326 



NATURE 



{Feb. 25, 1875 



sequence more characteristic, more " stringy." Schulze has ex- 

 tended his method to large pedal pipes, producing a stop of 

 remarkable beauty, called the " Violone." 



Applying the air-reed theory to this Schulze's " Gamba," 

 we shall see how fruitful it is in illustration of the actual process 

 of tone-making. Without diagrams and with but few technical 

 terms it may be made clear and comprehensible. Let us take a 

 specimen-pipe. It is of slender, graceful proportions, what is 

 called "narrow scale," length thirty-seven inches and a quarter, 

 diameter one inch and five-eighths, mouth or ciiibouihiii\- in breadth 

 one inch and a quaiter, and three-eighths of an inch high, and ils 

 pitch answers to the note E in the tenor octave. It has a very fine 

 wind-way, large foothole, and is considerably overblown, for it 

 will bear it. There is a bar in front of the mouth, fixed upon the 

 little upright strips projecting at the sides about a quarter of an 

 inch, which are termed ears ; they are common to pipes until 

 the size is too small to require it. Builders say the ears are 

 added to pipes to steady the tone. On the theory advanced in 

 these papers, we find their purpose is to prevent any flank move- 

 ment of the atmosphere during the vibration of our air-reed, for 

 the angle formed by the vertical line of the mouth and the line 

 of force of the outwardly inclined stream of air presents an 

 opening of weakness, and these ears are as ridges or outworks 

 thrown up to guard against any premature invasion by the 

 external air which, as intimated in an earlier letter, pierces 

 through at the proper time, only, just, under the edge of the 

 upper lip. 



We readily perceive that the " Gamba " pipe has three 

 specialties : overblown wind, to give a stififer reed ; a low-cut 

 mouth, as a provision for shortness of reed ; and wind much 

 thrown out as a means compulsory for ensuring a greater ampli- 

 tude in the reed's motion, — the result of the combination being 

 that the tone is rich in harmonics ; harmonics precede the ground- 

 tone, and follow it, and coalesce into it, and linger behind as 

 though the last to quit the pipe. Thtre is nothing more beautiful 

 in all the varied wealth of an organ than a weU-voiced " Gamba." 

 Every tone suggests a symphony, many-tinted, autumnal. There 

 is another remarkable feature peculiar to these — the artist can 

 shade them with less depth of ground-tone and more varied and 

 delicate hues in the harmonics, which nevertheless come out more 

 brightly in the contrast, and compensate the ear with a new 

 variety, toned with less body yet with equal fulness, through the 

 heightening of the harmonic colour, and the more gradual 

 blending of the whole. 



In the pipe we are examining we shall find that the wind is 

 not so much thrown out as in the older class of the species, and 

 herein lies the real meaning of the difference, for by the agency 

 of the bar an equal amplitude is enforced in the air-reed, but 

 one of new form: and see how gracefully it is drawn, — yes, 

 happily we can see, fur the new form bears an impress highly 

 significant. A little bit of paper deftly applied will enab'e us 

 to watch the piocess of nature. Take away the bar, and the 

 pipe will not sound ils ground-tone— it is only able to produce 

 its string of brilliant harmonics. Look at the air-reed : how minute 

 a space it traverses whilst these high notes are thrilling in your 

 ears. In substitute for the removed bar, now lay a small pencil 

 across the mouth, and see how in coy consent the air-reed yields, 

 comes out to you with a fine curve, and all the power of the pipe 

 is affirmed coincidently with this visibly extended amplitude of 

 the reed's motion. Vou can change it from one state to the 

 other by this movable bar, and you have to notice that the reed 

 is almost upright in stem, but btnds over, arching at the tip, — 

 notice also that the inward curve of the reed is less than the 

 outward curve. The explanation of this influence will be quickly 

 divined if you fully comprehend the way in which the reed builds 

 itself up in a curve, leaning outward upon the external air : the 

 air composing the reed issues from the wind-wayin adense stream ; 

