512 



NATURE 



[April 2^, 1876 



class is three-fourths of the half-wave length, and then in accord- 

 ance with varying diameters above stated all larger diameters 

 demand length to be increased in ratio, and more allowance to 

 be made for the diverging than for the uniform bore ; greater or 

 less amount of wind, and greater or less degree of pressure also 

 enter into calculation, and practically are convertible in effect, 

 the one doing duty for the other. 



In the distinctive mode of action of this class we may find 

 reasons for the varying relations of the pipes to each other, and 

 for the contrasts shown in comparison with the other class acting 

 under its own peculiar mode. In these propulsive pipes in both 

 the wide and narrow scales, the wind-current, after entering the 

 foot of the . pipe or boot, passes into the body of the pipe by a 

 very contracted inlet formed by a hollow plug usually of metal 

 called " the beak," or more commonly " the reed," to the con- 

 fusion of inquirers ; properly named, as we see it in old authors, 

 it is "the shallot," from its resemblance in shape to the once 

 favourite esculent the eschallot ; ordinarily we speak of "the 

 tongue " the elastic strip of metal covering it, as " the reed," 

 for in the clarionet this part is really a reed. The main impulse 

 of the current passes into the cone of the pipe through the mass 

 of air in a central direction, and thus in a wide pipe, as com- 

 pared with its course in a narrow pipe, the current has exchanged 

 the friction upon the sides for the lesser friction of air upon air, 

 still restricted, but less so in degree as the cone expands, as of a 

 swift river escaping the confinement of banks, flooding the quiet 

 expanding delta, agitating its waters with gradually-decreasing 

 strength, and then becoming diffused in surrounding ocean. 



Utmost exactness in length is quite as important lor pitch and 

 tone in these as in flue-pipes. Although the reed tongue has 

 a determinate pitch of itself, yet a proper length of tube to 

 reciprocate its action is indispensable, any inaccuracy only " up- 

 sets the tone," as the technical phrase says, and gives rise to 

 curious freaks of behaviour. The slim tapering oboe is so sen- 

 sitive that if we make it a quarter of an inch too long, or if we 

 merely pat the top of its bell whilst sounding, the tone will im- 

 mediately leap to its third above — not to a harmonic — a problem 

 as puzzling as that of some echoes falling successively by thirds. 



The action of the air-reed as causing suction by the velocity of 

 passage of wind over the mouth was illustrated by me in a pre- 

 vious paper by reference to the abstracting power of a current of 

 air, as shown in the spray-diffuser where globules of liquid are 

 lifted and withdrawn by its agency. The action in these beating 

 reeds is also susceptible of as simple an illustration. Take six or 

 eight feet of India rubber tubing of |-inch bore, for this length 

 defines action more clearly — ^coil the length round your hand, 

 and placing ' >ne end in the mouth blow through the tube sharply, 

 at the same time allow the tip of your tongue freedom of play 

 near the orifice, and you will find it drawn suddenly to the tube 

 by the suction of the current passing down it, and released only 

 on the exit of the current into the atmosphere. Lightly press- 

 ing the coil ia )our hand you may likewise feel the throb of the 

 passing air-pulse. The trombone-player is conscious of his lip 

 being forcibly drawn into the cup by a like cause. A stream of 

 air suddenly cut off cannot pass down a tube without leaving a 

 vacuum behind it. Organ and orchestral trumpets and oboes, 

 and all of like propulsive action, are subject to ihis power, and 

 only through it are able to generate tones. Suction is thus seen 

 to be the final cause of vibration, the vacutim exists until the 

 initial pulse of the vibration has made exit at the outer orifice, 

 or in the second and succeeding courses until the pulses reach 

 the colliding point or place of the prime node. Always thus in 

 every musical pipe the current is essential to the suction, but with 

 the striking difference that in the flue-pipe there is continuity of 

 stream, and the continuity of flow is made available by conver- 

 sion in reciprocating motion, but in the propulsive class the 

 action is effective through discontinuity, by abrupt cessations 

 and sequences of stream. 



