INVESTIGATIONS OF THE STEAMER ALBATROSS. 241 



If the point is to be passed at a distance of 5 miles or less, it may 

 be found convenient to have the lines on the scale represent half miles 

 instead of miles. In reading - the scale, fractions of a mile are estimated 

 to tenths to correspond with the divisions of the patent log. 



EXAMPLE. 



First bearing, 30° from ship's head (or E). 



Second bearing, 65° from ship's head (or E). 



Distance by log between first and second bearings, 8 miles. Set arm 

 A on 30° for first bearing, and arm B on 65° lor the second bearing. 



Then, 8 miles, the distance run, equals GH between the arms A 

 and B. 



CG measured on CE or CD equals 12.6 miles, distance of point at 

 first bearing. 



CH measured on CE or CD equals 7 miles, distance of the point at 

 second bearing. 



Ill measured on CE or CD equals 3 miles, distance to be run from 

 second bearing to bring the point abeam. 



CI measured on CD equals G.3 miles, distance the point will be from 

 the vessel when it is abeam. 



The distances CI and HI are those mostly used in practice, but if the 

 distances CG or CH are required, grasp the arm A at G, or arm B at 

 H, and swing them to CE or CD and read off the distance from the 

 scale. 



The distance finder in use on board the Albatross was improvised by 

 Ensign Henry B. Wilson, United States Navy. The scales were marked 

 in India ink on Irish linen writing paper, which was then glued to a 

 wooden frame, and finally given several coats of shellac varnish. Sew- 

 ing silk was used for the arms, which were held in place by an ordinary 

 elastic band resting in the groove, and a small nail constituted the pivot. 



It will be observed that the left quadrant of the semicircle is used 

 in the description and the example; the right one may be used in like 

 manner by assuming that the ship's head is at F. The instrument is 

 used as though the vessel was at C, steering to E, on the line CE, but 

 in reality she was at G when the first bearing was taken, at H at the 

 time of the second bearing, steering for I, on the line GHI, and the 

 pivot C is the point on which both bearings were taken. 



The distance finder and Table 5A of the new Bowditch Navigator 

 are constructed on the same principle. 

 F. R. 91 10 



