240 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



THE BUSH DISTANCE-FINDER. 



By Commander Z. L. Tanner, U. S. Navy. 



This simple and admirable little instrument was devised by John B. 

 Blish, lieutenant, United States Navy. It lias been used to advantage 

 on board this vessel for about two years, and we have found it partic- 

 ularly valuable at night and in stormy weather. 



With the course and distance and two bearings of a point of land, 

 without computation or reference to books or charts, the instrument 

 will give the distance of the point at the time of the first and second 

 bearings, the distance to be run from second bearing to bring it abeam; 

 also the distance at which it will be passed if the course is maintained. 

 Repeated observations will show whether the vessel is actually making 

 her course. 



Referring to the sketch, Fig. I is a plan view, full size, and Fig. II a 

 sectional view. 



Scales of degrees and points are marked on the arc, and there is a 

 scale of equal parts on CD, CE, and CF, which may be used as miles 

 or fractions of a mile. A and B are silk threads pivoted at C and drawn 

 under an elastic band which rests snugly in a groove surrounding the 

 instrument, as shown in Fig. II. The band permits free movement of 

 the arms, yet holds them in place when set. The vessel is supposed to 

 be heading at all times from C to E, hence all bearings are plotted 

 from E. 



To use the distance finder, take a bearing of a point, note the number 

 of degrees or points it bears from the ship's head, note the reading of 

 the log, and set the arm A, counting the degrees from E; steer the same 

 course until the bearing is sufficiently changed to make a good angle, 

 then take another bearing, note distance inn between first and second 

 bearings, and set arm B on the number of degrees or points the object 

 bears from the ship's head, counting from E as before. Then find 

 the distance by log, GH, parallel with CE and between the arms A 

 and B. 



To find the distance of the poiut when the first bearing was taken, 

 measure the interval CG on the scale CE or CD. 



To find the distance of the point when the second bearing was taken, 

 measure CH on CE or CD. 



To find the distance to be run from the second bearing to bring the 

 point abeam, read the interval HI on CE. 



To find the distance the point will be when abeam, read CI on the 

 scale CD, which is equal to the interval between CE and GHI, and 

 may be read anywhere between those lines. 



