382 



FERGUSON'S LECTURES. 



LECT. Then, to log. L=log. sin. 51 30' 1.89354* 

 **~v^, add log. D=log. sin. 20 0' 1.53405 



snes. 



Their sum ....... 1.42759 



gives L Zfcilogarithm of 0.267664, in the natural 

 nes. , 



And, to log. H=]og. sin. 15 O' 180 1.41300 

 j log. / = log. sin. 38 O' 181 1.79414 

 *. log. d=]og. sin. 70 0" aa 1.97300 



Their sum ....... 1.18015 



gives .ff/cfcilogarithin of 0.151408, in the natural 

 sines. 



And these two numbers (0.267664 and 0.151408) 

 make 0.419072=^1 ; which, in the table, is the nearest 

 natural sine of 24 47', the sun's altitude sought. 



The same hour-distance being assumed on the other 

 side of VI, then LD-Hld is 0.116256, the sine of 6 

 40J' ; which is the sun's altitude at V in the morning, 

 or VII in the evening, when his north declination is 

 20. 



But when the declination is 20 south (or towards 

 the depressed pole) the difference H I dL D becomes 

 negative, and thereby shews that, an hour before VI in 

 the morning, or past VI in the evening, the sun's center 

 is 6 40' below the horizon. 



EXAMPLE II. 



In the same latitude and north declination, from the 

 given altitude to find the hour. 



Note 119. Here we consider the radius as unity, and not 10.000, 

 by which, instead of the index 9 we have 1, as above : which is of no 

 farther use, than making the work a little easier. Note by th* 

 Author. 



Note 120. The distance of one hour from VI. Idem. 



Note 121. The co-latitade of the place. Idem. 



Note 122. The co-declination of the sun. Idem. 



