371 
The error of hearing is considerably increased; that of sight 
a little lessened, but the tremor is only a seventh part of its 
original amount. 
«¢ Tt is evident that the same equations apply to the new 
mode of observation if uw represent the error of touch; and it 
is to be hoped that a similar discussion of its probable errors 
may be soon instituted, for there are a number of inquiries 
which must be answered before its superiority will be fully ap- 
preciated. Independent of the possibility that the means 
employed to close and break the voltaic circuit may disturb 
the clock’s pendulum, and that the promptness of the register 
may vary with the intensity of the battery, it is certain that 
in the obedience of the finger to the will there must be a per- 
sonal equation, and it is possible that this, unlike that of the 
ordinary transit observer, may be variable. For any regular 
succession it will probably be insensible, as I infer from some 
observations given by Mr. Mallet in the report of his valuable 
experiments on the propagation of Earthquake Waves, p. 306. 
Starting a chronograph at a given beat of a clock, and stop- 
ping it at another, he gives the differences from the mean, 
whence I compute «, for himself =+ 0*0449, and for his son 
 +£0*0592. Each of these involves two errors of ear and two of 
finger, so that the measure of one of each is 0°0318 and 
0°0419. These come so near my u, that any error of touch is 
scarcely possible ; the case is, however, a special one, and may 
be compared to the counting seconds without a clock, which 
a practised observer will do with surprising accuracy. _Phe- 
nomena not regularly recurring could scarcely be taken so 
accurately. 
«‘ The error of sight will, for the reason already given, be 
less in the case of stars; as to the sun and moon, it is more 
doubtful. In the transit they have larger probable errors than 
the stars. For the sun I obtained in 1830 the first limb 
. + 0°116, the second + 0*087 ; the moon gave + 0°149 ; while 
_ stars observed at the same hour, and near the same parallel, 
VOL. V. 20 
