272 
PROFESSOR FORBES ON THE EXTINCTION OF THE SOLAR RAYS 
9. Treating the observations on Bouguer’s hypothesis of an uniform ratio of extinc- 
tion to the intensity of the incident ray, we obtain for the value of the vertically 
transmitted share of solar heat in the entire atmosphere : — 
By the relative intensities at Brientz and the Faulhorn, Art. 69. . . -6842 
By the observations at the Faulhorn alone, 1st method, Art. 101. . *6848 
By the observations at the Faulhorn alone, 2nd method, Art. 103. . *7544 
By the observations at Brientz alone, 1st method, Art. 101. . . . ‘7602 
Bv the observations at Brientz alone, 2nd method, Art. 103. . . '7827 
Additional Notes. 
Note A. — On the Absolute Values of the Degrees of the Actinometers employed. 
Since writing this paper Sir John Herschel, to whom I submitted the results, has 
favoured me with the following information : — 
“ It happens very fortunately that as regards actinometer G, No. 7 , I find a series 
of direct comparisons of this with my standard H, No. 8, which is that I employed 
to determine the parts of its scale in actines ” [see Art. 19. of this paper]. “The 
series in question was made March 15, 1828, and gave the results of alternate sets 
as follows : — 
G. 7. 20*8 
H. 8. 21*3 
21*5 
21*6 
20*7 
21*2 
20*75 
21*0 
20*65 
19*9 
20*9 
21*0 
Rejecting the last 21*3 
Whence it results that the same radiation which raises G. by 209 parts would raise 
213 
H. by 213 parts ; or 1 part of G. 7- is equivalent to ^ = 1*019 parts of H. 8. 
“Now the value of 1° of the scale of H. 8. I ascertained by an elaborate series of 
experiments under a sun as nearly vertical as the Cape latitude would allow, and in 
eminently favourable circumstances, to be 6*093 actines ; so that one part of G. 7- is 
equivalent to 6*209 actines.” 
In the preceding paper the indications of G. 7- have been reduced to those of B. 2. 
Assumed as a standard, it has been found (Art. 54.) that the factor of reduction for 
the readings of G. 7- to those of B. 2. is 1*168. Hence to invert the process or reduce 
B. 2. to G. 7 - we must multiply by 
1 
1*168 
= 0*856; 
