404 



Prof. H. H. Turner. 



1894; but the standard squares had not received a sufficiently long 

 exposure and additional experiments were required. These were 

 carried out by Sir W. Abney during the year ; but causes which need 

 not here be dwelt on (chiefly the desire to make further measures 

 which other work has hitherto prevented but which are now being 

 made) have delayed the publication of the results far too long : and, 

 while still reserving the details for a more complete account, I publish 

 one or two general results which may be useful to others in preparing 

 for the forthcoming eclipse. 



Three plates were measured, taken by Serg. Kearney, at Fundium. 

 He was provided with a "double-tube," which took photographs of 

 two sizes, the diameters of the moon's image being 0*6 inch and 1*5 

 inches respectively. The following table shews the details of ex- 

 posure : — 



Table I. 



Plate n 



umbers. 



Exposures. 



0-6 inch 







Time in seconds 



1^ inch. 



Duration. 



from commencement 



moon. 







of totality. 







seconds. 





1 



lA 



20 



13 to 33 



2 



2a 



120 



41 „ 161 



3 



3a 



50 



169 „ 219 



4 



4a 



5 



227 „ 232 



5 



5a 



2 



240 „ 242 



6 



6a 



1 



250 „ 251 









1^50 



The plates measured were those numbered 3a (large scale), 3 and 5 

 (small scale), of which the first was measured rather elaborately along 

 four radii extending due N., S., E., W. from the limb respectively, and 

 the reference table or curve of standard lights was constructed for this 

 plate. 



The following table shows the actual measures, each number being 

 deduced from the mean of three sector readings by application of the 

 curve of standard lights. 



The unit of the table is the effect caused by an amyl acetate lamp 

 shining on the plate from a distance of 9 feet for 1 second. 



The numbers represent powers of 2, giving the intensities in terms of 

 this unit. Thus 7*7 means 2'-^ or 208 times the unit. 



The distances from the limb are in terms of a cardboard scale, and 

 it was found by me? surement of the moon's diameter that 



100 div. = 15''6 = solar radius nearly. 

 Hence 10 div. may be regarded as O'l solar radius. 



