produce silence. This is caused by the interference of the sound-waves. If we throw two stones into the water near each other, there will be seen a line where the waves meet in such a way as to destroy one another, along which the water will be calm. Sonnd-waves may produce similar effects, and at such points no sound can be heard. Sound-waves may partly destroy one another, and very much weaken the sound; or they may operate together and increase the sound. Mixed gases, owing to the different lengths of the waves in each, may be bad conductors of sound. The gases, however, which compose atmospheric air, are so related as to produce no such effect.

An echo is one of the most interesting phenomena in acoustics. It is produced by the reflection of the soundwaves, as waves in water are reflected from smooth surfaces. A rough surface is a bad reflector of sound, as of light, because the irregularities reflect it in so many different directions, that the various waves interfere with one another. The velocity of reflected sound-waves is the same as that of direct, so that we can easily determine the time required for an echo to reach us, when we originate the sound, by considering that the sound has to pass over twice the distance between us and the reflecting surface at the rate of 1,125 feet a second. The number of syllables that we can hear distinctly echoed will depend on the rapidity with which we pronounce them, and the distance of the reflecting surface. If the reflecting surface be near, the echo and the direct sound will reach us so nearly together that the former will strengthen the latter. There is a limit to this, however, and it is evident that a speaking hall should be constructed in accordance with this principle. In large rooms used for speaking purposes, all echoes which can accompany the voice of the speaker, syllable by syllable, are useful for increasing the volume of sound; but all that reach the hearers sensibly later only tend to produce confusion. Professor Henry found by experiment that if a sound and its echo reach the ear within from one-fifteenth to one-twentieth of a second, depending upon the nature of the sound, they seem as one. This is called the limit of perceptibility. This gives

1868.]

THE PHENOMENA OE SOUND.

77

us for the distance of the reflecting surface from thirty to forty feet.*

If we take the mean of these numbers as the usual limit, we see that if a lecture hall have its walls farther from the speaker than thirty-five feet, some arrangement must be made to prevent the echo from interfering with the distinctness of the direct sound. Those who are within thirty-five feet of the echoing surface will hear the speaker more distinctly than without its effect; but others will find it a disadvantage. Distant walls should be broken up into small portions, presenting surfaces in different directions. This may be effected in various ways. There may be a gallery with the seats and the floor rising rapidly behind. one another, so that much of the sound which would otherwise reach the remote wall, will be caught directly by the hearers. "Especially should no large and distant surfaces be parallel to nearer ones, since it is between parallel walls. that prolonged reverberation occurs."

Walls intended to aid a speaker by their echoes should be smooth, but not too solid. It is found that plaster on lath is better than plaster on brick or stone; the first echo is louder and the reverberations less. Drapery behind a speaker deprives him of just so much echoing surface. A. lecturing hall is improved by causing the wall behind the speaker to change its direction to the right and left of the speaker, at a very obtuse angle, so as to exclude the rectangular corners from the room. The voice is in this way reinforced by reflection, and the resonance arising from parallel walls is in a measure avoided. The ceiling should not be too high; and concave surfaces, generally, should be avoided.. "An equal diffusion of sound throughout the apartment, not concentration of it to particular points, is the object to be sought in the arrangement of its parts."+

In Chamber's "Information for the People," it is said that "the best known form of apartment for the proper distribution of sound, is that in which the length is from

*An. Sci. Dis. for 1852, pp. 153-4.

† See a paper on "Acoustics applied to Public Buildings, by Professor Joseph Henry,. in the Proceedings of the An. Assoc., Albany, 1856. Vol. i., p. 210.

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THE PHENOMENA OF SOUND.

[December,

a third to a half more than the breadth, the height somewhat greater than the breadth, and having a roof bevelled off all round the sides. This species of ceiling, called, technically, a coved or coach roof, from its being lower at the sides than centre, is in all cases best suited for conveying sounds clearly to the ears of auditors."

