Chapter 6

The Right Hon. Lord Rayleigh lately delivered a lecture at the Royal Institution upon "The Colors of Thin Plates," a term which he explained was applied to thin films of substances, such as oily films on the surface of water or the equally familiar soap bubble. Although the reflection of colors from the surface of a soap bubble is probably the most noticeable, yet the "plate" which lends itself most readily for experiment is a film of air confined between two sheets of glass. If a ray of white light be reflected from the surface of the film upon a screen, the so-called Newton's rings, a series of colored concentric rings, are obtained. If, instead of reflected light, the ray of light transmitted through the film of air be allowed to fall upon the screen, the same phenomenon is observable, but the effect is very considerably minimized, owing to the great preponderance of white light, which overlies as it were the colored rings. Even in the first instance, as the lecturer was able to show later on, the colors are not nearly so intense as they may be obtained, owing to some white light being reflected from the surfaces of the two sheets of glass. With regard to the appearance of the phenomenon, it is observed that the part which corresponds to the thinnest part of the film is considerably darker than the rest of the spectrum; around this is a bright ring of white, succeeded by constantly increasing concentric rings of different colors apparently repeating themselves. Lord Rayleigh also obtained the same results with a film of a solution of soap and glycerine, but in this case the dark portion was observed at the top of the spectrum, the other colors arranging themselves in order in the soap film thinned by the force of gravitation, thus showing that the colors vary according to the thickness of the film. Another form of the experiment called forth a considerable amount of applause from the audience. Lord Rayleigh caused a gentle stream of air to play obliquely upon a soap film, so that the part struck was moved forward and the whole film rotated. Then with the alteration of the force of the current of air, which of course regulated the centrifugal force, alternating thicknesses of film were obtained, causing a varying display of beautiful colors and combinations of colors. This last experiment also tended to prove that the bands of color are not arranged in a certain order, but vary according to the thickness of the film, a conclusion arrived at by Brewster, who observed that if a film reflecting certain colors be carefully inverted so as not to disturb the gravity, the colors reflected are also inverted. Lord Rayleigh explained the phenomenon by referring to Young's wave theory of light. He regarded the film as having two surfaces from which light is reflected, an anterior exterior surface and a posterior interior surface. If a ray of light be thrown upon the film, a part of the light is reflected from the first surface, but the greater part is transmitted, and some of this is reflected from the second surface, passes back through the film, and is combined with the light reflected from the first surface. If then the light reflected from the second surface be in the same state of vibration as that reflected from the first surface, the effect of their combination will be to increase the amount of light reflected from the first surface, but if otherwise, the effect will be a partial neutralization of the light reflected from the first surface. That is to say, if the retardation of the light which is reflected from the second surface, owing to its twice traversing the thickness of the film, be equivalent to a wave length of the vibration of the light, it will increase the intensity of the light reflected from the first surface. If, however, the retardation be only equivalent to half a wave length, the intensity of the light will be decreased. Thus, then, with a ray of monochromatic light it will be seen that the effect of difference in the thickness of the film will be to alter the intensity of the reflected ray, but with a white light composed of several colors the result will be more complicated. As each color has a different wave length in vibration, it will be seen that each color will act independently of the others, and a certain thickness of film which, upon the combination of the two reflected rays, will cause one particular color to be intensified, will at the same time cause the other colors to be more or less obscured.

Thus as the thickness of the film is altered different colors preponderate, causing the appearance of rings or bands, according to the nature of the experiment. The dark appearance on the screen corresponding to the thinnest part of the film is probably due to refraction of the ray of light reflected from the second surface, consequent in its passing from a rare into a denser medium, and again from the denser medium into the rare, which refraction Lord Rayleigh considers to effect a retardation equivalent to half a wave length. Lord Rayleigh supported this theory of the formation of Newton's rings by several interesting experiments. A beam of light was intercepted by two of Nicol's prisms, one of which acted as a polarizer and the other as an analyzer of the light, so that no light was able to pass through both on to the screen. Between the two prisms a double refractive lens was now placed, in this case a double concave lens of selenite, when the same series of concentric rings observed with the film of air was obtained on the screen, only much more intense, while a wedge of selenite gave the bands of color in the same order as with the soap bubble.

But perhaps the most striking proof of the dependence of the colors upon the thickness of the film was shown by the reflection of a beam of light from a piece of mica composed of twenty-four very attenuated plates overlapping each other. With each layer a marked gradation in color was visible.

