382 Astronomicnl and Nautical Collections. 



keep in mind that there is a mistake of the sign in the 1st table 

 page 578, column 4th. The whole of that column which gives 



the log. (^^J^^—'\iwm\80°to225°oithe sun's longi- 



^ V 360 ; 



tude ought to have the sign + in place of — which has there 

 been assigned to it either through the inattention of the cele- 

 brated author, or from an error of the press. There is also 



another mistake in the 2d table in the log. ( — - — - i 



^ Vtang. (15° t) ) 



corresponding to S*" 20" of half-intervals, and which ought to be 

 0.7660 instead of 0.7460. 



Finally, we cannot do less than recommend to astronomers 

 and travellers, who are desirous of regulating their timekeepers 

 by equal altitudes taken on two or more consecutive days, the 

 advantage which results, without any increase of trouble, from 

 making all the observations corresponding ones ; that is, if in 

 the forenoon and afternoon of the same day equal altitudes are 

 obtained, it is very desirable that those of the subsequent day 

 should not only be equal between themselves, but also equal to 

 those of the preceding day ; and also that the same should be 

 the case on the subsequent days. Proceeding on with this care, 

 the time of noon and midnight may be accurately found, and 

 consequently the exact rate of the chronometer from 12 to 12 

 hours, thus establishing confidence in any observation made by 

 that timekeeper during the interval from one rating to another. 



It is also useful to take altitudes in the afternoon when clouds 

 have prevented them from being observed the preceding fore- 

 noon, and with these and corresponding ones next forenoon the 

 chronometer's absolute rate for midnight may be found ; this is 

 still more requisite if any observation is to be made by that 

 chronometer during the same night, for it is interesting to ob- 

 tain a rate for the timekeeper which will assure the apparent or 

 mean time as near as possible to the time as shown by it when 

 any phenomenon takes place. 



It appears that many foreign Astronomers practise this 

 method, and thus my advice is principally addressed to my 

 countrymen, among whom I have seen none use it, notwith- 

 standing its facility and utility. 



