NO. 13 THE MELIKERON ALDRICH 9 



Assume direct absorption for solar rays' of therlo strip = 

 70 per cent, then of the other i8 cm.^ 30 per cent is 

 lost=.o54 cm.^ Hence, the total correction for in- 

 complete triangles is .054 +.18 = .234 cm.^ 



Area of irregular indentations that can lose energy by 

 direct radiation = .06 cm.^ 



Of this, ^ is lost=.03 cm.^ (because radiation from one 

 side of perpendicular is lost, other side is absorbed) . 



Total losses of all kinds = .096 +.234 +.03 = .36 cm.^ 



Corrected area = 5. 86 — .36 = 5.50 cm.^ 



Resistance of strip= 1.555 ohms. 



Computed constant (without glass hemisphere) = 



1-555x60 _ 

 4.183 X 5.50 -4°5 



(2) Observed Constant. 



The constant determined by comparison with pyrheliometers may 

 be given more weight. The melikeron was mounted equatorially and 

 a hood placed around it, similar to that supplied with the pyranometer, 

 exposing the instrument only to the sun and a small area of sky 

 around it. A double, ventilated shutter, blackened below, served to 

 cut off the radiation at intervals. The first comparison was made on 

 Mount Wilson, California, August 29 and 30, 1920, using secondary 

 pyrheliometer No. IV. All the following values are without glass 

 hemisphere. 



First determination — Melikeron mounted so that sun rays fall nor- 

 mally on the instrument. 



Calories by Pyr. No. IV f per ^^ j = 1.468 (mean of 3). 



(Current)^ of Melikeron = .348 (mean of 3). 



1468 - , ,., 



-—g= 4.22 = constant Melikeron No. 2. 



Second determination — Melikeron mounted so that sun rays strike 

 the instrument at an angle of 8°. 5 (cos. = .989). 



Calories by Pyr. No. IV= 1.437 (mean of 3). 

 (Current)* of Melikeron= .360 (mean of 3). 



360^ ^ ~ ^'9^ ~ constant of Melikeron No. 2. 



From the ratio of these two results it appears that 6.8 per cent 

 of the normal beam is absorbed and scattered, probably largely by 



^ For rays of great wave-length the absorption is much less, so that this part 

 of the loss would be increased. The difference cannot be serious, however, 

 because this correction is after all very small. 



