of Edinburgh, Session 1879-80. 407 
the luminous phosphorescent patch produced on the glass by the 
molecular bombardment. When this is seen it is due to a stream of 
blue light from the centre of the negative disc. This stream is not 
deflected by a magnet as is the stream producing phosphorescence. 
Since the molecules are driven off perpendicular to the surface of 
the negative electrode, any object placed in their path shields the 
phosphorescent glass from the molecular bombardment, and thus 
a shadow of the object is thrown on the glass. The author drew 
attention to the fact that there was no penumbra to this shadow. 
Considerable heat is developed on the glass or any other object 
exposed to this molecular bombardment. If the negative electrode 
be a concave part of a sphere, the molecules are concentrated at the 
centre of the sphere, and produce there sufficient heat to melt 
platinum. 
We know from the experiments of Rowland that a body charged 
with electricity, when in motion, acts like an electric current. So 
here these charged molecules in motion are deflected by a magnet as 
a current would be. But they do not yield to the electromagnetic 
force so much as a perfectly flexible linear conductor would do. 
The author showed that the stream of molecules, when falling on 
glass, could be reflected on to a piece of mica covered with a phos- 
phorescent powder; but he has not yet been able to determine 
whether they are reflected according to the laws of the reflection of 
light. He also drew attention to certain small black spots which he 
has occasionally noticed on the phosphorescing glass which move 
over it like bubbles, disappear, and are succeeded by others. 
He suggested that efforts should be made to determine what 
happens to molecules at the positive pole — also to discover by what 
means the negatively electrified particles, after having been projected 
along the length of a tube, find their way back again, if not by 
regular reflection. 
4. Additional Note on Minding’s Theorem. 
By Professor Tait. 
