This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1888 edition. Excerpt: ...image being simply shifted off the slit thereby produces no injurious results upon the definition. Many excellent photographs of the spectrum of the nebula in Orion were obtained by Dr. Draper in addition to those of the nebula itself. Two contrivances were made use of to obtain this spectrum: First, a direct ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1888 edition. Excerpt: ...image being simply shifted off the slit thereby produces no injurious results upon the definition. Many excellent photographs of the spectrum of the nebula in Orion were obtained by Dr. Draper in addition to those of the nebula itself. Two contrivances were made use of to obtain this spectrum: First, a direct-vision prism placed in the cone of rays from the objective before they had reached a focus; and, second, the two-prism spectroscope which had been employed to produce stellar spectra. To obtain good results with the direct-vision prism without a slit, it was necessary that the image should be kept stationary on the sensitive plate throughout the entire exposure of two hours.. The most striking feature of these spectrum photographs, perhaps, is the continuous spectrum of the two portions of the nebula just preceding the trapezinm, indicating that at these points there is condensed matter, either in the form of gas under great pressure or in the liquid or solid form' But neither in these portions nor in others which show the continuous spectrum more faintly was Dr. Draper able to detect any stars of a magnitude sufficient to produce this effect. Of these spectra Dr. Draper writes as follows: " The hydrogen line near G, wave length 4,340, is strong and sharply defined; that at h, wave length 4,101, is more delicate, and there are faint traces of other lines in the violet. Among these lines there is one point of difference, especially well shown in a photograph where the slit was placed in a north-and-south direction across the trapezinm; the H f line, A 4,340, is of the same length as the slit, and where it intersects the spectrum of the trapezinm stars a duplication of effect is visible. If this is not due to flickering motion in the...
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