Fig. 481.—Section of “atmospheric” boat.
Let us now calculate the force engendered by this apparatus. We know that a litre of water at boiling point gives 1,700 times its volume. The steam, as it quickly issues from the opening of the boiler, carries along at least ten times its volume, or 17,000 litres of air, which, driven under the water, assumes an ascending force equal to the difference of the densities of water and air, or about the weight of the displaced water. Therefore in a litre of water transformed into 1,700 litres of the steam, which carries off into the water 1,700 × 10 = 17,000 litres of air, a force is developed represented by 34,000 kilograms. In fact, by reason of the inclined position of the drain on which the pressure of air acts, and its restricted dimensions, the quantity of force employed in the propulsion of the boat is but a fraction of the total force produced. Moreover, the resistance of traction increases with the size of the boat, and as the dimensions of the inclined pipe cannot be indefinitely enlarged, the result is that the propulsive action is soon insufficient, so that the invention is not, in its present condition, applicable to navigation on a large scale. Its superiority to the steam-engine cannot, therefore, be demonstrated; and we are only now discussing the contrivance in order to show that it is possible, with only moderately powerful generators and extremely simple mechanical appliances, to obtain considerable dynamic effects, susceptible of more serviceable application than is commonly believed.
Circulating Fountain.
Fig. 482.—Circulating fountain.
The apparatus given in fig. 482 is the subject of a very charming experiment, showing the influence of capillarity on the movements of liquids. Two glass balls, B B´, are connected by two tubes; one straight and of rather large diameter, the other extremely slender, and winding in and out in a more or less complicated manner. The large tube passes into ball B´, and forms a slender point, J, at the orifice of the narrow tube. At the lower end of the ball is a bulb, which is closed with a cork, and contains a coloured liquid. The apparatus is fixed to a board with a ring at each end, by which it can be hung on the wall. When commencing the experiment, it should be hung so that the ball B´ is uppermost. The liquid then flows through into the ball B, without presenting any particular phenomenon. The apparatus is then turned, and the liquid descends again with great speed, shoots through the opening, J, and rises into the twisted tube. The air displaced from ball B´ also rises, however, and mingles with the liquid, and it can be seen circulating through the winding tube in a number of air-bubbles, mingled with drops of liquid, gradually transmitting the pressure of the column contained in the upper ball and straight tube; so that by means of a similar phenomenon to that of the fountain of Nero, the liquid rises higher than the level of the reservoir, a part falling into ball B, which causes the experiment to be a little prolonged. This circulation of air-bubbles and coloured drops through the twisted tube of the apparatus has a very pretty effect.
The Pneumatic Pencil.
This ingenious invention is productive of results similar to Edison’s electric pen. It is the invention of an American gentleman, Mr. J. W. Brickenridge, of Lafayette, Indiana. The illustration (fig. 483) explains the mechanism of the pneumatic pencil. The whole apparatus is figured on the left side of the picture, while the longitudinal section of the pencil is shown on the right, the small cut at the top being a vertical section of a portion of the motive power. Compressed air furnishes the power of pressure, which is accomplished by means of a perforating needle.
If the treadle is put in motion, a backward and forward movement is imparted to a flexible diaphragm, as in the upper section in the centre of the illustration. By this movement the air is permitted to enter, and is compressed by the diaphragm into the flexible tube with which the diaphragm is connected. The air is thus brought into contact with another diaphragm at the end of the tube and presses on it. The pencil is fixed to the latter. When it is desired to use the pencil the apparatus is set in motion, and by a series of sharp, quick perforations, any writing can be traced, as by the electric pen. This indentation can be copied over and over again in a press, the writing acting as the negative; and if ink be first run over it, as in a stencil plate, by a proper “roller,” the latter will come out as plainly as possible.