1882.] On Actinometrical Observations made in India. 51 



Mean from five clear days. 

 „ three hazy days 



565 

 535 



Decrease. 



30 



or about 5 J per cent. If this may happen at a height of 6,700 feet, 

 and the haze was by no means of maximum density, what may be 

 expected at lower and less favoured localities ? 



15. T. 8 exhibits an abstract of the bulk of the work now pre- 

 sented. The series extends over thirty- two days, in which four blanks 

 • occur unavoidably ; the visible atmospheric conditions were excellent, 

 and the work was done with great care and with two different kinds 

 of instruments. Attention is called to the variable nature of the 



factor due probably to imperfections in A. 



A. 



16. Turning for a moment to another subject. As the photo-heliograph 

 in daily work at Dehra Doon is under my charge, the negatives were 

 available for finding areas of sun-spots in the autumn of 1881. My 

 means for making these measurements in a limited time were not very 

 rigorous; notwithstanding I believe the results obtained, of visible 

 •areas, are sufficiently exact. Nor was there leisure to find these 

 areas for any considerable period, i.e., before, after, and including that 

 *of the actinometrical observations of autumn 1881, and a considerable 

 range of the kind is obviously essential for a complete inquiry as to 

 connexion in time and circumstances between solar causes and terres- 

 trial effects. Under existing pressure, I chose the daily negatives 

 corresponding to the days of actinometer work, and obtained numerical 

 values of areas for umbra and penumbra. 



17. Looking now at curves C 2, the exhibit was intended to pre- 

 sent curve projections of radiation and spot-areas only in autumn 

 1881 ; as, however, there is space on the exhibit, the autumn radiation 

 curves for 1869, 1879, and 1880 have been added. The day-letters for 

 1881 have also been introduced, attention being here called to those 

 ^containing a C or c. I repeat, that the presence of these letters by no 

 means implies that the results are vitiated and rejectaneous from 

 visible causes, but that merely invisible interpositions may possibly 

 have prevailed. Now, as already said, the curves of 1881 are exhibits 

 of simultaneity between radiation and spot-areas, and that being the 

 argument, neither contrariety nor similarity decidedly appears between 

 the two curves, which, therefore, in the exhibit, yield no answer as to 

 spot temperature. If we discard the argument of simultaneity as 

 improbable* in presence of our own heat arresting atmosphere alone. 



* I can only aver that my thermometer sunk in the ground 26 feet still continues 

 to mark a falling temperature, although on the surface we are now fast approach- 

 ing maximum summer heat (April 1, 1882). 



E 2 



