226 ASTRONOMY. 



for 1877. The work was done by Professor Holden during 1876 and 1877. 

 The exact dimensions of the objective were measured and the radii of 

 curvature computed so that they are known within yfo of an inch. The 

 indices of refraction could not be determined as the makers did not pre- 

 serve any fragments of the glass. The focal length was measured and 

 computed with assumed indices, and these agree to about 0.05 inch. 

 The periodic and progressive errors of the screws were determined by 

 means of a dividing engine and found to be practically zero. The two 

 screws were made by the Messrs. Clark. The lengths of 1 revolution 

 are— Screw I, 0.018775 ± 0.000902 inch ; screw II, 0.0187G3 i 0.000001 

 inch, at 32° F. 



The values of these revolutions in arc have been determined in five 

 different ways. 



A refractor of 36 indies for the Lick Observatory. — The trustees of the 

 Lick Observatory have finally closed the contract for the optical part of 

 their great telescope. There has been considerable doubt whether a 

 refractor or an enormous reflector would be selected, but the decision 

 is in favor of the former. The object glass is to be 3 feet in diameter, 

 and the Olarks of Cambridge, Mass., are to make it for $50,000. The 

 mounting for the instrument is not yet provided for. It will i^robably 

 be about three years before the telescope is finished. If the instrument 

 proves successful, it will be the most efficient ever pointed at the heav- 

 ens. Its power will exceed that of the Pulkova glass by 44 per cent., 

 and it will be almost twice as powerful as the great telescope at Wash- 

 ington, which at present is the best of its kind. — San Francisco Scien- 

 tific Press. 



A novel way of comparing clocks, distant from the standard clock, 

 has been introduced at the Washburn Observatory, where it has been 

 applied to a tower-clock, some 2,000 feet distant. 



A single telegraph wire was led on poles from the observatory to the 

 clock, with a ground connection at each end. In the circuit at the clock 

 an ordinary microphone (Blake-transmitter) was i>ut through a four- 

 XJointed switch at the observatory; the telephone can be thrown into 

 the clock circuit, and a battery (usuaUy of one or two standard Daniell's 

 cells) is also brought into circuit. 



When this is done the beats of the clock (every 2 seconds) can be dis- 

 tinctly heard. If the means of identifying the beginning of each min- 

 ute are at hand, accurate comparisons between the tower-clock (error 

 and rate unknown) and any of the observatory clocks can be made. 



This has been accomplished in a very simple way as follows : On the 

 wheel which moves the second hand (which revolves in one minute), a 

 brass disk about 2 inches in diameter, which revolves with it, has been 

 put. Kear the outer edge of this disk is a steel pin. Six seconds before 

 the beginning of each miuute this pin picks up the short end of a lever, 

 some 5 inches long, and raises the hammer end during 6 seconds. 

 Exactly at 60 seconds the piu releases the hammer, which falls through 



