386 FERGUSON'S LECTURES. 



LECT. the Pl e being 109 5', and the horary distance from the 



^X- meridian, or the angle d P Z, 36. 



To log. sin. 74 51' . . . 1.98464 

 Add log. sin. 36 0' ... 1.76922 



And from the sum . . . 1.75386 

 Take the log. sin. 81 32'' 1.99525 



Remains 1.75861 = log. 



sin. 35*, the azimuth distance south. 117 



When the altitude is given, find from thence the hour, 

 and proceed as above. 



This praxis is of singular use on many occasions ; in 

 finding the declination of vertical planes more exactly 

 than in the common way, especially if the transits of the 

 sun's center are observed by applying a ruler with sights, 

 either plain or telescopical, to the wall or plane, whose 

 declination is required. In drawing a meridian-line, 

 and finding the magnetic variation In finding the bear- 

 ings of places in terrestrial surveys ; the transits of the 

 sun over any place, or his horizontal distance from it 

 being observed, together with the altitude and hour. 

 And thence determining small differences of longitude. 

 In observing the variation at sea, &c. 



The learned Mr. Andrew Reid invented an instrument 

 several years ago, for finding the latitude at sea from 

 two altitudes of the sun, observed on the same day, and 

 the interval of the observations, measured by a common 

 watch. And this instrument, whose only fault was that 

 of its being somewhat expensive, was made by Mr. 

 Jackson. Tables have been lately computed for that 

 purpose. 



Note 127. In all these calculations the angles are taken out to 

 the nearest minute only : for the method of performing these calcu- 

 lations more exactly, see the Introduction to Button's Mathematical 

 Tables. For calculations, like those used in dialing, which do not 

 require very great exactness, a small collection of Tables has been 

 published by Mr. Whiting of Brompton, highly commendable for 

 their elegance and moderate price. 



