Читать книгу The Dominion Astrophysical Observatory, Victoria, B.C - J. S. Plaskett - Страница 3
ОглавлениеIntroduction
This description of the observatory, its equipment and work has been written by the director in response to a need, frequently expressed by the numerous visitors to the institution, of a non-technical account of the principles of the telescope and of the work of the institution. This account will commence by a short historical sketch of the beginnings of the undertaking followed by a description of the observatory and telescope and concluded by a resume of its work.
Historical Sketch
This observatory is a branch of the Department of the Interior of the Federal Government, the department which has charge of the administration of the western lands of the Dominion. In the colonization of these lands, one of the obvious first needs was a survey of the boundaries and subdivision into townships and sections. This need led to the organization of a surveys branch of the department and out of the necessity of accurate astronomical observations to delimit the boundaries and define the position of the base lines for subdivision work arose the astronomical branch. The first Chief Astronomer of Canada, the late Dr. W. F. King, was a man of sterling integrity and remarkable ability and to his genius must be ascribed in large degree the present development of astronomy in Canada. As Chief Astronomer and H. M. Commissioner of International Boundaries, he early realized the need of an observatory for an initial meridian, for housing and standardizing the instruments, and for some astronomical research. He was successful in having the fine Dominion Observatory erected on the Experimental Farm, Ottawa, in 1905 which housed the Astronomical Branch, the staff of the International Boundary Surveys and later the Geodetic Survey of Canada, of which he was the first superintendent.
The Dominion Observatory was equipped with a 15-inch refractor provided with micrometer, photometer, solar and stellar cameras, and spectrograph. The writer was entrusted with the work with this telescope and the spectroscopic work especially was energetically developed and helped, with the other activities of the institution, to bring gratifying recognition from the scientific world. The need of a larger aperture for extending this part of the work was soon realized by the writer and was brought to the attention of the Government. After some delays, owing to various circumstances, it was finally decided early in 1913 to provide a large reflector for extending the work. Enquiries were at once made, specifications prepared and estimates obtained from prospective makers of the instrument. Contracts were finally awarded in October 1913 to the John A. Brashear Co. of Pittsburgh for the optical parts and to the Warner & Swasey Co. of Cleveland for the mechanical parts of a 72-inch reflecting telescope.
Location
It was necessary to know the location of the instrument before the design of the mounting could be completed as the angle of the polar axis depends upon the latitude of the site. When the new telescope was first proposed there was no thought of locating elsewhere than at the seat of government at Ottawa. However, upon further consideration it was decided that the telescope should be located where, in Canada, the best observing conditions prevailed. To determine this location preliminary selection of five likely stations was made by the aid of Sir Frederic Stupart, chief of the Meteorological Service from the meteorological records. These stations, at Ottawa, at Medicine Hat, at Banff, at Penticton, and at Victoria were occupied by Mr. W. E. Harper, astronomer at Ottawa and the astronomical conditions were observed by means of a 4.5-inch telescope. Victoria was unmistakably superior in “seeing” or defining power, in low diurnal and seasonal range of temperature and about equal so far as quantity of clear sky is concerned. For such a large telescope as a 72-inch there could be no question of the marked astronomical advantages of such a location, and it was therefore decided to locate the telescope at Victoria. While the observatory should not be in the city itself it should not be too far away, not only on account of accessibility and facility in obtaining supplies, but also the advantageous conditions of good seeing, low diurnal range of temperature and small rainfall were confined to a relatively small area near Victoria. An isolated monadnock called locally Little Saanich Mountain but now named Observatory Hill, was selected. This hill is about 7 miles north of Victoria and has a main road and an interurban railway passing its base. It has an elevation of 730 feet, sufficient area around the summit for all necessary buildings and was by far the most suitable site available.
Construction
The Provincial Government had generously agreed to give $10,000 for the purchase of a site and to build a road to the summit. This undertaking was fully met and the road, splendidly located and constructed and costing over $25,000, was completed in the spring of 1915. Contracts for the construction of the telescope pier and the circular steel walls of the building were awarded to a local firm and this work was completed in 1916. The revolving dome with accessories for the operation of the telescope was made by the Warner & Swasey Co., the builders of the telescope mounting, and was completed and erected in 1916, thus making the building ready for the telescope.
The design of the mounting was very carefully gone into by the Warner & Swasey Co. in collaboration with the writer and was completed in the autumn of 1914. Construction was at once begun and the mounting was completed and temporarily erected at Cleveland in May 1916. It was then shipped to Victoria and permanently erected in its building by November 1916.
The order for the large disc for the 72-inch mirror and for an auxiliary flat of 55 inches diameter for testing the 72-inch was given to the St. Gobain Glass Works of Paris by the Jno. A. Brashear Co. as soon as the contract was awarded. The 72-inch disc was cast and annealed by June 1914 and was fortunately shipped at once without waiting for the 55-inch disc. It left Antwerp only about a week before war was declared and it was only by this small margin that Canada now has a 72-inch telescope. Grinding and polishing were at once begun but the lack of the large flat and other difficulties delayed the completion and it was not until April 1918, about a year and a half after the completion of the mounting, that the figuring was finally completed and the telescope ready for work. Nevertheless, for an undertaking of such magnitude the work was completed in record time, four and a half years after the awarding of the contracts.
