Air-Gun
2 of the 7 encyclopedias on this shelf carry an entry for Air-Gun. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a contrivance whereby a missile is thrown by means of condensed air. The simplest air-gun is a joint of bamboo or other straight, hollow reed with a smooth interior. The natives of various parts of the world use air-guns of this description to shoot, or at least stun, birds. The missile may be a pellet or an arrow so constructed as to fit the tube. In either case it is propelled by the hunter's breath. Before the introduction of fire-arms these blow-guns were quite extensively used in the forests of the Amazon, of Africa, and India. As now understood, however, an air-gun is shaped like a shotgun. The barrel is connected with a reservoir into which air is forced with a plunger or condensing air-pump. When the trigger is pulled, the condensed air is released, and the ball or bullet is projected with great force. 2026 Editor's Note: Air guns turned out to be more than the near-toy this implies: Lewis and Clark carried a formidable repeating air rifle that astonished the tribes they met, and today air-rifle and air-pistol shooting are Olympic events, while precision modern air rifles hunt game. (Ed: BR 2026-07-18)
Collier's New Encyclopedia (1921)
an instrument designed to propel balls by the elastic force of condensed aid. A strong metal globe is formed, furnished with a small hole and a valve opening inward. Into this hole a condensing syringe is screwed. When, en by means of this apparatus, the condensation has been brought to the requisite point of intensity, the globe is detached from the syringe and screwed at the breech of a gun, so constructed that the valve may be opened by means of a trigger. A ball is then inserted in the barrel near the breech, so fitting it as to render it air-tight, and, the trigger being pulled, the elasticity of the condensed air impels it with considerable force.