The remainder of the lecture was devoted to an explanation of the determination of the chromatic relations of the colors of the spectrum. Lord Rayleigh at this point made a rather startling statement that any color can be produced by two other colors. As an example of such a formation, a ray of white light was passed separately through a solution of yellow chromate of potash and an alkaline litmus solution, throwing respectively a yellow and violet-blue color upon the screen. When the ray was made to pass through the two solutions successively, an orange-yellow color was obtained upon the screen, which color Lord Rayleigh asserted to be made up of red and green rays. To prove this, the ray of white light was decomposed by means of a prism, and the decomposed rays passed through the two solutions. The one solution was found to exclude all the yellow and orange rays from the spectrum, while the other excluded all the blue and violet rays, so that when the ray had passed through both solutions, only the red and green rays were left. If, instead of allowing the decomposed ray of light to pass through a slit, and thus obtain definite bands in the spectrum, the ray was passed through a circular hole, the red and green colors overlapped each other on the screen, forming by their combination the identical orange-yellow color obtained with the primary white light. It was then stated that if three definite positions be taken in a spectrum in the red, green, and violet bands respectively, and these positions be represented by the corners of an equilateral triangle (Clerk Maxwell's triangle), it has been mathematically determined in what position within this triangle the colors of Newton's rings would fall. Lord Rayleigh, by means of a diagram and the selenite wedge, showed that the relations to the three standard colors in practice were identical with the position assigned them by theory.

In conclusion, the lecturer showed a piece of glass, the surface of which had been decomposed, a ray of light transmitted through which showed upon the screen patches of very pure color. These he considered to be due to the glass consisting of a number of thin plates, some of which had been removed by the decomposition.

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BELT JOINTS.

From time to time, serious accidents have taken place, and the progress of work stopped, by the sudden snapping of driving belts in machinery, and, as a general rule, it is found that the collapse is attributable either to faulty leather or insecure joining. A great improvement of the leather intended for belts has been brought about during the last few years, by the introduction of improved processes for currying and the subsequent treatment. Paterson has worked successfully a patent for rendering belt leather more pliable, and lessening the tendency to stretch. Under this treatment the leather is either curried or rough dried, and then soaked in a solution of wood, resin, and gum thus, or frankincense, first melted together, and then dissolved, by the application of heat, in boiled or linseed oil. The leather, after this process, is soaked in petroleum or carbon bisulphide containing a little India-rubber solution, and is finally washed with petroleum benzoline. Should the mixture be found to be too thick, it is thinned down with benzoline spirit until it is about the consistency of molasses at the ordinary temperature. The leather so prepared is not liable to stretch, and can be joined in the usual way by copper riveting, or the ends can be sewn. A good material for smaller belts, and for strings and bands for connecting larger ones, is that recently patented by Vornberger, in which the gut of cattle is the basis. After careful cleansing, the gut is split up into strands, and treated with a bath of pearlash water for several days. The strands are then twisted together, and after being dipped in a solution of Condy's fluid, are dried. They are then sulphured in a wooden box for twenty-four hours, after which the twisting can be completed. They are by this process rendered pliable, and can be used in this state for stitching the leather ends of larger belts, or can be stiffened by plunging them into a bath of isinglass and white wine vinegar. After drying they are susceptible of a fine polish, emery cloth being usually employed, and the final "finish" is given to the material with gum arabic and oil.

Canvas and woven fabrics, coated with India-rubber, are also now being used for driving belts and for covering machine rollers. As this material can be made in one piece, without the necessity of a joint, it is uniform in strength, and is recommended as a substitute for leather belts requiring joints. A patented material of this description is due to Zingler, who boils the canvas or similar woven fabric under pressure in a solution of tungstate of soda for three hours. It is then transferred to a bath of acetate of lead solution, and drained, dried, and stretched. When in this condition it is coated, by means of a spreading machine, with repeated layers of a composition consisting of India-rubber, antimony sulphide, peroxide of iron, sulphur, lime, asbestos, chalk, sulphate of zinc, and carbonate of magnesia. When a sufficient thickness of this composition has been applied, it is vulcanized under pressure at a temperature of 250° F., or a little higher. The material produced in this manner is said to have the strength and durability of the best leather belts. Attempts have recently been made to obtain a glue suitable for joining the ends of driving belts, without the use of metal fastenings or sewing, and Messrs. David Kirkaldy & Son have reported favorably on such a belt glue, which is being introduced by Mr. W.V. Van Wyk, of 30 and 31 Newgate street, E.C. In the test applied by them, a joint of this "Hercules glue," as it is called, in a 4 in. single belt was stronger than the solid leather. When a tensile stress of 2,174 lb., equivalent to 2,860 lb. per square inch of section, was applied, the leather gave way, leaving the joint intact. Belts fastened by a scarf joint with this glue are said to be of absolutely the same thickness and pliability at the joint as in the main portion of the belt, and thus insure freedom from noise and perfect steadiness. The instructions for use are simple, and it requires only fifteen minutes for the joint to set before being ready for use. From a rough chemical analysis of the sample submitted to us, we find that it consists of gelatine, with small amounts of mineral ingredients. Josef Horadam, some few years ago, patented in Germany a process for preserving glues from decomposition, by the addition of from 8 to 10 per cent. of magnesium or calcium chlorides. The addition of these salts does not impair in any way the strength of the glue, but prevents it from decomposing, and it may be that the "Hercules glue" is preserved in a similar manner.

