A. A. Michelson— Rate of Tuming-forks. 61 
ance of the balance. It is unfortunately the case that in all 
the forms of induction balance described above, lead gives the 
poorest effect of all metals. If people would only make their 
sensitive to lead and not 
more markedly influenced by lead than iron. 
B hope to continue these researches in the future; and cer- 
tainly no man can have a higher incentive to renewed exertion 
than the hope of relieving suffering and saving life. 
ArT. 1V.—A Method for Determining the Rate of Tuning-forks ; 
by AuBertT A. MICHELSON. 
THE tuning-fork is already employed to a great extent as a 
measurer of small intervals of time, and this use promises to 
become more extended as its advantages become more fully 
appreciated. Any method which will facilitate the operation 
of finding the rate, or increase its accuracy should therefore 
merit consideration. 
The following plan appears to be open to fewer objections 
than any now in use, and its accuracy is limited only by the 
accuracy of the pendulum. 
The fork to be rated, for example an Ut, making about 128 
double vibrations per second, is compared with an Ut, kept in 
vibration by electro-magnets and which shall be desi 
EUt,, and this is compared directly with the seconds pendulum, 
and then the two forks are once more compared, to make cer- : 
tain that EUt, has not changed in the interval. Thus Ut,is — 
