3882 S& P. Langley—Allegheny System of Time Signals. 
(AT, dt, being the usual symbols for the respective corrections 
of error and rate) : : 
9 LHerculis, 
Aug. 10, 1872. Time-stars | si ital A. E. F., observer. 
(0 Herculis, 
At mean 9b AT. ot. 
Sidereal clock, + 79°32 +1518 
Break-cireuit chronr. +2™°22°18  -+3°*30 
Chron, 3242, + 50°05 +311 
Mean time standard — 00°27 -+0°46 
The mean time clock is here 0°27 fast by actual observation, 
but when the next comparison is made the following morning 
(at 21 hours), its error can usually be obtained only by compar 
ison with another clock. If it be compared with each of the 
other clocks in turn, each, owing to the variations of its rate 
during the night, will probably give a slightly different result, 
but supposing all the time-keepers equally reliable, the prob- 
able error will be less, in taking the mean of the four, than by 
any. single one. ( 
he above corrections for error and rate having been applied 
to the sidereal clock ; a comparison is taken with it in the morn- 
ing, and the resulting time of the mean-time clock noted, on 
the assumption that the sidereal clock is an exact standard. 
The same comparison is made with each, after the respective 
corrections and rates have been applied, each being succes: 
sively treated as an independent standa 
The results will then be entered in this form. 
1872. August, 104 21". . 
Error of mean time standard, — 0°19 (by sidereal clock.) 
“ 6 % “ — 0°05 “ break-circuit chron. 
- : n - + 0°11 “ chron’r 3242. 
“é “ i74 < ‘14 aoe 0°04 “6 its own rate. 
The mean or “adopted” error of the mean time standard is then 
— 0* 
sate oe SRG 
4 — 0°04, 
In the absence of any more absolute criterion, the time of 
the standard in this instance is assumed to be four one bun- 
not abruptly, but gradually during the ensuing twelve hours. 
It is of course impracticable to stop the clock and raise OF 
lower the adjusti twice daily for such minute corrections 
