412 TRANSACTIONS OF SECTION A. 
increase being about 100 per cent. The two maxima just mentioned develop 
decidedly, so that at the lowest temperature reached the fluorescence shows 
two narrow overlapping bands, one with a maximum at ‘514 » and the 
other at “633 ». While the steepness of the curve increases on both sides 
of these bands, yet it is much more marked on the violet side, there being 
a slight decrease in fluorescence on that side at the base of the band for the 
lower temperatures. 
DEPARTMENT OF CosmicaL Puysics. 
The following Paper and Report were read :— 
1. Seasonal and Storm Vertical Temperature Gradients. 
By Professor W. J. Humpnreys. 
2. Report on the Present State of our Knowledge of the Upper 
Atmosphere.—See Reports, p. 71. 
WEDNESDAY, SEPTEMBER 1. 
DEPARTMENT OF GENERAL Puysics. 
The following Papers were read :— 
1. The Effect of Temperature Variations on the Luminous Discharge 
in Gases for Low Pressures. By Rost. F. Harwart. 
The apparatus used in this investigation consisted of a small glass bulb, 
in which two parallel electrodes were sealed. These electrodes were 5 mm. 
apart. Suitable tubes permitted the bulb to be evacuated, the pressures 
being measured with a McLeod gauge. 
The bulb was contained in an electric furnace, which could also be used 
as a container for carbon dioxide snow when measurements for discharges 
occurring at low temperatures were taken. 
Potentials required to produce a luminous discharge for pressures vary- 
ing from 0°2 mm. to 5 mm. were made, and for temperatures varying from 
—78° C. to 325° C. The gases operated upon were air, hydrogen, and carbon 
dioxide. 
Potentials required to maintain the luminous discharge under similar 
conditions were also measured. Families of curves showing the effects of 
temperature and pressure for potentials required both to produce and to 
maintain luminous discharge were given. 
They indicate that Paschen’s law holds approximately for the discharge 
in air until temperatures in the neighbourhood of 300° C. are attained. 
Here Paschen’s law does not hold even approximately. The effect of 
temperature variation on the potential required to maintain the discharge 
is much less than for the production of the initial discharge. 
2. Diffraction of Hlectric Waves. 
By Professor H. M. Macponatp, F.R.S. 
