in mechanics, a machine used for raising or lowering great weights. For the principles on which these machines act, see DYNAMICS in this Supplement, and likewise MECHANICS, Encycl., where descriptions are given of several very powerful cranes.

The crane in common use is employed with some danger to those who work it; and therefore a machine of this kind, acting upon a simple and certain principle, by which the men walking in the wheel can lower goods with safety as well as expedition, has long been considered as a great desideratum in mechanics. Repeated premiums have been offered by the Society for the Encouragement of Arts to induce ingenious men to attempt the invention of such a machine; and various have been the contrivances for accomplishing so desirable a purpose. A clergyman, who subscribes E. C. we suppose as the initials of his name, proposes, through the medium of the Repertory of Arts, to accomplish it merely by introducing the action of a worm or screw into the crane.

Whenever a worm of two threads is introduced into a machine, all retrograde motion is stopped, unless that worm receive its reaction from the first moving force; for, powerfully as a worm acts upon a wheel, a wheel has no power upon a worm, whatever force may be applied to it. Suppose, then, the first motion in a crane were given by a worm upon the axis of the wheel in which the man walks, the man would have perfect command of the machine, to raise or lower the goods at pleasure, with the remotest possibility of being overpowered by the descending weight.

"Were I to construct (says the author) a crane upon this principle, I would have the axis of the wheel in which the man walks, and the axis of the worm, in separate parts, and occasionally united by a coupling-box. When goods were to be raised, the two axes should be connected; when lowered, they might be disunited, and the worm turned by a winch, which would be done much more expeditiously than by the wheel. For the reasons before suggested, the descent of the weight could be accelerated or flopped at pleasure, at the direction of the person turning the winch.

"This contrivance might be not inconveniently applied to a crane already erected upon the common principle: Let there be a wheel put upon any convenient axis in the machine as it now stands; upon this let there lie a worm, that can be thrown in or out of gear at pleasure; and let the lever by which it is done lie within reach of the man's hand in the wheel. The goods being fastened to the crane, and raised off the floor of the warehouse ready for letting down, the man puts the worm into gear, leaves the wheel, and lets the goods down by the winch. Provided it can be conveniently done, it would be advisable to throw the wheel in which the man walks out of gear when the winch is made use of; this, however, I should apprehend, would not be a matter of absolute necessity."

Our author is aware of two objections which may be urged against the introduction of a worm into a crane in the manner which he proposes. The first arises from the slowness of the motion produced by the turning of a screw, which he considers as unworthy of regard; because the necessary speed is to be gained by the first pair of wheels and the diameter of the barrel of the windlass.

To the second, arising from the supposed greater friction between a worm and wheel, he replies, that as the friction between the teeth of two wheels (if not formed on the true epicycloidal principle) must, while it lasts, be greater than between a worm and wheel for the same space of time, it seems no unreasonable supposition that the aggregate of friction will, in the two cases, nearly balance each other; especially if it be taken into the account, that to obtain the power of one worm and wheel, there will be, in most cases, required two pair of wheels, and two additional axes—all which will add to the friction. But, granting the balance of friction to be against the action of the worm, the power to overcome it is greater in proportion than to overcome the friction of two wheels.

Mr James Whyte of Chevening, in the county of Kent, whose improvement in the construction of pulleys, has, with due respect, been noticed elsewhere*, gives, in the Transactions of the Society for the Encouragement of Arts, &c. the following description of a new crane for what is: A (fig. 1.), a circular inclined plane, moving on a pivot underneath it, and carrying round with it the axis E. A person walking on this plane, and pressing against the lever B, throws off the gripe D, by means of an iron rod C; and thus admits the plane and its axis to move freely, and raise the weight G by the coiling of the rope F round the axis E.

To shew more clearly the construction and action of the lever and gripe, a plan of the circular inclined plane, with the lever and gripe, is added (see fig. 2.), where B represents the lever, D the spring or gripe. In this plan, when the lever B is in the situation in which it now appears, the spring or gripe D presses against the periphery of the plane, as shown by the double line, and the machine cannot move; but when the lever B is pressed out to the dotted line H, the gripe is also thrown off to the dotted line I, and the whole machine left at liberty to move. One end of a rope or cord, of a proper length, is fixed near the end of the lever B, and the other end made fast to one of the uprights, serving to prevent the lever moving too far when pressed by the man.

The properties of this crane, for which the premium of 40 guineas was adjudged by the society to the inventor, are as follows:

1. It is simple, consisting merely of a wheel and axle. 2. It has comparatively little friction, as is obvious from the bare inspection of the figure. 3. It is durable, as is evident from the two properties above-mentioned. 4. It is safe; for it cannot move but during the pleasure of the man, and while he is actually pressing on the gripe-lever. 5. This crane admits of an almost infinite variety of different powers, and this variation is obtained without the least alteration of any part of the machine. If, in unloading a vessel, there should be found goods of every weight, from a few hundreds to a ton and upwards, the man that does the work will be able to adapt his strength to each as to raise it in a space of time proportionate to its weight; he walking always with the same velocity as nature and his greatest ease may teach him.

It is a great disadvantage in some cranes, that they take as long time to raise the smallest as the largest weight, unless the man who works them turn or walk with such velocity as must soon tire him. In other cranes, perhaps, two or three different powers may be procured; to obtain which, some pinion must be shifted, or fresh handle applied or reported to. In this crane, on the contrary, if the labourer find his load too heavy as to permit him to ascend the wheel without its turning, let him only move a step or two toward the circumference, and he will be fully equal to the task. Again, if the load be so light as scarcely to resist the action of his feet, and thus to oblige him to run through so much space as to tire him beyond necessity, let him move laterally towards the centre, and he will soon feel the place where his strength will suffer the least fatigue by raising the load in question. One man's weight applied to the extremity of the wheel would raise upwards of a ton; and it need not be added, that a single-flèched block would double that power. Suffice it to say, that the size may be varied in any required ratio; and that this wheel will give as great advantage at any point of its plane as a common walking-wheel of equal diameter, as the inclination can be varied at pleasure, as far as expediency may require. It may be necessary to observe, that what in the figure is the frame, and seems to form a part of the crane, must be considered as a part of the house in which it is placed; since it would be mostly unnecessary should such cranes be erected in houses already built. With respect to the horizontal part, by walking on which the man who attends the gib occasionally assists in raising the load, it is not an essential part of this invention, where the crane is not immediately contiguous to the gib, although, where it is, it would be certainly very convenient and economical.

Crane is also a popular name for a syphon, employed in drawing off liquids.