A. MATHEMATICS AND ASTRONOMY. 21 



VO'', or at 70 and 85, lose when exposed to temperatures 

 beyond these limits at the rate of 1.5 seconds daily for a 

 change of fifteen degrees in temperature. 5. That when the 

 connection between temperature and daily rate has been well 

 determined, it will remain constant in good instruments for a 

 long time, which need in general to be examined only once 

 in one, two, or three years. 



The vital importance of this subject to the interest of safe, 

 speedy navigation, will be impressed upon every one by the 

 disaster that befell the Atlantic, consequent upon being some 

 twenty miles (or ninety seconds of time) out in her reckon- 

 ing- 



KEPORT OF THE ALLEGHANY OBSEEVATOEY. 



Professor Langley, as director of the Alleghany University, 

 at Pittsburgh, in his report recently published refers w^ith sat- 

 isfaction to the recovery of the fine object-glass of the tele- 

 scope of the university, which was stolen on the 8th of July, 

 1872. When recovered it was somewhat scratched, and was 

 placed in the hands of Messrs. A. Clark & Sons, w^ho succeeded 

 in restoring it nearly to its pristine condition. The observa- 

 tory has been very active during the year, both in a utilitarian 

 and a purely scientific point of view. One of its labors con- 

 sisted in a connection with Austin, Texas, by a telegraphic 

 circuit of about three thousand miles, for the purpose of de- 

 termining, with the co-operation of the Cambridge Observa- 

 tory, the longitude of that point, so that it might serve as a 

 base for the future settlement of western longitudes. 



The observatory has also been constantly employed in fur- 

 nishing time signals to the lines of railroads that pass through 

 Pittsburgh, these beirig sent at all hours of day and night to 

 Harrisburg, Philadelphia, New York, and many other points 

 in the East and West as far as Chicago. The entire move- 

 ment of freight and passenger traffic over this great system 

 of roads is now regulated by a single clock at the Alleghany 

 Observatory, which may thus be considered as having its 

 beats rendered audible at every railroad and telegraph office 

 on the routes named. 



In addition to this class of labor, extensive observations 

 have been made with a zenith telescope, and remeasurements 

 of the longitude sheets of 1869, while observations have been 



