installed. Practically they include parallel mouthpieces, placed either within or without the tank or reservoir, mouthpieces that converge, or that diverge, and compound mouth pieces which are convergent for a portion of their length, and divergent for the remainder.

If a short parallel tube is attached within a tank, that is as bad a form as a simple opening in a thin plate, giving only about 0-52, and it is therefore not to be considered. But if the

parallel tube has a length of twice the bore, Fig. 12, B, the coefficient is increased, for the diameter of the jet at the contracted part becomes 0.9 and its area 0-8 that of the orifice. If the tube is attached outside, as at c, the efficiency is also increased, and its amount depends on the particular relation which exists between the diameter and length. The best results are obtained when the bore is equal to from one-half to one-third of the length, giving a coefficient of 0.81 to 0.82. With further increase in length the value gradually diminishes.

Between the short tube and the thin plate there is the case of a thick plate, which, as might be expected, gives a result midway between the two, since its thickness obviously approximates to the length of the tube.

The highest results are obtained from a converging mouthpiece, which explains why this form is adopted generally for the outlets of tanks. If the angle included between the sides ranges from 13 degrees to 17 degrees, Fig. 12, D, a coefficient of from 0.94 to 0-99 is obtained. A diverging mouthpiece gives similar results, that shown at E, from Venturi's experiments, giving a divergence of 5 deg. 6 min. on a length nine times the diameter, as the best. Converging and diverging shapes are combined in one mouthpiece with results equal to those of single

cones.

Afterwards it came to mean one-sixth of the IHP.

Admiralty Knot.-1.15152 statute miles, or 6,080 feet, or 1853-169 metres.

Admiralty Tests.-These relate to tests made on boiler plates, angles, and other sections. See Boilers, Materials for; Forge Tests; Tests-Official.

Admission.-Denotes either the instant of the entrance of steam to an engine cylinder, or the entire period during which it is admitted until the moment of cut off, when expansion begins.

Admission Corner.-The corner of an indicator diagram which shows the method of the entry of the steam into an engine cylinder. See Indicator Diagram.

Admission Line. The line or curve which denotes the rise of pressure produced by the steam during its admission into an engine cylinder. See Indicator Diagram.

Admission Port.-The port through which steam is admitted into an engine cylinder. Steam is admitted to, and exhausts from each port alternately in an ordinary slide valve engine. In a Corliss engine the two functions are confined to distinct ports.

Adulteration of Oils-See Oils. Advance. See Slide Valves, Valve Gears.

Advance,-Angles of.-See Slide Valves, Valve Gears.

the most common way in which the axe operates. There is a difference also in the method of grinding, the adze having its bevel on one face only, the inner one, while the axe is doubly bevelled. The plain face of the adze is not a true plane, but is curved approximately to the radius which the tool makes when being swung by its handle. Hence the surface cut by the tool is composed of a number of minute concave facets.

The great value of the adze lies in its capabilities for roughing down heavy timber rapidly, operating both as a splitting and a finishing tool. Its value is greatest in roughing pieces of irregular outlines, or very heavy masses which either cannot be reduced with a circular saw, or band saw, or cannot be transported to the saws. It is the principal tool employed by

ceives chalk and sulphuric acid, the combination of which produces carbonic acid gas, as in the manufacture of mineral waters. The gas is conveyed thence by a pipe through water to a reservoir, ready to be pumped into the mixer. Adjacent also to the mixer is a shoot through which the flour is put into the mixer, to be amalgamated with and by the acidulated and aerated water. The dough is received from a tap in the bottom of the mixer, weighed, and sent into the oven, in which the carbonic acid gas passes off.

Aerial Cableways. See Cables, and Cableways.

Aerial Conveyors.-See Aerial Transportation.

Aerial Transportation. - Transport by means of ropeways supported at a convenient

A

B

shipbuilders in wood. It is employed largely in engineers' heavy carpentry for dressing down balks, timber jibs, and timber framings generally.

Adze Block.-A term sometimes applied to the cutter block of a wood-planing machine. See Cutter Block.

