



154 The Electrical Measurement of Starlight. [May 16, 



Now, although the accidental obstruction renders this comparison 

 unsatisfactory, it is remarkable that these numbers accord fairly 

 well with the "magnitudes" of the two stars, as given by Miss 

 Clerke ('System of the Stars,' Appendix, Table III). Thus, the 

 " magnitude " of Regulus is given as 1'4, and that of Procyon as 

 0-5. 



Now, in equation (5), if we put B/B' = (190/127) 2 , and assume the 

 magnitude of Regulus = 1'4, while that of Procyon = m, we have 



5 log iff = l-4-w, 

 /. m = 0'53, 



which is a rather close coincidence. 



On the same data equation (4) gives the result 



Intrinsic energy of Regulus = 3*6 x intrinsic energy of Procyon. 



It is hoped that these measurements will be resumed about the end 

 of next September, at Daramona, by the same observers ; and, in the 

 meantime, some improvements will be effected in the cell-holder 

 which will facilitate observation. An endeavour will also be made 

 to improve the cell itself in the directions indicated at the beginning 

 of this Report. 



The experiments prove conclusively that there is little difficulty in 

 obtaining fairly accurate measurements of the light of stars of the 

 first and second " magnitudes," even without the employment of a 

 multiplying condenser or a larger telescope. A telescope with an 

 aperture of 5 or 6 feet would certainly annex a very great number of 

 .stars to the list. 



It is right to put on record the fact that the first photo-electric 

 observations of planets and stars were made by Mr. Monck, in Dublin, 

 in the year 1892, in conjunction with Professor Fitzgerald. My cells 

 were at that time much less sensitive than the present ones ; and, for 

 reasons set forth in this paper, their sensitiveness fell off after about six 

 hours. . The liquid in those cells was acetone, and the aluminium on 

 which the selenium was deposited was not insulated from the liquid. 

 Nevertheless, Mr. Monck and Professor Fitzgerald were able to observe 

 electromotive forces due to the light of Venus, Jupiter, and, I think, 

 Mars. Mr. Mo nek's telescope is a refractor of 9 ins. aperture, so 

 that large results were not to be expected. These observers were not 

 quite certain whether Vega and Capella produced measurable effects 

 or not ; but their observations were much interfered with by draughts 

 of air, and other things, in their observatory. 



