106 
which it is compared ; but while freely exposed at all times 
to direct sun-light, it ought to be protected as much as pos- 
sible from disturbing influences. 
4. Solar radiation observations made on a plan similar 
to that adopted at Oxford, show that the calorific intensity 
of the sun’s light continued to diminish during the years 
1865-6, when the frequency of solar spots was also diminish- 
ing, thus giving additional weight to the probability that 
changes in the heating power of the sun’s rays are inti- 
mately connected with variations in solar spot frequency. 
