December 14, 18S8.] 



SCIENCE. 



283 



energy ; and it is plain tliat tliere is no possibility of very much im- 

 provement in the efTiciency of conversion. The regulation of the 

 electric motor is accomplished in some cases by artiticial means ; 

 but in the most approved type of electric motors the regulation is 

 in the machine itself, and depends upon an electrical principle as 

 interesting and wonderful as any fact in the whole range of the 

 science. Comparatively speaking, it is this. Dynamos and motors 

 are interchangeable : when we put mechanical power to the ma- 

 chine, and make thereby electrical power for further use, we call 

 the apparatus a dynamo-electric machine ; if we reverse the pro- 

 cess, however, and bring forth mechanical power by putting a cur- 



motor take up its increased load. The chinge in the electrical con- 

 dition is practically instantaneous, so that no change in the speed 

 of the motor is perceptible within the moderate changes in the 

 work which it is doing. With a nia.\imum change in the load 

 which the motor is carrying, the variation of the speed of the motor 

 is within two per cent of its normal speed. Such close regulation, 

 it is needless to say, is all that can be desired in any machine. The 

 motors of the Thomson-Houston Electric Company, like all the other 

 apparatus of that system, have been widely introduced, and are in 

 use in many printing-offices, machine-shops, and small factories. 

 They are made in sizes to furnish from one-half to seventy-five 



rent of electricity through a machine, it becomes an electric motor. 

 Every motor, while receiving the electric current and doing me- 

 chanical work, is at the same time retaining to some degree its 

 character as a dynamo-machine ; for it is generating a current 

 directly in opposition to the current which causes it to run. This 

 opposing current serves as a resistance to the current supplied to 

 the motor, and varies with the speed of the motor. 



Now, in the Thomson-Houston motor, which is here illustrated, 

 if the speed has a tendency to slacken, this opposing current neces- 

 sarily becomes less, and thus admits to the motor more of the supply- 

 current, which, in its turn, brings back the speed of the motor to 

 its normal speed. The working-power of the motor increases as 

 the square of the current, so that a slight increase in the current (due 

 to the momentary slackening of the speed) is sufficient to make the 



horse-power. The larger sizes are, of course, especially valuable 

 for the transmission of power from waterfalls whose distance un- 

 fits their utilization by the old methods. Factories may be placed 

 some distance from the water-supply, and get power over the wires. 



In addition to the stationan,- motor, the Thomson-Houston Com- 

 pany have developed extensively those applicable to electric street- 

 cars, having in operation twenty-three electric roads, and eleven in 

 process of construction. 



The accompanying illustration represents two Thomson-Hous- 

 ton motors in the exhibition of the Board of Trade at New Bedford, 

 >rass. These motors are supplied by current from the central 

 electric-lighting station of the New Bedford Gas Company, and are 

 furnishing to the shafting all the power required in the various ex- 

 hibits at this fair. 



