3^4 



NATURE 



\_heb. 14, 1684 



was screwed. The wood was tuned by planing it away 

 at the top and bottom, while the air cavity was tuned by 

 enlarging the circular opening in front. In the later 

 researches the box stood on four feet made of india- 

 rubber tubing. The note of the fork so mounted was 

 very strong. At 40 cms. distance it would set the sound- 

 mill in motion. 



Dvorak's second apparatus, a " rotating resonator," 

 consists of a short cylindrical box, constructed of stiff 

 glazed paper, having four projections, shown in plan and 

 elevation in Fig. 3, each of which bears at its side a short 

 open tube of paper. It is, in fact, a resonator with four 

 openings, arranged so that it can be hung upon a silk 

 fibre. A fine needle projects also below to steady the 



motion during its rotation, which occurs whenever the 

 apparatus is brought near to the sounding-fork. For the 

 note g the dimensions were : diameter, 7 cms.; height, 

 3-6 cms. ; diameter of openings, o'6cm. 



The third apparatus is the "sound-radiometer" de- 

 scribed by Dvor.'ik before the Imperial A'iennese Academy 

 in 1881. Its cause of action is less readily explained, 

 though its construction is even more simple. Its form is 

 shown in Fig. 4 D; there being, as before, a light cross 

 of wood, pivoted by a glass cap upon a vertical needle. 

 To the four arms of the cross are cemented four pieces of 

 fine white card, about 008 cm. thick, perforated with 

 holes which are depressed conically at one side, and 

 raised at the other. These holes may be made by punch- 



/Uv 



M 



h C i 



ing the card upon a lead block with a steel perforating- 

 punch of the form shown in Fig. 5, a, the dimensions o:' 

 which are : ah = 0-38 cm. ; c d = 02 cm. The holes 

 should be from 06 to 065 cm. apart from one another. 

 When a card so perforated is held in front of the opening 

 of the resonant-box of the tuning-fork it is repelled if the 

 smaller ends of the conical holes are toward the box ; or 

 is attracted if the wider openings are toward the box. A 

 better, but less simple, way of perforating the cards is by 

 the use of the conical steel punch shown in Fig. 5, B, and 

 the matrix, Fig. 5, c. The angle of the cone is 55", and 

 the narrow projecting nose of steel is 0-3 cm. The card 

 should be damped, laid on the matrix c, and the hole 



pierced by two or three blows upon the die. Dr. Dvorak 

 prefers this plan : it throws up a high burr or edge behind 

 the conical hole, and such perforations are more effective. 

 The cards may be varnished, and are then mounted upon 

 the cross. The rotations are more rapid if the cards are 

 set on oblicjuely in the fashion shown in Fig. 4, E, the 

 burred sides being outwards. Cards with twenty-five 

 perforations so mounted rotate briskly when the "mill" 

 is set in front of the resonant-box. 



The fourth apparatus of Dvordk is called by him an 

 "acoustic anemometer." It is shown in Fig. 6. This is 

 merely a little " mill " of simple construction, the vanes 

 being small pieces of stiff paper or card slightly curved. 

 The sounding-box previously described is placed a little 

 way from it, and between them is held an ordinary Helm- 

 holtz's resonator, with its wide mouth, b, turned toward 

 the box, and its narrow opening, a, toward the mill. From 

 what has been previously said it will be understood that 

 the internal increase of pressure in the resonator at a has 

 the effect of driving a jet ot air gently against the sails of 

 the mill, which consequently rotates. Dr. Dvorak also 

 suggests that this two-aperture resonator may be replaced 

 by one having but one aperture, as shown at R, with its 



open side, /, turned towards the mill. This resonator is 

 formed of a glass ball cut a^-ay at one side and cemented 

 to a glass plate having a small hole at the centre. It may 

 be remarked that when the air ejected from the mouth of 

 this resonator is examined by the method of mixing 

 smoke with it, and then viewing it through slits cut in a 

 rotating disk, the currents are seen to consist of a series 

 of vortex-rings. 



A second kind of "acoustic anemometer" may be 

 made by taking a card pierced with too conical holes, 

 as previously described, and placing this between the 

 resonant-box and the " mill." The latter rotates in the 

 wind which passes through the conical holes. 



Space doe5 not admit of a comparison being drawn 

 between these instruments and those of Mayer, Mach, 

 and others, which are very closely akin in their design 

 and mode of action, interesting though such a comparison 

 might be. Nor can we here compare the a'ltion of these 

 instruments with the "phonomotor" with which Mr. 

 Edison literally accomplished the feat of talking a hole 

 through a deal board. But this remarkable machine was 

 a purely mechanical toy, which converted the vibrations 

 of the voice, by means of a very finely-cut ratchet-wheel, 

 into a motion of rotation round an axis. 



SiLv.'iNUS P. Thompson 



■ NOTES 



In the last week British science has su^tained a great loss in 

 the death of Mr. Thomas Cheiiery, the editor of the Times, 

 During his all too short reign the leading journal of Europe has 

 been in strict harmony with the real progress of humanity, 

 instead of being merelya chronicle of "politics" and "society," 

 and day by day it has been wonderful to watch uith what con- 

 tinuous well-balanced vigour and skill the general public has 

 been made interested in the victories achieved in the domains of 

 science, literature, and art, as only a daily journal can interest it. 



