Page:Popular Science Monthly Volume 87.djvu/229

Rh read that the nebulæ in general abhor the Milky Way. In the northern hemisphere they cluster most densely in the neighborhood of the pole of the galaxy. In the southern hemisphere they show the same tendency, but not so strongly. There are nebulae in the Milky Way, but

they are relatively few. Herschel's and Proctor's conclusions related only to the brighter nebula?, which had been discovered by visual methods.

Before Keeler began to photograph nebulæ with the Crossley reflector, in 1898, some 10,000 of these bodies had been discovered and catalogued. A few plates exposed by Keeler here and there over the northern sky recorded several hundred additional nebulæ. Using his photographs of small areas of the sky as samples, he estimated conservatively that at least 120,000 nebulæ are discoverable with the Crossley reflector. Further observations by Perrine with the same instrument and by Fath with the 60-inch Mount Wilson reflector have shown that the number discoverable with fairly short exposures is considerably greater than 120,000. Path's plates, uniformly distributed over the northern sky from the North Pole to declination 22°.5 south of the Equator, recorded 864 nebulæ previously unseen. The numbers on the individual plates are set down in the corresponding area. The curve drawn across the chart represents the central line of the Milky Way. The north pole of the galaxy is at N. The distribution of these faint nebulæ is seen to be patchy, but the fact is in evidence that the faint nebulæ, like those bright enough to be discovered by visual methods, abhor the Milky Way.