46 ROYAL SOCIETY OF CANADA 
ing the solar lines from those due to the absorbing influence of the 
earth’s atmosphere. This was accomplished by an application of the 
principle that the spectral lines of the light which is emitted by a 
source in relative or absolute motion are displaced. The general ex- 
perimental arrangement consisted in causing the two extremities of 
the solar diameter to fall rhythmically upon the slit of the spectro- 
scope. Thus it was found that the solar lines were displaced, while 
the telluric lines remained fixed. 
A large number of lines of atmospheric origin was found near D 
and also near A, B and the band called K in Augstrôm’s map was 
determined. Those that were considered to be due to water vapour 
are indicated specially. 
Important work upon the variation of the water vapour lines 
was conducted by C. 8. Cook.! Observations were made upon the 
hygrometric state of the atmosphere and upon the intensity of a line 
near the D lines as seen when the spectroscope was pointed to different 
azimuths. These were carried out at different stations, one at the 
foot, and the other at the summit, of a mountain, the difference in 
altitude being three thousand feet. The results showed a marked 
similarity between the curves representing the humidity gradient and 
the difference in the intensity of the lines at the bottom and top of 
the mountain. 
A very important paper by Theodor Arendt? details work done 
by him upon the variation of the aqueous vapour lines. His method 
of comparison was the “Step-by-step” Method. Numerous curves are 
given to show the changes in the intensity, the humidity of the atmos- 
phere, the temperature and the barometric pressure. 
The general result is that the rainband is not trustworthy as a 
guide to the weather. 
APPARATUS AND METHOD OF OBSERVATION. 
For several years records have been made by Professors McLeod 
and Barnes of the difference of temperature between the base and 
summit of Mount Royal. They have shown that, under conditions 
not yet understood, the temperature differences show considerable 
variation over extended periods. The present work was undertaken 
at the suggestion of Professor Barnes, to see how far variations in the 
water vapour lines were connected with the changes in the temper- 
ature gradient in the lower atmosphere. 


1 Science, 2, 488 (1883). 
American Journal of Science and Arts, 39, 258 (1890). 
2? Beitrage zur Physik der freien Atmosphare, Zweiter Band, 4 Heft, 135 (1907). 
