160 



Mr. J. B. N. Hennessey. 



[Dec. 16, 



the time-range adopted. It will be found that the work was practi- 

 cally simultaneous. The radiation results hereafter discussed, are 

 those in terms of A, glass off, the unit being a tenth of a millimetre, or 

 about 0°-002 Fahrenheit. 



10. Table VI. — To test the constancy of radiation during the time- 

 range of +-J hour adopted, we might compare the successive indi- 

 vidual results with one another in each half-hour, just as they stand 

 in Table V ; this comparison, however, would be burdened by errors 

 of single values, which may be reduced with advantage. To secure 

 this end, I subdivide each half hour into three similar sub-time-ranges, 

 and within these limits I take the mean of all the available results for 

 each day to form a group mean ; hence, each daily series of group 

 means will be six in number, provided the series was completely 

 observed. The sub-time-ranges adopted, are — 





h. 



m. 



h. 



m. 





11 



30 



to 11 



40 





11 



40 



„ 11 



48 





11 



48 



„ o 

















„ o 



12 







12 



„ o 



20 









20 



„ o 



30 



Now, each group mean is the mean of three to five individual 

 results ; the exact numbers of the latter will be found indicated by 

 subscripts. Entering the group means in their proper columns, we 

 obtain in the case of Mussooree, fourteen complete series (omitting the 

 nineteenth, as it supplies only four of the six groups) ; and, taking the 

 mean for each sub-time-range, we now find mean results from so many 

 as from thirty-eight to sixty-one individual results. These mean sub- 

 time- range values may be considered practically free from all variations, 

 except those due to intrinsic or residual causes (Article 7) ; no doubt, 

 daily instrumental constants are present, but as the latter will be 

 eliminated in the proposed comparison, inter se, the results in question 

 may be accepted as highly eligible, for the purpose of testing how 

 far the radiation is constant within the HH| hour time-range. 



11. As regards Dehra, the group results, from accidental causes 

 already explained, present but three complete series. I pass on to 

 notice the exhibits of Tables VII and VIII before entering on a brief 

 discussion of all the facts. 



12. Table VII. — This table also is compiled from Table V, and 

 shows, daily, the sun's meridional zenith distance, and the mean values 

 of radiation for each half-hour time-range, and for the day, together 

 with readings of barometer and thermometers, and declarations as to 

 the wind and aspect of sky at noon. Finally, individual and mean 

 di fferences of radiation, M. — D. (i.e., Mussooree minus Dehra), as well 

 as the mean radiation at each station are deduced. 



