in Magnetism and Electricity. 85 



and four of the same cells, in series, would melt two, three, and 

 four times the length of wire of the same diameter that one cell 

 would melt. Two, three, and four of the same cells, arranged 

 for quantity, would melt a 2-, 3-, and 4-fold strand of the same 

 wire and of the same length that one cell would melt. 



101. I have chosen to adopt the melting of a given quantity 

 of wire as the measure of the magnitude of the current from the 

 electromotors above mentioned, because I have not yet found any 

 other method which can at all compare with it in expressing 

 easily and without ambiguity the associated properties of quan- 

 tity and intensity, especially when dealing with currents of such 

 magnitude as those evolved from the 5- and 10-inch machines. 

 By comparing the absolute quantity of wire melted by a standard 

 Grove's cell with that melted by the machines, under the differ- 

 ent conditions to which attention will be directed, a tolerably 

 good idea of the magnitude of the forces brought into operation 

 may be obtained. 



102. The other electromotors employed in these experiments 

 were: — (5) a weakly charged battery of thirty-three DanielPs cells, 

 such as are commonly used by the Electric Telegraph Company 

 for signalling-purposes. This battery was arranged in three 

 troughs of eleven cells each. (6) A large well-excited DanielPs 

 cell ; and, lastly, a single pair of zinc and platinum plates excited 

 by dilute sulphuric acid, spec. grav. 1*110. 



103. The building which contained the various electromotors 

 is situated about 100 feet from the edge of the basin of a navi- 

 gable canal, in which most of the following experiments on the 

 electric condition of the earth have been made. Connexion 

 between the various electromotors and the electrodes and other 

 conductors submerged in the canal was made by means of two 

 lengths of copper-wire rope, each 140 feet in length and nearly 

 half an inch in diameter. These wire-rope connexions consisted 

 of seven thick copper wires twisted togther, and were supported 

 through the air and insulated from one another by means of a 

 pole fixed upon the bank of the canal. 



104. The conductors to be submerged, which also served the 

 purpose of electrodes, consisted of two lengths of naked copper- 

 wire rope, each 169 feet long, and of exactly the same diameter 

 and construction as those used for the aerial connexions (103). 



105. Two other lengths of copper rope., of the same length 

 and diameter as the preceding (104), were each carefully wrapped 

 with a double covering of linen tape, in the manner adopted for 

 insulating the coils of the large electromagnet of the 10-inch 

 machine (68). These two lengths of tape-covered copper rope 

 were laid parallel with each other and then bound tightly 

 together with string wound round them in a spiral direction, so 



