The purpose is to provide morse communication by means of light flashes. Signals are readable during daylight at a distance of two miles, with the naked eye, and 3-4 miles by telescope. At night may be read with naked eye at 6 miles and up to 12 miles by telescope.

Lamp, signalling daylight, long range.

Purpose: Same as the short range lamp, but is bigger, and gives greater range of communication : up to 8 miles in daylight.

HELIOGRAPH 5inch Mk. V.

This instrument is designed to send morse messages by reflection of the sun's rays. The divergence of the beam is 8 yards either side of the beam at a distance of one mile. It is carried in HELIOGRAPH 5in. Mk. V CASES LEATHER, and when in use is mounted on STANDS LAMP OR HELIO­GRAPH A Mk. III. Provision is made for the use of, one or two mirrors. The single mirror is used when the sun is between the instrument and the distant station, and the duplex mirror is used at all other times. Under these conditions the sun's rays are reflected from Signalling to the Duplex mirror, and thence on to the distant station.