The following is an extract from the gauges, and gives the average number of stars in each field at the points noted in right ascension and north polar distance:
---------------------------------------------------------- | N. P. D. || | N. P. D. R. A. | 78° to 80°. || R. A. | 92° to 94°. | No. of Stars. || | No. of Stars. ------------|-----------------||-----------|-------------- H. M. | || H. M. | 11 6 | 3.1 || 15 10 | 9.4 12 31 | 3.4 || 15 22 | 10.6 12 44 | 4.6 || 15 47 | 10.6 12 49 | 3.9 || 16 8 | 12.1 13 5 | 3.8 || 16 25 | 13.6 14 30 | 3.6 || 16 37 | 18.6 ----------------------------------------------------------
In this small table, it is plain that a different law of clustering or of distribution obtains in the two regions. Such differences are still more marked, if we compare the extreme cases found by HERSCHEL, as R. A. = 19h 41m, N. P. D. = 74° 33', number of stars per field = 588; and R. A. = 16h 10m, N. P. D. = 113° 4', number of stars = 1.1.
The number of stars in certain portions is very great. For example, in the Milky Way, near _Orion_, six fields of view promiscuously taken gave 110, 60, 70, 90, 70, and 74 stars each, or a mean of 79 stars per field. The most vacant space in this neighborhood gave 60 stars. So that as HERSCHEL'S sweeps were two degrees wide in declination, in one hour (15°) there would pass through the field of his telescope 40,000 or more stars. In some of the sweeps this number was as great as 116,000 stars in a quarter of an hour.
When HERSCHEL first applied his telescope to the Milky Way, he believed that it completely resolved the whole whitish appearance into small stars. This conclusion he subsequently modified. He says:
"It is very probable that the great stratum called the Milky Way is that in which the sun is placed, though perhaps not in the very centre of its thickness.
"We gather this from the appearance of the Galaxy, which seems to encompass the whole heavens, as it certainly must do if the sun is within it. For, suppose a number of stars arranged between two parallel planes, indefinitely extended every way, but at a given considerable distance from each other; and calling this a sidereal stratum, an eye placed somewhere within it will see all the stars in the direction of the planes of the stratum projected into a great circle, which will appear lucid on account of the accumulation of the stars, while the rest of the heavens, at the sides, will only seem to be scattered over with constellations, more or less crowded according to the distance of the planes, or number of stars contained in the thickness or sides of the stratum.