NA TURE 



[November 16, 1905 



five-foot reflector should throw light on the past and future 

 condition of the sun. All the principal researches will thus 

 be made to converge on the problem of stellar develop- 

 ment. The name " Solar Observatory " is regarded as 

 appropriate, since the spectroscopic study of stars and 

 nebulae, to be carried on in connection with the solar 

 work, are essential elements in any attempt to determine 

 the mode of origin, the development, and the decay of the 

 sun as a typical star. 



How, then, shall we attack in an effective manner the 

 complex problem of stellar evolution? It goes without say- 

 ing that I can offer no general answer to this question ; 

 I ran only point out the three principal lines of attack 

 which we hope to pursue at the Solar Observatory. These 

 involve : — 



1 1 ) 1 he more complete realisation of laboratory con- 

 ditions in astrophysical research, through the employment 

 of fixed telescopes of the ceelostat type, and through the 

 adoption of a comic mounting for the five-foot reflector. 

 This should permit (a) the use of mirrors or objectives 

 ol greal focal length, thus providing a large image of the 

 sun for study with spectroscopes and spectroheliographs ; 

 (fe) the use of long focus grating spectroscopes, mounted 

 in a fixed position in constant 

 temperature laboratories, for the 

 photography of stellar spectra requir- 

 ing very long exposures; (c) the use 

 of \arious laboratory instruments, 

 such as the radiometer, which cannot 

 be employed in conjunction with 

 moving telescopes. 



(2) The development of the spectro- 

 heliograph in the various directions 

 suggested by recent work at the 

 Yerkes Observatory, including the 

 photography of the entire solar disc 

 with dark lines of hydrogen, iron, 

 and other elements; further applica- 

 tion of the method of photographing 

 sections of flocculi corresponding to 

 different levels; special studies of sun- 

 spots, &c. ; and daily routine records 

 of calcium and hydrogen flocculi and 

 prominences. 



(;) 'I lie construction of a five-foot 

 equatorial reflector, with ctutdc 

 mounting, and its use in the photo- 

 graphy of nebulae, the study of stellar 

 and nebular spectra, and the measure- 

 ment of the heat radiation of the 

 brighter stars. 



It was originally intended that a 

 prolonged series of determinations of 

 (he solar constant, extending over at 

 least one sun-spot period, should be 

 made an important feature of the 

 observatory's work. The plans outlined 



in " Year Book " No. 2 accordingly included an equipment 

 at Mount Wilson for this purpose, and suggested, in 

 harmony with Dr. Langley's view, that provision be made 

 for two additional stations, one near the summit of a 

 high mountain, at an elevation of about 12,000 feet, the 

 other at a much lower level on the same mountain. The 

 principal purpose of these two stations was to measure 

 tie atmospheric absorption, in order to eliminate it from 

 the solar constant determinations. The recent develop- 

 ments of Dr. Langley's researches at Washington have led 

 Mr. Abbot, who is associated with Dr. Langley in the 

 work, to the conclusion that entirely satisfactory results 

 can 1» obtained there by the method employed. The poor 

 atmospheric conditions with which the Washington 

 observers have so successfully contended, and the disturb- 

 ances arising from ground tremors in the heart of a large 

 city, would he largely eliminated at Mount Wilson. For 

 this reason it seems probable that results of higher pre- 

 cision could be obtained at this site. 



In addition to the above mentioned observations, pro- 

 vision will be made at Mount Wilson for various laboratory 

 investigations necessary in conjunction with solar research. 

 In view of the importance of securing a complete record of 

 solar phenomena when magnetic storms are in progress, 



NO. l88l, VOL. 73] 



suitable magnetic apparatus, recommended by Dr. L. A. 

 Bauer, in charge of the department of terrestrial magnetism 

 of the Carnegie Institution, will be installed at a sufficient 

 distance from the electrical machinery. 



As no description of the Snow telescope has been pub- 

 lished, the present brief account may be prefaced by a 

 statement regarding the construction of the telescope. 



In 1900, after Prof. Ritchey had succeeded Prof. Wads- 

 worth as superintendent of instrument construction at the 

 Vi 1 kes Observatory, a ceelostat with mirror of 15 inches 

 (38 cm.) aperture was made, from Prof. Ritchey's designs, 

 for the total solar eclipse of that year. This gave such 

 satisfactory results that the plan of constructing a large 

 ceelostat was again taken up. Unfortunately, however, no 

 funds were available for this purpose. In 1901, during a 

 visit to the observatory of Prof. Cross, chairman of the 

 Rumford committee, I showed him the details of the 

 instrument, as worked out by Prof. Ritchey. The design 

 called l"i a ceelostat of 30 inches (76 cm.) aperture, with 

 second plane mirror of 24 inches (61 cm.) aperture, the 

 latter mounted so as to slide north-east and south-west on 

 rails lying east of the ceelostat. The concave mirror, to 

 which the light was reflected from the second plane mirror. 



The Snow Telescope when 



tory. 



had a local length of 61 feet, and a second concave mirror, 

 of 165 feet (50-3 m.) focal length, was also to be used. 



At the kind suggestion of Prof. Cross, a grant of 500 

 dollars was made by the Rumford committee in aid of an 

 investigation to be undertaken with this telescope. Sub- 

 sequently, through the kindness of Prof. Pickering, chair- 

 man of the Draper committee, two other grants, of 500 

 dollars each, became available. With these funds, helped 

 out by small amounts obtained from other sources, the 

 work was begun. 



A gift of 10,000 dollars from Miss Helen Snow, of 

 Chicago, in memory of her father, the late George W. 

 Snow, provided sufficient funds to complete the telescope 

 and to instal it in a suitable house. The ceelostat was 

 mounted on a brick pier, at a height of 15 feet (4-57 m.) 

 above the ground. In Prof. Ritchey's design of the 

 previous instrument the rays were reflected in a north- 

 easterly direction from the ceelostat mirror to a second 

 plane mirror, which sent them toward the south-west to 

 one or the other of the concave mirrors. In designing the 

 Snow telescope, a new arrangement of the second mirror 

 was adopted by Prof. Ritchey, at the suggestion of Mr. 

 C. G. Abbot. As Fig. 1 indicates, the light is reflected 

 upward and to the south from the ceelostat mirror to a 



