8 
Figure 7 represents one of the instruments as installed on board ship. The 
only protection accorded to it is a cover for the telescope when not in use. The 
apparatus is made of iron and aluminium 7 . 
bronze, with a wrought-iron shield to protect 
the observer from rifle tire. Water, even a 
green sea, has no effect on the galvanometer. 
The total resistance of the circuit is in fact 
only T5 ohms, whereas salt water has a re¬ 
sistance so far superior that it is not likely to 
cause any deflection of the needle. 
The graduation is made up to 30,000 
yards, or about 17 miles, to admit of obser¬ 
vations being made by a cruiser at the 
extreme limit of view. 
In experiments made on board the French 
barbette ship “ Formidable ” the distances 
were measured to ships moving at varied 
speeds from 0 to 28 knots; in the most diffi¬ 
cult cases the error was less than 5 per cent, 
of the range, the base being 69 metres. The 
error is much less with a fixed object,-viz., 
about 3 per cent. A heavy sea naturally 
affects the observations, but not so much as 
it affects the laying of the guns. The instru¬ 
ment may be very useful at night, the flash 
of a gun discharge possibly sufficing to 
measure the range of the ship which fired it. 
Combined with a sextant the telemeter can 
determine the height of an enemy’s mast. 
This knowledge might be very useful in the 
event of the telemeter being damaged in the 
course of an engagement. 
The United States cruisers “Baltimore” 
and “ Chicago ” have both been fitted with automatic range-finders. The “ Balti¬ 
more’s ” report of the 21st January, 1891, gives an account of many experiments 
during a cruise of several months. The greatest error recorded was one of 700 
yards on a distance given by a chart as 15,600 yards, or less than \\ per cent. 
At such a great distance more accuracy is scarcely attainable, owing to the extreme 
fineness of the graduation, which becomes more and more difficult to read as the 
distance increases. But at high gun ranges, such as 5000 yards, the mean error 
is only ’33 per cent., or 16-| yards. 
In these experiments the results were gauged on a large chart, but the mere 
displacement of a ship at anchor by the action of tide and current causes more 
variation of range than the errors of the instrument. However this influence 
was eliminated in an experiment made at Spezia on the 18th December, 1890.- 
The “ Baltimore ” was anchored between the Fort Santa Maria and a lighthouse, 
and on their alignment. The distances between the ship and each of these points 
were measured, twelve times to the fort and eight times to the lighthouse. The 
mean measurement to the fort was 3486 yards, with a mean error of 35 yards; 
to the lighthouse 1074 yards, with a mean error of 1 yard. So that, accord¬ 
ing to the telemeter, the distance between the fort and the lighthouse was 3486 + 
1074=4560 yards, whereas the chart gave it 4580 yards: mean error 20 yards, 
or *43 per cent. 
On the 14th January, 1891, in the roads of Villefranche, the “Baltimore” 
practised at ranges of 850 and 1400 yards with good effect, the elevation being in 
