330 Dr. T. Ewan on the Absorption-Spectra of 



(1 \2 



which gives /3 = 0*0433 and j3" = 0*00325. The fraction of 

 light transmitted by 7* 64 centim. of water is taken from 

 Table V. Putting these values into the expression given for 

 the ordinary troughs, we get 



, t 0-485 x(l -0*0433) 2 





1 l) ~ (l-*00325) 2 x 0-997x1-003 





= 0-4473. 



As 



log(l-p) 

 = length of layer, 



where I - 





le— — log (1—p) 





= 0-34944. 



Again, 



a c cl . 



A=- = T ; 



e el 



log A = log c + log I — log el 



= log (2-113) + log (7-64) - log (0-34944) ; 



c = concentration in gram equivalents in 1 litre of solution. 

 On calculating out the above expression, 



A=46-2. 



Probable Error. 

 As there is no reason why the error should be greater in 

 one set of measurements than in another (the measurements 

 being all of the same kind), I have only calculated it for one 

 set of numbers, obtained with a solution of copper chloride 

 containing 2*113 equiv. in 1 litre. The probable error was cal- 

 culated by the formula +0*6745 a /— ; 



are contained in Table VI. 



Table VI. 



i(n-l)' 



The results 



Region in 



Number of 



(1-P). 







Spectrum. 



Readings. 



Y. 



Z. 



551-6— 534-1 



15 



0083 



+0-0014 



+3-5 



531-1—518-2 



15 



0-2599 



•0016 



1-3 



518-2-502-3 



10 



0-4855 



•00289 



1-3 



502-3—488-3 



15 



0-7020 



•00371 



1-1 



488-3—474-6 



15 



07972 



•00469 



1-3 



474-6—462-8 



10 



0-7676 



•00616 



1-7 



462-8—452-2 



10 



0-6125 



•00410 



1-5 



452-2-443-1 



10 



0-3893 



•00376 



3-5 



443-1— 434-2 



5 



0-1899 



•00334 



3-7 



