156 TRANSACTIONS OF THE [MAY 4, 
an Image at Its Focus.” It consists in mounting a convex lense 
so as to concentrate the beam of sunlight upon one surface of 
a double reflecting prism, the lense being so mounted to rotate 
upon a polar axis as to keep the sunbeam continuously upon 
the mirror. <A negative lense near the prism rendered the beam 
parallel. A second double-prism set the beam in any desired 
direction. The advantages of this heliostat are a very powerful 
beam of light which can be made to emanate from a point and 
from which the heat rays have been almost entirely absorbed by 
its passage through the various pieces of glass. It is especially- 
adapted to work with the solar microscope. The paper was dis- 
cussed by Prof. R. S. Woodward. 
The following notes were presented by Mr. Wallace Goold 
Levison: (1) On photographs of Geisler and Crookes radiant 
matter tubes. Mr. Levison presented a very interesting series 
of photographs of Geisler and Crookes tubes taken by their own 
light. Many of these showed very beautifully the stratification 
in the Geisler tubes and the difference between the anode and 
cathode. Healso showed a series illustrating the disturbances in 
the stratification produced by plunging the cathodes to various 
depths in water. The photographs of the Crookes tubes showed 
not only the fluorescent spot opposite the cathode, but showed 
also very distinctly the bundle of cathode rays which are always 
invisible to the naked eye. (2) In this connection Mr. Levison 
pointed out the resemblance between the succession of colors 
with varying pressure in Geisler tubes and the color variation 
in the aurora and suggested that the experiment described bare 
out the idea that the aurora is an electric discharge through the 
atmosphere at various heights and pressures. A possible con- 
nection between these phenomena and the solar corona and 
comets was also pointed out. (3) The third note was the de- 
scription of a similar apparatus for obtaining X-ray photographs 
by long exposure with a small induction coil and four Bunsen 
cells. (4) The fourth note was descriptive of certain plates 
which were exhibited appearing to indicate the action of a mag- 
net on photographic films. These were called magnetographs 
and were made by placing various objects directly on the photo- 
