636 PROFESSOR CHRYSTAL ON THE DIFFERENTIAL TELEPHONE. 
without a condenser. The result was much like that described above. 
“ Nature,” xvu. p. 164. 
Lord Ray eicH has, I believe, made a similar observation on the thud, 
which is heard (without a telephone) when the primary is broken. He found 
its pitch to vary with the capacity of the condenser introduced into the 
secondary. 
The following list of memoirs on subjects related to the contents of the 
above paper may be of some use to English readers. I know some of them 
only through abstracts in WIEDEMANN’s Beiblitter ; but, so far as I am aware, 
there is not sufficient community between the results of any of them with the 
above to call for special mention, although there are of necessity points of 
contact. 
Dv Bots Reymonp, Archiv. f. Physiol., 1877. 
Hetmuotrz, Wied, Ann., N. F. v. p. 448 (1877). 
F. Weser, Abs. Wied. Beibl. iii. p. 291 (1878). 
Lorenz, Wied. Ann, N.F. vii. p. 166 (1879). 
NIEMOLLER, Wied. Ann. N.F. viii. p. 656 (1879). 
Aron, Wied. Ann. N.F. vi. p. 403 (1879). 
Hacensacu, Ibid. p. 407. 
Wiet.ispacu, Abs. Wied. Beibl. iii. p. 650 (1879). 
Hueues, Phil. Mag. vol. viii. p. 50 (1879). 
Lopeg, Phil. Mag. vol. ix. p. 123 (1880). 
Grant, Phil. Mag. vol. ix. p. 352 (1880). 
