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length as the envelope. These two tubes are closed by a common base.

In the central tube is retained compressed carbonic acid produced by the reaction of hydrochloric acid on Carrara marble. This gas, being dried, is stored in an oil gasometer (G) of I cubic metre capacity.

At a pressure of from 4 to 6 atmospheres the carbonic acid easily liquefies under these circumstances. The resulting liquid is led into a long copper tube (B), 4 metres in length and 4 centimetres in diameter.

Two pumps, P, and P2, coupled together like the first, exhaust carbonic acid either from the gasometer (G) or from the long tube (B) full of liquid carbonic acid.

The ingress to these pumps is governed by a three-way tap, H. A screw valve cuts off at will the ingress of liquid carbonic acid in the long tube; it is situated between the condenser of carbonic acid and this long tube. When this screw valve is closed, and the two pumps draw the vapour from the liquid carbonic acid contained in the tube 4 metres long, the greatest possible lowering of temperature is produced; the carbonic acid solidifies and descends to about — 140°. The subtraction of heat is maintained by the working of the pumps, the cylinders of which take out 3 litres per stroke, and the speed is 100 revolutions a minute.

Both the sulphurous acid tube and the carbonic acid tube are covered with a casing of wood and non-conducting stuff to intercept radiation.

In the interior of the carbonic acid tube, в, passes a fourth tube, A, intended for the compression of oxygen; it is 5 metres long and 14 millimetres in external diameter. Its internal diameter is 4 millimetres. This long tube is consequently immersed in solid carbonic acid, and its whole surface is brought to the lowest obtainable temperature. These two long tubes are connected by the ends of the carbonic acid tube, consequently the small tube extends about 1 metre beyond the other. I have curved this portion downwards, and given the two long tubes a slightly inclined position, but still very near the horizontal, as I have shown in the accompanying drawing.

The small central tube is curved at A, and screws into the neck of a large howitzer shell, c, the sides of which are 35 millimetres thick; the height is 28 centimetres, and the diameter 17 centimetres.

This shell contains 700 grms. of chlorate of potash and 256 grms. of chloride of potassium mixed together, fused,

then broken up, and introduced into the shell perfectly dry. When the double circulation of the sulphurous and carbonic acids has lowered the temperature to the required degree, I heat the shell over a series of gas-burners. The decomposition of the chlorate of potash takes place at first gradually, then rather suddenly towards the end of the operation. A pressure-gauge, M, at the extremity of the long tube, lets me constantly observe the pressure and the progress of the reaction. This gauge is graduated to 800 atmospheres, and was made for me expressly by Bourdon, of Paris.

When the reaction is terminated the pressure exceeds 500 atmospheres; but it almost immediately sinks a little, and stops at 320 atmospheres. If at this moment I open the screw-tap, r, which terminates the tube, a jet of liquid is distinctly seen to spirt out with extreme violence. I close the tap, and in the course of a few moments a second jetless abundant, however, can be obtained.

Pieces of charcoal, slightly incandescent, put in this jet inflame spontaneously with inconceivable violence. I have not yet succeeded in collecting the liquid, on account of the considerable projectile force with which it escapes, but I am trying to arrange a pipette, previously cooled, which possibly may be able to retain a little of this liquid.

Yesterday I repeated this experiment before the majority of the members of our Physical Society, and we had three successive jets, well characterised. I cannot yet determine the minimum pressure necessary, for it is evident that I have a surplus pressure produced by the excess of gas accumulated in the shell, and which could not condense in the small space represented by the interior tube.

I hope to utilise a similar arrangement in atempting the condensation of hydrogen and nitrogen, and I am especially occupied with the possibility of maintaining low temperatures very easily, thanks to four large industrial pumps which I have at my disposal, worked by a steam-engine.

The following experiment was performed for the fourth time on Thursday, December 27th, in the presence of ten scientific men-among others, Prof. Hagenbach, of Bâle, who came expressly to assist at this important experiment, the success of which called forth the applause of all present:

At 10 o'clock in the evening the manometer, which had risen to 560 atmospheres, sank in a few minutes to 505, and remained stationary at this figure for more than half-anhour, showing by this diminution in the pressure that part

of the gas had assumed the liquid form under the influence of the 140 degrees of cold to which it was exposed. The tap closing the orifice of the tube was then opened, and a jet of oxygen spirted out with extraordinary violence.

