70 Dr. Herschel on the Nature and Construction 
that of an equal star placed at such a distance, I ought to re- 
duce the aperture of my 20-feet telescope to less than the two- 
and-twenty hundredth part of an inch ; when certainly I could 
no longer expect to see any star at all. 
The same remark may be made, with regard to the number 
of very close double stars ; whose apparent diameters being 
alike, and not very small, do not indicate any very great mu- 
tual distance. From which, however, must be deducted all 
those where the different distances may be compensated by the 
real difference in their respective magnitudes. 
To what has been said may be added, that in some parts of 
the milky way, where yet the stars are not very small, they 
are so crowded, that in the year 1792, Aug. 22, I found by 
the gages that, in 41 minutes of time, no less than 258 
thousand of them had passed through the field of view of my 
telescope* 
It seems, therefore, upon the whole not improbable that, in 
• The star-gages ran thus : 
From 19 11 35' to 19 11 51' 600 stars in the field 
19 51 _ i 9 57 4+0 
19 57 20 12 360 
20 12 20 l6 260 
The breadth of the sweep was 2° 35', the diameter of the field 15', and the mean 
polar distance 73 0 54'. Then let 
F, be the diameter of the field of view, 
S, the number of stars in each field, 
B, the breadth of the sweep, plus F, 
T, the length of the sweep expressed in minutes of space, 
<p, the sine of the mean polar distance, 
C, the constant fraction ,7854, 
and the stars in these four successive short sweeps will be found by the expression 
equal to 133095. 36601. 74866. 14419. or in all *58981. 
