the same strain, or the same work may be produced with half the former strain; i. e., by a bar having an area of only half a square inch. In a similar manner, if we move the bar with the velocity employed in teleodynamic transmission, viz., about eighty feet per second, then, while doing the same amount of work, the strain on the bar will be reduced from 5,000 to 125 pounds, and the bar wil need a section of one-fortieth

of a square inch. To put an extreme illustration, we might conceive of a speed at which an iron wire, as fine as a human hair, would be able to transmit the same amount of work as the original one-inch bar.

"By the application of these simple principles in Hirn's apparatus, the greater part of the force is first converted into velocity, and at the place where the power is required, the velocity is changed back into force."

The employment of repeated coils for the purpose of increasing friction is an idea which has often been employed for many purposes, and its origin is apparently unknown. The principles upon which it is based, however, are not as well known, perhaps, as they should be, and a brief examination of the subject may be of interest.

Everyone who has seen the operation of bringing a vessel to her moorings has noticed the ease with which the strength of a single man can be used to withstand the momentum of a heavy vessel when aided by the friction of a few turns of a rope about a post.

A few experiments will serve to show the rapidity with which frictional resistances can be multiplied by this method, and the practical application will become obvious.

If a cylindrical drum, placed in a horizontal position, be fixed from revolving, and a rope thrown over it, with weights attached to each end of the rope, the tension produced by the weights will cause friction to be generated between the and the drum.

If we take the coefficient of friction at one-thi sure produced by the weights, which on smooth far from the truth, a given weight on one side v

ne

weight three times as large on the other side before any slipping takes place.

In this case the rope only embraces one-half the circumference of the drum. Now, if we pass the rope completely around the drum, we will find that one pound tension will support nine pounds before slipping, and that every whole coil multiplies the friction nine times, and every half coil multiplies it three times. These are only round numbers, but Professor Weisbach has investigated the subject thoroughly, and the following table, calculated from his formula, will show more accurately how enormously the holding power of friction may be increased by repeated coiling:

This arrangement of stationary drum and slipping rope, of course, has but a limited use, and so efforts have been made, more than once, to make the principle more general in its application. One of the earliest applications was made in the capstan of a ship; but the difficulty there appears of the tendency of the coils to travel along the axis of the winding cylinder. In order to meet this objection, the capstan is made tapering, and when the coils have wound along to the large end they are pried back again to the small end, and this operation is repeated as often as necessary.

As long ago as 1670 the famous architect, Sir Christopher Wren, read a paper before the Royal Society, upon a method for obviating this objection; and, as the communication is both short and curious, I reproduce it from Willis' Mechanism, with its quaint spelling and rough engraving:

"A Description and Scheme of Dr. Wren's Instrument for Drawing up Great Weights from Deep Places."

Read May 5, 1670.

"Having considered that the ways hitherto used in all engines for winding up weights by roaps have been but two, viz., the fixing one end of a roap upon a cylinder or barril, and so winding up the whole coyle of roap; the other, by having a chain or a loose roap catching on teeth, as is usual in clocks; but finding with all that both these wayes were inconvenient, the first, because of the riding of much roap in winding one turn upon another; the other, because of the wearing out of the chain or roap upon the teeth, I have, to prevent both these inconveniences, devised another, to make the weight and its counterpoyse bind on the cylinder, which it will doe if it be wound three times about.

"But because it will, then, in turning, scrue on like a worm, and will need a cylinder of very great length, therefore if there be two cylinders, each turned with three notches, and the notches be placed alternately, the convex edges to the concave, as in the figure here adjoined, the roap being wound three times about both cylinders, will bind firmly without slydip ond work up the weight with a proportionable count the other end of the roap.

Since Wren's time the arrangement has met with numerous applications, but they appear to have been confined to winding systems. When applied to continuous motion, however, as in the manila rope transmission system, the advantages are most apparent.

In the study of belt transmission the amount of friction between the belt and pulley governs the transmitting capacity; but in the manila rope system the principle of multiplied coil friction adopted renders it possible, with a few turns, to remove all possibility of slipping, and the transmitting capacity becomes merely a question of the tensile strength of the rope, and the velocity at which it moves; so that the whole subject is entirely under control.

In this way the old principle has met with a new application which bids fair to extend its usefulness to a greater extent than ever before.

But to eliminate theory as far as possible and come down to the plain facts, which will be more interesting to you than any unverified theoretical discussion can be, I will now describe the American system as it is in use in the works of Dodge Manufacturing Company, and where you are, individually and collectively, cordially invited to inspect it at any time when your convenience shall enable you to do so.