The Astrophysical journal . ls on Mount Wilson duringthe best observing hours of the dry season has made it seem advisa-ble to try the experiment of using the inner tower alone at first,depending for stability on a large number of steel guy ropes. Theinner tower will be used as a skeleton, without covering, so as toexpose but little area. If it does not prove to be steady enough,the other tower, with louvres, will be erected later. The second mirror stands near the middle of the tower. It is to beelliptical in form, with major axis of 22\ inches ( cm) and minoraxis of i2f inches ( cm).
The Astrophysical journal . ls on Mount Wilson duringthe best observing hours of the dry season has made it seem advisa-ble to try the experiment of using the inner tower alone at first,depending for stability on a large number of steel guy ropes. Theinner tower will be used as a skeleton, without covering, so as toexpose but little area. If it does not prove to be steady enough,the other tower, with louvres, will be erected later. The second mirror stands near the middle of the tower. It is to beelliptical in form, with major axis of 22\ inches ( cm) and minoraxis of i2f inches ( cm). Both this mirror, and the coelostatmirror (17 inches = cm in diameter), will be 12 inches ( cm 1 President Woodward assures me, after his experience in observing from thesummit of lofty wooden towers, similarly shielded, in the work of the Coast Survey,that no trouble from vibration need be feared. 2 Contributions from the Solar Observatory, No. 4; Astrophysical Journal, 23,6, 1906. MINOR CONTRIBUTIONS AND NOTES 71. Fig. 1.—Vertical Coelostat Telescope 72 MINOR CONTRIBUTIONS AND NOTES thick). Experiments made by Professor Ritchey have shown that whena silvered mirror is heated by radiation, the front (warmer) surfacebecomes convex and the rear surface concave. By placing an elec-trically heated disk near the rear surface the form can be quicklyrestored, though the figure, when thus corrected, is not perfect. Thisexperiment, and others involving a test of the curvature of the surfaces,show that the effect of exposing the mirror to sunlight is to producean actual bending of the mirror. The simple expedient of greatlythickening the disk, so as to increase the resistance to bending, natur-ally suggested itself to me. The second mirror is given an elliptical form, so that it may becompletely filled with sunlight without undue increase in the size ofthe coelostat mirror. Its position in this design is such that thepolished and silvered back can easily be exposed to the Sun
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
