7 
/ 
8 D —This result is effected by giving the two metallic arcs a circular meaure- 
ment inferior to 180°; thus, when they are about 167°, the indications 
of the range-graduated galvanometer are rigorously exact at 45° on 
either side of the normal to the base, which corresponds therefore to a 
field of 90°. It is this measure of 167° for the regulation of the elec¬ 
tric current which has been adopted by the inventor. 
We shall see presently that experience has confirmed the accuracy of his calcu¬ 
lation. 
The working of the Automatic Kange-Finder is most simple. The apparatus 
comprises two telescopes with alidades or needles (Fig. 6) installed at the posts of 
observation, and a graduated galvanometer placed near the commander of the guns, 
or else at the observatories, which simplifies the transmission of orders. The 
latter is the case in the sketch where we see the galvanometer close to the telescope. 
The three posts are united by telephone connected with the same circuit, and so 
arranged that an observer has his eye on the telescope, the receiver against his 
ear, and the transmitter before his mouth. When the two telescopes are exactly 
on the object the range is read on the galvanometer. 
As during the movements of a ship it will be impossible for the two telescopic 
observers to be constantly “ on ” the object, they are supplied with electric-bell 
calls, within reach of their hand, which they ring every time they are “ on.” 
When the commander of the guns hears the two bells simultaneously he reads the 
galvanometer. 1 
Fig. 6. 
1 This will remind some of my contemporaries of our range-finding at moving objects at Aider- 
shot with Colonel Nolan’s excellent instrument so long ago as 1865.— F.JE.B.L. 
