MARVELS of MODERN ASTRONOMY

New Zealand Graphic, Volume XV, Issue X, 7 September 1895, Page 284

MARVELS of MODERN ASTRONOMY

BY

Rose Ohalloran

THE expected completion of the Yerkes telescope before the end of the present year awakens many thoughts and hopes and fears in the minds of astronomical students throughout the world, as to the possiblities vested in the elaborate equipment of the new observatory. Like the Lick telescope, it has been manufactured with the view of surpassing all others previously made. If it were but a matter of money, sire and time, fulfilment might be assumed, but optical science has to contend with drawbacks that strengthen and grow in proportion to the size of the lens. There is no doubt, however, but that the munificence of Mr Yerkes in the cause of science will yield great and enduring results. On an elevation near the shores of Lake Geneva, Wisconsin, many miles removed from the disadvantages of city surroundings, a cruciform structure has been erected, mainly with a view to stability, though its gray brick walls and domed roofs have also attained no small share of architectural merit. The large dome on the west side, being ninety feet in diameter, will afford ample space for the great telescope, which is a 40 inch refractor.

All important details have received more than usual thought and study, and as the construction of a large telescope and its accessories is no longer an untrodden path there has been a wide scope, both for the avoidance of mistakes and the adoption of approved experiments. The chief instrument, as the illustration shows, is similar in general aspect to the Lick refractor, with which American astronomers and a large portion of the Californian public are already familiar. The colossal tube, which alone weighs six tons, varies in diameter from 42 inches near the lens to 52 at the central part and 38 at the eye end, and is 62 feet in length, being two feet longer and four inches wider in diameter than the tube at Mount Hamilton.

On account of the unfortunate tendency of these heavv tubes to flexure, or a drooping of both ends from the propped up central part, which is fastened to the declination axis, special care has been given to attain rigidity in its construction, as such flexure counteracts

to some extent the excellence of lens and eyepiece. By many ingenious mechanical contrivances the mounting is also given the full benefit of past experience. As in the case of all giant refractors, it has an equatorial motion, and keeps pace by means of a driving clock with the movement of the heavenly bodies westward, thus counteracting the effect of the earth’s rotation. The movable floor is nearly similar to that of Mount Hamilton, but, with the movements of the dome and telescope, is controlled by electric motors convenient to the observer.

The two smaller domes will be used for telescopes of medium size, one a 12-inch and the other a 16-inch, and between them is a room occupied by the heliostat, an instrument so constructed as to cause the sunbeam under observation to remain fixed and unaffected by the diurnal motion.

The meridian-room at the east end of the structure is destined to hold a telescope of more than orainary efficiency for observing heavenly bodies on the meridian and making accurate measurements of their positions. The meridian circle, as it is named, is devoted exclusively to this most important duty of an observatory. Spectroscopic, physical, and chemical laboratories, photographic apartments, a library, and many other accessories to a thoroughly equipped observatory occupy the central portion of the building. The director. Professor George E. Hale, will devote special attention in person to solar observations, and photographs of the sun will be taken every few minutes on clear days. The chief centre of attraction, the 40-inch lens, first designed for a proposed Southern California observatory, will be devoted to those researches that are most thwarting to the powers of average instruments ; such as the discovery of new satelltes, uebular and planetary details, and close double stars, which have been chiefly discovered by Professor S. W. Burnham, now a member of the staff.

The coming winter will probably forecast the achievements of the great telescope. Those who understand the possibilities of optical science are not likely to be disappointed, but the enthusiasts who are yearning for a message from Mars will no doubt find that interplanetary signal service is still in a backward condition.

A short account of the other great observatories of the worid may be of some interest at this time. Of the Lick Observatory, already a familiar subject to the reading public, it need only be said that it will prove a close rival to any astronomical institution likely to appear for many years. As terrestrial divisions are of little moment in a science that reaches beyond the stars, the ‘ four corners of the earth ’ being all too limited for the aim in view, the description will proceed in the order of size and efficiency without regard to country, continent or period of construction. It is not generally understood that a

reflecting telescope in order to be the peer of a refractor, must be about double its tubular diameter, and then weight and unwieldiness hamper its use and] accuracy, though for photographic and spectroscopic work it possesses compensating facilities that leave the conceded superiority of the refractor open to some exceptions. On the ground of general preference, the large reflectors will be considered first and separately. Five miles west of Paris the ruined Castle of Meudon, once the scene only of royal pageantry and revels, is now devoted to a nobler use and holds in its lordly tower an instrument destined for greater achievement than any of the royal occupants of former years. More than thirtytwo inches in diameter and fifty-five feet in focal length, it is inferior in size only to the Lick and the Yerkes telescopes. Somewhat unique in construction, it has been made with a view to meeting the requirements of the * new astronomy,’ which previously were a secondaryconsideration in the designing of a giant telescope. This so-called new branch of the science is comparatively new to mankind, preoccupied as they have hitherto been with wars and superstitions, while the great works of nature rested unknown. After half a century of investigation it is still in its infancy, though with a promising future opening before it. It deals with the knowledge gained by means of the spectroscope of the vaporous material of which the luminous orbs of heaven are composed; and also includes the photographic discoveries withheld from telescopic vision. The 32inch lens is mounted in a square tube of steel which is also adapted to hold a 24-inch lens specially suited for photographic work.

The spectroscopic equipment will soon place the observatory in the lead of astrophysical research, and the specimens of photography that have already appeared are of the highest excellence.

