( md ) 



unit surface. (According to results obtained by Laxgley and by Frost 

 we shall suppose the radiating power to vary only with the distance 

 from the center, not with the position angle). One of the strips will 

 contribute to the radiation : 



(J = (fj .)'y -j- rf, .f.5 -f . . . . (f„ .t'v, 



if it cuts out of the first zone an area (f,, out of the second zone 

 an area d, etc. Tiie next strip contributes : 



e = f 1 Xy_ + f , ,r^ -f . . . . a„ .«„, 



and so on. We get 39 equations from which a\, x^, ... x., may be 

 resolved. 



Determination of the coefficient.'^ of the n unknown quantities. 



I have found the coefficients ffj, rf, . . . f,, 5^ . . . by weighing. 

 On a piece of excellent homogeneous paper the solar disk was drawn 

 and divided into a suitable number of concentric zones, which were 

 intersected by arcs representing the Moon's limb in itS' successive 

 positions. The following astronomical data, necessary for making the 

 drawing, have been kindly procured to me by prof. A. A. Nijland. 



contact I II III IV 



position angle 293=,4 104°,5 304°,9 114°,9 



local time 23'>33"^10^ 0'' ol-" 58^ O'' 55™ 39^ 2M2™I4^ 

 Moon's radius : Sun's radius = 132,8 : 126,8. 



Now the strips were carefully separated from each other and 

 weighed (for subsequent control). Then each strip was cut along 

 the zone circles, and the pieces were weighed separately. In order 

 to make the pieces recognizable, the zones had all been differently 

 painted, each with a narrow line of water-colour. The weighings, 

 which were accurate to half a milligram, ga^'e the coefficients of 



the unkno\A n quantities ji-^, a',3 ï'v So the unit of area, adopted 



for measuring the surface of the solar disk, corresponds to a piece 

 of our drawtiig paper weighing 1 milligram. 



The breadth of each of the outer five concentric zones was '/jo 

 of the Sun's radius; then came seven zones with breadth YioOfthe 

 radius each, leaving round the center a circle with radius Y^j. The 

 average distances of (he zones from the center, expressed in thou- 

 sandth parts of the radius, will now be used as indices «,(?.... of 

 our 13 unknown quantities ; so these will be written : 



47^ 