Here also in the beating-reed pipes we come upon distinct 

 evidence of the interval of rest lengthening the period of vibra- 

 tion. The pitch of beating-reeds is regulated to consort with 

 the pipe by means of a tuning-wire altering the vibrating length 

 of the tongue ; thus regulated, the pitch may, however, within 

 limited degree be altered by changing the force of wind, or by 

 cutting off rim of pipe, or by adding thereto. Let it be ob- 

 served that whether the tongue is pressed to the beak slowly or 

 quickly, it will spring back in recoil in just the same time. By 

 additional weight of wind, pitch may be raised, and in this case 

 the tongue flies to more rapidly, but possibly any gain of speed 

 in the advance may be counteracted by the recoil being impeded 

 in the more compressed medium in which the tongue moves ; 



the only remaining effect, otherwise is that of an increased swift- 

 ness of the current of air more vigorously propelled in its course, 

 and this in itself would account for the acceleration of pitch. 

 On the other hand, leaving the force of wind constant, we may 

 by temporary addition to the rim of upper orifice sensibly flatten 

 the pitch, for the current takes longer time to pass this extra 

 boundary, hence the tongue is in consequence held longer upon 

 the beak by the suction, its recoil delayed, or in other words 

 recognising the physical result, its interval of rest is lengthened. 



Many indications that come before me in my experiments 

 lead directly to the inference that in all wind instruments this 

 interval of rest is an important influence both on the pitch 

 we regulate and in the quality we perceive ; and in the estimate 

 I shall have to give of the interior process of working in the flue 

 organ-pipe, I shall draw upon this inference that vibration is an 

 activity tempered by rests. 



One point has been unnoticed. It would be easy to find a 

 diapason-pipe of the same pitch showing precise agreement in 

 length with the trumpet above specified, and similarly for other 

 various kinds. The recognition of numerous like correspond- 

 ences has led to the supposition that in relation to wave-length 

 these two classes of pipes exhibit a parallelism, t hope to have 

 made it clear that on the contrary, never parallel, the two classes 

 proceed on two distinct systems of relation to wave-length, and 

 are governed by a law, simply expressed as a law of divergent 

 variation ; they meet, it is true, but only at one point, where 

 they cross in divergent lines, and they develop in opposite 

 phases both in the ascending and descending extents of their 

 range, the pitch of the one rising under an enlarging, and the 

 other under a diminishing diameter. 



Heyond the particular effects of friction already stated, the 

 agency of the friction of air in the sound of wind instruments 

 appears to me inadmissible. Reasons for this conclusion will 

 occupy another paper in connection with details of my experi- 

 ments bearing thereon under a simple device so-newhat on the 

 principle of the siren, and which may be named a "displace- 

 ment siren." Hermann Smith 



Solar Halo 



On Saturday last at Penruddock station, between Penrith and 

 Keswick, about one o'clock, I observed a solar halo which at 

 first was not perfect, but showed a reddish tint in the arc below 

 the sun. Afterwards the circle became complete and continued 

 so with small intervals until about half-past f jur, when I went 

 indoors. At five o'clock the halo had disappeared in the haze. 

 The day was thick, so hazy indeed that I could hardly distin- 

 guish the outline of Saddleback from Penruddock. The colour 

 disappeared when the circle was complete, but occasionally I 

 thought I could distinguish a reddish tinge on the inner side of 

 the arc. I had no means of accurately measuring the radius, 

 but with two pieces of stick which I picked up I estimated the 

 tangent at %, which would give nearly 24". This is more than 

 your correspondent Mr. Gledhill found in his observations, but 

 my measurement is confessedly rough. James Heelis 



April 21 



Safety Matches 



Mr. Tomlinson's remarks on safety-matches in Nature, 

 vol. liii., p. 469, reminded me that, not long ago I accidentally 

 kindled one of those matches by rubbing it on the edge of a 

 Wedgwood-ware mortar. This miterial appears even better 

 adapted than those mentioned by Mr. Tomlinson for igniting 

 such matches, and I found that a common earthenware dish 

 (glazed inside) answered the same purpose admirably. I tried 

 to ascertain the degree of certainty with which a safety-match 

 could be kindled by friction against these two materials, and was 

 surprised to find that they are little inferior in this respect to 

 amorphous phosphorus itself. After a little practice in the man- 

 ner of striking, it is easy to kindle nearly every match. Thus 

 I have lighted forty matches out of fourty-four (most of them at 

 the first or second stroke), using the glazed portion of the basin 

 referred to. I should add that the surface becomes improved 

 by use, which can hardly he said of the composition on the 

 sides of the safety-match boxes. 



Manchester, April 18 Francis Jones 



"The Ash Seed Screw" 



The delicate twist in the samara of the ash is clearly not that 

 best calculated to retard descent. The more decided the twist, 



