Mr. R. H. M. Bosanquet on Practical Electricity. 257 



to such a source is negligible, so long as there is acid in the 

 solution. 



A key to the nature of the phenomenon may be found by con- 

 sidering what happens when the cells are being exhausted. If 

 a current of 10 amperes, such as I have used for charging, be 

 demanded from the accumulators, the tension falls off. If the 

 demand continues, the cell becomes exhausted. If we let it 

 stand, it will recover itself, just as is the case with a Leclanche 

 cell, for instance*. 



Now the simplest way of accounting for this, as well as for 

 the rise of tension in charging, is to suppose that the chemical 

 action, in which the storage consists, does not actually reside 

 on the surface, but penetrates to a certain extent into the sub- 

 jacent layers of the mass. It is easily conceivable that such 

 an action should be only capable of transference through the 

 mass at a certain rate; that when too large a current is de- 

 manded from the cell, the chemical change does not return 

 from the interior layers to the surface with sufficient rapidity 

 to maintain the current; and that when, on the other hand, 

 a high-charging current is employed, it cannot get away fast 

 enough into the substance from the surface, and is accumu- 

 lated there and forced to a higher intensity. It is simplest to 

 assume that this heaping-up is directly proportional to the 

 current which causes it. 



So far as the excitation of the magnets goes, the method of 

 balanced charging is more economical than charging in series; 

 but as a double current passes through the armature, there is 

 some considerable waste in heating it. 



The electromagnetic attraction of the machine is in this case 

 roughly double that of charging in series (assuming for the 

 moment that the magnetization is proportional to the current). 

 This gives the engine a better hold of its work in the case con- 

 sidered without making the load so very heavy as when the 

 double current passes through both magnets and armature. 



The lead of the dynamo machine, or the angle at which 

 the brushes have to be set forward on the commutator, is about 

 double what it is under other circumstances. This is no doubt 

 due to the exalted magnetism of the armature due to the double 

 current taking longer than usual to be affected by the compa- 

 ratively weak field-magnets through which only a single cur- 

 rent is passing. This appears to point to the reduction of the 



* So, if we try to drive an arc light, we can get for a short time a cur- 

 rent of more than 20 amperes and a good light ; but the battery soon 

 begins to be exhausted, and a most curious effect sets in : the alternations 

 of exhaustion and recovery succeed each other with great rapidity, and 

 the carbons begin to chatter in a most extraordinary way. 



Phil. Mag. S. 5. Vol. 14. No. 88. Oct. 1882. S 



