6 
Transactions of the Boyal Society of South Africa. 
From which we obtain as final equations — 
6y^f 1 + I V 1-464 I - 17-611 = 0 
+ 0-390^+ 3-117 = 0 
a 
a solution of which yields — 
y = 0-17 m. 
d = 0-005. 
Eeducing the coefficient of atmospheric absorption to sea-level, we 
have the final value for this important factor — 
0-19 m. 
The value of the height of the atmosphere obtained from the equa- 
tions, viz., 0-005, or 20 miles, is of course too small. But this small 
value may mean that above 20 miles the air is too rare to stop light to 
any appreciable extent. 
3. Deductions fkom the Above. 
The principal determinations of the coefficient of absorption are — 
Seidel 0-25 m. 
Langley 0-13 
Pritchard 0-19 
Muller , 0-21 
Picl^ering 0-25 
The mean of these results is — 
0-21 m., 
agreeing very closely with that obtained at Lovedale — 
0-19 m. 
Taking the mean of all the results, we obtain as the value of the coefficient 
of atmospheric absorption — 
0-20 m., 
which, interpreted into other terms, means that 17 per cent, of all rays 
that strike the atmosphere perpendicularly are absorbed by the atmo- 
sphere. That is, a star in the zenith shines with 83 per cent, of its 
intrinsic brightness ; on the horizon this is reduced to such an extent that 
the star shines with only about one-fortieth of its zenith brightness. 
