374 On a solar Calorimeter used in Egypt 



insurmountable task. This is put forward only as an illus- 

 tration, and in no way as an explanation of the source of 

 the heat of the sun. 



With this caution, however, I should like to call attention 

 to a coincidence. 



The specific heat of Fe 3 O 4 is 0-1678, and its molecular 

 weight 232, whence the water value of the gr. molecule is 

 38'93 grs. The molecular heat of combination is 264,700 

 gr. C. Dividing this number by 38*93 we get 6800 C. as 

 the temperature of the Fe 3 O 4 produced. Adding 273, we 

 have 7073 C. as the absolute temperature which may be 

 produced. In a recent work 1 Scheiner gives 7010 C. as the 

 most probable effective absolute temperature of the sun. 



Whilst the maximum value recorded by the calorimeter 

 is the most important for the determination of the sun's 

 heating power, the other values obtained are of use for testing 

 the working of the instrument. The principal disturbing 

 element is wind. During the forenoon of the i8th there was 

 an almost complete absence of wind. We take the observa- 

 tions of that forenoon, neglecting those that show a diminution 

 of intensity as noon is approached, because the sun's heating 

 power cannot diminish as noon is approached. They are 

 collected in the following table. In the first column a is the 

 mean time corresponding to the mean rate of distillation 

 under d. Under b we have the sun's zenith distance at this 

 time, and under c the secant of this angle, so that c = sec b. 

 Under d are the mean rates of distillation, in c.c. per minute, 

 for quantities of 20 c.c. collected. Under e are these rates 

 reduced to their value per square metre per minute, e = i ro6 d. 

 Under // we have the values of e corrected for the obliquity 

 of the sun's rays. For this purpose the formula given by 

 Herschel in his Meteorology is used 2 . It is, using the letters 

 in our table, 



e =/()' whence /= ^ . 



1 Strahlung und Temperatur der Sonne, von Dr J. Scheiner: Leipzig, 1899, 



P- 39- 



- Meteorology, by Sir John Herschel, Bart.: Edinburgh, 1861, p. 10. 



