IOO DYNAMO-ELECTRIC MACHINES. 



use to which they maybe applied, varies greatly. This not so much, 

 perhaps, where the machine to be driven is a long distance from the 

 driver, as where they are used for doing work very irregular in quan- 

 tity. When the distance is great a considerable portion of the power 

 will always be absorbed in overcoming the resistance of the conduc- 

 tor. In that case, the work to be done in overcoming distance will 

 perhaps form a very great portion of the whole. In the case men- 

 tioned of Deprez's machine, in use at the exhibition at Munich, 

 where it worked a small rotary pump, the power given out after 

 traversing 36 miles, was estimated as low as 25 and as high as 37 

 per cent, of that sent through the dynamo at Meisbach. On the 

 other hand, where the work to be done is not far from the machine 

 supplying the current, there may be a demand for the maximum 

 at one moment, and at the next it may be reduced to a minimum. 

 Perhaps no conditions in this case would vary so much as those in 

 which a dynamo is used for hoisting purposes, either in ordinary 

 hoists, or lilting weights with a crane. The weight to be lifted, 

 under either circumstance, if it was as great as possible, would absorb 

 the whole of the power supplied whilst suspended. When the load 

 was delivered and the crane or hoist was descending empty, the 

 minimum only of which the machine was capable would be absorbed. 

 So with any other purpose to which the machines might be applied. 

 On some of the sugar farms in France, dynamos have been largely 

 used successfully, in ploughing and otherwise preparing the land for 

 the cultivation of beet. Four men, two dynamo machines, identical 

 in construction, with an expenditure of 25 H. P., plough an average 

 of 2 x / 2 acres per hour, turning a fallow of ten inches in depth. The 

 average distance of the dynamos which do the ploughing from those 

 which supply the current to them, is about 950 yards. The work 

 accomplished under these circumstances is very nearly uniform. 

 There would be very little waste of energy in consequence. 



When dynamos are used for electric lighting purposes, the 

 extremes vary between 1 lamp and 60 the highest number of arc 

 lamps yet lighted by one machine. If all lamps were the same resis- 

 tance, the work done in every case would be in the ratio of the number 

 employed. No makers, however, have produced lamps that do not 

 vary in resistance arid they vary as much as 3 to 1. The work done 

 then, in any one case, will be found by multiplying the resistance of 



