10 
Fig. 17. 
In Figure 18 we have a gun protected by Fig - l 8 - 
a shield which turns with it, and to which 
the telescope is attached, on one side of and JAgnp. 
parallel to the gun. The screw is adjusted so 
that its graduation is at zero when the gun 
platform and the telescope are both horizontal. _ 
In the same way, the positions are marked 
beforehand for various elevations, for which 
under the same conditions the gun is horizon¬ 
tal, i e., parallel to the telescope. If now we 
desire to shoot at an angle a, while a ship is 
rolling, we place the gun at the marked position, bring it parallel to the platform, 
and we move the adjusting screw till the telescope makes the angle a with the 
platform. The commander of the gun, holding with his left hand a convenient 
handle, easily keeps his eye at the telescope. When the optic axis passes through 
the object, the gun makes the angle a with the horizon, and the commander fires 
with his right hand. If the rolling of the ship be inferior to the angle a the gun 
is laid at an angle with reference to the deck of the ship, at most, equal to the 
angle of rolling, by means of the marked graduation referred to above, and the 
complement is given to the telescope For instance, if the required elevation is 
6 °, and the angle of rolling 4°, we lay the gun at 4° to the deck of the ship, and 
the telescope at—2°. 
For night-firing the telescope is provided with cross-wires which can be made 
incandescent by means of a current, a process often adopted in astronomy. This 
telescope has given good results on board the United States cruiser “ Yorktown.” 
Another one is on trial on board the French barbette ship “ Formidable.” 
VII. Resume. 
Excepting the telescope for laying ship guns, the divers inventions of Captain 
Fiske’s are closely allied. They mark, as they progress, a series of improvements 
and simplifications of the same idea, starting with the Slide Range-Finder, now 
abandoned by its author, and which has only been described here to facilitate the 
descriptions of its successors founded on the same principle. 
The Automatic Range-Finder has been well received everywhere. It is of 
course suitable for coast defence or siege works as well as for ships. It admits 
of great latitude in the selection of a base which may be small, or vertical, or slop¬ 
ing at any angle. 
As regards the electric apparatus for indirect laying, it seems doubtful whether 
recourse will ever be had to such a complicated system of electric communications. 
But the common principle of a peculiar adaptation of Wheatstone’s Bridge, to 
correct the solution of an oblique-angled triangle, is very ingenious. 
