Fig. 1, is a front elevation of the machine; fig. 2, a side elevation; and fig. 3, a sectional side elevation of part of the framework, showing the slide, T, and also, in dotted lines, the slide T. A, is the framework of the machine; B, the driving shaft; C, fly-wheel; D, crank on the shaft, A B; E, connecting rod attached at its lower end to the crank, D, and at its upper end to the carriage, F, which is alternately raised and lowered thereby; this carriage supports the levers G G2, working on fulcra at **; the lower ends of these levers form jaws, which (when the upper ends are distended or pushed away from each other,) clip the drill, H, whereby the drill is raised along with the levers, and the carriage, F. I, a tappet, or rod, furnished at 12, with inclined surfaces, which, when the rod is forced upwards, push the upper ends of the levers, G G2, away from each other, and thereby effect the "clipping" referred to. K, a bent lever which works at one end on a fulcrum at K2, and through a guide-fork L, is attached at its other end to a rod, M, which connects it with a lever, N, made fast to one end of the rod or shaft, O, as is also the lever, P, to its other end. The lever, P, is furnished with an arm, P2, which is jointed thereto at one end, while its other end rests upon a screw, P3, by which its action is regulated. Q, is a cam on the shaft, B, so shaped and situated as to raise the lever, K, at or about the time when the crank, D, is at the lower end of its two null points, by means of the intermediate parts, MN, O, P. The lever, K, raises the end of the arm, P2, before (or quicker,) than the carriage, F, and presses the tappet, or rod, I, upwards, whereby (as before described) the jaws of the levers, G G2, are made to clip and raise the drill, H, with them. Just before the crank, D, is at the higher of its null points, the top of the tappet, or rod, I, strikes against the piece, Q, fixed to the framework, and thereby disengages the drill, which falls in the direction given to it by the guidepiece, A2, of the framework and the guide-rollers, A3, A3; which direction

27

is regulated by screws, R, which fasten the rod, S, so as to hold the upper part of the framework from the joints, A+ A+, at any angle at which the drill may be required to work. The carriage, F, has grooves which work on the slides, T T2; and being shaped and placed "on the skew," and slanting in opposite directions, give to it, and with it, to the drill also, a slight or partial rotary motion when in the act of being raised, so that the edge of the drill may be presented in a continually altering position upon the ground or work on which it operates. U, is a lever for sliding the shaft, or rod, O, laterally, and thereby throwing the arm, P2, out of gear with the tappet, I, when required. VVV V, are screws passing through nuts embedded in the corners of the frame, for the purpose of adjusting it to the inequality of the surface on which it may be required to stand. W, driving pulley with grooved periphery for rope.

ON VAPORISATION, (IN CONTINUATION OF THE ARTICLES ON "THE EMPLOYMENT OF HEAT AS A MOTIVE POWER.")

The conversion of liquids into gases by heat, as exhibited either in the slow evaporation of nearly all fluids at common temperatures, or in the production of gases having great pressure with or without the appearance of boiling-is a subject treated of by such a number of firstrate men, and on the illustration of which such a mass of experiment and observation has been heaped up, that it is evident we must attribute the very imperfect and unsatisfactory state in which, after all, it still remains, to the extreme difficulty of the subject itself. In fact, we have in this, as in so many other branches of physics, arrived at a point where conjectures and hypotheses on the nature of molecular forces are all that is left to us -where direct observation ceases, and the phenomena whose agency we are desirous of tracing are altogether beyond the limits of our senses. We have got on one side an innumerable crowd of every-day facts, such as the boiling of a tea-kettle, or the drying of clothes after washing, which we hardly ever think worth inquiring into at all-and on the other hand, a few accidentally-observed facts, which we call "curious," and having put them into a magazine, and

wondered at them very much, as usual, we forget all about them too. To any one, however, who wishes to test any theory he may have formed by fact, these curiosities stowed away in old magazines, and altogether lost, are of the greatest value. One of the chief objects in this paper is to induce those who may read it, and who are interested in the subject, to be on the look-out for these sort of facts, and of which it is extremely probable that nearly every person engaged in manufactures, &c., could supply some. The experiment of Mr. Coathupe, which will be mentioned in the course of the next paper, may be taken as an example.

