W. Crookes—Lines of Molecular Pressure. 221 
the intensity of the coil and well insulating the tube and 
wires leading to it. Beyond that exhaustion nothing has been 
observed. 
Focus of Molecular Force.—In an apparatus specially con- 
structed for observing the position of the focus the author 
found that the focal point of the green phosphorescent light 
was at the center of curvature, showing that the molecules by 
which it is produced are projected in a direction normal to the 
surface of the pole. Before reaching the heat exhaustion for the 
green light, another focus of blue-violet light is observed; this 
varies in position, getting further from the pole as the exhaus- 
tion increases. In the apparatus described, at an exhaustion 
of 19°3 M, these two foci are seen simultaneously, the green 
being at the center of the curvature, while the blue focus is 
the negative pole, or below it, or by its side. 
the residual gas be nitrogen, hydrogen, or carbonic acid. 
d 
exhaustion in different gases. 
a preliminary note and a diagram* of the variation of viscosity 
of air, hydrogen, and other gases at exhaustions between M 
0: 
* Proc. Roy. Soc., Nov. 16, 1876, vol. xxv, p. 305, 
