198 SCIENTIFIC RECORD fOR 1884. 



the bands of the Government commissioner at Washington — photographs 

 wliich Professor Harkness reports as "Ukely to yield valuable results"; 

 to the partial reduction of observations made with the heliometer; and 

 to the appointment in January, 1884, of Dr. Elkin as the astronomer 

 in charge of this instrument for a period of three years. In addition to 

 a thorough general investigation of the new heliometer, Dr. Elkin 

 reports a series of observations of the diameter of the planet Venus, the 

 determination of a large number of positions of the Moon, and good 

 progress in his principal work, the triangulation of the group of the 

 Pleiades. Mr. Sherman, assistant in the observatory, has been engaged 

 in magnetic observations, and in determinations of the form, polariza- 

 tion, and position of the Pons-Brooks comet. The details of Dr. Wal- 

 do's report on the horologic and thermometric bureaus occupy- more 

 than half of the entire pamphlet. He notes a marked increase in the 

 excellence of the watch-movements submitted to the observatory tests. 

 An international system of watch trials has been agreed upou, by which 

 the. operations at Geneva, Kew, and New Haven will be strictly com- 

 parable. The work of the thermometric bureau has been much ex- 

 tended over previous years, and there has been a total of more than 

 6,000 thermometers examined. (The Nation.) 



ASTRONOMICAL INSTRUMENTS. 



In 1879 Privy Counsellor Otto von Struve, director of the observatory 

 at Pulkova, near St. Petersburg, visited America and contracted with 

 the Messrs. Clark for the construction of an object-glass 30 inches in 

 diameter. It was completed last year and accepted by Dr. Struve, who 

 came to this country to examine critically its performance. The mount- 

 ing for this great glass has been made at the shojis of the Eepsolds, 

 where many cardinal improvements in the mounting and mechanical 

 accessories generally have been devised.* This telescojje will be set up 

 at Pulkova, and ready for work, at some time during the present year. 



A section of Professor Newcomb's late report relates to the new equa- 

 torial coude at the Paris Observatory, a refractor in which the rays of 

 light are brought to the object-glass after reflection from two plane mir- 

 rors. The chief advantage of this construction is that the observer does 

 not have to follow the eye-piece of his telescope, but always sits in a 

 given position in a comfortable room. This form of instrument is not 

 suitable when the highest optical power is sought; but it surpasses all 

 others in convenience of use. 



The French astronomers have lately devised a new method of sup- 

 porting a revolving dome, wherein the base of the dome will be an an- 

 nular caisson, floating in a similarly shaped trough filled with water so 

 treated as to prevent its freezing. The dome to which this plan is to 

 be aiiplied is 65 feet in diameter. 



* It is understood that the cost of this elegant and elaborate mounting -was 36,250 

 dollars, 



