

^^ 



( 



Miscellaneous Intelligence. 299 



cost of the instrument was $19,842. The object-glass arrived in Cam- 

 bridge on the 4th of December, 1846, but the tube and mounting did 

 not arrive until the 1 Ith of June following. The instrument was mount- 

 ed on the 23d of June, 1847, and on the evening of the same day was 

 first pointed to the heavens. 



The tube of the telescope Is of wood, veneered with mahogany and 

 polished on the outside. Within, it is lined with paper, and is strength- 



ened with iron diaphragms. The flexure of the tube is counteracted 

 and its balance preserved by two brass rods seventeen feet in length, 

 having at their extremities nearest the eye-end, brass spheres filled with 

 lead, eight inches in diameter. These rods turn on a universal joint 

 near the middle or centre of motion, and oppose the influence of gravi- 

 tation on the longer and heavier part of the tube in every position. The 

 centre of motion of the whole instrument is twelve feet nine inches 

 above the floor of the dome. The focal length oi the finder telescope 

 IS forty-five inches, and its aperture three inches. 



The transit circle is by Sims of London. The object-glass, by Mcrz, 

 IS four j|nd one-eight inches aperture, and sixty-five Inches focal length. 

 The circles are four feet in diameter, being cast in one piece, and are 

 both graduated on silver from 0° to 360^ into five minute spaces, which 

 are again subdivided by micrometers, a single division of the microme- 

 ter head being equal to one second of arc, and may be read to two- 

 tenths of a second. 



Besides these, the Observatory is furnished with many smaller instru- 

 ments, and a complete set of meteorological instruments, an astronomi- 

 cal clock, and siderial chronometers. 



One of the most ingenious contrivances connected with the Observa- 

 tory is the " observer's chair," invented by the director. By means of 

 this chair, the observer can transport himself to any part of the dome 

 without moving from his seat. 



The new method o^ finding the motion of the earth has been tried at 

 the Observatory, and also by Prof. Horsford, at the Lawrence Scientific 

 School. 



During the Summer of 1848, the director being engaged with the 

 United States Coast Survey in determining differences o^ longitude, 

 turned his attention to the electro-magnetic method o{ recording astro- 

 nomical observations. The apparatus which it has been found conven- 

 Jeni to adopt at this Observatory, consists of a Grove's hattery, a cir- 

 cuit^breaking siderial dock, and a ''spring-governor.'" These are 

 connected by means of copper wires, leading to all the principal in- 

 struments. 



The spring-governor is a machine devised to carry a cylinder with 

 an equable rotary motion, so that it may make one entire revolution m 

 one minute of siderial time ; on this cylinder the commencement and 

 termination of each second of the astronomical clock is recorded in 

 exact coincidence with the beats of the clock, the observer at each tel- 

 escope is furnished with a break-circuit key, by means of which he is 

 enabled to cause a record of his observation to be made on the paper 

 covering the cylinder of the spring-governor among the second marks 

 of the clock, in such a manner that the tenths, and even hundredths of 

 a second may be read off without difliculty, as the sheet of paper, when 



