PROBLEMS AND EXERCISES. 427 



5. I once tried to obtain an electric light by using a battery 

 of 3000 telegraph Daniell's cells in series, but without success. 

 Why did this enormous battery power fail for this purpose? 

 Could it have been made to give a light by any different arrange- 

 ment of the cells ? 



6. A battery of 2 Grove's cells, a galvanometer, and a little 

 electromagnetic engine, were connected in circuit. At first the 

 engine was loaded, so that it could only run slowly ; but when 

 the load was lightened it spun round at a tremendous speed. 

 But the faster the little engine worked the feebler was the 

 current indicated by the galvanometer. Explain this. 



7. A current of 9 ivebers worked an electric arc light, and on 

 measuring the difference of potential between the two carbons 

 by an electrometer it was found to be 140 volts. What was 

 the amount of horse-power absorbed in this lamp ? 



Ans. i'66 H.-P. 



8. You have a lathe in your workshop which requires power 

 to turn it. There is a stream of water tumbling down the hill- 

 side, two miles off, with power enough to turn twenty lathes. 

 How can you bring this power to the place where you want to 

 use it ? 



9. What is the use of the electro-dynamometer ? Assum- 

 ing that the moment of the force acting on the movable coil of 

 the electro-dynamometer is proportional to the product of the 

 strengths of the currents in the two coils, show that the work 

 performed by a current is really measured by the electro- 

 dynamometer of Marcel Deprez, in which one set of coils has a 

 very small resistance and the other a very high resistance (con- 

 sisting of many turns of fine wire), the latter being arranged as 

 a shunt to the lamp, motor, or other instrument, in which the 

 work to be measured is being done, the former having the 

 whole current passed through it. 



QUESTIONS ON CHAPTER VIII. 



I. A strong battery - current is sent, for a few moments, 

 through a bar made of a piece of antimony soldered to a piece 

 of bismuth. The batteiy is then disconnected from the wires 

 and they are joined to a galvanometer which shows a deflection. 

 Explain this phenomenon. 



