158 TRANSACTIONS OF THE [fEB. 15, 



II. ON" THE NEED OF A NORMAL TIME SYSTEM FOR OBSERVA- 

 TORIES. 



Any observatoiT can, when supplied with a good transit in- 

 strument and a fine clock, determine very accurately tlie error 

 of that clock at the time the observations are made, but owing 

 to the non-constant character of the rate of the clock it is im- 

 possible to calculate, with the desired accuracy, the error of the 

 clock after the lapse of several days, during which, for any reason, 

 observations have not been taken. Cloudy weather often pre- 

 vents, for many days, the taking of observations. 



The people of this country have been educated to an apprecia- 

 tion of accurate time — time which is correct to within less than 

 a second, or even one-half a second. Time balls are dropped in 

 many of our large cities, and the error of the " drop " is usu- 

 ally published the next day in feiitlts of seconds. Jewellers de- 

 pend for rating watches, etc., on the close accuracy of the " time 

 signals " received by them over the wires of some time distribut- 

 ing company. Scientific observers often are compelled to rely 

 on the stated errors of the telegraphic time signals sent over 

 considerable lengths of line. 



It becomes necessary, therefore, for those managing time 

 systems to be very careful in sending out-" time signals," and in 

 stating the errors of those signals. 



In the New York City Telegraphic Time Service, of which 

 Mr. Jas. Hamblet is the manager, the central clock distributing 

 the signals throughout our city is now checked by daily chrono- 

 graphic comparisons with several observatories. Several years 

 ago these comparisons were made with the observatories at Har- 

 vard, Yale, Alleghany, and Washington, all of wliich have fine 

 time systems in operation. The discrepancies between tiie cal- 

 culated errors of the New York clock, as determined from the 

 several comparisons, were often quite large, in some cases ap- 

 proaching to five seconds. 



These comparisons were discontinued for several years, but 

 recently have been undertaken again. My attention was drawn 

 to the desirability of tlio continuance of these comparisons by 

 the impossibility of making my time observations agree with the 

 stated errors of the New York system — founded only on the 

 standard noon signal sent from the Washington observatory. 



On my calling Mr. Hamblet^s attention to the matter, he offered 

 to take up again tlie old system of many comparisons, and has 

 sent me the following records. 



All the comparisons except those for Columbia College were 

 made by Mr. Hamblet at the rooms of the time system. These 

 comparisons for Columbia College were made on our own clirono- 



