238 



In order fully to test our apparatus, we have observed the action 

 effected by a coal-gas flame of constant dimensions on our apparatus 

 on different days. Determinations made in June last gave the follow- 

 ing results : 



Action in 1 min. Diff. from mean, 

 llth June .. 14-00 .... + 0-01 



12th .. 14-26 .... +0-35 



13th .. 13-80 .... -0-11 



19th .. 13-83 -0-08 



21st .. 13-88 -0-03 



2Gth .. 13-72 .... -0-19 



Mean value. . 13-91 



Observations made with the constant flame placed at different 

 known distances from the insolation vessel, proved that the amount 

 of chemical action produced varied inversely as the square of the 

 distance ; and experiments made in September with the standard 

 flame gave results which agreed most exactly with those obtained in 

 June. From the exact agreement of these various observations we 

 are assured of the accuracy and reliability of the measurements made 

 with our instrument. 



In order to see whether the variation of the atmospheric tempera- 

 ture exerted any influence on the sensibility of the electrolytic gas, 

 we saturated the apparatus at various temperatures lying between 

 18 and 27 C., and found that the difference between the action at 

 any two temperatures lying between the above degrees was so slight, 

 that it did not exceed the unavoidable errors of experiment. 



In the next communication we shall consider the relations of the 

 interesting phenomena of photo-chemical induction. 



