center of gravity should be so well within its base that there will be no danger of its being upset by the ordinary uses to which it is exposed. Pots and pans, pitchers, lamps, and candlesticks, of general and daily household use, should have bases so broad and weight so low that the accidental bump of the inexperienced "help" will not be inevitably fatal.

When utensils are made more for show than for use, as those in Fig. 10, and are to occupy places of comparative security, beauty more than utility may be considered in the proportions of their supports. Where utility has disappeared altogether and the suggested outline of a vase, for instance, is used for purely ornamental purpose, supports may be done away with altogether, as appears in these drawings of Italian tapestries of the seventeenth century (Fig. 11).

The stability of pendant objects must also be considered. It is evident that the perpendicular line of suspension must be the line of equilibrium, and that these two must correspond with the design (Fig. 12). Whether any objects should under any circumstances be exposed to the real and apparent danger of falling is a question. We have got so into the habit of hanging pictures, engravings, and other works of art in our houses, and of seeing them hung in galleries, that we have lost sight of the incongruity of the custom. Pictures should be impaneled, and be permanent parts of the walls on which they appear. But, then, how could they be moved when owners tire of them, or tire of their houses, or how could they be gathered together in museums for purposes of study. and public enjoyment? Picture frames are of comparatively modern invention. The idea of buying a picture for the purpose of selling it again was not entertained before the fifteenth century. Pictures were as substantial parts of churches and houses as were shrines and fireplaces.

Having very cursively reviewed the elements of form, we are in a position to understand decoration, which is simply the application to form of ornament.

THE highest authenticated points at which flowering plants have heretofore been found growing upon the Andes are at about 17,000 feet, although the Kew Herbarium contains several specimens labeled as having been found at altitudes of from 17,000 to 18,000 feet. Sir Martin Conway has brought back from his recent explorations in the Bolivian mountains at least half a dozen species from 18,000 feet and upward, the highest being from about 18,500 feet. They include a saxifrage, a mallow, a valerian, and several Compositæ. Composite likewise attain the upper limit of phanerogamous vegetation in Thibet, where, in latitudes from 30° to 34°, one was found by Dr. Thorold at 19,000 feet.

STEAM TURBINES AND HIGH-SPEED VESSELS.*

ALL

BY THE HON. CHARLES A. PARSONS, F. R. S.

LL heat engines at present in use take in heat from a source at a high temperature and discharge most of it at a lower temperature, the disappearance of heat in the process being the equivalent of the work done by the engine. In all cases at the present time the source of heat is from fuel of some kind, and after working the engine the residue is discharged in the case of the steam engine either to the condenser or in the exhaust steam when non-condensing. In the gas engine it is discharged in the waste gases and into the water jacket around the cylinder.

The earliest records of heat engines are found in the Pneumatics of Hero of Alexandria, about 200 B. C. He describes a reaction steam turbine, a spherical vessel mounted on axes supplied with steam through one of the trunnions from a boiler beneath; the steam escaping through two nozzles diametrically opposite to each other and tangential to the sphere, causing the sphere to rotate by the reaction or momentum of the issuing steam, and analogous to a Barker's water wheel.

Thus, the first engine deriving its motive power from fuel was a crude form of steam turbine, and though it could have been applied to useful work, and could easily have been made sufficiently economical to replace manual and horse power in many instances, yet it lay dormant till 1629 A. D., when Bianca suggested the same principle in a different form. Bianca's steam turbine consisted simply of a steam jet fed from a boiler impinging against vanes or paddles attached to the rim of a wheel which was blown round by the momentum of the steam issuing from the jet.

The piston engine is, however, of comparatively modern origin, and dates from about the year 1700 A. D. Engines of this class are so well known that it suffices to say that they have been practically the sole motive-power engines from fuel in use from 1700 up to 1845, and have constituted one of the most important factors in the development of modern engineering enterprise.

