. 
A short account may be given of a few experiments on the diffusion 
of radium emanation from vesssels containing the emanation mixed 
with air to vessels containing cocoanut charcoal. The apparatus used, 
fig. 1, was an emanation electroscope, which consists of two chambers, one 
above the other. The lower chamber is an air-tight, cylindrical vessel of 
brass of about one litre cubical capacity, serving as an emanation 
reservoir, while the upper is a vessel covering the gold leaf system, which 
can be observed through a mica window by a microscope with a scale 
in the eye-piece. The gold leaf is at the upper end of a brass rod which 
extends down into the lower chamber and is well insulated. The lower 
chamber is fitted with tubes and stop-cocks, through which air charged 
with emanation can be admitted or withdrawn at will by means of a 
pump. Connected with the emanation reservoir by a short tube of large 
cross-sectional area was a glass bulb containing a few grammes of cocoa- 
