Part 8

If the two vases which are represented in the view by vertical and horizontal, straight and curved lines, were actually before us you would have difficulty in finding any vertical lines, and the horizontal lines would turn out to be circles. The lines in the view mark the apparent terminations of the surfaces. For purposes of study, however, you must regard objects of three dimensions as bounded by lines, just as they appear in photographs, drawings, or other flat representations, geometric or perspective. In regarding objects from the point of view of decoration there is still another element to be considered; that is, the element of material, the substance of which objects consist, for it is evident that the ornament which would be appropriate to wood, for instance, might not be appropriate to metal or to stone. The element of material is of great importance in practical decoration, but of less importance in theoretical decoration. Lines and surfaces are therefore the two chief elements of decoration to be considered at present. Color, being an element of an entirely independent nature, will not be considered at all.

First, lines. The lines down one side of an object may be called the profile of the object, while the lines surrounding the object may be called the contour or outline of the object.

Profiles and outlines are made up of any number of straight and curved lines connected at any and every variety of angle. The view (Fig. 2) shows a few possibilities of combination of lines into profiles. The particular thing to be observed in these profiles is that individual curves are preceded or followed by curves which curve in the same direction or in the opposite direction--that is, regarding the curves as concave or convex from a given side of the profile, sometimes a concave curve meets a concave curve, sometimes it meets a convex curve. In these particular profiles the straight lines which unite the curves are so small and so insignificant that they appear as mere connections. Where the adjoining curves are homogeneous the connection is called continuous--_raccords continus_, as Mayeux puts it. When the adjoining curves are different, the connection is called contrasted--_raccords contrastés_. In the view all continuous connections are marked _a_; all contrasted connections are marked _b_. Now follow these lines up and down slowly and deliberately--not once or twice, but a number of times. See exactly where the connections occur, and where the connections are continuous, and where they are contrasted. In these profiles are shown forth and made evident two of the most important and general laws not only of ornament, but of all artistic composition: First, that connected curves of the same kind must run substantially in the same direction; and, second, that for purposes of strong contrast curves of different kinds must be joined--that is to say, that where contrasted connection is desired, the difference in direction must be abruptly and sharply indicated. In the profiles in the view the various curves have been continued in dotted lines beyond the profiles, so as to bring out and make clear these two laws. You see that wherever there is a _b._ the dotted lines cross at, or nearly at, right angles, and that wherever there is an _a._ there is no crossing at all of the dotted lines. The essence of these two laws is of such importance in all artistic and decorative composition that beginners might well be put to drawing profiles until the principles involved have been absorbed and made a part of artistic apprehension. The profiles in the view are all pleasing, because the laws are observed. Try your hand at drawing profiles in which the laws are not observed, and you will quickly perceive the difference. The most beautiful of pure profiles are those presented by Greek entablatures. The most beautiful of Greek outlines are those presented by Greek vases. The beauties of Greek sculpture and of renaissance design belong so strictly to the domain of pure art that they may not be used for comparison in an article on ornament.

As outlines are composed of profiles, the same laws govern. That the curved line is the line of beauty stands out most evidently in the study of antique designs. Vertical lines and horizontal lines are the lines of support and strength, and must always have proper consideration; but in pure ornament the office of straight lines seems to be confined to connecting curves and to emphasizing their contrasts.

The next view (Fig. 3) is to illustrate the progress already made. On the upper line are the three rough outline sketches for modern articles, of which the final use and destination are shown on the lower line. In the sketch to the left the fine effect is produced by a few curves, of which the connections are boldly and finely contrasted. In the second sketch an equally pleasing effect is produced by curves, of which the principal ones are continuously connected, while in the third sketch there is a pleasing exhibition of both kinds of connections. The lower line gives you your first notion of the use of ornament in marking and embellishing the lines of form.

The next view (Fig. 4) exposes forms in which the above laws are violated, and by whose ugliness you can not fail to be impressed. On the top line are objects of which the curves are so weak and undecided that it would be difficult to state whether the connections are continuous or contrasted. In the second line is shown how ugly is the effect when straight lines are substituted for curved lines, and in the third line is shown how ugly effects may be produced even by curved lines when not used in obedience to some accepted and apprehended principle.

There is another presentation of form which is in reality but a modification of profile, but which, because it looks as if it had been separately applied, and also because it is separately treated in books, must be considered by itself. The term “molding” has been given to variations in surfaces which have both useful and ornamental uses. Moldings are as old as architecture, and vary with schools of architecture.

