greatest importance. It forms an atmospheric sea or ocean which completely surrounds our globe. We live at the bottom of this sea; it is our natural element, and we could not exist out of it for an instant. It extends many miles above our heads and presses upon us with great force. And now we learn that without the atmosphere there would be no sound. Here is the enchanted abode of music, whose voice we hear but whose form we do not see, and at the command of the accomplished musician she moves the heart and gladdens the soul of man. Light, you know, moves with the velocity of nearly 200,000 miles in a second of time; sound travels much more slowly; at the ordinary temperature of the air a sound-wave moves at the rate of 1125 feet in a second. The length of the wave is dependent upon the nature of the sound. Suppose the wave resulting from the vibration of a tuning-fork be three feet long, then in one second 375 waves will strike the ear. In the same time when the eye looks at a violet ribbon the enormous number seven hundred and eighty-nine millions of millions of waves strike the nervous network of the eye. Some remarkable facts result from the great difference in the velocities of light and sound. During a storm the flash of the lightning is seen several seconds before the thunder is heard. A peculiar impression is made upon one who witnesses artillery practice of ships at sea. If the observer is two or three miles from the man-of-war the puff of white smoke and the roar of the cannon seem to have no connection with each other; several seconds will pass between the appearance of the smoke and the explosion. The fall of a woodcutter's axe is seen before the blow is heard. The explanation of these and all similar phenomena you can now easily give. When sound-waves strike against an opposing body they are reflected and obey the same laws as those of light. Under certain conditions the reflection or repetition of sound produces what are commonly known as echoes. Among the rocks and glens of mountain scenery very fine echoes are heard. Professor Tyndall speaks thus about the echo: "In mountain regions this repetition and decay of sound produce wonderful and pleasing effects. Visitors to Killarney will remember the fine echo in the Gap of Dunloe. When a trumpet is sounded in the proper place in the gap the sonorous waves reach the ear in succession after one, two, three, or more reflections from the adjacent cliffs, and thus die away in the sweetest cadences. There is a deep cul-de-sac called the Ochsenthal, formed by the great cliffs of the Engelhörner, near Rosenlaui, in Switzerland, where the echoes warble in a wonderful manner. The sound of the Alpine horn echoed from the rocks of the Wetterhorn or the Jungfrau is in the first instance heard roughly. But by successive reflections the notes are rendered

more soft and flute-like, the gradual diminution of intensity giving the impression that the source of sound is retreating further and further into the solitudes of ice and snow." A striking instance of the phenomenon of the echo came under my own observation a few years since. On a certain summer evening I was walking through a romantic part of the north of England. Hills rose on all sides around me, and the last rays of the setting sun were resting upon their crests. As I drew near to a lone house on the road I distinctly heard the sound of music. On moving out of a certain line the sounds were partly lost, but when I took up my former position they were again heard. I at once concluded that the house was acting as a reflector of the musical sounds which reached me from some undefined quarter. After walking some distance I found that the strains proceeded from a band on a village green. The phenomenon of the echo appealed to the imaginative powers of the ancients, and they personified it. Echo they believed was a nymph who used to engage the ear of Juno while Jupiter sported with the nymphs. Juno discovered the trick and changed the nymph into an echo. The fair nymph then fell in love with Narcissus, but her love was not returned, so she pined away, and at last only her voice remained. This is a beautiful myth. The ancients could not explain the phenomenon of the reflection of sound, but the matter is plain enough to us. Still there is something wild. and strange in the repetition by the rocks and glens of words that we have uttered aloud. An amusing instance of the results which sometimes follow from the reflection of sound has been cited by Sir John Herschel. In one of the cathedrals of Sicily was a confessional. This was by accident so placed under the curved roof that the whispers of the penitents were reflected and brought to a focus at another part of the building. A certain person discovered this focus, and for once the secrets of the confessional were revealed. But he did not keep the secret; he used to bring friends with him. One day, it is said, the gentleman's wife was engaged in confession, and great was the confusion of the husband when he, in the presence of his friends, heard secrets anything but amusing to himself. No longer can we deny that the "very walls have ears." There are echoes which reflect the same sound twenty or thirty times. An echo in the Château of Simonetta in Italy repeats a sound thirty times, and at Woodstock there is said to be one which repeats from seventeen to twenty syllables. In large empty rooms the mingling of the sounds reflected from the walls causes a strengthening or resonance. Carpets and furniture deaden the sound. Whispering-galleries also present an interesting illustration of the effect produced by the reflection of sound

waves.

Such galleries have a continuous curved form and smooth walls. The words uttered by a speaker at one part of the gallery are successively reflected from panel to panel of the curved surface until they reach the ear of the listener. You have all heard of, and some perhaps been in, the whispering-gallery of St. Paul's. We must now ask your attention to an important distinction between sounds. Most sounds that reach our ears are caused by irregular blows or concussions; these are called noises. The report of a cannon, the dashing of the waves on the sea-beach, a rap on the table, the banging of a door, are examples of noises. But there are also musical sounds; such are produced by a regular and sufficiently rapid series of pulses or shocks. You will have observed that not all sounds called musical are sweet or pleasant in their character. The screeching of a pencil on a schoolboy's slate, the screaming of a whistle, are not delightful sounds to hear, and yet strictly they must be called musical. Musical sounds can be produced in several ways. Savart elicited them from the revolution of a toothed wheel against a card. The vibrations of strings or of air in tubes or pipes yield musical sounds. When a stretched string is plucked aside it oscillates with great rapidity and throws the surrounding air into vibration, but the waves produced by the string alone are not sufficiently powerful to affect the ear strongly. But the sound can be increased by extending the string across two bridges fixed on a long wooden box with thin sides. Any instrument which can throw the air into rhythmic pulses may be used for producing musical sounds. When a number of glass tubes of different lengths are rubbed up and down with the fingers or a resined cloth exceedingly sweet pure musical notes are given out. A skilful musician could elicit from such an instrument very pleasing music. The harp is renowned both in sacred and profane story for its wild and rich notes. The heart of Saul was soothed by David's harp, and ancient bards in many a baronial hall used to enchant the ears of noble listeners. In the violin, the piano, the guitar, musical sounds are produced by the vibrations of strings. Notes also result from a rapid succession of puffs of air. An instrument called the syren has been devised for producing sounds in this manner. By the rapid revolution of a perforated disc over a similar disc which forms the covering of a metal box, into which air is forced, musical sounds are yielded. The syren is used to ascertain the pitch of a note or the number of vibrations from which a note results. It has also been employed to discover the nature of the humming or buzzing sounds of certain insects. And it has been made evident that these sounds are not produced by vocal organs, but by the rapid flapping of the wings through the air or against the body. The

