314 SCIENTIFIC RECORD FOR 1882. 



Halstead Observatory. — The new telescope at Princeton is now at last 

 in position and nearly ready for work. It was made by A. Clark & 

 Sous, of Cambridge, the glass disks being furnished by Feil, of Paris. 



The diameter of the object-glass is 23 inches, and the focal length 

 within an inch or two of 30 feet. At present its only superiors in the 

 United States are the 26-inch telescopes of the Naval Observatory, at 

 Washington, and of the University of Virginia. In Europe the 27-inch 

 refractor of the Vienna Observatory and the 25-inch telescope of Mr. 

 Xewall surpass it. Five other instruments of larger dimensions are in- 

 deed now constructing, two in Paris, and three in Cambridge ; but it 

 will be some time before any of them are finished. 



In the Princeton telescope the lenses which compose the object-glass 

 are separated by a space of nearly seven inches, allowing a free circu- 

 lation of air between them, and securing a rapid equalization of temper- 

 ature. This construction also prevents the "ghosts" (formed by re- 

 flections between the lenses), which are A^ery troublesome in some Iffrge 

 instruments. 



The spherical and color corrections are very fine in the Princeton 

 telescoi)e, and the performance of the object-glass, so far as can be 

 judged from a few nights' use, is entirely satisfactory. It is intended 

 to devote the instrument for the present mainly to spectroscopic obser- 

 vations of the stars. The spectroscope is of Christie's direct vision form, 

 which has been successfully used at Greenwich for several years. Mr. 

 Christie (Astronomer Eoyal) very kindly supervised its construction 

 (by Hilger, of London), and there is every reason to hope that it will 

 prove a magnificent instrument. It is much larger and more powerful 

 than anything ever used before in stellar work ; it is nearly six feet long, 

 and admits through the prisms a beam 2\ inches in diameter. 



A four horse-power gas-engine works the dome and shutters. It also 

 drives one of Edison's dynamo machines, which furnishes a powerful 

 current for ijurposes of illumination, and for producing the spectra of 

 metals or gases to be compared with those of the stars. 



Yale College Ohservatory. — From a late report of Prof. H. A. New- 

 ton, director of Yale College Observatory, we leaiu that the Board of 

 Managers are to proceed at once to erect suitable buildings on the ob- 

 servatory grounds for the new heliometer just received from Messrs. 

 Kepsold, of Hamburg, and the new equatorial telescope, purchased of 

 Howard Grubb, of Dublin, last summer. The towers for these instru- 

 ments are now being erected, and the heliometer is expected to be in 

 place by the first of August, that the observers may have ample time 

 to prepare for the best use of the instrument at the transit of Venus in 

 December, 1882. The new equatorial of eight inches aperture is ex- 

 l^ected from the makers about the middle of August, and it will also be 

 ready for use early in the autumn. The domes for these instruments 

 were made by Mr. Grubb. The longitude of the transit house of this 

 observatory was recently determined by exchanges of telegraphic sig- 



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