A reflecting telescope three feet and a third in diameter completes the important part of the equipment, which will owe much of its efficiency to the scientific zeal of M. Janssen, the director, who was the first to announce that the solar flames could be viewed without the sheltering shadow of an eclipse. This noted French savant it was who soared in a balloon beyond the-reach of German rifles during the siege of Paris for the purpose of vewing a solar eclipse in the line of totality. Unfortunately a cloudy day frustrated his efforts and the instruments he had conveyed under such difficulties were unused. Though advanced in years he ascended to the summit of Mount Blanc in IS9O, and took some valuable solar observations at that high altitude, where an observatory has since been established.

The director of the Imperial Observatory, Pultowa, Russia, ordered a lens thirty inches in diameter from Messrs Clark, of Boston, in 1879, and what at that time was the largest refracting telescope in the world was completed in 1882. It is considered to have a slight advantage over the Lick in the matter of colour correction and the obtrusive violet halo is less conspicuous in observations on that account. The mounting of the polar axis was officially commended by Professor Newcomb a few years ago, when visiting the European observatories, and also the method of illuminating the finding circles so as to be readable at the eyepiece by the observer.

This latter convenient device was then almost unknown in this country, though since put in use on a more effective scale at Mount Hamilton. The detection of close double stars, the measurement of star distances, and investigations ss to the constitution of the rings of Saturn, are among the researches to which this great instrument has been devoted. The observatory also contains a 15Jz-inch refractor, excellent meridian circles, an astro-physical laboratory, equipments for photographic work, an extensive astronomical library containing many

rare and valuable books, and is thus fully fitted to compete in work with any of the European institntions. Considering the bleak northern skies through which it seeks to penetrate the mysteries of space, its contributions to science are of solid valce, though startling discoveries do not often emanate from that distant shrine.

The close rivalry to the Pulkowa instrument is the more recently erected 29 9-10th inch refractor of Nice. The gift to science of M. Bischoffsheim, a wealthy banker of Paris, it has the advantage of many previous experiments, of an altitude of 11,000 feet and of a genial sky. It must be admitted, however, that the mists of the Mediterranean hovering over Mount Gros, on the once barren summit on which it has been erected, interfere seriously with the good definition of observed objects. The still further discouraging new, also comes that it is the experience of M. Perrotin, the director that two hours' work with a large instrument is as fatiguing as eight with a small one, the labour increasing in proportion to the cube of the aperture, the chances of seeing decreasing in the same ratio, while the gain in enlarged views rarely keeps pace with the disadvantages.

He is admirably true to science in thus putting the outcome of the expenditure in the light in which it has appeared to him. In the extensive enclosure on the mountain top the buildings are unconnected, which may be inconvenient to the astronomers, but it is an advantage in the use of the smaller instruments which are freer from draughts and obstructing higher domes. A peculiar feature is the method of revolving the large dome, which is nearly similar to that of the Lick telescope in dimensions and weight. Lieutenant Winterhalter, V.S.N., who was officially deputed to inspect the leading astronomical institutions of Europe in 1887, describes the contrivance by which the dome floats round in a ring-shaped tank of water in the following words : ' The weight of the dome is taken up by means of a circular float attached to and making a circuit of its base and resting in tanks of the same shape, partly filled with water. The dimensions of the float are, of course, calculated to give the buoyancy necessary to float the dome, which weighs about ninety-six tons. The depth and width of the tank are necessarily somewhat greater than the corresponding dimensions of the float. They are calculated to be somewhat more than sufficient for the u;e of water, a liquid of the least density that is likely to be employed as a floating medium. About half of the tank projects beyond the line of the masonry and is there supported by heavy cast-iron standards turning up into hanging knees and by intermediate angle-iron. ‘ The dome thus becomes a hemispherical vessel floating and turning in a circular basin.’

To avoid the impediment of a frozen surface on the water, a small quantity of the glycerine of commerce can be added, or the tank can be slightly heated with gasjets underneath.

At full speed the dome sails round its restricted channel in eight minutes, and for moderate speed the attached rope needs only the effort of one hand. The unique mechanical conception has been found to work with entire satisfaction. Machinery resembling that by which the Lick dome rolls round so smoothly and swiftly has also been provided at Nice to forestall any failure in the design of M. F. Eiffel, who was the constructor.

The cost of the construction of such a dome is estimated to be 540.000. A 15-inch refractor, an excellent meridian circle, a portable transit instrument and all the usual acessories of a first-class modern observatory are to be found in this scientific institution, which has been fitted up at the cost of $200,000.

The measurement of double and multiple stars and a search for new satellites moving around the major planets have been part of the work of the great telecope, but in the latter respect at least it has looked in vain. When the observatory of the University of Vienna was built on a slight elevation above the Danube the advantage of a high altitude had to be overlooked and a clear region within easy reach of the citv was all that was attained. It was completed in 1880 and the refractor, twenty-seven inches in diameter, was looked on as a colossal achievement, surpassing in size even the twenty-six inch refractor of Washington, then in use for some years. Being entirely constructed by one firm, that of Sir Howard Grubb of Dublin, it was certainly a marvel of versatility in mechanical skill, and many of the methods adopted have not been superseded, though new requirements have given them a new and more perfected form. This is mere to be wondered at, as some of them, though wel'designed, were untried experiments. The illumination of parts of the instrument at a distance from the observer by

one lamp was arranged by several refracting prisms, which scattered the light in the angles required till the object could be distinctly seen bv the means of microscopes near the eyepiece.