SepL.i% 1878] 



NATURE 



559 



3. Apparatus of Neumann ^ and Le Roux." 



II. Estimation of the velocity of sound by the number of 

 vibrations and- the wave-length of musical sounds. 



A . Direct methods : — 



I . Method of Bernouilli, with sonorous tubes. 

 , 2. Method of Chladni,^ with rods. 



3. Method of Kundt. 



4. Methods of Stefan * and Warburg.* 



Ij. Methods based on the interference of sonorous waves : — 



1. Method of Savart.^ 



2. Method of measurement of the wave-length with Quincke's 

 interference tubes.^ 



3. Method of Zach.^ 



4. Method of beats. 



The way in which the velocity of sound is affected by certain 

 circumstances, especially intensity and pitch, requires further eluci- 

 dation. Up till recent times it was believed, in accordance with 

 the earlier observations and the theoretical formulae of Newton 

 and Laplace, that sound is propagated with a uniform velocity in 

 the same medium, the temperature remaining constant ; that the 

 velocity of sound in air at zero, e.g. , is an invariable quantity. 

 After an observation by Parry related by Sir James Ross, that 

 the sound of a cannon was always heard sooner than the word of 

 command to fire, Schroder van der Kolck was led by theory to a 

 formula giving the velocity of sound in a gas as a function of the 

 I'elation of the two specific heats and the degree of compression 

 of the medium. This velocity would be greater the more intense 

 and grave the sound, and would diminish with the distance 

 traversed. 



Regnault set himself to determine rigorously the ratio of the 

 two specific heats of gases, with a view to deducing the me- 

 chanical equivalent of heat. He remarked that Newton and 

 Laplace had assimied, in their formulae, that the gases were per- 

 fect, i.e. (i), that they followed Mariotte's law exactly; (2) that 

 their elasticity, was not altered by surrounding bodies ; and~(3) that 

 gas opposes no inertia to the transmission of sound-waves. Ac- 

 cordingly the propagation of sound was supposed the same what- 

 ever the intensity. Regnault's more complete formula indicated 

 that the velocity is greater the greater the intensity of the wave. 

 Experiment proved that the intensity of the wave diminishes 

 in a tube more rapidly the smaller the section. The wave is 

 weakened by the reaction of the elastic walls of the tube, 

 causing a considerable loss of vis viva ; and the diminution of 

 intensity, according to Regnault's formula, should result in 

 diminution of velocity, which diminution must be more rapid 

 the nan-ower the tube. This was confirmed by experiment. 



As regards experiments with the human voice and wind- 

 instruments, the following are the principal observations of 

 Regnault ; acute sounds are propagated with much less facility 

 than grave sounds ; in very wide pipes, it is necessary to sing 

 with a baritone voice in order to be well heard ; the fundamental 

 sound is heard before its harmonics, which succeed in order of 

 pitch, and the timbre is thus altered. The velocity was found 

 independent of pressure, as indicated by the formulae. Lastly, 

 with different gases, the velocities are inversely proportional to 

 the square roots of the densities. 



In connection with the foregoing, it is interesting to compare 

 the results that have been obtained by Kundt. ^ The idea of his 

 method was suggested by Chladni's figures. A tube of glass is 

 used about 2 m. long, containing a certain quantity of lycopo- 

 dium powder (distributed as regularly as possible), and closed at 

 the two ends. You rub the tube longitudinally, so as to produce 

 a sound. The powder is then seen to accumulate at the nodes 

 of vibration, so that the sonorous waves of the gas are, in a 

 way, rendered visible. The distance from one node to the next 

 being half a wave length, suppose that we have twelve in the 

 tube ; the length of the tube vibrating transversely, will be the 

 half of a wave-length in the glass. Under such conditions, then, 

 the length of half a wave in the glass is sixteen times the length 

 of half a wave in the air. It will follow that the velocity of 

 sound in the glass is sixteen times that in air. Other gases may 

 be used in the tube, and the velocity of sound similarly found in 

 them. 



By a simple modification of the apparatus, this method gives 

 the velocity of sound in a large number of solid bodies, and the 



' Pogg. Ann,, t xcii. p. 483. ' Cotn^tes Rendus, t. Iv. p. 609. 



3 Pogg. Ann., t. cxxviii. p. 307. 



* Confutes Rendus, t. Iv. p. 662. 5 Chladni's "Acoustics." 



