The Birmingham age-herald., 1906-09-18
BIGGEST TELESCOPE.
In the World to be Mounted in Harvard
 Observatory.
From the Boston Herald.

From the Boston Herald.
 The biggest telescope in the world Is the Common telescope, five full feet in diam eter and twenty inches wider than the Yerkes. It was constructed about ten years ago by Dr. A A. Common. a we'll known astronomer of England, who wanted 1t for research work that he was doing. He died soon afterward, and his fine telescope became idle. Two years ago it was purchased by the Harvard Col lege observatory, which proceeded at once to mount 1t on the observatory grounds at Cambridge
 The first sod was turned September 2S, 1904. Since then the work has gone on steadily but it has been necessarily rath- CT slow, for mounting q great telescope is not like building a house. Moreover. this telescope has very unusual kind or mounting Most large telescopes are sup ported by Q pedestal or foundation pier of cast iron. cement or masonry firmly built upon the ground but this telescope Is held in position by a big hollow sylinder that floats in a tank of water,
 In the first place deep excavation was made on the spot where the telescope was to stand, and a tank was constructed with thick walls of solid concrete 15 feet deep at the farther end and 21 feet long, the bottom of which slopes upward from the deep end at an angle of about 45 de- grees to the surface of the ground.
 In this tank the water tight steel float or cylinder, which Is IS feet long and ! feet inches in diameter, Is ballasted at the same angle as the bottom of the tank the buoyancy of the water support ing its weight, and delicate pivots at each end serving to steady it in position. Above this, and securely fastened to 1t by a strong iron fork and bolts Is the great tube of the telescope.
 The tube Is not circular, as one might suppose, but rectangular. Nor has 1t solid walls. The upper part of the tube for a distance of about fifteen feet Is a kind of skeleton, constructed on angle iron, which Is now covered with thick canvas, and has an inside measurement six feet square The lower end, which supports the mirror and is bolted to the iron fork just mentioned, Is a hollow cube with sides six feet in length that are made of steel plate.
 The whole structure weighs a number of thousands of pounds, but it Is so deli cately poised that it appears to have no weight at all. So strong are the bolts and pivots that 1t can be moved In any direction, up, down, or sideways. with out the slightest jar or slip. The tele- scopes in most observatories are handled by clockwork that runs by a system of weights, but the Common telescope Is to be controlled entirely by electricity.
 People are apt to think of an astron- omer as perched on ladderlike flight of steps and shlvering in a big, lonely dome on an icy winter night, yet gazing up eagerly through ponderous tube that will hardly move in response to his number fingers. Here, while sitting com fortably in a warm room, by merely look ing down an ordinary appearing little tube, the observer can see all the won ders of the sky pass mlrrored before him. while the recorder, without single effort beyond the touch of a button or the nov ing of a switch, turns the great instru- ment outside here or there, to reach any part of the starry sphere from horizon to horizon as the observer directs.
 It may sound rather odd to speak of looking down a tube at a star This re- quires some explanation. There are two kinds of telescopes, reflecting and re- fracting The reflecting telescope has mirror of glass covered with a thin coat of solver, and shows the star in the same way as the mirror over your dressing table, shows your image and the room behind you, by throwing back the light that falls upon it. The refsacting tele- scope has a lens made of two or more discs of clear glass that are set in the tube at the upper end, and through them the light rays from the star pass down the tube to the eye of the ob- server just as though he were looking through a big magnifyng glass.
 The Common telescope is a reflector, and It's great mirror, five feet in diam eter, Is placed at the lower end of the tube, so that the light from any star that is to be examined reaches 1t by pass ing down the length of the tube. Then other smaller mirrors placed along the tube above reflect this light back again up the tube to the "eyepece" or small CT tube which passes through the wall of the observing room to the observer. The end of this eyepiece through which the observer looks Is closed by power full magnifying lens. so that the image of the star, which appears as q very small point on the mirror, Is a little en- larged.
 This great telescope is intended chiefly for photometric work. that is, measuring the light of the stars. Professor Edward c. Pickering, who Is the director of Har- yard college observatory. has spent good many years in this work, and he h. tends to devote the rest of his life to 1t. Of course, he has a great many other duties, but this photometric work Is hIs personal work, and he spends three or four hours each clean night at it.
 He has already measured more than