INDUCTION-BALANCE. 



INTEROCEANIO CANAL. 608 



ide. The sonometer is capable, therefore, of 

 measuring the intensity of sound, as the sound 

 increases in the exact ratio of the distance 

 from the neutral point, which distance is indi- 

 cated on thu graduated rod. 



When the secondary currents are in equilib- 

 rium, if a piece of metal is placed in either of 

 the primary coils of an induction-balance, the 

 balance is disturbed, and a sound can bo imme- 

 diately heard on the telephone. Bringing then 

 a sonometer connected with the induction-bal- 

 ance into circuit by means of a circuit-changing 

 key, and moving the sliding coil from the neu- 

 tral position to such a distance that the same 

 degree of sound is heard as on the telephone 

 of the induction-balance, so that by moving 

 the key up or down and connecting either tel- 

 ephone with the circuit, no difference in the 

 intensity of the sound can be detected ; then 

 the exact amount of the disturbance caused 

 by the piece of metal is measured on the grad- 

 uated scale of the sonometer. Experiments 

 show that the sounds produced by the same 

 piece of metal remain constant, but that differ- 

 ent metals and different masses of the same 

 metal produce different sounds, as also the 

 same piece of metal in different molecular con- 

 ditions. As every metal has its own sound- 

 measure, which is always the same for equal 

 weights and coincides with that of no other 

 metal, the sonometer may be employed in de- 

 tecting the nature of samples of metals of un- 

 known character. Standard gold gives a dif- 

 ferent degree of sound from any of the alloys 

 used in imitating coin, so that counterfeit 

 pieces can bo instantly detected by the aid of 

 the sonometer. "When two genuine coins are 

 placed one in each primary coil, the equilibrium 

 is maintained ; but with a debased coin in one 

 and a standard coin in the other of the coils, 

 the telephone will give forth a sound. The 

 sensitiveness of the instrument is so keen that 

 when a freshly coined shilling is balanced 

 against one which is the least worn, or even 

 rubbed in the hand, a sound is produced by 

 the microphone. Experiments made upon 

 various alloys with the induction-balance and 

 sonometer in the British Mint, by Chandler 

 Roberts, proved the instrument to be so ex- 

 tremely sensitive that it may be of practical 

 use to the assayer. The slightest alloy of sil- 

 ver in gold or of gold in silver was indicated 

 by the sonometer. 



The sound-measuring part of the instrument 

 has been employed successfully by Dr. B. W. 

 Richardson in testing the hearing powers. 

 When employed for this purpose, the sonome- 

 ter is called the audiometer. The graduated 

 bar is divided into two hundred parts. It was 

 found that a person who hears the sound per- 

 fectly well when the coil is in a certain posi- 

 tion may not be able to detect the slightest 

 trace of sound when it is reduced by moving 

 the coil only two degrees toward the center. 

 Right-handed people hear best with the right 

 ear, and left-handed people with the left ear. 



When tho barometer stood at thirty inches 

 Dr. Richardson waa able to detect sound* when 

 tho coil wus removed the minutest distance 

 from tho zero, but could not hear within two 

 degrees of the zero when the mercury waa low- 

 er. Deaf persons can decide through tho au- 

 diometer upon tho value of different kinds of 

 artificial drums. Dr. Richardson concludes 

 that tho best material for artificial drums is 

 fine gold. In one case, where tho natural tym- 

 panum had been destroyed, tho introduction 

 of a gold drum had the effect to improve the 

 hearing by fifty of the two hundred degrees 

 on tho measured scale. The audiometer ena- 

 bles the aurist to decide, also, whether a case 

 of partial deafness is caused by a defect in the 

 ear itself, or whether it is throat-deafness 

 caused by a closure of the Eustachian tube. 

 Tho audiometer can not fail to prove of high 

 value in determining the qualifications of per- 

 sons for positions on railways, for example, 

 where great acuteness of hearing is required. 



INTEROCEANIO CANAL, THE. The In- 

 ternational Congress for the study of tho In- 

 teroceanic Canal met at Paris, in the rooms of 

 the Geographical Society, May 15, 1879. The 

 Congress was opened by Baron de la Ronciere 

 de Noury. Count Ferdinand de Lesseps waa 

 elected President ; Commodores Ammen, of the 

 United States Navy, and Likhatscheff, of the 

 Russian Navy, Colonel of Engineers Sir John 

 Stokes, of the British Army, and Cristoforo 

 Negri, Italian Minister Plenipotentiary, were 

 chosen Vice-Presidents ; Henri Bionne, Gen- 

 eral Secretary ; and Boissevin, H. Capitaino, J. 

 Jackson, and Charles Wiener, Secretaries. Five 

 committees were appointed : one on statistics, 

 to estimate the probable traffic of the canal and 

 the tonnage which would pass through it, as 

 well as the probable share of each nation in 

 the traffic ; the second on economical and com- 

 mercial questions, which should consider the 

 advantages and saving in the costs of transpor- 

 tation which would accrue to each nation from 

 tho use of the canal, and the influence which 

 it would exercise upon the commerce of each 

 country through opening new markets and in- 

 creasing trade and industry ; the third on navi- 

 gation, to consider the class of vessels which 

 would be likely to frequent the canal and the 

 adaptation of the canal to the requirements of 

 navigation and commerce, the influence which 

 the canal would have on naval architecture, 

 the influence of the prevailing winds and ocean- 

 currents on the frequentation of the canal, the 

 meteorological and climatic conditions of the 

 Isthmus, and the influence of these conditions 

 upon the conservation of the canal ; a fourth 

 on technical questions, for the technical exami- 

 nation of the different routes, the estimation 

 of the cost of construction, the annual cost of 

 working, the annual cost of maintenance and 

 repairs, the facility and security of navigation 

 in the canal and harbor approaches ; the fifth 

 on ways and means, to estimate from the prob- 

 able traffic the probable gross revenue, and to 