Aerated Bread Machinery. The feature by which this is distinguished is the substi-. tution of carbonic acid gas for yeast, which renders handling of the dough unnecessary. The machinery comprises the following:

Principally, a globular mixer of cast iron, within which the dough is mixed by rotating arms or beaters, under a pressure of six atmospheres. Round this mixer subsidiary apparatus is ranged in the following order. A strongly made wooden cask, or "generator," of oak, re

height above the ground, has advantages which often make it a more suitable method than a road or railway on the surface. The idea is very ancient, but it is only during recent years that it has been much developed and commonly used. It was first recognised as being a very economical and satisfactory method of transporting light loads over hilly, undeveloped country, and over rivers. It was later seen that even in the midst of highly civilised conditions, where roads and railways already existed, it still had advantages under some conditions. More than for anything else, it has been used in mining districts for the conveyance of the products of the mines across rugged country. It is cheaper to erect an overhead cableway for this purpose than to make a road with rails, and the former also has the advan

tage of being removable from one place to another.

Next to the cheap transport of material across rough country, perhaps the most important application of aerial cableways is for building and excavating operations. For this purpose they are a cheap, and often more efficient means, than an ordinary rigid traveller or a travelling crane. In bridge building, for instance, an aerial cable can be extended across a river, and the materials for the bridge can be deposited where required without having to carry it out in barges, and have the difficulties of current and tide to contend with. In excavating a canal or dock, an overhead cable attached to a travelling tower on rails on each bank will carry the excavators, and obviate the necessity of employing a number of cranes, with rails laid to run them on.

In the loading and unloading of ships, an aerial cable is often more suitable than cranes. The cargo can be deposited or brought from places some distance back from the edge of the dock, or quay wall, and the tower on the dock side can be provided with a boom for running the carriers out over the vessel. In cases where there is no dock, as in Fig. 14, Plate I., a ship may lie at some distance from the shore, and cargo be transported by means of a connecting cable. In the construction of Beachy Head Lighthouse, Fig. 15, Plate I., communication with the shore was by means of cables.

In the coaling of warships at sea, aerial transport is recognised as being the only economic method possible. Except in still water, ships cannot lie side by side. A space of not less than 300 feet is necessary for safety, and the communication must be by cable, means being provided to compensate as much as possible for increased or relaxed tension of the cable.

In large factories and mills, products can often be best conveyed from the floors of one building to the floors of another building at some distance away, by an aerial cable, or a very light aerial railway. This is especially an advantage where constant communication between upper floors of separate buildings is necessary.

Aerial transport is often the only way of conveying material across a railway. In such cases a light guard bridge is generally built

beneath the cableway as a precaution against anything falling on to the line.

For passenger transport, aerial cables are used to some extent.

The earliest and simplest type of aerial cableway was an endless rope passing round a pulley at each terminus, and having carriers attached to it, which travelled with the rope. This type is still used, and for very light work is generally considered the more suitable, because of its cheapness. The later type, and the one more commonly used, has a fixed rope which serves as a rail for the carrier to run on, and a separate travelling rope which pulls the carrier along. In the simple type, one rope both supports and carries the load. In the other kind there is a separate rope for each of these purposes, and this gives much greater power and efficiency. Details vary considerably, but all the systems in use may be roughly reduced to the two mentioned. The system best suited for any particular case depends on the conditions, and on the work required of it. With the steel ropes of modern times there is scarcely a limit to the loads that can be transported, and there is no limit to the inclines that can be followed.

For transportation on a level, or up inclines, or for hoisting, motive power is necessary. For carrying loads down inclines the force of gravity alone generally does the work, and in some cases even supplies power for other purposes. On level ground the motive power required is often reduced by making the tower from which the loads are despatched, higher than the tower at the other end of the cable. Cableways of great length are supported at frequent intervals, as in Fig. 16, Plate II., but when necessary very long unsupported spans can be employed. Cableways of comparatively short length, which are supported only by a tower at each end, are made movable, if the work they are intended for requires it. They are thus enabled to cover an immense area of ground. The two towers may be mounted on wheels and travel parallel with each other on lines of rails, or one tower may wheel in an arc, and provision be made for sufficient amount of swivel at the rope connections on the fixed tower. In the fixed rope type of cableway, the