A recent German experimenter, Magnus, concludes one of his articles with the following sentence:-" There does not exist an older physical experiment, nor one more frequently repeated, than that of boiling water; but, nevertheless, what occurs in the process was not sufficiently known, and even now much still remains unexplained." As the clearest description of this process which I have met with in any of the popular treatises, I shall translate here that given by Pouillet in his Elément de Physique:-"When the ebullition of a liquid is observed, in general nothing is seen excepting a movement, more or less rapid, which mingles together the whole mass, and agitates it in every direction; but when the experiment is made in a glass vessel, we perceive the continually-varying cause producing these motions. Bubbles of vapour are seen to be formed on the heated sides of the vessel, which bubbles rise in consequence of their lightness, and burst on arriving at the surface. At the moment of their formation they are small, but grow larger as they ascend; and those which proceed from the hottest parts of the vessel are those which succeed each other with the greatest rapidity. In order that these bubbles may be capable of existing and ascending in the midst of the liquid mass which presses upon them on all sides, it is obviously necessary that the vapour composing them be of a tension equal to the surrounding pressure. This it is which determines the boiling point of different liquids, and also that of the same liquid when submitted to different pressures. Hence the first condition for boiling is, that the temperature be sufficiently high to enable

the elastic force of the vapour to overcome all the pressures which are being exerted in the liquid mass. The second condition is, as we have already seen, that the vapour be supplied with that latent heat which is essential to its formation."

In order to obtain anything like a comprehensive view of the general nature of vaporisation, under all its varied modifications, we must consider it as a mechanical problem. In every drop of water converted into steam, we have a contest of opposing forces. Let us take an example, and go through it, step by step. In the first place, then, let us suppose the water to be perfectly pure, and placed in a metallic vessel over a fire, and under the ordinary atmospheric pressure. We must consider what happens to each of the indefinitely small particles of which the whole mass of water is made up. There are many reasons which induce us to consider these small particles to be of a spherical form; there must, at any rate, be innumerable interstices or spaces unoccupied by the watery particles throughout the mass. Each of these small spheres most probably consists of a number of still smaller particles of water, and each of the ultimate particles of water is again composed of particles of oxygen and hydrogen. At present, however, we need not trouble ourselves with these latter, or with the still simpler molecules into which it is possible that both oxygen and hydrogen may be decomposed. In all the ordinary phenomena, we have merely a change of state from the larger compound waterparticle into the smaller and less compound vapour-particle. This partial disintegration is effected by heat, and if we were, in any experiment, to go on applying heat to the vapour-particles, we should still further decompose them into their simpler elements of oxygen and hydrogen. From solid to liquid, from liquid to vapour, and from vapour or compound gas to the constituent gases, oxygen and hydrogen, we see only one uniform process of decomposition: from the more compound system, the individual elements of which are held together by mutual attractions, we get, by the application of heat, to the less compound system; whose individual elements seem, however, to have a still more powerful attraction for each other-and

one of

from this to a still simpler system, having yet stronger internal forces. Each of these compound systems we nevertheless in common language call a particle : thus if we take up on the point of a needle a mass of water, and, if possible, divide that into still minuter portions until mechanical agency can reach no further, so that the ultimate mass arrived at is only capable of still further decomposition by the agency of heat-we may give to this the name of a particle of water. Every particle of water, then, W, consists of a number of particles of vapour, each of which we shall call, V, all of which, whilst in the liquid state, are bound together by strong mutual attractions. Let us consider in th the water particles, W, as it exists is e midst of the surrounding fluid. 1 system of particles acted on by interal and also by external forces. Amongst these latter we have (1) the pressure of the atmosphere transmitted by the surrounding mass of water, and (2) the weight of the superjacent column of water reaching to the free surface of the fluid. All these forces must be overcome by the agency of the heat before the vapour particles, V, can burst their bonds and assume an independent existence. The common books on physics give abundant illustrations of the influence of these external forces-and some of them are laughable enough; as, for instance, the astonishment of a traveller, who after a toilsome ascent of a lofty mountain, being desirous of a cup of tea, put his kettle on the fire forthwith, and was rejoiced at seeing how soon it boiled. “All is not hot that boils." His tea

was

little better than lukewarm, and do all he could, though he found it easy enough to "get up the steam," to make the water hot he found was quite a different thing, and not to be effected without several more pounds per square inch of atmospheric pressure than was to be had in that region. If his kettle lid had been tight, however, and he had thought of blocking up the spout, he might have made the water as hot as he liked. For a similar reason, it would require more heat to make a certain quantity of water boil in a long narrow tube (the fire being applied at one end) than if the same quantity were exposed to the fire in a broad shallow dish.

The influence of these external cir

29

cumstances is, then, so far, well under stood. There still remain, however, a great many very intricate questions to be answered as to the actual process by which the originally fluid particle becomes converted into a number of vapour-particles; to say nothing about the equally difficult question as to how the heat is propagated through the successive layers of fluid, from bottom to top. And in the first place, with regard to the influence of the pressure exerted on the surface of the fluid, either by the atmosphere or confined vapour, all that is shown by the popular illustrations just alluded to is, that the water cannot be heated beyond a certain degree of temperature dependent on the pressure at the surface and that according as this pressure is greater or less, the greater or Jess will be the temperature at which the phenomenon called boiling occurs.

