Augusts, 1878] 



NATURE 



rabaissement du quart de ton qui a ete fixe par la commission. 

 Je voulais, avec quelque raison, je crois, fixer le ton du diapason 

 a 888 vib. qui avait pour base Vut de 32 pieds egal a 33 vib. par 

 seconde, le la geometrique = a 880, et le la tempere 888, ainsi 

 que je I'ai explique dans la petite brochure, ' De la Determina- 

 tion du Ton Normal ou du Diapason pour I'Accord des Instru- 

 ments de Musique,'" published originally in V Amide la Religion, 

 February 6, 1859, before the normal La was fixed. At the 

 close of this paper M. Cavaille-Coll say?, in favour of 888 v. s., 

 besides his present remarks, "Ce nombre, qui se trouvede's 

 vibrations plus eleve que le la normal du congres de Stuttgard 

 et de 8 vibrations plus bas que le diapason de I'Opera de Paris 

 [en 1857] aurait, suivant nous, le merite, s'il etait adopte, de 

 concilier les exigences de la science physique et les besoins 

 de I'art musical," The peculiarity that C 264 gives a just 



■A- 440 = J X 264, and a tempered A 444, has been productive 

 of some confusion. The committee called together by the 

 Society of Arts in 1859 recommended the Stuttgart pitch A 440, 

 which they considered would give C 528, whereas on equal tem- 

 perament it would give C 523^ Hut they made C 528 their 

 standard, which would give the tempered A 444, and the Society 

 of Arts commissioned the late Mr. J, H. Griesbach to make them 

 such a fork, for which he employed the instrument now in room Q 

 of the South Kensington Museum, and to this he endeavoured 

 to make an equally tempered A, His results in place of C 528, 

 A 444, were, when reduced from Appunn's to Scheibler's stan- 

 dard, C 535 and A 446, which do not even agi-ee with each 

 other, for his C requires an A 450, and his A requires a 

 C 530, both bemg rather sharper than was intended. In the 

 organ of the cathedral of St. Denis M. Cavaille-Coll measured 

 the pitch as A 444-25, by means of the siren, but before the 

 application of his bellows of precision. The Bolognese fork, 

 already mentioned as being nearly A 444, was also measured at 

 ±5oIogna by the siren, but the result is not stated in the report 

 preserved by the Society of Arts. 



As regards the introduction of equal temperament into 

 l-rance, M. Cavaille-Coll informs me that up to 1834 their house 

 tuned on the old mean- tone principle, but that subsequently to 

 1634 he has consistently laboured to carry out the equal tempera- 

 ment. He thinks, however, that equal temperament was u=ed 

 for pianos before that date. I may mention that the change was 

 made at Broadwood's, in London, between 1841 and ''1846 

 That at the first Great Exhibition of 1851 in London, only one 

 organ (by Schulze) used equal temperament, and that at lea^t 

 three organs had not adopted it a year a^o (St. George's, Windsor 

 Turvey Abbey, and Norwich Cathedral), 



Kensington, W., July 13 Alexander J. Ellis 



Peaucellier Cell 



The following application of the Peaucellier Cell may pos- 

 sibly interest some of your readers. The object of this arrange- 

 ment IS to make two points— one on each side of a lens— move 

 in such a way as always to remain at conjugate foci. 



In the accompanying wood-cut p, r, and p', r', are the poles 

 cf two cells, alike in all respects, which have a common origin 



383 



From the property of the cell, 



^ - p ^ ~ p' '^^'tere k is, a. constant, 



l=r + r' 



I I 



':'ihl) 



Hence, if - is the fecal length of the lens, p and p' are con- 

 jugate foci, 



Mr, Francis Galton wanted to use the above arran<rement 

 but found he could not get sufficient range unless the cells were 

 made of unwieldy size, Horace Darwin 



The Microphone 



In reproducing the experiments first made by Prof, Huo-hes 

 with the microphone, I interposed in the circuit a galvanometer 

 and first found with the battery used (made with three ^mall 

 glass cones, as used by Prof, Hughes), when the microphone was 

 not in the circuit, the current was sufficiently strong to deflect 

 the needle to 40°, Now interpoi-ing the microphone, made of 

 mercurised carbon peas in a small glass tube, it acted well as a 

 transmitter only m hen the pressure on the carbon peas was so 

 adjusted that the needle of the galvanometer stood about 15°, 



When the pressure was very slight and the resistance to the 

 current so great that the needle swung only to 5° or 8°, then the 

 " continuous distant waterfall roar" of the telephone was plainly 

 audible. The slightest sound of the voice in the room would 

 produce the painful /«/, pat, indicating an intermittent current 

 and not a continuous one of varying intensity. 



This " distant waterfall roar" emitted by the telephone, not 

 unlike the " murmur of the sea-shell," was in all respects similar 

 to the sound familiar to those who have attempted to use a tele- 

 phone whose line was greatly affected by the induced currents of 

 a number of proximate telegraph lines in active use. When the 

 pressure of the carbon peas was so slight and consequent resist- 

 ance great, the vibrations of the air in the room, vhen most 

 quiet, so increased and diminished the resistance to the electric 

 current as to cause the incessant tremor of the tympanic plate 

 of the telephone, and thus rendered audible the constant 

 murmur. 



Among many other methods I tried a torsion pendulum, made 

 by suspending, with a small cotton cord, a double cone of mer- 

 curised carbon an inch long, between two pieces of carbon less 

 than an inch apart, to which the connecting wires were attached.. 

 The pressure was regulated by the torsion of the cord. In this 

 simple manner any required delicacy was easily attainable. 

 Vanderbilt University, Nashville, Wm. LeRoy Eroun 

 Tenn., July i 



at o ; and the poles R and r' are connected together by a bar 

 with a slot in it, through which the pin which forms the pivot 

 at o passes. Then if p, r, p', r', are constrained to keep in a 

 straight line, P and P can approach or recede from o, only in 

 such a way that, if there is a lens of proper focal leneth at o 

 P and p will always be conjugate foci. * ' 



This is easily proved thus : — 



Suppose P o =/, p' o = r', 

 R o = r, r' o - /', 

 and the bar r r'- = /, 



Of the many ingenious forms the microphone has taken— and 

 I believe I am acquainted with most of them— none is, I think 

 more efficacious than the one I offer for your inspection. The 

 jarring sound in the principal instruments in use, which, by 

 vibration, may emanate from passing vehicles, &c., is entirely 

 obviated, and the sound of a piece of fine silken thread, or the 

 now well-known tramp of a fly, is heard with double the dis- 

 tinctness of any microphone I have listened to. 



It consists simply of a cup and ball of carbon, the cup being 

 fastened to a small piece of board, and one of the insulated 

 wires attached to it in the usual manner, while the other is 

 carried through the bottom of the cup sufficiently far to touch 

 the ball without disturbing it in its socket. 



From this little instrument I have obtained the most satisfac- 

 tory results, and have heard distinctly that which I had to strain 

 my hearing to catch before. Unless my "idea" is already- 

 anticipated, might I ask you to make it known to your numerous 

 readers? Gerald B. Francis 



23, Bessboro' Gardens, S.W., July 24 



A Simpler Form of the Phoneidoscope 



Most of your readers will be familiar with Messrs. Tisley and 

 Spiller's beautiful instrument, known as the plumeidoscope. 

 In using it, however, I have found certain defects, which my im- 

 proverr.ent on it is intended to obviate. 



