ASTRONOMERS suspected for a long time that the cosmic scheme included other galaxies than our own. Herschel about two hundred years ago, with what we of to-day would call a small telescope, saw enough to suggest the idea that there were other galaxies or island universes. When our modern telescopes and cameras were brought to bear upon the skies, there was no more doubt. Other galaxies were there. We called then "nebulae," and to distinguish them we very sensibly gave them numbers instead of the names of mythological gods.
Again it is necessary actually to see with one's own eyes photographs of these nebulae in order to gain a conception of them. Words can tell their distances and their weights, but only a picture can convey an idea of their appearance and the highly significant evidence they present. Several photographs of extra-galactic nebulae are reproduced here. They are among tire most impressive of all astronomical pictures, for they actually show the "Great Beyond." Since we on Earth must necessarily look through our own galaxy in order to see other galaxies, we see large numbers of the stars of our own galaxy in front of them.
This accounts for the peppered effect in the photographs. The less distant large stars show large white areas, where their light "spatters" on the sensitive emulsion, making the image appear larger than it should. The more distant stars appear as white dots. We must overlook these in contemplating a picture of an extra-galactic nebula.
Detail is always lost in reproduction and in printing. In the original photographs much of the haze of a nebula can be seen to be made up of minute, dustlike specks, but in the reproduction processes they blend and become a haze. Each time a larger telescope is built, collecting more light and concentrating it, we resolve more haze into individual specks. But we also bring in additional haze. When the 100-inch reflecror at Mount Wilson was built, we resolved immense areas of haze into individual stars, but there was new haze added. Tire Carnegie Institution of Washington is building for its Mount Wilson Observatory a 200-inch reflector. We know before we get it that it will repeat the performance of the 100-inch--will resolve much haze but also will bring in a like amount of new haze.
With this preparation let us examine the photographs, perhaps to many of us the first glimpse into the mysterious hinterland of cosmic space.
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