Scientific Lectures. 191 



cries, not unlike those of infantile distress or anger. These sounds 

 are sufficiently ludicrous, I admit ; but they have for us a deeper 

 meaning; they teach us that, in this purely mechanical way, out of 

 the taps on a card, it is possible to build up sounds which bear some 

 resemblance to those uttered by human beings. 



I wish, in the next place, to make an analogous experiment, in 

 which the resemblance to musical notes will be more complete. The 

 little piece of apparatus I have in my hand is so contrived that, when 

 set in operation, it allows the air to pass through it in puffs, like those 

 of a tiny locomotive. "With the organ bellows I drive a current of 

 air through it, and now, leaning over it, I hear a succession of these 

 puffs, which, as the current of air is increased, will follow each other 

 more rapidly and also gain in strength. We have, at last, a deep 

 musical note issuing from it, which, as you notice, rises regularly in 

 pitch each instant, becoming at last quite shrill and loud. The instru- 

 ment was contrived by Cagniard de la Tour, and is called a syren, 

 because it is capable of uttering its musical tones under water. It is 

 provided with an attachment, by which I could easily count the num- 

 ber of puffs emitted in a second, and thus determine the number of 

 impulses due to a given note, and, hence, knowing, as we do, the 

 velocity of sound in the air, easily measure the length of the wave 

 producing that note. 



But we must pass on to the consideration of another matter, and 

 will return once more, for an illustration, to our waves of water. 

 While out at sea, those of you who were able must have noticed that 

 the large waves of water which lifted and rolled the ship were, for 

 the most part, not simple in form, but covered with minor wavelets 

 which curved their surfaces with ragged and ever-changing outlines. 

 They demonstrate for us the possibility of the coexistence of two or 

 more sets of waves, and show us the manifold forms assumed by water 

 acted upon by several independent wave-like impulses. I have in my 

 hand a large tuning-fork, which is vibrating in a certain way, and, by 

 drawing the fork over this smoked glass, the little wire attached to it 

 renders these vibrations visible, and we have them now delineated on 

 the screen under the form of a straight band, which consists of a mul- 

 titude of minute waves. But I can also communicate to the fork a 

 second motion, still preserving the first, and you see it has traced on 

 the screen a series of larger waves, whose mountains and valleys are 

 built up of the little undulations. Just so it is vdth the waves of 

 sound. They are often, indeed almost always, thus broken up; it 

 being seldom that simple sounds, produced by smooth, clean-cut waves, 