 the particles are most compressed at the root, and gradually 

 expand and become less energetic as they reach higher freedom 

 — the velocity of the upward stream motion attracts the 

 external air with force, strongly, to the root, bearing with lessened 

 force on the less compressed portions higher up, and the gra- 

 dation of force so mani'ested gives rise to the curve — the 

 curve delineates the force, we may say the curve expresses the 

 constant flow of the surrounding air to this diversified region of 

 "least pressure," its impulses being in graduated power from root 

 to tip. By the bar we interfere with the direction of this flow, 

 concentrate it more on the lower portion of the stem, and shield 

 the lip of the reed from its influence ; the upper portion, having 

 thus lost so much of its natural support, is bent by the outflowing 

 nodal wave of the pipe in a more supple curve, and to an extent 



equal to the required amplitude for its pitch. The form diflTers 

 now. The curve of the " Gamba " is not the same[as the curve 

 of the " diapason. "- 



The distinct agency of the air-reed and the nature of the air- 

 column in relation therewith being evident, the inference follows 

 that the note produced is dual, consists of two unisonous notes 

 blended into one sound. Quite unexpectedly tlie chosen pipe 

 furnished me with the talisman to prove its truth. When the 

 reeil and the pipe are suitably mated, the union is one of perfect 

 harmony ; but the reed rules always : it may be sharp to the pipe, 

 but the pipe can never be sharp to the reed, for on the first inti- 

 mation of such the reed is roused, and starts forth to a tone of 

 higher velocity. How slight a matter may derange the union of 

 the reed and pipe. If we tease the pipe with this pencil, peace 

 is disturbed. Our beautiful little "Gamba" is'very seirsitive 

 and high-spiiiled, and cannot help letting us hear a little of the 

 inner life of the home when things go a trifle wrong. There is 

 one particular place across the mouth for the fixture of the bar: 

 if, resting the pencil at the upper points of the projecting ears, 

 you leisurely bring it down, you will hear the changing har- 

 monics ; then, halting just a hair's breadth or .so before the true 

 position is arrived at, all tone will be lost, and there \iill suddenly 

 break forth a wailing " who-hoo, who-hoo ; " that torture will 

 continue until you relieve the suspense by moving the pencil 

 another shade in descent, when the discord will resolve into the 

 perfect tone, instantaneously, as two dew-drops when they touch 

 melt into one. Precisely the same "who-hoo" as we hear 

 when tuning two separate diapason pipes so nearly in tune that 

 they are only a shade out of imison and just on the point of 

 accord. The "Gamba" pipe and the reed were similarly at 

 variance ; '.he air-reed, not having quite yielded to the outward 

 influence of the bar, was a trifle sharp to the pipe ; the super- 

 nodal wave was too short and unable to eftect a synchronisation 

 with precision, and therefore the phenomenon of beats was mani- 

 fested. We could have lengthened the supernodal wave and 

 flattened the note by adding a piortion to the top of the pipe, 

 when concord would have followed, as it did by lowering the 

 bar, for in tuning it matters not which note of two is altered to 

 bring about unison ; we might alter either pitch of pipe or pitch 

 of reed ; but by the lowering of the bar we flatten the reed, and 

 cause thereby the descent of the node (then an uneasy fulcrum) 

 and the lengthening relatively of the supernodal column. As a 

 listener remarked "there was surely a fight goirg on inside," 

 we settled it by favourhism, taking sides with the Utile " Gamba," 

 and gaining the reed over', in concession of its strength for the 

 sake of concord. That is the explanation as it suggests itself to 

 me, praclically, exhibiting how a strong reed drives the node 

 higher up in the pipe, anda weak reed favours the opposite; thus 

 determining the variations in the lengths of pipes of unisonous 

 pitch, so long an unsolved problem. 



Another point of some importance is also illustrated — that the 

 earliest harmonics in the theoretical series may be out of tune 

 with the fundamental. Here the introductory or transitive har- 

 monics are, it is evident, all sharp to the ground tone, since the 

 influence of the bar does not coirie into effect until ils flattening 

 power ushers in the fundamental ; phenomena of this kind occur 

 in other instruments mostly unacknowledged — it is admitted to 

 be the case in the trumpet, which has iTo. 5 in the series flat, 

 7 still flatter, and 9 sharp. A diapason pipe will, however, 

 exhibit the same in the small pipes of the higher octave ; they 

 may be blown to imitate exactly the clash of the trumpet. 



As showing the essential nature of the curve of the reed under 

 the influence of the bar, it is worth notice that in the earlier 

 " Violone " stops thus treated a square-faced bar was fiited, but 

 with not so good effect as when the rounded bar was adopted ; 

 and in the light of our explanation we see why it should be so, 

 for the curve could not form itself truly. The best form of bar 

 is that given by a split pencil, the half-round, with the flat 

 surface outward. Many other points of interest will be dea't 

 with in another letter, on the interior movements of vibrating air- 

 columns. 



The study of the organ-pipe in every mood of its behaviour 

 vrill make untenable the elegant fancy of a promiscuous assem- 

 blage of pulses fluttering and clamouring at the lip of the pipe, 

 one of which out of a thousand it selects. It is a fair-seeming 

 explanation, and under the commanding name of Prof. Tyndafl 

 generally accepted, for nothing better had been devised in philo- 

 sophy. Not too strictly interpreting an ideality of expression, 

 there yet remains an implied theory which is not in any sense 

 borne out by the teachings of experience. The artist has some 

 prescience of the powers that are to work his will ; in practice 



