328 REMARKS ON 



quence of this idea I applied fome thin mofquita * cur- 

 tain as a covering to the quickfilver, and found it ef- 

 fectually excluded the wind, and admitted the fun ; and 

 what is of equal confequence in this country, it totally 

 kept away thofe minute infects that difturb the furface 

 of the quickfilver in obferving. In fhort, it formed fo 

 complete a horizon, that I could not before have 

 hoped for any thing fo perfect ; and it is equally appli- 

 cable to the fun and ftars. 



For taking very great or very fmall elevations of the 

 fun, (which with the common horizon fextants are im- 

 practicable in the direct method,) a polifhed metalline 

 inftrument might be made in the form of part of a 

 hollow obtufe cone: this might have its axis fet perpen- 

 dicular to the horizon at any time by means of f crews 

 in a variety of methods ; and obfervations might be 

 made by it with great exactnefs. 



In finding the latitude, when meridian obfervations 

 cannot be taken, either there is an opportunity of 

 taking altitudes on both fides of the meridian, or not. 

 When there is not, the bed method is to calculate the 

 latitude from two altitudes, and the time between, ex- 

 actly by fpherical trigonometry, (firit correcting the 

 declination to the beginning and end of each interval,) 

 as the approximating methods of Dowes, and others, 

 are totally infufficient. When obfervations can be 

 taken both before and after noon, it is belt to take a 

 number of altitudes in both, and then make out the 

 equal altitudes by proportion; then having found the 

 true time of noon by the ufual method, correct the two 

 intervals, and the declination to each time, and the lati- 

 tude may be found as follows. 



Add 



* A kind of silk gauze as close as book-muslin, and perfectly 

 transparent. It is to be .stretched over a hoop, which stands with- 

 out touching the vessel containing the mercury. 