A ray of electric light being thrown on the escaping jet showed that it was chiefly composed of two parts;-one central, and some centimetres long, the whiteness of which showed that the element was liquid, or even solid; the other exterior, the blue tint of which indicated the presence of oxygen compressed and frozen in the gaseous state.

VIII. THE PHONOGRAPH.

O sooner had the wonderful simplicity and marvellous capabilities of Mr. Graham Bell's articulating telephone been practically demonstrated in England than we were startled by an announcement in the American journals that another instrument had been invented, by Mr. T. A. Edison, which would not only receive and register, but also reproduce at any distant period, whatever sounds were uttered into it by the human voice. The first accounts

of the wonders of the instrument were evidently somewhat coloured: that it does, however, actually re-produce vocal sounds was demonstrated by Mr. W. H. Preece, at his Lecture on the Telephone, at one of the Friday evening meetings at the Royal Institution, when he exhibited the Phonograph for the first time in England. By the courtesy of the Editor of "Engineering" we are enabled to place before our readers drawings and descriptions of different forms of this instrument.

Fig. I is a general view of Mr. Edison's instrument, which has recently been brought to this country by Mr. Puscus, his representative. It consists of a brass cylinder, which, by a winch handle, can be rotated on a horizontal axis, upon which is fixed a heavy fly wheel for the purpose of controlling, to some extent, its speed of rotation. One end of this horizontal axis is screwed, and turns in a screwed bearing, so that the cylinder is not only rotated on its axis, but has imparted to it a lateral movement from end to end when the winch is rotated. Around the circumference of the cylinder

FIG. 1.

is turned a spiral groove, the pitch of which is the same as that of the screw on the horizontal shaft, so that if a fixed pointer were to be set in the groove at any portion of its

[graphic]

length it would remain in it as the cylinder was rotated until it worked out at either end.

In front of the cylinder and directed to its axis is fixed a thin metallic diaphragm, carried by an arm attached to the

stand of the instrument, and provided with adjustments by which a steel pin projecting from its centre may be accurately set in the middle of the groove and at a proper depth; and in front of the diaphragm a mouthpiece is fixed, very similar in form to that employed in Professor Bell's telephone.

From the above description it will be evident that if the diaphragm be set into vibration by sounds being uttered into the mouthpiece, the steel pin attached to it, partaking of that vibratory motion, will enter into greater or less depths into the groove on the cylinder, according as the amplitude of vibration of the diaphragm by which its motion is controlled be large or small. If, while this vibration is going on, the cylinder be rotated in its screwed bearing, the point of the pin will trace out a spiral undulating path of motion within the groove, the amplitude of whose waves will be equal to that of the vibrations of the diaphragm, their length and form being dependent upon the rapidity and character of the undulations of the metallic membrane combined with the surface speed of the cylinder.

In order to obtain a permanent record of this wave-like path a sheet of ordinary tin-foil is fastened round the cylinder, being secured in its place by brass caps, shown on the drawing; and, as the centre of the diaphragm is adjusted so as always to be opposite to the middle of the groove, which is bridged over by the tin-foil, it follows that the pin in vibrating with the diaphragm must indent the tin-foil, which, at any spot below it, is unsupported by the resisting surface of the cylinder, having nothing but a groove behind it, and as the cylinder is rotated a chain of indentations is produced, which is in every particular a record of the sounds which originated them.

So far the apparatus is complete as an instrument for recording sounds, and as such is not superior to many of its predecessors, such as the very beautiful logograph of Mr. W. H. Barlow, F.R.S., the phonautograph of M. LeonScott, or the instruments of Prof. Marey and the late Sir Charles Wheatstone, but the most wonderful feature of Mr. Edison's phonograph is that it not only interprets its own record, but does so by re-converting it into sonorous vibrations, repeating the sounds, whether articulate or otherwise, in the actual voice in which they were originally communicated to the mouthpiece.

In Mr. Edison's first apparatus this was accomplished by employing a second diaphragm of paper, fixed on the opposite side of the cylinder to the first diaphragm, and thrown

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