202 PROF. H. E. ROSCOE ON THE CHEMICAL INTENSITY 



therefore, my investigation has failed to establish the 

 validity of Mr. Mackereth's conclusions, it vrill, I trust, 

 serve to show the desirability of giving increased attention 

 to observations of atmospheric ozone, and of attempting to 

 determine with greater certainty and exactness than has 

 yet been done, the nature of the changes to which this 

 important constituent of the earth^s atmosphere is subject, 

 and of their relation to other atmospherical phenomena. 



XIII. On Measurements of the Chemical Intensity of Total 

 Daylight made during the recent Total Eclipse of the Sun, 

 by Lieut. J. Herschel, R.E. By Prof. H. E. Roscoe, 

 F.R.S. 



Kead December 1 5th, 1868. 



The following communication contains the results of ob- 

 servations upon the varying intensity of the chemical 

 action of total daylight during the total eclipse of the sun 

 on August 1 8th last, made at Jamkhandi (75° 20' E. ; 

 16° 30' N.), in India, by Lieut. John Herschel, R.E. The 

 method employed was that described by me in the Bakerian 

 Lecture for 1865 (Phil. Trans., 1865, p. 605), and consists 

 of the comparison of tints effected by the total daylight 

 acting for a given time upon uniformly sensitive chloride- 

 of-silver paper. The weather at Jamkhandi during the 

 eclipse was most unfavourable for such observations. 

 Lieut. Herschel writes that ^' in truth nothing could have 

 been more disturbing than the constant and rapid hurrying 

 over of cloud of all degrees of darkness at low altitudes 

 combined with light fleecy ones, nearly stationary, at a 

 greater height.^' At no time during the eclipse did the 

 estimated amount of cloud fall below 4, the average being 



