OF ARTS AND SCIENCES. 17 



On December 5, 6, and 7, at noon, the Washington signals were 

 received at Cambridge, and compared by chronograph with our sidereal 

 clock. The result, after allowing for the difference in longitude, was 

 that the Washington clock was fast 0'.6, 0'.4, and 0'.3 on the three 

 days respectively. The signals were promised for December 4 also, 

 but were not received, as the lines were occupied in transmitting po- 

 litical news. A good example is thus afforded of the importance of 

 depending on the local observatories for supplying the public with 

 time. 



The clock distributing the mean-time signals from the Harvard 

 College Observatory is kept as nearly as may be 15'.5 fast. The 

 time is therefore that of the meridian passing through the State House 

 in Boston, and 4*^ 44" lo^5 west of Greenwich. On the day of the 

 transit the deviation of the Washington signals was noted, and, to 

 avoid the confusion arising from two systems, our signals were brought 

 to an approximate agreement with them, rather than with our own 

 determination of the local time. Frequent comparisons were made with 

 our sidereal clock, and showed that at December 5.8 our signals were 

 0'.6 fast ; at December 6.0, 0^5 fast ; at December 6.3, 0'.5 fast ; 

 and at December 6.8, 0'.2 fast. Allowing for the difference of longi- 

 tude, these signals therefore did not differ more than a tenth of a 

 second from the Washington signals, but to reduce them to the true 

 time both should be regarded as about 0'.5 fast. In other words, in 

 reducing to Greenwich mean time, the longitude for the Washington 

 and Boston signals should be taken as 5^ 8™ 11^7 and 4'' 44"" 15\0 

 respectively. Since the observed times of contact are known to be 

 liable to variations of several seconds, these corrections in any case 

 are small, and may be neglected without serious error, especially as 

 it is useless to give the resulting times of contact more closely than 

 to sinole seconds. 



O' 



Contacts. 



A statement of the results of the contact observations is given below, 

 in Table 11. The upper part of the Table contains in successive 

 columns the names of the observers and recorders, the apertures and 

 focal lengths of the telescopes in centimeters, their magnifying powers 

 in diameters, and the corrections required at ingress and at egress to 

 reduce the observed times to Cambridge mean or sidereal time 

 according to the timepiece employed. These corrections are given 

 in accordance with the assumption that the signals furnished by the 

 mean-time clock give the time of a meridian 4'' 44™ 15\5 west of 



VOL. xviii. (n. s. X.) 2 



