97 
slightly elevated temperature. The author’s experiments 
do not support this view, since the substances described by 
him, when submitted to the action of the mixed nitric and 
sulphuric acid of the strength employed for making gun 
cotton, do not yield explosive compounds. 
PHYSICAL AND MATHEMATICAL SECTION. 
January 28th, 1868. 
Joseph Baxendell, F.R.A.S., Vice-President of the Section, 
in the Chair. 
a On Solar Radiation,” Part II., by Joseph Baxendell, 
F.R.A.S. 
It has been shown in the first part of this paper that the 
curve laid down from the monthly means of solar radiation 
derived from the five highest values in each month, or those 
corresponding to the five clearest days, exhibits two maxima 
and two minima occurring respectively in April and Sep- 
tember, and June and December. In order however to 
determine the influence of the seasons upon the amount of 
solar radiation on clear days, it will be necessary to correct 
these means for the difference of meridian altitude of the 
sun in the different months of the year. For this purpose 
I have employed the table given in the article on Climate 
in the Encyclopaedia Britannica, referred to by Sir John 
Rerschel in a note at foot of page 11 of his admirable 
Treatise on Meteorology ; and I have neglected, as being 
immaterial for our present purpose, any correction which 