A cement of this nature, if thoroughly to be relied on, must be of great value, although the great variation in the quality of leather, apart from the difficulty hitherto experienced of securely connecting the ends together, opens a wide field for a material of uniform composition, and capable of being made in one piece in suitable lengths for driving belts and other machine gear.--_Industries._

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INAUGURATION OF THE STATUE OF DENIS PAPIN.

A large crowd was present recently at the inauguration of the statue of Denis Papin, which took place in the court of the Conservatoire des Arts et Metiers, under the presidency of Mr. Lockroy, Minister of Commerce and the Industries.

In the large hall in which the addresses were made there were several municipal counselors, the representatives of the Minister of War, Captains Driant and Frocard, several members of the Institute, and others. A delegation from the Syndical Chamber of Conductors, Enginemen, and Stokers, which contributed through a subscription toward the erection of the statue, was present at the ceremony with its banner. Mr. Lanssedat, superintendent of the Conservatoire, received the guests, assisted by all the professors. Mr. Lanssedat opened the proceedings by an address in which he paid homage to the scientists who were persecuted while living, to Denis Papin, who did for mechanics what Nicolas le Blanc did for chemistry, and to those men whose entire life was devoted to the triumph of the cause of science.

After this, an address was delivered by Mr. Lockroy, who expatiated upon the great services rendered by the master of all the sciences known at that epoch, who was in turn physician, physicist, mechanician, and mathematician, and who, in discovering the properties of steam, laid the foundation of modern society, which, so to speak, arose from this incomparable discovery.

Speeches were afterward made by Mr. Feray d'Essonnes, president of the Syndical Chamber of Conductors, Enginemen, and Stokers, and by Prof. Comberousse, of the Central School, who broadly outlined the life of Papin.

Along about four o'clock, the Minister of Commerce and the Industries, followed by all the invited guests, repaired to the court, and the veil that hid the statue was then lifted amid acclamation.

Papin is represented as standing and performing an experiment.

Upon the pedestal is the following inscription:

DENIS PAPIN BORN IN 1647, DIED ABOUT 1714, INVENTED THE STEAM ENGINE IN 1690

NATIONAL SUBSCRIPTION, 1886.

The inauguration is due to the initiative of Mr. Lanssedat, for it was he who in 1885 suggested the national subscription, which was quickly raised.

Denis Papin was born at Blois on the 22d of August, 1647. He was the son of a physician. After the example of his father and of several of his relatives, he studied medicine and took his degree; but his taste for mathematics, and especially for experimental physics, soon led him to abandon medicine.

It was in 1690 that he published in the _Actes_ of Leipsic the memoir which will forever and irrevocably assign to him the priority in the invention of steam engines and steamboats, and the title of which was: "New method of cheaply obtaining the greatest motive powers."

In 1704, Papin, poor and obliged to do everything for himself, finished his first steamboat; but for want of money he was unable to make a trial of it until August 15, 1707. The trial was made upon the Fulda and Wera, affluents of the Weser.

The operation succeeded wonderfully, and, shortly afterward, Papin, being desirous of rendering the experiment complete, put his boat on the Weser; but the stupid boatmen of this river drew his craft ashore and broke it and its engine in pieces.

This catastrophe ruined Papin, and annihilated all his hopes. The great man, falling into shocking destitution, broken down and conquered by adversity, returned to England in 1712 to seek aid and an asylum.

Everywhere repulsed, he returned to Cassel about 1714, sad and discouraged; and the man to whom we owe that prodigy, the steam engine, that instrument of universal welfare and riches, disappeared without leaving any trace of his death.--_Le Monde Illustre._

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DECORATION.

THE STUDY OF ORNAMENTS.

[Footnote: _Authorities consulted in preparing this paper:_ "Analysis of Ornament," Wornum; "Truth, Beauty, and Power," Dresser; "Lectures on Art." F.W. Moody; "Hopes and Fears for Art," Wm. Morris; "Ornamental Art," Hulme; "Manuals of Art Education," Prang.]

By MISS MARIE R. GARESCHE, St. Louis High School.

