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. 



" It is evident that the same equations apply to the new 

 mode of observation if u 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 j, for himself = + S, 0449, and for his son 

 ± s * 0592. Each of these involves two errors of ear and two of 

 finger, so that the measure of one of each is 3 -0318 and 

 s * 04 19. 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 

 ± 8 -116, the second + 3 -087 ; the moon gave + s - 149 ; while 

 stars observed at the same hour, and near the same parallel, 

 vol. v. 2 o 