The principles of acoustics are well understood, but they are too seldom applied to the construction of speaking rooms. In many instances costly assembly halls and churches are very defective in regard to public speaking. The fancy of the architect seems rather to be consulted in their construc

tion, than scientific principles. The subject urgently demands consideration in connection with architecture."*

Reflecting surfaces may be so related to one another as to cause multiple echoes. At Srevley-Fels, on the Rhine, is a position in which a sound is repeated by echo, seventeen times. At the Villa Sinsonetta, near Milan, is another where it is repeated thirty times.† In Woodstock Park there is an echo which repeats seventeen syllables by day and twentyeight by night. Sir John Herschel mentions an echo in the Manfroni palace at Venice, where a person standing in the centre of a square room, about twenty-five feet high, with a concave roof, hears the stamp of his feet repeated a great many times, but as his position deviates from the centre the echoes become feebler and at a short distance they entirely cease.+

If a sound be made in one focus of an ellipsoidal surface, it will be reflected to the other focus. Whispering galleries are constructed upon this principle. The ear of Dionysius is celebrated in ancient history. It was a grotto cut out of the solid rock at Syracuse, in which a person placed at one point could hear every word, however faintly uttered, in the grotto.

Lastly, we may refer to the moral effect of sounds, especially very loud sounds. The red man hears the voice of the Great Spirit speaking from out the cloud when it thunders;

* Chamber's Encyclopædia, vol. i, p. 32.

↑ Bartlett's Acoustics, p. 89.

Brewster's Natural Magic, p. 205.

and a similar feeling, mingled with some fear, has a tendency to prevent man from wrong doing when the thunder roars, or when he hears such subterraneous sounds as accompany earthquakes.

ART. V.-1. Report: Orange Lodges, Associations or Societies in Ireland. Ordered by the House of Commons to be printed, July, 1835.

2. Report: Orange Institutions in Great Britain and the Colonies. Ordered by the House of Commons to be printed, September, 1835.

3. Reports from the Select Committees appointed to inquire into the nature, character, extent, and tendency of Orange Lodges, Associations, or Societies in Ireland, with the Minutes of evidence, Appendix and Index. Ordered by the House of Commons to

be printed, 1835.

4. Mr. Hume's Speech in the House of Commons, Feb. 23, 1836. 5. Battle of Magheramayo. Newry: James Henderson, 1849. 6. Mr. Berwick's Report to the Lord Lieutenant of Ireland, on the occurrences which took place in the District of Castlewellen, on the occasion of an Orange Procession, on the 12th of July, 1849. Dublin Evening Post, 17th October, 1849.

A LARGE proportion of those who inflict the most serious injuries on their neighbors do so under the impression that they are doing right; hundreds are guilty of conduct as members of a faction or society from which they would shrink with horror as individuals. The moralist as well as the philosopher should take this into account in estimating the amount of violence or depravity manifested in any particular community. Even those who are injured are bound to take into consideration the motives of their assailants. It is true that if one's leg or arm is broken, for his house burned, his pain or loss is not diminished by learning that his assailant was prompted by erroneous motives. Nevertheless no

one who reflects entertains the same feeling towards those who injure him through ignorance, under the impression that they are serving a good cause, which he does towards those who are actuated by personal malice or avarice. In this point of view ignorance is little better than insanity; the wisest of the ancients made but little distinction between the two conditions of the mind; and what great difference can be made at the present day between an ignorant man who is highly excited-especially if excited by fanaticism, a partisan spirit, and, perhaps, intoxicating drink-and a maniac ? The principal difference is that while the law holds the former responsible for his conduct, it expressly exempts the latter from punishment.

In making this comparison in allusion to the conduct of the Orangemen of Ireland we do not mean to make any attack on that body. We have no grudge to gratify against them; they have never disobliged us personally in any manner; on the contrary we cheerfully acknowledge that we have experienced much friendship from individual Orangemen, while we made no effort to conceal our dislike of a society which had contributed so much to the ruin of Ireland. Often we have reasoned with Orangemen in a public journal published in one of their own strongholds, endeavoring to induce them to reflect on their conduct and make themselves acquainted, at least in part, with the history of those in whose name, or in commemoration of whom they committed such deplorable excesses. Nor do we mean to pursue any more unfriendly course in this article; at the same time we shall not shrink from presenting the facts to our readers.

Our object in taking up the subject at the present day is two fold: the American people have but little idea of the real character of the Orange Society; and this little is by no means correct. It is but natural that Protestants should think that when other Protestants have had conflicts with Catholics as such, the latter, and not the former, must be the party to blame; but in this instance at least the reverse is the case. That the lower order of the Catholics of Ireland often commit excesses, far be it from us