Decoration is the science and art of beautifying objects and rendering them more pleasing to the eye. As an art, individual taste and skill have much to do with the perfection of the results; as a science, it is subject to certain invariable laws and principles which cannot be violated, and a study of which, added to familiarity with some of the best examples, will enable any one to appreciate and understand it, even if lacking the skill and power to create original and beautiful designs.

The study of decoration offers many advantages. It cultivates the imagination and the taste; it develops our capacity for recognizing and enjoying the beautiful in both nature and art; it adds to the pleasure and refinement of life. Practically, its importance can hardly be overestimated, as it enters into almost all the industrial pursuits. We can think of but few classes of objects, even the most simple, in which some attempt at ornamentation is not made.

Ornament is one of the principal means of enhancing the value of the raw material. A piece of carved wood, or an artistically decorated porcelain vase, worth perhaps many hundred dollars, if reduced to the commercial value of the material of which they are composed would be valued at but a few dollars or cents. The higher the ornamentation ranks, from an artistic point of view, the greater becomes the value of the article to which it is applied. Knowledge of good designs is thus evidently important, to the purchaser of the object ornamented as well as to the designer who planned it. This can only be attained by cultivation.

To know and appreciate the best ornament should be an aim set forth in any scheme of general education. This knowledge and appreciation can be obtained by studying the application of the laws and principles of ornamental art as exemplified in the works of masters, and also by endeavoring to apply these principles in designs of our own creation.

PRINCIPLES OF ORNAMENT.

We can only arrive at a knowledge of these principles by a consideration of the object. In other words, nature and history must be studied. First, _nature_, for she is the primary source and origin of all good ornament, whether ancient or modern; and if, as in everything else, we would not become servile imitators and weak copyists, we must go to the fountain head. Second, _history_, for by the study of the ornament of past ages we will not only become acquainted with the highest developments of which ornamental art is capable, but will moreover broaden our views as to its object and scope, and will stimulate our own imagination and invention, by leading us to the contemplation of the myriad beautiful and protean forms it has assumed, when surrounding conditions, such as religion, climate, temperament, nationality, etc., have been different. Knowledge of historic ornament will also prevent the imposition on the public, so common in our day, of weak and unworthy productions which claim to be based on classic originals, and which constitute a great stumbling block to the progress and appreciation of good art. The result is somewhat analogous to that produced upon conscientious but ill-informed minds, who make every effort to appreciate and enjoy the spurious productions of a great author, not knowing that they are not genuine.

POSITION AND SCOPE OF ORNAMENTAL OR DECORATIVE ART.

I. _Object of Ornamental Art._--The object or purpose of ornament, as in the other fine arts, is to please. In music and poetry this enjoyment is conveyed to the mind through the ear; in the decorative and pictorial arts, through the eye. Generally, the meaning that we find in such productions, the appeal that they make to the understanding or feelings, is as great a source of interest to us as their intrinsic beauty. Poetry and vocal music are greatly dependent for their effect upon the meaning they convey in words; painting and sculpture, upon the ideas or sentiments they suggest. In all four, however, and most decidedly in music unaccompanied by words, the appeal is frequently made almost exclusively to the æsthetic sense, the mind or intellect remaining almost dormant under the impression. Gems of rhythmical verse, such as Poe's "Bells," "The Raven," Whistler's "Symphonies in Color," nameless forms in statuary, expressionless save in the mere beauty of their proportions and curves, and, as has been stated, nearly the entire field of instrumental music, are cases in point. In the ornamental and decorative arts, as well as in architecture (from which they are indeed inseparable), beauty alone, in like manner, should be the principal aim and purpose. In the former, of course, it is indispensable that such should be the case, as they are entirely subordinate and accessory in their nature, their only _raison d'etre_ being to beautify or render more agreeable objects already created for some purpose.

It must not be imagined that such artistic impressions--viz., where the appeal is made almost solely to the æsthetic sense, regardless of the reason, judgment, or feelings--are necessarily of a lower order. Their effect is almost analogous to that which nature herself produces upon us--the starry heavens, the mighty ocean, the tender flower. The impression, whether the object belongs to the domain of nature or art, may be a merely sensuous one; and if it stops there, as it certainly does for the majority of people, it ranks without doubt far below productions where the æsthetic element is only used to stimulate and heighten the appeal to the mind or the feelings. But if it extend beyond, and makes the sensuous impression but the parting link to the contemplation of ideal, abstract beauty, without the intermediate aid of the heart or the reason, it is the shortest and quickest road toward the realization of the infinite, and makes us indeed feel that it is but a short step "from nature up to nature's God." Thus architecture, which embodies, more than any other of the space arts, principles of abstract beauty, has been with reason called the noblest of them all.