234 Scientific Intelligence. 
when, as in most cases, the difference of temperature is the result 
of radiation, very irregular effects may be produced by the dif- 
ferent absorbing or radiating power of the surfaces for the various 
_ It does, however, still remain to show that the dynamical theory 
of heat is quantitatively as well as qualitatively confirmed by the 
a 
sent very great experimental difficulties, and t ta thus far 
obtained can only be regarded as rough estimates, and for this 
reason we attach much importance to the criticisms of 
tension of the residual air is about 0°19 millimeters, but he has 
succeeded in reducing it to 0-0076 millimeters, and then the 
velocity of the motion was only one-tenth of the maximum 
0 ; 
the exhaustion, he has been able to reduce the tension to one OF 
two millionths of an atmosphere, and that he can most readily 
secure the condition of greatest sensitiveness by first pushing 
the exhaustion to the utmost limit of the power of his app@ 
ratus,* and then with the aid of a peculiarly constrneted = 
i i h Mf 
allowing gas to enter until the proper tension is reache 
* Crookes has obtained these later results with a new form of the Sprengel 
