ing surface of the radiator. For merely qualitative experiments the use of a vibrating interrupter is not so very prejudicial, as along with the ineffective discharges there are present some which are oscillatory. But where successive discharges are to give rise to radiation of equal intensity, it becomes necessary to avoid all sources of uncertainty. For these reasons I prefer a single break for the production of a flash of radiation. With some practice it is possible to produce a number of breaks, each of which is effective. If the surface at the break is kept clean, and the break is properly effected, successive flashes of radiation up to a certain number are about equally intense. When the sparking has been taking place for too long a time, the surface no doubt undergoes a deterioration. But twenty or thirty successive sparks are equally efficacious when sparking takes place between platinum surfaces. The use of a single flash of radiation is preferable on another account. The receiver at each adjustment responds to the very first flash, but becomes less sensitive to the subsequent flashes. The conditions of the different experiments are similar, when the action on the receiver is due to a single flash of radiation, instead of the accumulated effect of an unknown number of flashes.
I give below the deflections of the galvanometer produced by four successive flashes of radiation.
- (1) ……… 115 divisions.
(2) ……… 122„
(3) ……… 113„
(4) ……… 108„
When very careful adjustments are made, the successive deflections are approximately equal. There are,
