Dr. Herapath on the Detection of Strychnine. 197 



the equation 



fix, 0) ^(x) +/0r, 1) ^ + &c. = (Fx). 

 Assume 



<pix) = \ e^'^ 4^(6). (Id, 



Hi 



a, ft being constants, and ip{d) a function of to be determined. It 

 is always permitted to assume this equation. 

 By this means, writing for shortness 



f,{x, e) =f{x, 0) +f{x, 1) + &c.. 

 the equation becomes 



r 



e«^f{x,Q)^{e)dB = Y{x), 



which is of the desired form. 



A solution which occurred to the author after the memoir was 

 drawn up, is as follows : viz. given, as before, the equation 



pA*.0)?(^+0)^9 = F(^), 



then *(w V ~ 1 being determined by the equation 



=0.) 



r 



and putting, for abbreviation, 

 ^(*a, 7~ (^^_^^zri) Y e«*(<- V~) f^x, 6) dd = fix, u,V^), 



the equation 



1 r"" e^^^-^'^FCwV-l)^ 

 ax = — \ , ^ — . ^ dw 



gives the solution of the problem. 



The above-mentioned formulae are selected out of a great number 

 of very general results contained in the memoir. 



" Letter from Dr. \V. Bird Herapath to Professor Stokes, ' On 

 the Detection of Strychnine by the formation of lodostrychnine.' " 



Bristol, June 7, 1856. 



My dear Sir, — Will you do me the favour to announce to the 

 Royal Society, that I have been engaged during some time past in 

 the application of my discovery of the optical properties of iodo- 

 strychninc to the detection of this alkaloid in medico-legal inquiries ? 

 I find it is f)erfectly possible to recognize the 10,000th part of a 

 grain of strychnine in pure solutions by this method, even when 

 experimenting on very minute quantities. In one experiment I took 



