172 



ASTRONOMICAL AND NAUTICAL COLLECTIONS. 



No. V. 



i. M. Delambre's direct Method of computing the Latitude 

 from Two Observations of the Suns Altitude, and the Time 

 elapsed between them. From the Connaissance des Terns for 

 1822 ; with Remarks. 



There is scarcely any problem in Nautical Astronomy so 

 important, or of so frequent occurrence, as the determination 

 of the latitude and the time from two observations of altitudes : 

 and the future improvements, which may be anticipated, in the 

 construction and general employment of timekeepers, will pro- 

 bably render this computation almost the only one that will be 

 required for determining a ship's place in all common cases. 



The approximative method of Douwes has been recommended 

 in the Requisite Tables, and generally practised in the British 

 Navy : but, like most other contrivances of the kind, it gene- 

 rally gives more trouble than it is intended to save. Dr. 

 Brinkley has proposed two much simpler and more convenient 

 methods, which, however, agree with it in requiring a sup- 

 posed latitude, as an element of the computation ; and it seems 

 to be at least more elegant to assume nothing that is not imme- 

 diately derived from the observations themselves. 



M. Delambre, in an essay published in the Connaissance des 

 Terns for 1822, has made the very important remark, that the 

 method of Douwes is not only as long, if once repeated, as 

 the direct method, but that it is wholly void of any convergence, 

 since, when conducted with rigid accuracy, it leads back pre- 

 cisely to the supposed latitude, at least when that latitude hap- 

 pens to be very near the mark. He has given examples, in 

 this elaborate paper, of the strict trigonometrical mode of 

 computation, and of animproved formula invented by M. Querret 

 of St. Maloes. M. Dubourguet, of Dieppe, has also very lately 



