. The principles of physics. t beingvery near the object-glass, the image is formed much beyond theprincipal focus, and is greatly magnified, so that both the object-glass and the eye-piece magnify; while in the telescope, the heavenlybody being at a great distance, the incident rays are practically 428 ETHER DYNAMICS. parallel, and tlie image formed by the objeet-glass is mucli smallerthan the object. The only magnification which can occur is pro-duced by the eye-piece, which ought therefore to be of high magnifying power of this instrument i equals approximatelythe focal length of
. The principles of physics. t beingvery near the object-glass, the image is formed much beyond theprincipal focus, and is greatly magnified, so that both the object-glass and the eye-piece magnify; while in the telescope, the heavenlybody being at a great distance, the incident rays are practically 428 ETHER DYNAMICS. parallel, and tlie image formed by the objeet-glass is mucli smallerthan the object. The only magnification which can occur is pro-duced by the eye-piece, which ought therefore to be of high magnifying power of this instrument i equals approximatelythe focal length of the object-glass divided by the focal length of theeye-piece. 388. The Netvtonian reflecting telescope. For an instrument of moderate cost, specially adapted to schooland college use owing to the ease of manipulation and the comfortwith which the observer may view any part of the sky, the New-tonian reflecting telescope meets with much favor. It also possessesthe great advantage of giving a colorless image of bright objects,. Fig. 327. which cannot be obtained in a refractor.^ Fig. 327 represents ahorizontal sectional view of this instrument. Incident rays arereflected from the parabolic mirror, M; striking the rectangularprism, m n, they undergo total reflection, and form at a 6 a smallimage of the heavenly body. The image is viewed through an eye-piece inserted in the side of the telescope. The reflector serves asan object-glass, and is of course free from chromatic aberration,while spherical aberration is corrected by the shape given the 1 The student may ascertain the magnifying power of a terrestrial telescope byviewing a scale directly with one eye, and its magnified image as seen through thetelescope with the other eye. (See the authors Laboratory Manual and Note Book.) 2 On the whole, however, if the matter of expense be disregarded, the balance ofadvantage is generally considered to lie with the refracting telescope. Briefly, itschief advantages are : (1) it gives a br
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
