_Powers and limitations of the acetylene signal lantern._--As conditions are usually more uniform at night than in the daytime, the signal lantern is probably the most reliable of all visual signaling outfits. The advantages of this form of apparatus are its portability, speed of operation, and comparatively great range. The principal disadvantages are due to the interference caused by rain, fog, and moonlight. The speed attainable with the lantern is about the same as that attainable with the heliograph. ROCKETS AND SHELLS. Two distinct kinds of rockets and shells are issued, one of which is adapted to day and the other to night signaling. Shells and rockets of the amber smoke type with parachutes are used in the daytime, while shells (red and white) and sequence rockets are used at night. [Illustration: FIG. 11.--Signaling rocket and accessories.] [Illustration: FIG. 12.--Signaling shells.] _Description._--The shells are all single shot and are fired from a 5-inch portable mortar, attaining a height of about 550 feet. The report of explosion can be heard at varying distances up to 5 miles, depending on weather conditions. The parachute attached to the smoke shell suspends a small light wooden tube which, after ignition, emits smoke for from four to six seconds. The red and white shells, on bursting, discharge a shower of red and white fire which can be observed for some time, in fact almost until the sparks fall to the ground. Rockets for both day and night signaling are equipped with parachutes. The smoke rocket is of similar construction to the smoke shell. The sequence rocket is so arranged at the base that threaded sections of combustible material burning either red or white can be attached to it. Rockets ascend about 700 feet. Each rocket and shell is supplied in a cylindrical sealed tin can, which also contains a port fire, wind matches, and for the rockets a stick in four sections. On the outside of the can is a label designating the kind of shell or rocket therein contained. These cans are easily opened by pulling a ring and require no special opening tool. _Operation._--In firing shells the mortar should be surrounded by earth or sand, preferably placed in sacks. The fuse for all shells is very rapid and should be ignited by attaching the port fire to a long stick. All of the old type Signal Corps mortars, originally designed to withstand a pressure of 1,000 pounds per square inch, and made of ordinary iron pipe, are considered unsafe and should be immediately destroyed. The new mortars, recently made for the Signal Corps by the Ordnance Department, are of cold-drawn steel having a tensile strength of 6,000 pounds per square inch, which is more than the maximum pressure for firing any of the Signal Corps bombs. They are stamped "Signal Corps, U. S. A., Model 1907," or "Rocket Gun, Watertown Arsenal, 1907."