136 NATURE [Fuly 3, 1873 
-magnets 2 # 7, is placed an interruptor different in each } gives the speed of the wheel Y for each moment) ; for 7, the 
og ices : for ine law of rotation of the wheel / (it | seconds of time ; they are seat by an ele:ttical clock ; for /, it 
en ne ge 
registers the time of appearances and disappearances of the light, | during the experiment, Each experiment with six, and even 
by means of a Morse-key, on which the obseryer keeps his hand | seven disappearances, lasts about two minutes, 