note of the syren is made to correspond exactly with the humming of the insect and the resulting number of vibrations read off the index. It has been found by this means that the wings of a gnat flap at the rate of 15,000 times in a second.

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Sounds audible to most people range between 16,000 and 38,000 vibrations, but not all ears are sensitive to the higher vibrations. "Nothing can be more surprising," says Sir John Herschel, “ than to see two persons, neither of them deaf, the one complaining of the peculiar shrillness of a sound, while the other maintains that there is no sound at all.” Professor Tyndall says that when crossing the Wengern Alp in company with a friend the grass at each side of the path swarmed with insects which to him rent the air with their shrill chirruping, but were not heard by the friend at his side. There are many strange and wonderful facts in nature. A few of these in relation to sound we have endeavoured to place before you to-day; they are a very few, for we have but touched upon the subject, but here we must draw to a close. Throughout all spaces, then, the Creator has diffused an ether by which the inexpressible and infinite beauty of nature is revealed to the eye, and around our earth the Creator has thrown an atmosphere which not only supports life, but is an inexhaustible source of delight and pleasure to the ear. ISAIAH TANSLEY.

TWO SUNS.

No one can doubt that the correct and truly scientific mode of induction is, as Dr. Tyndall says, "to seek the unknown in the terms and facts of the known." The grand discovery of the law of universal gravitation was revealed by this process. It is now well known what the results of this law are, and that too with mathematical accuracy; but that the vastness of the fields of unexplored truth may appear, it need simply be pointed out that though the discovery of the universality of this law is as old as the time of Newton, yet to this day nothing is known of its nature and origin beyond what is seen in its modus operandi. And it will be only the statement of a fact if it be asserted that science really knows nothing of any subject or phenomenon beyond what is manifest in its modus operandi.

Now the way in which a thing acts or a phenomenon is seen, brings before the student two separate considerations: (1) the whence of the motion; and (2) the mode and purpose of its action. Most of our

philosophers would be glad to abandon the search for the whence, it being admitted on all hands that the search for it only leads to mere guessing. No honest inductive philosopher likes guessing. And

nothing must sooner put him to the blush than a suspicion that he is guilty of it. But prying man, for some reason or other, will not desist, like inquisitive children, from continually putting this dreadful question, Whence? The importance, however, of the question is the cause of this essay. "There is no whence," says the physical philosopher, "all is present here before our very eyes. Action is its own cause, and its law is its mode of operating. If you want to go beyond this you are insane, for how can there be a beyond in a present and an impenetrable fact?" Thus ingeniously the true way of scientific discovery is stopped, and there is written over the entrance, "No ROAD ;" and so from the known to the unknown" there is no way. Here the truly scientific maxim has lost its force. But the portending and restless whence will intrude where it ought not. And when, with

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all its army of mind, emotion, intellect, and will, with the ever-teeming evolutions of mental power, it demands its territory, our physical philosopher is bound to yield. He says with all the force he can command, "Then take what ye seek, there is your whence bound up in and streaming from the fires of the sun;" or to put origins in the exact language of Dr. Tyndall, “they were all once latent in a fiery cloud.” There, inquisitive man, there is your answer, and are you not satisfied? Why, reasonable man, where else would you have a great philosopher lead you? It has been demonstrated, and almost beyond the shadow of a doubt, that all the elements and forces of the earth have originated in the sun; and so must it not come to pass that everything of the earth must have that source only? Of course, why not? Well, perhaps for this simple reason, that a fountain cannot give what it does not contain. And if there be no evidence that the sun contains within itself the power of growth from within, then it cannot give that power. (I would rather, if my reader will allow me, speak of the sun in the neuter gender.) There is no such evidence. Nay, on the contrary, the periodical action called "the sun-spot period" of the photosphere, a name which is given to the sun's source of light, is considered to be due to the action or influence of the planets on the external surface of the sun. This doctrine of supplied force to the sun deprives it of being even the origin of force. But not every one who has studied solar physics attributes this solar disturbance to this Some think, and with very considerable experience, that all solar disturbances are due to forces existing within the sun itself. But force means the presence of power, and whatever we may find the characteristics of this power to be, we shall certainly find that it does not include the power of growth from within. If this be found so, why call a witness to give evidence which has not a word of information on the subject? But let us for a moment consider the solar power as manifest in its forces. Whatever may be the modes and intensities of these forces, they are all only mechanical. Now the mechanical force of a sphere is either from the centre to the circumference or from the circumference to the centre. The geometry of the sphere admits of no third alternative, whilst it teaches that the

cause.