BY PKOFESSOK ALEX. MCAULAY, M.A. 91 



that we should be able to give them the same time as they 

 received in Sydney, for it they receive it from ns, they 

 can ascertain their chronometers' rates at sea, and they 

 cannot obtain these rates otherwise. 



I have said before, and I say again, that it is in ex- 

 treme cases sometimes necessary to know the time to one 

 second, in order to make the necessary provision that means 

 all the difference between life and death to many souls. 



With regard to this question of keeping time, I 

 again quote from Mr. Baracchi's letter, and you will see 

 that I was wrong in saying that in a first-class observatory 

 an accuracy of 1/100 of a second was attainable : — 



"(5th). Whether an accuracy of u.Ols. is attained in 

 time keeping at this Observatory. — In time deter- 

 minations, we aim at an accuracy of 0.01s., but I do 

 not think we attain it often. I can't say whether 

 we ever attain it. Under the best conditions in re- 

 gard to atmosphere, instrument and observer, M^ith 

 a complete set of observations, viz., from six to ten 

 standard clock stars, and from two to four azimuth 

 stars, the clock error at the middle time of the ob- 

 servations can be determined probably within 

 0.03s. ; greater accuracy is possibly attained on 

 occasions, but is uncertain. Changes in personal 

 equation are the disturbing causes. 

 ''In ordinary time-keeping, viz., dropping of time signal 

 at 1 p.m., and rating chronometers for the ship- 

 ping, in all of which cases we have to rely on the 

 rate of the standard clock for several hours, the un- 

 certainty is much greater and the limit of accuracy 

 that we can depend upon with safety is 0.1s." 

 I should also here like to read a quotation from Mr. 

 Morton's paper in the Papers and Proceedings of the Royal 

 Society for 1900-1901 (p. 122), and another from the paper 

 by Mr. Abbott, to which Mr. Morton's paper directed 

 me : — 



''In May, 1865, the attention of the Society was 

 directed to the necessity of some method of estab- 

 lishing a time signal which should give the time 

 regularly, so as to be available for the whole of 

 Tasmania. The first duty of fixing a time signal 

 was soon after undertaken by Colonel Chesney, who 

 arranged for three guns to be fired at 4 p.m. on 

 the first Thursday in every month, or, if that day 

 proved wet, they were fired on the first fine day fol- 

 lowing." 

 [Quotations from "Time Signals," by Abbott, May, 

 1865, p. 45.] 



