260 YEAR-BOOK OF PACTS. 



the Royal Observatory is nearly thirteen inches diameter, and the 

 length of the telescope appears to be about fourteen or fifteen 

 feet. It is so nicely balanced on its axis as to be moveable ver- 

 tically with the slightest touchy so that it can be elevated or 

 depressed to the view of any object between the horizon and the 

 zenith with such facility that it seems as if it moved self-supported in 

 air, without the least friction on the supporting pivots. 



The movement of the polar axis in longitude bearing the telescope 

 upon it is a more difficult matter, and exhibits a variety of contri- 

 vances, by which the beautiful application of the telescope and the 

 vast framing by which it is supported are carried round by a clock 

 with the most perfect smoothness, so that in watching, through a 

 microscope, the gradual onward movement of the minute scale not 

 the slightest unevenness or irregularity in the movement can be per- 

 ceived ; and this, considering that the whole apparatus set in motion 

 by the clock weighs many tons, is a proof of great skill in contri- 

 vance, and great perfection in the workmanship. The connexion of 

 the clock with the polar axis is not permanent, but is struck in 01 

 detached with perfect facility in an instant of time, so that the 

 astronomer using the telescope directs it in equatorial or vertical 

 motion with the most perfect command. If he desires to examine 

 the object he has found, he attaches the telescope to the polar axis 

 and brings the clock motion iuto operation almost in the same in- 

 stant, which then moves the telescope equatorially in an opposite 

 direction to the movement of the surface of the earth, so that the 

 line of sight through it continues directed to that one object, whether 

 it be the sun, the moon, any one of the planets or satellites, or any 

 fixed star which the observer wants particularly to examine. Behind 

 the object-glass are perceived minute cobweb lines, which enable the 

 observer to measure with accuracy the movement inherent in the 

 object he is examining, such as its revolution on its axis or the pas- 

 sage of a satellite across a planet. 



The usual astronomical observations have been made during the 

 past year, and their reduction ami printing have been carried on with 

 great regularity. The same may be said of the magnetical and 

 meteorological observations, with the exception that the dipping- 

 needles are still a source of anxiety. "The form which their anoma- 

 lies appear to take (says Mr. Airy) is, that of a special or peculiar 

 value of the dip given by each separate neeille. With one of the 

 ;i inch needles, the result always differs about a quarter of a degree 

 front that of the others, lean see nothing in its mechanical 

 struction to explain this, and 1 have been driven to the following 

 conjecture. The theory of determination of din rests on the assump- 

 tion that, when thr magnetism is r e v e rsed by double touch, the mag 



netic axis will be 1 1 » • - same u before. Nowit is < oeivable that 



tin' magnetizable particles of steel mayoonsial of two series, of which 

 one M prepared to take one kind of magnetism and the other to til.' 

 t],,- other Kind; and that the axes of these two scries may not be 

 parallel. I am supported by Professor Faraday in the ides that this 

 is not iir- bavs any foundation, 



