the love of tracing out law and order inspired in them by indulging their youthful tastes for classifying. I would fain see boys learn to classify languages in this way from the very first. Our boys have the great advantage of starting with English, that singular compound of Teutonic and Romance; so that, from the very first, a boy beginning Latin has the means of comparing the language which he is learning with a modern form of the same, while he possesses the additional advantage of possessing as his birthright a Teutonic grammar and a Teutonic stock of words to compare with his Romance vocabulary. Then I would have each boy learning Latin commence the study of French as young as possible, and would have it impressed on him from the first that Latin is but old French, and that French is but modern Latin; or, to be more accurate, is but the descendant of that form of Latin spoken by most ancient Italians. This would, I believe, stimulate his interest much in the same way as it stimulates the interest of a boy to learn that the provincial expressions used by the working-men on his father's farm are in many cases good old Saxon words which have merely by some accident escaped being retained as classical.

Another point on which it seems wise to insist is, that while these three languages, English, French, and Latin, are being taught together, a moderate amount of practical knowledge of each language should precede any explanation of their grammar. A boy should be taught that certain phenomena are common to all these languages alike; that certain words fulfil certain functions in the sentence, and that certain words modify the form which other later parts of the sentence will have to take. But not till he has his mind fairly stocked with the facts and phenomena of language would I teach him the technical terms of grammar, and even then it should be diligently impressed on him that words are not to be parked off into certain fixed and unchanging categories of substantives, verbs, &c., but that they are to be classified according to the function which they perform in the sentence.

Now, when our student has gained a fair mastery of Latin, how should we lead him on to take a real interest in it for the sake of the literature it enshrines? My answer to this would be, by endeavouring to make him picture to himself the scenes and objects of which he is reading. I would have his text-books illustrated with as many woodcuts as possible, and the walls of his class-room hung with as many pictures illustrative of classic scenes as possible. I well remember in my own case the flood of light cast by Lessing's

criticism upon Virgil's description of Laocoon's fate, when read by the side of a good photograph of the celebrated sculpture representing the same scene, and I am sure that many another student has felt the same. Good photographs of Rome and Athens and of their antiquities are now-a-days so cheap and common that it seems surprising that they are not more commonly met with in classrooms. Sure I am that they are far more impressive and useful than many painfully elaborated treatises on classical antiquities, or than texts of classical authors, valuable only by their antiquity, such as we too often see purchased at a great price for our libraries. But I confess I would, in the higher educational institutions, go further than this, and would add to the existing means of teaching a regular classical museum. The nucleus of such an one exists, I believe, at the Sydney University, and I wish that at least in this case we could eclipse our rival. In this I would have models of the chief buildings of antiquity, such as the Parthenon, the Coliseum, the Arch of Titus, &c.; busts of as many of the sages of classical times as possible, models of the private houses and baths and aqueducts of the Romans, and as complete a collection of coins as could be procured. A museum like this "vires acquirit eundo,” and if once founded would speedily be enriched by the donations of those many Australians who think little of flitting from Collins-street to the Corso within the year. In this way might the reproach of not caring for the arts be removed from classical teaching; nay, in this way might classical training be rendered the most fitting and natural introduction to the arts. Of course this method of teaching presupposes an able and conscientious teacher, otherwise a lecture would be apt to degenerate into a mere picture-show. But with all that we spend on education, might we not spare a few hundred for an object like this?

I believe, then, that by teaching the classical languages in the light of philology, we might utilise them to foster, and not to oppose science; while that by illustrating them by some such method as I have briefly indicated, we might make them the very best allies of both history and art.

H. A. STRONG.

THE TRANSMISSION OF LIGHT AND SOUND.

It is now universally believed, that light is the vibration or undulation of an extremely attenuated medium, described as the luminiferous ether. One of the grand characteristics of this ether is involved in the discussion of the mode in which light is transmitted. This article has for its principal object, the consideration of this characteristic—the continuity of the ether.

ner.

The following paragraph puts the difficulty in a striking man"When the undulatory theory was started, it was not imagined, that the vibration of light could be transverse to direction of propagation. The example of sound was at hand, which was a case of longitudinal vibration. Now the substitution of transverse for longitudinal vibrations in the case of light, involved a radical change of conception as to the mechanical properties of the luminiferous medium. But though this change went so far as to fill space with a substance, possessing the properties of a solid, rather than those of a gas, the change was accepted, because the newly discovered facts imperatively demanded it. Following Mr. Martineau's example, the opponent of the undulatory theory might effectually twit the holder of it, on his change of front. "This ether of yours,' he might say, 'alters its style with every change of service. Starting as a beggar, with scarce a rag of property to cover its bones, it turns up as a prince, when large undertakings are wanted. You had some show of reason when, with the case of sound before you, you assumed your ether to be a gas in the last extremity of attenuation. But now, that new service is rendered necessary by new facts, you drop the beggar's rags, and accomplish an undertaking, great and princely enough in all conscience, for it implies, that not only planets of enormous weight, but comets with hardly any weight at all, fly through your hypothetical solid without perceptible loss of motion.' This would sound very cogent, but it would be very vain. Equally vain, in my opinion, is Mr. Martineau's contention, that we are not

justified in modifying, in accordance with advancing knowledge, our notions of matter."*

