SECTION III, 1916 [51] TRANS: RSC: 
Comparison of the Callendar Sunshine Recorder and the Angstrom 
Pyrheliometer 
By JoHN PATTERSON, M.A., (Cantab). 
Presented by Sir R. F. STUPART, F.R.S.C. 
(Read May Meeting, 1916) 
In the summer of 1911 the author! made a comparison of the Ang- 
strom pyrheliometer and the Callendar sunshine recorder by giving 
them a similar exposure. In this comparison it was shown that the 
difference between the two instruments varied with the time of day: 
that the greatest excess of the Angstrom over the Callendar occurred 
between 9 a.m. and 10 a.m. (Kimball? obtained a similar result but 
found that, by orientating the sunshine receiver 90°, the greatest 
excess occurred in the afternoon) and that from 1 p.m. to 3 p.m. the 
percentage difference between the two instruments did not change 
appreciably. It was further shown that, if the Angstrom instru- 
ment were shielded with glass of the same kind as in the bulb of 
the Callendar sunshine recorder, the intensity of the radiation 
was diminished considerably. In an endeavour to find out the 
source of the difference between the two instruments they were 
compared in the same way as before with a second Angstrom pyrheli- 
ometer protected with glass of the same kind as in the sunshine re- 
ceiver. The Callendar sunshine recorder was mounted as before in 
a tube about 18 inches long and attached to an equatorial telescope 
so that the surface of the receiver was always exposed perpendicular 
to the sun’s rays. 
The instruments were all mounted ready for comparison in 
June, 1912, but before a clear day was obtained thick haze set in, 
and did not entirely disappear before May, 1913. Observations 
were taken on several days in March and April, 1913, but they were 
not satisfactory because the haze was crossing the surface of the 
sun and the variations were so great that the curves of radiation 
could not be compared. On April 29th, 1913, however, the haze did 
not show rapid fluctuations and observations were taken from 9 a.m. 
to sunset. The results are given in the following table and are plotted 
mtg. «1. 


1 Meteorological Service of Canada, M.S. 50. 
2U. S. Monthly Weather Review, Aug., 1914, p. 474. 