^ Sitzitngsberichte der Wiener Akademie, t. Ivii. pp. 197 and 708. 



^ P''tg- Ann., t. cxxxvi. p. 285. 8 Cotnpies Reiidus, t. vii. p. 1068, 



' P<'SS- Ann. t. v. p. 436. 



results agree pretty ^closely with those • found by different 

 methods. 



But Kundt's method does not give sufficient precision in 

 respect to the delicate questions investigated by Regnault. The 

 wave-lengths measm-ed never go beyond about 45 mm., making 

 the o'oooi386 part of the course traversed by sound in a second ; 

 hence an error of o"i mm. made in the measiu-ement of a wave- 

 length would lead to an error of ^ m. in the result sought. 

 With this reserve, Kundt's results may be here noted. 



1 . The length of sonorous waves, and consequently the velocity 

 of sound, diminishes proportionally to the diameter of the tube, 

 when this is less than a quarter of the length of undulation. 



2. In narrow tubes a high sound is transmitted more rapidly 

 than a grave one, and the diminution of the velocity of sound is 

 in inverse ratio to the wave-length. 



3. The velocity of sound is independent of the pressure in a 

 wide tube, but increases with it in a narrow one. 



It will be seen that these latter results are in contradiction 

 with those found by Regnault. 



It may be generally affirmed that every influence which tends 

 to increase the vis viva of the molecules of the sonorous medium 

 has an accelerating action on the velocity of sound, and every 

 influence tending to diminish the vis viva diminishes also the 

 velocity. 



The causes affecting the velocity of sound are (it is shown) 

 various. In an indefinite medium they are : — i. The tempera- 

 ture of the medium ; 2. The quantity of foreign substances 

 found in it, e.g., water-vapour ; 3. The pitch of the sound ; 4. 

 The direction and force of the wind ; 5. In solid bodies, the 

 direction of the sound in relation to the molecular structure. 



In sonorous tubes : — 



6. The diameter ; 7. The curvature ; 8. The rugosity of the 

 interior surface ; 9. The thickness of the walls. 



The action of the following additional causes is still dis- 

 puted : — 



I. The intensity of the sound ; 2. The length of course tra- 

 versed ; 3. The substance forming the tubes. 



There is complete disagreement between Regnault, Schroder, 

 Kundt, and Seebeck, as regards the influence of the pitch of 

 the sound. Regnault affirmed merely that an acute sound is 

 transmitted more easily, but not more rapidly, than a grave 

 sound ; Schroder finds that the velocity diminishes as the acute- 

 ness increases ; Kundt and Seebeck reach the contrary result. 

 Fresh experiments are required to settle this important question. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



A NEW supplemental charter having been granted to the Uni- 

 versity of London a few months since, on the joint application 

 of the Senate and of Convocation, empowering the Senate to 

 admit women t® graduate in its several faculties (Arts, Science, 

 Law, Medicine, and Music), on such conditions as the Senate, 

 with the concurrence of the Home Secretary, should deem ex- 

 pedient, the Senate lost no time in passing a resolution which 

 made all the existing regulations, relating not only to graduation, 

 but also to the various honours and rewards granted at the 

 several examinations open to female as well as to male candi- 

 dates. This resolution having been now approved by the Home 

 Secretary, female candidates will be admitted forthwith to the 

 matriculation examination ; and all such as have already passed 

 the general examination for women will be considered as having 

 matriculated, and will be admissible (after the required interval) 

 to the first degree examination in either of the faculties. Further, 

 with a view to the special encouragement of female candidates 

 desiring to go through a regular academical course, the trustees 

 of the Gilchrist Educational Trust have instituted two exhibitions, 

 one of 30/., the other of 20/., per annum, tenable for two year.-, 

 to the female candidates who pass highest in the honours division 

 at the matriculation examination ; and two exhibitions, one of 

 40/. , the other of 30/. , per annum, tenable for two years, to the 

 female candidates who pass highest at the first B.A. examination 

 (provided that they obtain in the first case two-thirds, and in the 

 second three-fifths, of the total number of marks), to assist them 

 in pursuing their studies at some collegiate institution approved 

 by the trustees ; with the further reward of a gold medal of the 

 value of 20/. (or of a book-prize of the same value) to the female 

 candidate who passes highest at the second B.A, examination, if 

 she obtains not less than two-thirds of the total number of 

 marks. These rewards are quite independent of those granted 



