sorts of labour-saving machinery, we ought, in extending the application of science, to avoid all occasion of obliging man to toil at what elementary powers can do perfectly well.

Let it be laid down, then, at once, that our driving-power for the wheels must come from a steam-engine, by endless band, or by water, or by steam-pipe; then clamping the gymbals of each wheel, a necessary proceeding at sea when driving the spinner to prevent strain on its pivots, let us proceed to examine the case.

Fig. 6.

SECTIONAL ELEVATION OF PRESSURE STAND.

Endless Band-Driving.-Such band must not be applied to the axle of the spinner itself, for it draws it to one side, spoils the pivots, and is not easy to disengage with safety. But it may be applied to a separate fixed axle below, constructed with very strong pivots, and with a central sliding-rod which can be slided up into the axle of the spinner by a hole through its lower bearing and pivot. This plan I have used on a 10 lb. spinner with velocities up to 80 revolutions per second; and it is a very effective plan as to the ease of making and breaking connection between the driving axle and the

spinners without shock, and without the prejudicial rattle of toothed wheels. But as the said axle is heavy, and spins as rapidly as the spinner itself, it must be adjusted with the gravity plugs also, lest it communicate too much vibration to the spinner. The lower pivot of the spinner for this sort of connection through its bearings, must be larger than if the impulse were communicated between its bearings; but the wheel experimented on ran as lightly and with almost as little friction as could be desired, so that the method is decidedly a practical one, when the band moves quickly enough.

Elemental Driving.-Even with an endless band, however, there will be difficulty in getting up the necessary speed, on account of the slowness of the first mover in a steam-engine. Intervening wheels and pinions multiply expense, vibration, and friction, and, after all, are not so extensively available for multiplying speed excessively as the motion of fluids pressed out of large tubes into small ones; as an extreme case of which may be taken the boiler of a steam-engine with some thousand times the area of the steam-pipe through which all the steam is conveyed away.

This method I have therefore experimented on in the case of water, air, and steam. The same means employed to utilize one will also suit the others; but air and steam are capable of producing much more velocity than water for the same pressure; and of the two aëriform drivers, steam is the more easily applied, as it can be brought to bear at once out of the boiler by a pipe without the intervention of pump machinery. The steam indeed at first proved troublesome, by its heat and moisture, on escaping after it had done its work, but it was soon found quite possible to carry off all this waste by a second steam-pipe placed in a small wooden chimney communicating with the box in which the driving apparatus was contained.

Elemental Driving from a second Axle.-Adopting the same species of axle and connecting-rod as described in p. 445. I applied to such an axle a double Barker's Mill according to the elegant method of Professor Redtenbacher for neutralizing the lifting power of the head of water. But the Barker's Mill did not answer; for, to produce high speed with a certain size of pump, or expenditure of water, it was necessary to make the

orifices of escape very small, and the radius of motion short; and then it was found that the water leaked so very freely at the joints, or space between the moving and fixed necks, that no sensible power was obtained. Internal leathers were next applied to check this escape of water, on the plan recommended. of old by Dr Robison; but the pressure of the water on these locked the whole apparatus immoveably. The depth of the leather collar was pared down by successive degrees; but not until there was no more left to press against the outer neck did any motion take place, and then the escape at the joint was as bad as before. The method might have answered well enough had the arms of the mill been long, and its rate of revolution slow, as in ordinary cases; but that described was necessarily very different.

New Hydraulic-Driver.-The cause of failure, then, being the impossibility of keeping the joint tight, without much. friction, and this objection holding equally with the "vortex," and other known wheels for high velocity, it occurred to me to devise a plan by which the water that escaped at the necessary joint should be made to play a useful part; in fact, that all the water should escape at the joint, which would then present no mechanical difficulties in the making or in keeping free from friction. To this end I took away the Barker's Mills and applied around the axle on which they had been fixed a series of vanes on which the water struck in escaping from the upward and downward orifices-these being now freely enlarged, so as to let as great a quantity of water escape there as was to have issued out of the mills. The axle carrying the vanes necessarily passed through the orifices of emission, and the fluid was consequently flashed out in a thin but continuous ring form through the annular space left between the outside of the axle and the inside of the nozzle. The pressure, therefore, exerted on the vanes was very uniform, and these were set at a very large angle to the direction of impact, so as to increase the speed of rotation-at the expense of power, of course-to a greater pace than that of the effluent particles.

As a specimen of the performances of this driver, I may state that, with the area of the annular spaces between the nozzles of escape and the spindle, equal in all to 0·6 of a square inch,

VOL. IV.

2 I

and with steam of 25 lbs. pressure, the driving axle, weighing 4 lbs., was driven (per counter) at 140 revolutions per second, and, with the 10 lb. spinner in addition, at 70 to 80 revolutions per second.

The following is the best form I have found for this driver.

Elemental Driving applied to the Spinner direct.-A neater method of driving the spinner by elemental power would be by dispensing with the subsidiary axle and its bearings, and such plan is very desirable for diminishing friction, and preserving truth of motion. To gain this end I have made many experiments, and have concluded with a small turbine on a pin which is fixed into the lower spinner pivot, and projects through its bearings. In the normal position of the apparatus, the turbine hangs down in the inside of the supporting stand or table; the steam or water pipe, fitted with a peculiar nozzle, is then raised so as to enter the void centre of the turbine, and flashes out the fluid in a horizontal sheet through the curved and open sides. The vanes forming these sides are purposely set nearly at right angles to the radii, in order to make the speed of revolution surpass the rate of efflux, and appears in a transverse sectional plan, as in fig. 8.

The power of this method is so great that the wheel moves

the instant the steam is applied, the

full velocity is obtained in but a few seconds, and the addition of the 10 lb. spinner hardly affects the rate of revolution of the 4 lb. turbine, which is about 70 to 80 per second.

Conclusion. With these powerful elemental methods of driving, and with large wheels in a precessional stand at high velocities, there seems no reason why platforms should not be constructed for use on ship-board capable of carrying both the observer and his telescope. Even an invalid might have his bed there arranged, so as to alleviate his seasickness, by experiencing no angular motion whatever.

Tremor might be feared, because we find it more or less wherever we find mill-wheels revolving; but that is because their centre of gravity is not adjusted symmetrically to their axis of motion. In our case we do employ accurate methods of effecting this important correction, and we may expect, therefore, the large wheels to revolve as smoothly and as silently as the small ones.

APPENDIX.

Before leaving the subject of free rotating machines, there are two or three note-worthy points about them, which, though flowing strictly from the theoretical principles of mechanics, are still new to many persons, and are too often put down when seen as paradoxical, as upsetting previous experience, and as breaking in upon the unity which has been traced so extensively in the works of creation.

Some explanation, therefore, of these cases may both tend