28 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



time dropping a time-ball erected by the Western Union 

 Telegraph Company on their main building in New York 

 City. The ball is dropped at New York noon, for the bene- 

 fit of navigators and others. This ball has been in opera- 

 tion for lour months without a single failure. It is al- 

 ways within 0.5 9 of the truth, and every day its error is 

 published in the New York papers, so that it is practical- 

 ly a perfect signal. 



A similar one is to be erected at Baltimore at the expense 

 of the Baltimore Board of Trade. 



The Observatory of Harvard College offers to supply 

 standard time to railways and others in New England in 

 extension of its present system, which is already widely 

 useful. 



The Navy Department has printed an important paper on 

 the rates of chronometers as affected by temperature, by 

 Lieutenant-Commander C. H. Davis, U.S.N., and the same 

 subject is elaborately treated by MM. de Magnac and Yil- 

 larceau in " La Nouvelle Navigation." 



INSTRUMENTS AND OBSERVATORIES. 

 .Astronomical Instruments. 



Alvan Clark and Sons, of Cambridgeport, have just com- 

 pleted an 11-inch photographic refractor for the Lisbon Ob- 

 servatory. It can also be used for visual purposes. The 

 general design of its mounting is very stable and elegant. 

 They have also finished the objective of a new 9^-inch equa- 

 torial for Princeton College. It is constructed on Gauss's 

 curves, and is said to be very fine and to have decidedly 

 less outstanding color than the ordinary forms of this aper- 

 ture. The crown-glass is capable of being rotated in the 

 cell of the flint, and is thus separated from it. In this way 

 it is intended to adapt this objective to photographic work. 

 Xo crown-glass has yet been ordered for the 27-inch flint- 

 glass belonging to Yale College, and the M'Cormick 26-inch 

 glass is still in the workshop, although it is fully completed. 



Mr. Howard Grubb, of Dublin, publishes an important 

 paper on the great telescopes of the future, in which lie 

 discusses, first, the advantages of each class of instrument, 

 and, second, the effect upon these advantages of increasing 