Air engines were introduced about the year 1845, and although the larger engines of the Stirling type were very economical in fuel, yet, on account of the inherent difficulty of heating large volumes of air within metal chambers or pipes-a difficulty arising from the low conductibility of air and consequently the overheating and

* Abstract of the Presidential Address to the Institution of Junior Engineers, November 3, 1899.

burning of the metal-they have only come into commercial use for very small powers.

During the last thirty-five years gas engines have been perfected, and more recently oil engines, and in point of efficiency both convert a somewhat larger percentage of the heat energy of the fuel into mechanical energy than the best steam engines. All successful oil and gas engines are at present internal-combustion engines, the fuel being burned in a gaseous form inside the working cylinder.

Very numerous attempts have, however, been made to construct internal-combustion engines to burn solid fuel instead of gas. Some have been so far successful as to work with good economy in fuel, but the bar to their commercial success has been the cutting of the cylinder and valves by fine particles of fuel. This difficulty is not present when the fuel is introduced in the gaseous or liquid form, and hence the success of gas and oil engines; but could this difficulty be overcome, the solid fuel would be the cheaper to use.

Internal-combustion engines, gas engines, oil engines, cannon, etc., owe their superior economy in fuel to the very high temperature at which the heat is transferred from the fuel to the working substance of the engine, and consequently the great range of temperature in the working substance of the engine. In steam engines the temperature is limited by the practical difficulties of deterioration of metal and materials involved in the construction.

About fifteen years ago I was led by circumstances to investigate the subject of improving the steam turbine. In recent times several attempts had been made to apply steam turbine wheels of the Hero and Bianca types to the driving of circular saws and fans. The velocity of rotation with either of these types must necessarily be very high in order to obtain a reasonable efficiency from the steam, a velocity much in excess of that suitable for the direct driving of almost all classes of machinery; gearing was considered objectionable, and it therefore appeared desirable to adopt some form of turbine in which the steam should be gradually expanded in small steps or drops in pressure so as to keep the velocity of flow sufficiently low to allow of a comparatively moderate speed of rotation of the turbine engine.

The method adopted was to gather a number of turbines of the parallel flow type on to one shaft and contained in one case, the turbines each consisting of a ring of guide and a ring of moving blades, the successive rings of blades or turbines being graduated in size, those nearer the exhaust end being larger than those near the steam inlet, so as to allow a gradual expansion of the steam during its passage through the turbines.

The form of the turbine was that of a rotating drum, with outwardly projecting rings of blades which nearly touched the containing cylindrical case, and on the case inwardly projecting rings of guide blades which nearly touched the drum. In the first examples of the engine there were two groups of turbines right- and left-handed on each side of the steam inlet, the exhaust taking place at each end of the turbine case, so as to completely balance end pressure from the steam. More recently one series of turbines only has been used, those on the other side of the steam inlet being replaced by packing rings or rotating balance pistons which

FIG. 2 SHOWS THE ARRANGEMENT OF MOVING BLADES AND GUIDE VANES IN A PARSONS's TURBINE. The top outer cover has been removed. The cylinder containing the revolving barrel has, as will be seen, a greater internal diameter than the diameter of the drum. It is the annular space thus formed through which the steam flows and which contains the revolving blades and the fixed guide blades. Between each two rings of moving blades there is a ring of guide blades, the latter being keyed into the containing case. The vanes are set at an angle, so that the steam acts on them as wind on the sails of a windmill.

balance the end pressure and divert the whole of the steam through the turbines on the other side.

The steam entering the annular space between the shaft and the case passes firstly through a ring of guide blades attached to the case, and is given a rotational direction of flow; it then passes to the succeeding ring of blades attached to the shaft, by which its direction of rotation is reversed, thereby impressing the difference of its rotational momentum in torque to the shaft. The steam then passes to the second ring of guide blades, and the process is repeated, and so on, gradually expanding by small increments at each ring of blades; the succeeding rings of blades get longer and wider, and at intervals the diameter of the turbine drums, cylinders, and rings are also increased. In condensing turbine engines