14 THE FARMER AT HOME. 



matter ; it is impenetrable, ponderable, compressible, dilatable, per- 

 fectly elastic, and its particles are operated on like those of other 

 bodies, by chemical operations. It is indispensable to the life of all 

 organic beings ; animals respire it incessantly, and decompose it ; a 

 part of its oxygen is transformed into carbonic acid, and this combina- 

 tion produces caloric, which contributes principally to the preserva- 

 tion of animal heat. Vegetables imbibe the carbon which the 

 carbonic acid, diffused through the air, contains. The air is the 

 agent of combustion ; the particles of bodies combine with its oxygen 

 and evolve light and heat. Air is also the principal medium of sound. 



AIR-BELLS are enlarged cavities in the cellular tissues of plants, 

 to produce buoyancy, if they are of the aquatic order. In birds they 

 are membraneous cavities communicating with the lungs, and travers- 

 ing all parts of the bird, even to the interior of the bones and quills. 



AIR-PUMP. A machine for exhausting the air out of vessels, in 

 the same manner as water is drawn up by a pump. The vessel 

 from which the air is thus exhausted is called the receiver, and the 

 space thus left vacant in the vessel, after withdrawing the air, is 

 called a vacuum. It is one of the most curious and useful of philo- 

 sophical instruments. By experiments with it, the weight, elasticity, 

 and many other properties of the air may be shown in a very simple 

 and satisfactory manner. If any animal is placed under the receiver, 

 and the air exhausted, it dies almost immediately ; a lighted candle 

 under the exhausted receiver immediately goes out. Air is thus 

 shown to be necessary to animal life and combustion. A bell sus- 

 pended from a silken thread beneath the exhausted receiver, on being 

 struck, cannot be heard. If the bell be in one receiver, from which 

 the air is not exhausted, but which is within an exhausted receiver, 

 it still cannot be heard. Air is therefore proved necessary to the 

 production and to the propagation of sound. A shrivelled apple or 

 cranberry, placed beneath an exhausted receiver, becomes as plump 

 as if quite fresh. They are thus shown to be full of elastic air. 



AJACIO. An extraordinary tree, that grows on the shores of 

 the Antilles Islands. St. Pierre states, on the authority ofLabat and 

 du Tetre, that it grows to such a prodigious size, that out of one log 

 of it a boat can be made capable of carrying forty men. This tree is 

 also the only one, of those shores, which is never attacked by the sea 

 worm, an insect so formidable to every other species of timber which 

 floats in those seas, that it devours whole squadrons in a very little 

 time, and occasions the necessity of sheathing the bottoms of the 

 vessels with copper. 



ALABASTER. A well known mineral, used by architects, stat- 

 uaries, plasterers and others. It is a sulphate of lime. Alabaster is 

 found of various colors and kinds ; snowy white, yellow, variegated, 

 reddish, and in masses of various shapes and sizes. Most of the ala- 

 basters are interspersed with veins of different colors. Alabaster is 



