August 29, 1902.] 



SCIENCE. 



339 



carry the case and fixed discs around with 

 it, which being prevented by a spring bal- 

 ance attached to a radical projection from 

 the case, the moment is readily obtained. 



Various interesting facts developed them- 

 selves in the use of this instrument and 

 experiments in progress by a large electric 

 company confirm the theoretical formulas 

 for the moment by which the dynamometer 

 can be correctly designed. 



The horse-power absorbed is adjustable 

 by varying the amount of water retained 

 in the case, which is easily done. 



A specially interesting thing was the ef- 

 fect of handling the water entering the 

 dynamometer; let the hands be wiped (not 

 washed) ever so carefully, after handling 

 the ordinary slightly greasy tools and parts 

 of machinery, and held under the stream 

 of entering water, there would be an im- 

 mediate reduction of the moment by about 

 ten per cent. 



As an illustration of the effectiveness of 

 this dynamometer it is suiHcient to say that 

 the two revolving disks two feet in diameter 

 absorbed the whole one hundred and ninety 

 horse-power of a turbine of twice their 

 diameter. 



The Dynamoplione, a new Dynamometer : 

 J. BuRKiTT Webb, Stevens Institute, Ho- 

 boken, N. J. 



The djTiamophone is a new form of trans- 

 mission dynamometer. In a large number 

 of cases when power is to be measured me- 

 chanically it is done by observing the extent 

 to which some elastic substance yields and 

 deducing therefrom the stress caused in it 

 by the transmission of the power to be 

 measured. Power is transmitted mechan- 

 ically mainly by rotating mechanism, and 

 such transmission is invariably accompa- 

 nied by a change of phase, that is, the driv- 

 en part lags behind the part that drives. The 

 simplest and most common example of this 

 is an ordinary line of shafting in which we 



have only to determine the torque and 

 number of revolutions to find by their pro- 

 duct the energy transmitted. About 1880 

 I was working under the direction of Pro- 

 fessor Helmholtz upon the change of phase 

 in an alternating current in a circuit con- 

 taining an electrolytic cell as well as 

 resistance, capacity and inductance, and in- 

 vented an apparatus (of which the dynam- 

 ophone is a modification) for making and 

 measuring a difference of phase. After my 

 return to the United States this remained 

 packed away, until recently the problem of 

 measuring the power transmitted to a ma- 

 rine propeller presented itself. The motor 

 being an improved form of turbine, the or- 

 dinary steam-engine indicator could not be 

 used, and so a portion of the shaft was pre- 

 pared for the purpose and exactly calibra- 

 ted by ascertaining the torque required to 

 twist it from one degree up to ten degrees. 

 To measure the twist of the shaft when re- 

 volving from 400 to 700 times a minute and 

 transmitting from 100 to 2,300 horse power 

 the dynamophone was successfully employ- 

 ed and in the following manner: 



Upon each end of the calibrated length of 

 shaft a wheel twelve inches in diameter was 

 mounted, having 36 teeth. In front of 

 each wheel a telephone magnet and coil was 

 supported, the axes of the magnets at right 

 angles to the shaft. The ordinary vibra- 

 ting disks of the telephones were thus re- 

 placed by the toothed wheels, which thus in- 

 duced in the telephone circuits a musical 

 tone the strength and quality of which 

 could be adjusted by screws which varied 

 the distance of the magnets from the wheels. 

 These telephones were further mounted so 

 that they could be revolved about the cen- 

 ter of the shaft with a scale and microscope 

 to measure their angular position, and such 

 a revolution must of course change the 

 phase of the tone vibrations. To compare 

 the phases of the two telephones, their cir- 

 cuits were connected in series with one (or 



