cooling by the circulation of water around small, thin copper tubes through which the air passes to the cylinder.

Do the chimes of the distant church bells lead one to the house of worship? The worshipper goes with the comforting assurance that the chimes which send forth such sweet harmonies are operated not by toiling, sweating men at ropes, but by a musician who plays as upon an organ, and works the keys, valves and stops by the aid of compressed air, and sometimes by the additional help of electricity.

Mention has already been made of office and other elevators, in which compressed air is an important factor in operating the same and for preventing accidents.

If a waterfall is convenient, air is compressed by the body of descending water, and used to ventilate tunnels, and deep shafts and mines, or drive the drills or other tools.

The pneumatic mail tube despatch system, by which letters, parcels, etc., are sent from place to place by the force of atmospheric pressure in an airexhausted tube, is a decidedly modern invention, unknown in use even by those who are still children. Tubes as large as eight inches in diameter are now in use in which cartridge boxes are placed, each holding six hundred or more letters, and when the air is exhausted the cartridge is forced through the tubes to the distance sometimes of three miles and more in a few minutes.

In travelling by rail the train is now guided in starting or in stopping on to the right track, which may be one out of forty or fifty, by a pneumatic switch, the switches for the whole number of tracks being under the control of a single operator. The

fast-moving train is stopped by an air brake, and the locomotive bell is rung by touching an air cylinder. The "baggage smashing," a custom more honoured in the breach than in the observance, is prevented by a pneumatic baggage arrangement consisting of an air-containing cylinder, and an arm on which to place the baggage, and which arm is then quickly raised by the cylinder piston and is automatically swung around by a cam action carrying the baggage out of or into the car.

Bridge building has been so facilitated by the use of pneumatic machines for raising heavy loads of stone and iron, and for riveting and hammering, and other air tools, aided by the development in the art of quick transportation, that a firm of bridge builders in America can build a splendid bridge in Africa within a hundred days after the contract has been entered upon.

Ship building is hastened by these same air drilling and riveting machines.

The propelling of cars, road vehicles, boats, balloons, and even ships, by explosive gases and compressed air is an extensive art in itself, yet still in its infancy, and will be more fully described in the chapter on carrying machines.

The realm of Art has received a notable advancement by the use of a little blow-pipe or atomiser by which the pigments forming the background on beautiful vases are blown with just that graduated force desired by the operator to produce the most exquisitely smooth and blended effects, while the varying colours are made to melt imperceptibly into one another as delicately as the mingled shade and coloured sunlight fall on a forest brook.

But to enumerate the industrial arts to which air

and other pneumatic machines have been adapted would be to catalogue them all. Mention is made of others in chapters in which those special arts are treated.

CHAPTER XIII.

ART OF HEATING, VENTILATING, COOKING, REFRIGERATION AND LIGHTING.

THAT Prometheus stole fire from heaven to give it to man is perhaps as authentic an account of the invention of fire as has been given. It is also reported that he brought it to earth in a hollow tube. If a small stick or twig had then been dipped into the divine fire the suggestion of the modern match may be supposed to have been made.

But men went on to reproduce the fire in the old way by rubbing pieces of wood together, or using the flint, the steel and the tinder until 1680, when Godfrey Hanckwitz of London, learning of the recent discovery of phosphorus and its nature, and inspired by the Promethean idea, wrapped the phosphorus in folds of brown paper, rubbed it until it took fire, and then ignited thereat one end of a stick which he had dipped in sulphur; and this is commonly known as the first invented match. There followed the production of a somewhat different form of match, sticks first dipped in sulphur, and then in a composition of chlorate potash, sulphur, colophony, gum of sugar, and cinnabar for coloring.. These were arranged in boxes, and were accompanied by a vial containing sulphuric acid, into which the match was dipped and thereby instantly ignited. These were called chemical matches and were sold at first for the high price of fifteen shillings a box.

They were too costly for common use, and so our fathers went on to the nineteenth century using the flint, the steel and the tinder, and depending on the coal kept alive upon their own or their neighbour's hearth.

Prometheus, however, did reappear about 1820-25, when a match bearing the name "Promethean " was invented. It consisted of a roll of paper treated with sugar and chlorate of potash and a small cell containing sulphuric acid. This cell was broken by a pair of pliers and the acid ignited the composition by contact therewith.

It was not until 1827--29 that John Walker, chemist, at Stockton-upon-Tees, improved upon the idea of Prometheus and Hanckwitz of giving fire to men in a hollow tube. He used folded sanded paper-it may have been a tube-and through this he drew a stick coated with chlorate of potash and phosphorus. This successful match was named Lucifer," whose other name was Phosphor, the Morning Star, and the King of the Western Land. Faraday, to whom also was given Promethean inspiration, procured some of Walker's matches and brought them to public notice.

In many respects the mode of their manufacture has been improved, but in principle of composition and ignition they remain the same as Walker's to-day. In 1845, Schrotter of Vienna discovered amorphous or allotropic phosphorus, which rendered the manufacture of matches less dangerous to health and property. Tons of chemicals and hundreds of pine trees are used yearly in the making of matches, and many hundreds of millions of them are daily consumed.

But this vast number of matches could not be supplied had it not been for the invention of machines