In the next view (Fig. 5), taken from Mayeux’s work, are given the most ordinary Greek moldings with their French names. However necessary it must be for the architect, and however admirable it may be for the art student, to know the names of all moldings by heart and to be able to describe each one accurately, such proficiency is not required at present and is not necessary for the understanding of the present theme. Some moldings have square edges, some round. The curved edges of some are simple, of others complex. Each has its name, and of some the name is descriptive. The term molding would seem to indicate that moldings were made apart and subsequently applied to the main object. Whatever be the origin of moldings, the same rules apply to them which apply to other profiles, with the additional rule that moldings must always be kept subordinate to the principal object. For instance, in the view (Fig. 6) the pedestal marked _bon_ is good, because the body of the pedestal is the principal object and it is clearly seen that the moldings at the base and at the top are subordinate and merely ornamental, while the pedestal marked _mauvais_ is decidedly bad, because more vertical space is given to the moldings than to the shaft, confusing outline, weakening the shaft, and destroying the sense of strong and steady support.

Readers may at once make use of the information already acquired by seeing how these rules apply to their own lamps, candlesticks, pieces of furniture, etc.

The next view (Fig. 7) shows incidentally how much better it is under all circumstances to mark with fillets and lines the changes from one curve to another, for you certainly see how much more substantial character and beauty has _B_ than _A_.

Finally, let it be said, and said emphatically, that though there are profiles which require the use of the compass to draw them, and though all architectural details must be worked out with mathematical accuracy, those profiles and outlines are the most beautiful where it is evident that artistic skill governing a free hand has controlled and where mechanical assistance is so subordinate as to be overlooked.

There is very little to be said about surfaces or forms of two dimensions. The principal requirement is that outlines should be agreeable and must be well defined. In fact, the two qualities are inseparable, for a well-defined outline is agreeable and a badly defined one is sure to be disagreeable. By well-defined is meant that its particular shape should easily appear and be clearly distinguishable. For instance, a square should appear with sides distinctly equal; a circle should have but one center. In an architectural opening either arch or entablature should prevail, and the character of the arch should be evident. In the examples presented (Fig. 8) in the view these principles are violated. The first figure is so clearly a square that at first, and before you have examined it closely, you think it is a square. It leaves an indefinite and consequently disagreeable impression. The same criticism applies to the second object, apparently a mirror. The glass is round, but the frame is so irregular that the impress of the circle is destroyed, and there is left an undecided and therefore uncomfortable sensation. In the third example the arch is so poorly defined and so weak, while the entablature above it is so strong and so prominent, that the result is a composition that fails to give pleasure, because no distinct idea is conveyed. In the last example the outlines of the arch are so indefinite that its character is indistinguishable. You can not see which prevails, the round arch or the pointed arch.

The same principles apply to smaller objects and to details, as seen in the next view (Fig. 9). To the left the date plate on top is bad in comparison with the one beneath it, because its direction is not so well marked and its corner projections are too large. In the lambrequins on the right, those are good in which the general direction is properly marked, and in which subdivisions are kept properly subordinated. Lambrequins have so entirely gone out of use nowadays that it is difficult to recall the time when they were regarded as indispensable parts of furniture.

There is one other point to which your attention should be called--that is, stability. If an object be intended to stand, its 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_. _Compositæ_ 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.[F]

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

[F] Abstract of the Presidential Address to the Institution of Junior Engineers, November 3, 1899.

All 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 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 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 of the larger size an expansion ratio in the turbines of one hundredfold and upward is attained before the steam passes to the exhaust pipe and condenser.

The loss of power present in engines of the piston class, due to cylinder condensation arising from the variation of steam pressure in the cylinder, is not present in the steam turbine, as the steam pressure remains constant at each turbine ring and each part of the cylinder and barrel, and the numerous tests of steam consumption that have been made have shown that compound steam turbine engines of moderate sizes when working with a condenser are comparable in steam consumption per effective horse power with the best compound or triple condensing steam engines of the piston type. They have been constructed in sizes up to about one thousand horse power for driving alternators and dynamos, and several sets of about two thousand horse power are nearing completion.

The application of the compound steam turbine to the propulsion of vessels is a subject of considerable general interest, in view of the possible and probable general adoption of this class of engine in fast vessels.

In the turbine is found an engine of extremely light weight, with a perfectly uniform turning moment, and very economical in steam in proportion to the power developed, and, further, it can be perfectly balanced so that no perceptible vibration is imparted to the ship. The problem of proportioning the engine to the screw propellers and to the ship to be driven has been the subject of costly experiments extending over several years, with the result that a satisfactory solution has been found, giving very economical results in regard to pounds of steam consumed in the engines per effective horse power developed in propelling the vessel, results which are equal or superior to those so far obtained with triple-expansion engines of ordinary type in torpedo boats or torpedo-boat destroyers. The arrangement adopted may be best described by saying that instead of placing, as usual, one engine to drive one screw shaft, the turbine engine is divided into two, three, or sometimes more separate turbines, each driving a separate screw shaft, the steam passing successively through these turbines; thus when there are three turbines driving three shafts, the steam from the boiler passes through the high-pressure turbine, thence through the intermediate, and lastly through the low, and thence to the condenser.