ON THE EFFECTIVE TEMPERATURE OF THE SUN. 
385 
(2) The ratio of the incident radiation on the gdass mirror of the heliostat to the 
reflected. This was given by the use of Fresnel’s formula 
_ I siiU (i — r) j tan- (i — r) 
E;. ^ sin^ (i + r) ^ taiU {i + /’) ’ 
where 
Rj = intensity of incident radiation, 
Ji,= „ „ reflected ,, 
i = angle of incidence, 
r = „ „ refraction, which was obtained by putting g = 1-5 in the 
ordinary formula, sin i — [x sin r. 
The values thus obtained for different angles of incidence were plotted down and a 
smooth curve drawn to give the value at any incidence (fig. 9). In the figure, a, *6, 
Fig. 9. 
i 
and c, are points experimentally determined by photometric measurement as a rough 
check on the accuracy of the calculations. (It may be noted here that the table 
given by Jamin* is erroneous as referring to common light; it is correct for light 
polarized in the plane of incidence. We mention this as anyone who took the 
accuracy of Jamin’s figures for granted would imagine that our curve was wrong.) 
* ‘ Cours cle PFysique,’ 4tF edition, vol. .3, p. 618. 
3 D 
MDCCCXCIV.-A 