Our

popular treatises amplify quite enough on this point, but we must inquire much more fully into the various other circumstances accompanying the variation of pressure before we can be said to understand much about the thing. The mere circumstance of "boiling" is of comparatively little importance. That which is of most importance, both in an economical and theoretical interest, to learn, is the connection between the following quantities:

1. The amount of heat supplied in a given time.

2. The quantity of water changed into steam by this heat.

3. The pressure and other physical properties of this steam at any given instant.

4. The corresponding temperatures, as indicated by mercurial thermometers immersed in the water and in the steam.

5. Atmospheric, or other pressure exerted on the surface of the water.

It is astonishing how very little has been really done, notwithstanding the immense number of experiments made by so many first-rate observers; how little, I mean, capable of giving any insight into the whole physical process. The chief object aimed at in nearly all these experiments, has been the formation of tables giving the temperatures and corresponding pressures. Everything that relates to the quantity of heat supplied, the time elapsed between any one given pressure and temperature to an

other, the actual amount of water vaporised, &c., &c., is wholly omitted. If such tables enable a man in charge of an engine to say at once what the actual pressure of the steam in the boiler is by looking at the thermometer immersed in the water or steam, they are of course of the greatest practical utility-and yet, nevertheless, this may be but a very imperfect contribution towards a thorough knowledge of the whole process. Moreover, with regard to those few experiments which have had reference to the other questions above mentioned, I have found that unless the original account by the experimenters themselves be consulted, no reliance whatever can be placed on the propositions which later writers have thought fit to announce as the result of such experiments-and, indeed, in some cases it is altogether impossible to say what is the exact meaning intended to be conveyed by the writers. For example, Dr. Lardner, in his "Treatise on Heat," (and thence copied into his "Treatise on the Steam-engine,") says, that it results from experiment; "that the same quantity of heat is necessary to convert a given weight of water into steam, at whatever temperature, or under whatever pressure, the water may be boiled." The experiment referred to is no doubt that of Watt, which I will now transcribe in his own words. (Note to article on Steam-engine, in Robison's "Mech. Philos.") "When the digester was set upon a steady fire for a given time, half an hour for instance, the steam being allowed to issue freely by keeping the safety-valve quite open, and the quantity of water evaporated in that time being ascertained; if the digester was again placed on the fire, and continued for an equal time with the safety valve shut, upon opening that valve a quantity of steam would issue with violence; and when the elasticity of the steam issuing was reduced to that of the atmosphere, I found the quantity of water evaporated in these circumstances was apparently the same as had evaporated in an equal time when the valve was constantly open. From whence I concluded, that the quantities of water evaporated in any given time were proportional to the quantity of heat which entered it, et cæteris paribus, to the surfaces exposed to the fire and not to the surfaces exposed to the air, as had been

supposed, and as is the case where the air is the sole agent of evaporation in heats below boiling."

It requires but very little consideration to see that this experiment does not at all prove that "the same quantity of heat is necessary to convert a given weight of water into steam at whatever temperature, or under whatever pressure the water may be boiled." For this simple reason-the amount of water converted into steam was only measured after the pressure had been reduced by the opening of the valve to the ordinary atmosp heric pressure. If the water had been contained in a glass vessel, so that the quantity v "iporised could be ascertained we; a ithout altering the pressure on the surfa rad if in this way it had been four Wthat the same quantity was converted ito steam in half an hour as under the usual pressure of the atmosphere, then indeed it would be proved that the same quantity of water is vaporised by a given amount of heat, whatever be the pressure under which it is produced. But in the experiment as described by Watt, there might, for anything we know, be an immense alteration in the rate of vaporisation at the instant of opening the valve.. It is possible, certainly, that this is not the experiment referred to by Lardner; but from the preceding references in the Treatise, I have no doubt that it is to this that he refers, and at any rate I have not met with any other experiment from which any such conclusion has been attempted to be drawn.

Another source of frequent annoyance to the reader is, that in many of the recorded experiments where it is absolutely necessary to know the quantities of heat employed to produce the effect mentioned, the writers have contented themselves with giving merely the temperatures. The thermometer has been relied upon far too much, and men are only now beginning to see the fallacies into which it may lead. The expansion of mercury is (as of course every body acknowledges verbally,) merely one of the effects of heat which is often useful as an indicator of other concomitant effects; but though thus verbally acknowledged the fact is frequently forgotten in practice. It cannot be too strongly or frequently urged upon experimenters, that no one of the effects produced by any physical agent