DEEP-SEA EXPLORATION. 
379 
THE BLISH DISTANCE-FINDER. 
This is a simple and admirable little instrument devised by Lieut. John B. Blish, 
United States Navy, and used on board the Albatross for several years, where it was 
found particularly valuable when coasting at night or during stormy weather. 
With the course and distance, and two bearings of a point of land, without com- 
putation or reference to books or charts, the distance-tinder will give the distance of 
the point at the time of the first and second bearings, the distance to be run from the 
second bearing to bring it abeam; also the distance at which it will be passed if the 
course is maintained. Eepeated observations will show whether the vessel is actually 
making her course. 
The (listance- finder, as improvised and used on board the Albatross, is shown in 
plate XXXVIII; fig. i is a plan, and lig. ii a sectional view. Scales of degrees and 
points are marked on the arc; C D, 0 E, and 0 F are scales of equal parts, which may 
be used as miles or fractious of a mile. A and B are silk threads pivoted at C and 
drawn under an elastic baud which rests snugly in a groove surrounding the instru- 
ment, as shown in fig. ii. The elastic band permits free movement of the threads of 
silk, yet holds them iu place when set. The vessel is supiiosed to be heading at all 
times from O to E, hence all bearings are plotted in iioints or degrees 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, set the arm A, counting the degrees from E, 
and note the reading of the log; steer the same course until the bearing of the point 
has changed sufficiently to make a practicable angle, then take a second bearing, and 
set the arm B on the number of degrees or iioints the object bears from the ship’s 
head, counting from E as before; also note the distance run between the first and 
second bearings. With the distance by log, taken from the scale of equal parts 0 E 
or O D on a pair of dividers, find G H between the arms A B parallel with C E. 
Then G will be the position of the ship when the first bearing was taken, and BE when 
the second bearing was taken; the interval 0 G is the distance of the vessel from the 
point when the first bearing was taken, 0 H the distance from the point when the 
second bearing was taken, H I the distance to be run to bring the iioint abeam, and 
0 I the distance at which the vessel will pass the point. 
If the vessel is to pass within 5 miles of the point, it will be found convenient to 
have the divisions on the scale of equal parts represent half miles instead of miles. 
In reading the scale fractions are estimated in tenths to correspond with the divisions 
of the iiatent log. 
EXAMPLE : 
First Fearing 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 the arm A on 30° for the first bearing, and the arm B on 65° for the second bearing. 
Thus 8 miles, the distance run by log, ecjuals G H. 
C G, measured on scale of e(iual parts, equals 12.6 miles, the distance of point at first bearing. 
C H equals 7 miles, the distance of the point at the second hearing. 
H I equals 3 miles, the distance to be run from the second bearing to bring the point abeam. 
C I equals 6.3 miles, the distance the point will be from the vessel when it is abeam. 
The intervals C I and H I are most used in practice, but should 0 G and 0 H be 
required, they may be measured on the scale with dividers, or by grasping the arm A at 
G, or the arm B at H, and carrying them to the scale. The distance-tinder in use on 
