446 SCIENTIFIC RECORD FOR 1884. 



Mercadier has presented to the French Academy the results of his re- 

 searches ou the laws of transverse vibration of elastic rods. The rods 

 were made of iron and steel, were rectangular in section, and were vi- 

 brated electro-magnetically, the vibrations being recorded ou the chrou- 

 ograph. He finds (1) that the vibrations are independent of the width, 

 (2) are directly proportional to the thickness (measured in the direction 

 of vibration), and (3) are inversely as the square of the length. Rep- 

 resenting these results by the formula w=^|^ Mercadier hais calculated 



the value of the coefficient k for steel from his measurements, and finds 

 it to be 5,329,503, while Poisson's formula gives 5,310,866. The mean 

 value, 5,320,134, being adopted, the author has calculated the number of 

 vibrations for different rods and compared them with those given by 

 experiment. The results are in very satisfactory accord, and show that 

 by means of this coefficient the dimensions of a rod required to give 

 any special pitch may be readily calculated. {G. R., xcviii, 803, 911, 

 March, April, 1884 ; J. Fhys., May, 1884, II, in, 189.) 



E. Weber has devised an electric siren, which is simple in principle 

 and which has many advantages. Its principal element is a disk, whose 

 periphery is divided into alternate segments of conducting and non- 

 conducting substance. Fifteen of these disks are placed upon an axis, 

 each being 4"° in diameter and sei^arated by 3""" from the others. The 

 first wheel has twenty-four metallic contacts, the second twenty-seven, 

 the third thirty, and so on up the gamut. Upon the edges of these 

 disks fifteen springs press, for the purpose of making electric contact 

 with the metallic segments, and so completing the circuit through the 

 axis. Each spring has its own cell of battery, the current passing- 

 through a telephone, in which is heard a note corresponding to the 

 number of interruptions made by the disk in the same circuit. The 

 siren may be driven by any form of power, but a small electric motor the 

 author finds very serviceable. A counter permits the number of rota- 

 tions to be determined. One curious result was obtained when four 

 disks were used, having the same number of teeth but differently spaced, 

 the metallic part being in the first -^2^ i" the second -j^, iu the third -j^, 

 and in the fourth -j\ of the insulating part. The sound produced by 

 the first, though feeble, was accompanied by its double octave ; by the 

 second, the tones 1:2:3:4:5:6:8; the third gave 1:2:3; and the 

 fourth, 1:2:4. Resultant tones were also very satisfactorily studied. 

 {J. Phys., December, 1884, II, in, 535.) 



Blaikley has continued his studies upon the phenomena connected 

 with the determination of the velocity of sound in air by means of the 

 nodal points in smooth brass tubes. He concludes (1) that these tubes 

 must speak with a pure tone; (2) that if partials are present the tubes 

 must be of such form as to have their proper tones in exact agreement 

 with the harmonic series ; (3) that the air-blast must not constrain the 

 pipe to speak any other tbau its natural resooant pitch j (4) that iu 



