CONVERSATION XXXII.

Of the Air-Gun, and Sound.

FATHER. The air-gun is an instrument, the effects of which depend on the elasticity and compression of air.

Emma. Is it used for the same purposes as common guns?

Father. Air-guns will answer all the purposes of a musket or fowling-piece: bullets discharged from them will kill animals at the distance of 50 or 60 yards. They make no report, and on account of the great mischief they are capable of doing, without much chance of discovery, they are deemed

illegal, and are, or ought to be, found no where but among the apparatus of the experimental philosopher.

Charles. Can you show us the construct tion of an air-gun?

Father. It was formerly a very complex machine, but now the construction of airguns is very simple; this (Plate vi. Fig. 23.) is one of the most approved.

Emma. In appearance it is very much like a common musket, with the addition of a round ball c.

Father. That ball is hollow, and contains the condensed air, into which it is forced by means of a syringe, and then screwed to the barrel of the gun.

Charles. Is there fixed to the ball a valve opening inwards?

Father. There is: and when the leaden bullet is rammed down, the trigger is pulled back, which forces down the hook

upon the pin connected with the valve, and liberates a portion of the condensed air; this

rushing through a hole in the lock into the barrel, will impel the bullet to a great dis

tance.

Emma. Does not all the air escape at once ?

Father. No: if the gun be well made, the copper ball will contain enough for 15 or 20 separate charges: so that one of these is capable of doing much more execution in a given time than a common fowlingpiece.

Charles. Does not the strength of the charges diminish each time?

Father. Certainly; because the condensation becomes less upon the loss of every portion of air; so that after a few discharges the bullet will be projected only a short distance. To remedy this inconvenience, you might carry a square ball or two ready filled with condensed air in your pocket, to screw on when the other was nearly exhausted. Formerly this kind of instrument was at tached to gentlemen's walking sticks.

1

Charles. I should like to have one of them.

Father. I dare say you would: but you must not be trusted with instruments capable of doing much mischief, till it is quite certain that your reason will restr; in from actions that might annoy other per

sons.

you

A still more formidable instrument is called the magazine wind-gun. In this there is a magazine of bullets as well as another of air, and when it is properly charged, the bullets may be projected one af ter another as fast as the gun can be cock ed, and the pan opened. The syringe in 1 hese is fixed to the but of the gun, by which it is easily charged, and may be kept in that state for a great while.

Emma. Does air never lose its elastic Dower?

Father. It would be too much to assert that it never will: but experiments have been tried upon different portions of it, which have been found as elastic as ever af

ter the lapse of many months, and even years.

Charles. What is this bell for?

Father. I took it out to show you that air is the medium by which, in general, sound is communicated. I will place it under the receiver of the air-pump, and exhaust the air. Now observe the clapper of the bell while I shake the apparatus.

Emma. I see clearly that the clapper strikes the side of the bell, but I do not hear the least noise.

Father. Turn the cock and admit the air; now you hear the sound plain enough:

and if I use the syringe and a different kind of glass, so as to condense the air, the sound will be very much increased. Dr. Desaguliers says, that in air that is twice as dense as common air, he could hear the sound of a bell at double the distance.

Charles. Is it on account of the different densities of the atmosphere, that we hear St. Paul's clock so much plainer at one time than another?