Sir John Herschel, in a foot-note to one of his lectures, gives as a possible conception, that the ether may be constituted of revolving molecules. The following gives the key by which we may open the shutters, that have been so long closed upon the windows through which our intelligence could perceive the possible constitution of the ether. "From this phenomenon (Faraday's lines of magnetic force) Thompson afterwards proved by strict dynamical reasoning, that the transmission of magnetic force is associated with a rotatory motion of the small parts of the medium. He showed at the same time, how the centrifugal force due to this motion would account for magnetic attraction. The explanation of electrastatic stress is less satisfactory, but there can be no doubt, that a path is now open, by which we may trace to the action of a medium all forces like electric and magnetic forces."+

The following also bears on the properties or powers of the ether. "Newton does not allow the possibility (or conceivableness) of one body acting upon another without intervening substance; and in the scholium at the end of the "Principia" he adverts to the agency of a certain "very subtle" medium (the ether) pervading the grosser bodies. It may be demonstrated, that no particle of the ether, supposed to be of unlimited dimensions, can be transferred across a plane fixed in space so as permanently to alter the quantities of fluid on the two sides of the plane. Consequently the motions are either vibratory or in re-entering currents. To the former the phenomena of light, heat, molecular adhesion and gravitation, are referable, and to the latter the phenomena of electricity, galvanism, and magnetism."+

Light is a vibration or undulation. Sound is a vibration or undulation. Sound is the vibration of some substance, whether a solid, a liquid, or a gas. The term vibration is perhaps hardly applicable to gases. If light is the vibration of some substance, the principles regulating the transmission of sound may hold good in the transmission of light. It will be well, therefore, to consider the laws by which sound is propagated.

* Professor Tyndall, in Nineteenth Century, November, 1878, article "Virchow and Evolution."

The late Professor Clerk Maxwell, in 9th edition, "Encyclopædia Britannica," article "Attraction."

Philosophical Magazine, January 1880. "The Rev. Professor Challis on Newton's Regula Tertia Philosophandi.”

First, however, let us consider a simple case of the communication of motion to any body or system of bodies. If one ball at rest is struck in a direct manner by an equalised ball, in motion, the moving ball is stopped and brought to rest, and the ball at rest acquires the motion of the ball that struck it. Let us suppose a number of billiard balls placed in a straight line. There may be any number, and one end ball may be considered red and the other orange colored, the rest may be white. Let them be, say, two inches in diameter, and place them two inches apart. Then, in a certain length of them, half this length will be filled by solid matter-the balls-while the other half will be empty space (so to speak)—the vacant spaces between the balls. Let the red ball be now struck so as to move at the rate of ten feet per second. The first white ball is struck by the red one, and acquires its motion, the red ball coming to rest. The first white ball moving at the rate of ten feet per second, drives on the second white ball at the same rate, coming itself to rest nearly in the spot occupied by the second white ball, and so on with all the rest of the balls. The balls are moving at the rate of ten feet per second, and ten feet of empty space will be gone over in one second. Ten feet of empty space, however, in this line of balls is divided (so to speak) between ten feet of solid balls. At the end of one second, therefore, the ball then moving will be twenty feet distant from the red ball. Though the balls were therefore struck so as to move at the rate of ten feet per second, motion is transmitted along this line of balls at the rate of twenty feet per second. If you place the balls only one inch apart, there will be to every ten feet of empty space twenty feet of solid balls. In this case, the red ball being struck as before, with exactly the same force, the rate of motion along the line of balls will now be thirty feet per second. If we place the balls only half an inch apart to every ten feet of empty spaces, there will be forty feet of solid balls, and the red ball moving exactly at the same rate as before, motion will be transmitted along the line of balls at the rate of fifty feet per second. The rate of motion will not be exactly as stated, but only very nearly so, owing to the balls being elastic. If, instead of the red ball moving at the rate of only ten feet per second, it had been struck so as to move at the rate of twenty feet per second, motion would have been communicated along the line of balls in all the three foregoing cases at double the rates there shown. If the red ball had been struck so as to move at the rate of thirty feet per second, the rate of motion along the line of balls would have been treble what it was in the