Page:Collected Physical Papers.djvu/364

344 to be exceedingly feeble at 6 a.m. The rise in the intensity was rapid, attaining the maximum at 12 noon.

This will be designated as the light-noon. The intensity of light then declined at a rate slower than the rise; after 5 p.m. the fall of intensity was extremely rapid.

It was stated that there was a possibility of change of resistance induced by diurnal variation of temperature. In order to determine the extent of this variation, a spark record was also obtained before exposure to light. The dotted record near the base (fig. 107) shows that the resistance remained practically constant, inspite of the variation of the temperature.