Feb. 14, 1884] 



NA TURE 



363 



A list of the fishes known to occur in the Arctic Ocean, 

 north of Behring's Straits, by Tarleton H. Bean, is 

 appended. The list is based exclusively upon specimens in 

 the United States National Museum, and is acknowledged 

 to be incomplete; it only contains twenty-one species, 

 eight others being added as "properly belonging to the 

 fauna.' No details beyond the localities where found are 

 given. 



SOUND-MILLS 



AFTER the notable researches of Crookes on radia- 

 tion, which culminated in the discovery of the 

 radiometer, or light-mill, it was a natural transition of 

 thought which suggested to several minds almost simul- 

 taneously the possibility of devising an apparatus which 

 should rotate under the influence of sound-waves as does 

 the radiometer under the influence of the rays of light 

 and heat. Such instruments were indeed devised inde- 

 pendently about six years ago by Lord Rayleigh, by Prof. 

 Alfred M. Mayer of Hoboken, by Mr. Edison, the well- 

 known inventor, by Prof. Mach of Prague, by Dr. A. 

 Haberditzel of Vienna, and by Prof. V. Dvorak of the 

 University of Agram (in Croatia). These researches, 

 though of great scientific interest, have been somewhat 

 overlooked in the rus'i of scientific inventions during the 

 intervening years. During the course of the past year. 



however, Dr. Dvorak has given to the world, in the pages 

 of the Zcitschrift der Iiistrumentenkiinde (vol. iii. Heft 4), 

 a detailed account of his experiments, together with 

 figures of various pieces of apparatus hitherto undescribed. 

 We propose to give a resume of the principal points of 

 Dvor/ik's researches. 



Four kinds of sound-mills are described by Dvordk, 

 two of them depending on the repulsion of resonant-boxes 

 or cases, and two others on different principles. 



The first of these instruments is depicted in Fig. i, 

 and consists of a light wooden cross, balanced on a needle 

 point, carrying four light resonators made of gla=s. These 

 resonators are hollow balls of 44 cms. diameter, with an 

 opening of 04 cm. at one side. They respond to the 

 note_£f' ( = 392 vibrations). When the note,§"' is forcibly 

 sounded by an appropriate tuning-fork, the air in each of 

 the resonators vibrates in response, and the apparatus 

 begins to rotate. As a resonator will respond when placed 

 in any position with respect to the source of sound, it is 

 clear that one single resonator properly balanced should 

 rotate ; and this is found to be the case, though, naturally, 

 the action is more certain with four resonators than with 

 one. 



Before proceeding to the other forms of sound-mill 

 devised by Dvorak, it miy be well to explain briefly the 

 cause of the phenomenon, and to describe Dvorak's 



particular method of exciting the appropriate sound 

 Dvordk has pointed out, as indeed has been done else- 

 where both by Lord Rayleigh and by Prof. A. M. Mayer, 

 that, when sounds of great intensity are produced, the 

 calculations which are usually only carried to the first 

 order of approximation cease to be adequate, because 

 now the amplitude of motion of the particles in the 

 sound-wave is not infinitely small as compared with the 

 lengths of the sound-waves themselves. Mathematical 

 analysis shows that under these circumstances the mean 

 of the pressures in the condensed part and in the rarefied 

 part of the sound-wave is no longer equal to the undis- 

 turbed atmospheric pressure, but is always greater. 

 Consequently at all nodal points in the vibrations of the air 

 in tubes or resonant-boxes the pressure of the air is greater 

 than elsewhere ; and therefore any resonator closed at 

 one side and open at the other is urged along bodily 

 by the slight internal excess of pressure on the closed 

 end. The apparatus. Fig. i, therefore rotates by reaction, 

 in the same way as Hero's primitive steam-engine rotated, 

 though the reaction is due to a different cause. 



To produce vibrations of sufficient intensity Dr. 

 Dvorak employs heavy tuning-forks mounted on rj- 

 sonant-cases, and excited electrically. For this purpose 

 he places between the prongs of the fork an electromagnet 

 constructed on the following plan. Two plates of iron 

 separated by a sheet of paper are used as a core. They 



are cut of such a breadth as to lie between the prongs 

 without touching them. This core is overwound with 

 insulated copper wire, as shown at E, Fig. 2, and the 

 electromagnet is then mounted by a bent piece of wood, 

 abc, upon the sounding-box, K, of the fork. The wires 

 are connected in a circuit with a battery, and with the . 

 electromagnet of a self-exciting tuning-fork of the same 

 note. Dr. Dvordk is extremely particular about the 

 arrangements of the resonant-boxes of bis tuning-forks. 

 They must not touch the table, the arm a h c being 

 clipped at about the point /•■ in a firm support. Moreover 

 the resonant-boxes themselves require to be specially 

 tuned, for all are not equally good. Dr. Dvordk points 

 out that, beside the tone of the fork, and the tone of the 

 air column in the cavity of the box, there is also a tone 

 proper to the wood of the box itself, which in most of the 

 forks used in acoustic researches is too base, the wooden 

 walls being too thin. To hear this tone the prongs of the 

 fork should be damped by sticking a cork between them, 

 and the cavity should be filled with cotton-wool, while the 

 wooden box is gently struck with the knuckle or with a 

 corkhanmier. It is important that the wood-tone should 

 be tuned up to coincidence with the tone of the fork and 

 with that of the air in the cavity. Dr. Dvordk himself 

 used the box depicted further on in Fig. 6, in which 

 drawing f is the socket into which the stem of the fork 



