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A single-lens telescope
May, I918.]
U . S . BUREAU OF STANDARDS NOTES.
705
running t o w a r d the red. Circums:tances indicated that this band might be due to titanium oxide, and experiments since made at the Bureau of Standards have shown a band in this position in the spectrum o,f the titanium arc. T h e greatest wave-lengths observed in stellar spectra appear, by extrapo,lakion, to be about o.87/,.. The general co.nclusions arrived at are as. follows: L M a n y stellar spectra possess sufficient intensity in the region of waveqength o.8o/* to enable this portion of the spectrum to be photographed o.rt plates sensitized with dicyanin. 2. In favorable instances stellar spectra can be well observed to wave-length o.85/,. 3. T h e region of g r e a t e r wave-length than o.7o~ contains features of importance, especially in the case o.f the: later spectral types. A Single-lens Telescope. ANON. (The Optical Journal and Review, vol. 4I, No. I3, p. 868, March 2I, I 918. ) - - T h e first telescope invented, several hundred years ago, consisted of two lenses, a convex lens for the objective and a minus lens for the eye-piece. We still have this form of telescope in use, but it is now made binocular; that is, the ordinary opera-glass or field-glass. The magnifying power of such an instrument would be the same if it consisted of one tube and not two. In fact, we can take two lenses from a trial case, one plus the other minus, and hold them at the proper distance so as to have a telescope in its simplest form. When the eye of the observer is hypermetropic i~ is possible to obtain a magnifying effect similar to that produced by a telescope, by means .of a single lens. The eye of a person, hypermetropic (farsighted) 1.5o D. (diopters), will be optically similar to that of an emmetrope (person with normal vision) wearing a minus 1.5o D. sphere. Therefore, if we select a suitable plus sphere and hold it out at the right distance in front of the uncorrected eye there should be a magnifying effect, and there is. Should a plus 0.75 D. sphere be used in this way, and held at a distance of 26 inches from the eye, there will be magnification of two times. If the hypermetropia is higher than 1.5o D., the magnification will be higher; also, if the low-power plus lens used as an objective is hung up in some convenient manner, a lower power can be used, the observer takes his position farther away, and there will be a greater magnification. Some years ago an amateur yachtsman, who had a hyperrnetropic error of 2 D., hung a large lens of low power in his club window, and then, by taking a comfortable position a few feet back of the lens, he could see the boats sailing by under a magnification of three or four diameters, and in perfect focus. VOL. I85, No. IIO9----51
U . S . BUREAU OF STANDARDS NOTES.
705
running t o w a r d the red. Circums:tances indicated that this band might be due to titanium oxide, and experiments since made at the Bureau of Standards have shown a band in this position in the spectrum o,f the titanium arc. T h e greatest wave-lengths observed in stellar spectra appear, by extrapo,lakion, to be about o.87/,.. The general co.nclusions arrived at are as. follows: L M a n y stellar spectra possess sufficient intensity in the region of waveqength o.8o/* to enable this portion of the spectrum to be photographed o.rt plates sensitized with dicyanin. 2. In favorable instances stellar spectra can be well observed to wave-length o.85/,. 3. T h e region of g r e a t e r wave-length than o.7o~ contains features of importance, especially in the case o.f the: later spectral types. A Single-lens Telescope. ANON. (The Optical Journal and Review, vol. 4I, No. I3, p. 868, March 2I, I 918. ) - - T h e first telescope invented, several hundred years ago, consisted of two lenses, a convex lens for the objective and a minus lens for the eye-piece. We still have this form of telescope in use, but it is now made binocular; that is, the ordinary opera-glass or field-glass. The magnifying power of such an instrument would be the same if it consisted of one tube and not two. In fact, we can take two lenses from a trial case, one plus the other minus, and hold them at the proper distance so as to have a telescope in its simplest form. When the eye of the observer is hypermetropic i~ is possible to obtain a magnifying effect similar to that produced by a telescope, by means .of a single lens. The eye of a person, hypermetropic (farsighted) 1.5o D. (diopters), will be optically similar to that of an emmetrope (person with normal vision) wearing a minus 1.5o D. sphere. Therefore, if we select a suitable plus sphere and hold it out at the right distance in front of the uncorrected eye there should be a magnifying effect, and there is. Should a plus 0.75 D. sphere be used in this way, and held at a distance of 26 inches from the eye, there will be magnification of two times. If the hypermetropia is higher than 1.5o D., the magnification will be higher; also, if the low-power plus lens used as an objective is hung up in some convenient manner, a lower power can be used, the observer takes his position farther away, and there will be a greater magnification. Some years ago an amateur yachtsman, who had a hyperrnetropic error of 2 D., hung a large lens of low power in his club window, and then, by taking a comfortable position a few feet back of the lens, he could see the boats sailing by under a magnification of three or four diameters, and in perfect focus. VOL. I85, No. IIO9----51