332 



Dr. T. Ewan on the Absorption- Spectra of 



distance of the lamp must therefore be measured from the 

 point at which the collimator just ceases to be filled with 

 light. A comparison with a set of measurements made with 

 pure water showed that at least a considerable part of the 

 difference observed is to be explained in this way. 



The following Tables contain a number of measurements 

 which were made with parallel light and distilled water in the 

 troughs. The good agreement found between the calculated 

 and observed numbers shows that the loss of light due to dust 

 in the liquids cannot have been very great. 1 is the ratio of 

 the intensities of the light after passing through the upper 

 and lower halves of the trough. 



Table VII. 



Region in 

 Spectrum. 



I (found). I (calculated) 



Difference. 



Schulz Cell. 



A 599-4— X 574-2 

 551-6— 534-1 



0-985 

 0-991 



0-987 

 0-985 



+0-002 

 -0-006 



Schulz Cell. 



A 627-7— A 599-4 



599-4— 

 574-2— 

 551-6 — 



518-2— 



574-2 

 551-6 

 534-1 

 5023 



0-983 

 0-979 

 0982 

 0-985 

 0-988 



0-987 

 0-987 

 0986 

 0-985 

 0-985 



+0-004 

 +0-008 

 +0-004 

 + 0-000 

 -0-003 



Layer of water, 7*64 centim. 



A 627-7- 



-A 599-4 



599-4- 



- 574-2 



574-2- 



- 551-6 



551-6- 



- 534-1 



534-1- 



- 518-2 



502-3- 



- 488-3 



488-3- 



- 474-6 



0949 

 0-939 

 0-948 

 0-935 

 0-926 

 0-909 

 0-919 



0-941 

 0-935 

 0-929 

 0-927 

 0-926 

 0-926 

 0-926 



-0-008 

 -0-004 

 -0019 

 -0-008 

 +0-000 

 +0-017 

 +0-007 



Layer of water, 22'87 centim. 



A 534-1— A 518-2 

 502-3- 488-3 

 474-6- 462-8 



0-927 

 0-925 

 0-917 



0934 

 0-933 

 0-931 



+0007 

 +0-008 

 +0014 



The effect of dust would be to make the observed numbers 

 higher than those calculated. This is sometimes the case, 

 sometimes the reverse. 



