< Page:Popular Science Monthly Volume 8.djvu
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THE POPULAR SCIENCE MONTHLY.

real nature, and he expresses his opinion that all nebulæ consist essentially of clusters of stars, more or less remote. His original researches were published in 1837, accompanied by figures, and they are of high authority on this subject. We give Lamont's figure above. These two drawings having been executed by different observers with different telescopes (Lamont's refractor of nine inches aperture, and Mason's reflector of twelve inches) will afford in the cases in which they agree indubitable evidence as to the existence of any feature shown in them. The non-existence of any feature not shown in either is probable, although not certain.

Sir John Herschel's "Results of Astronomical Observations at the Cape of Good Hope" was published in 1847, and his drawing (our Fig. 2), in the order of publication, belongs after Fig. 4,

In his first paper he describes Fig. 1 as follows:

"The figure of this nebula is nearly that of a Greek capital omega, Ω, somewhat distorted, and very unequally bright. It is remarkable that this is the form usually attributed to the great nebula in Orion, though in that nebula 1 confess I can discern no resemblance whatever to the Greek letter. Messier perceived only the bright eastern branch of the nebula now in question, without any of the attached convolutions which were first noticed by my father. The chief peculiarities which I have observed in it are—1. The resolvable knot in the eastern portion of the bright branch, which is, in a considerable degree, insulated from the surrounding nebula; strongly suggesting the idea of an absorption of the nebulous matter; and, 2. The much feebler and smaller knot at the northwestern end of the same branch, where the nebula makes a sudden bend at an acute angle. With a view to a more exact representation of this curious nebula, I have at different times taken micrometrical measures of the relative places of the stars in and near it, by which, when laid down as in a chart, its limits may be traced and identified, as I hope soon to have better opportunity to do than its low situation in this latitude will permit."

This opportunity was afforded him at his southern station, and his Fig. 2 is accordingly much more detailed. He says of it in the work last cited that his Fig. 1 is far from an accurate expression of its shape:

"In particular the large horseshoe-shaped arc . . . is there represented as too much elongated in a vertical direction and as bearing altogether too large a proportion to [the eastern] streak and to the total magnitude of the object. The nebulous diffusion, too, at the [western] end of that arc, forming the [western] angle and base-line of the capital Greek omega (Ω), to which the general figure of the nebula has been likened, is now so little conspicuous as to induce a suspicion that some real change may have taken place in the relative brightness of this portion compared with the rest of the nebula; seeing that a figure of it made on June 25, 1837, expresses no such diffusion, but represents the arc as breaking off before it even attains fully to the group of small stars at the [western] angle of the Omega. . . . Under these circumstances the arguments for a real change in the nebula might seem to have considerable weight. Nevertheless, they are weakened or destroyed by a contrary testimony entitled to much reliance. Mr. Mason, a young and ardent astronomer, . . . . whose pre-
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