105 
number of groups of solar spots observed in each year by 
Schwabe : — 
Ratios. 
Number of Groups 
of Solar Spots. 
1859 
233 
205 
1860 
2-57 
211 
1861 
2-17 
204 
1862 
1-74 
160 
1863 
1-64 
124 
1864 
1-61 
130 
1865 
1-57 
93 
1866 
117 
45 
The curves laid down from these two series of numbers 
present so close a resemblance in their general form, that it 
seems impossible to resist the conclusion that the causes 
which influence the frequency of solar spots also produce 
corresponding changes in the calorific intensity of the 
sun’s rays. 
In addition to the conclusions drawn from the discussion 
in the first part of this paper we have now the following : — 
1. The power of the atmosphere to absorb the heating 
rays of the sun is much greater in the summer than in the 
winter months, and depends apparently upon the amount of 
aqueous vapour which it contains. 
2. Clouds and haze are less prevalent during the day, or 
their power to intercept the heating rays of the sun is less 
active in the spring and autumn than in the winter and 
summer months. 
3. Observations of solar radiation made with a black 
bulb thermometer, to be of value, ought to be taken with 
the radiation thermometer placed at the same height above 
the ground as the shaded maximum thermometer, with 
