ASTRONOMY. ' 225 



Paris, but it took him foui years to produce perfect one§, anc. the diffi- 

 culty he experienced was the main cause of the delay of the work. 

 Although the entire moviU;^ parts weigh seven tons, through counter- 

 I)oises and other expedients they can be operated at will by one man very 

 easily. The circles are carefully and minutely divided, and the observer, 

 while sitting in his chair, can read any of them by means of a little tel- 

 escope attached to the side of the tube of the main telescope. A single 

 gas lamp, hung by gimbals at the end of the declination axis, serves to 

 light up each vernier and circle that may be required to be read. The 

 castings of which the frame is formed are about ten tons in weight. The 

 clock-work is controlled by Mr. Grubb's frictional governor and his new 

 electric control apparatus. There are two right ascension circles, each 

 2 feet in diameter, one of which can be read from the eye end of the 

 telescope and the other from the ground floor. The declination circle is 

 5 feet in diameter, and is read from the eye end of the telescope. This 

 tine refractor is already placed in the magnificent observatory of Vienna, 



Mr. Gnibb has reprinted from Engineering his interesting papers on 

 the manufacture of this telescope. We shall look with interest for an 

 account of its actual performance. 



The observatory of Williams College has mounted its new 5-inch 

 Eepsold meridian circle, and Professor Safford intends, we believe, to 

 prosecute his zone observations which were unfortunately interrupted 

 by his leaving Chicago. 



This instrument is similar to those of Bonn, Brussels, and Strassburg 

 in design, and is of the same size as those made or ordered for the ob- 

 servatories of Tokio, Wilhelmshafen, and Madison. 



Mr. Burnham has lately invented a lamp for illuminating, the webs 

 of a filar micrometer through the end of the box, which is perfectly sat- 

 isfactory in all respects. The first apparatus was made at the Wash- 

 burn Observatory in Madison, and is described in its Publications ISTo. 1. 

 The second was made by Alvan Clark & Sons for the new 12-inch tele- 

 scope of the Lick Observatory. They are prepared to supply them to fit 

 any micrometer. 



The practical importance of this device is very great as it saves time 

 and trouble, and by a steady and satisfactory illumination of the 

 threads conduces to accurate bisections. Either oil or gas can be used 

 in these lamps. 



A refractor of 30 inches. — The flint glass for the 30-inch refractor for 

 llussia has been finished by Alvan Clark & Sons within the year 1881, 

 and we learn that the crown disk has been received from Fell and is 

 found to be satisfactory so far as can now be known. Two attempts 

 were made before the final successful casting. M. Feil will now pro- 

 ceed to the 36-inch disks for the Lick Observatory. 



The Washington refractor of 26 inches. — An investigation of the ob- 

 jective and of two filar micrometers of the 26-iuch Clark telescope of tho 

 Naval Observator3^ forms Ai^pendix I of the Washington Observations 

 S. Mis. 1C9 15 



