490 Notices respecting New Boohs. 



From the general equation : 



SV A Q'a + ^Eab C' ab =:£V'a Qa + 2E'ab Cab 



the required reciprocal relations follow at once. 



(i.) Let every Q and Q' be zero, and every E except Eab, 

 and every E' except E'cd- 



Then :' Eab C'ab=E'cd Ccd, and if E A b= ±E'cd then 

 Ccd=±C'ab, or, in words, if an E.M.F. in one branch 

 produces a certain current in a second branch, then an equal 

 E.M.F in the second branch will produce an equal current in 

 the first ; and, according as the direction of the latter E.M.F. 

 is the same as or opposite to that of the former current, the 

 direction of the latter current will be the same as or opposite 

 to that of the former E.M.F. Again, if Ccd is zero, C'ab 

 will be zero, which leads to the definition of conjugate 

 conductors. 



(ii.) Let every E and E' be zero, and every Q except Qa 

 and Qb (which will be — Qa), and every Q' except Q'c and 

 Q'd (which will be —Q'c). 



Then: (V C -Vd) Q'c= (VJa-V'b^ Qa, and if Qa=Q'c, 

 Vc — Vd = V / a — V'b; that is, if a certain current led in at A 

 and out at B produces a certain excess of potential of C over 

 D, an equal current led in at C and out at D will produce an 

 equal excess of potential of A over B. 



L. Notices respecting New Books. 



Report on the Total Solar Eclipse of January 21-22, 1808, as ob- 

 served at Jeur in Western India. By Kavasji Dadabhai 

 Naegahvala, M.A., F.R.A.S., Director of the Observatory. 

 Bombay : Printed at the Government Central Press. 



HPHIS Eeport was published at Poona in November 1901. 

 -■- Prof. Naegamvala thinks it necessary to account for the delay 

 in its appearance, which was due to his desire to compare the 

 spectrum of the " flash," which was for the first time adequately 

 obtained at the Indian Eclipse of 1898, with stellar spectra and 

 other related types. He has since been engaged in laborious 

 efforts to secure these for purposes of comparison with the eclipse ; 

 but finding that his progress was much hampered by certain mecha- 

 nical defects in the prismatic camera, he finally decided to publish 

 an account of his observations at Jeur without further delay. As is 

 well known, he is Director of the Maharaja Taktasingji Observatory 

 at Poona, and feeling the importance of taking part in the obser- 

 vations of the eclipse in question, he memorialized the Government 

 of Bombay on the subject as early as February 1896. To prepare 

 himself for efficient participation, he accompanied the expedition 

 sent to Norway to observe the total eclipse of August 9 in that year ; 



