Mr R. Adie's Account of Electrical Ejcperiments. 331 



electrical current is stated to have been passed through nearly 9 

 miles of earth with a very trifling loss. These results establish the 

 fact that the wet soil is by much the most perfect electrical conductor 

 known ; and as this is very far from being the case when wet earth or 

 water is tested in masses of definite section, I suspected that it was 

 the change in the sectional area of the conducting medium which 

 produced the efttct noted ; and it was to test this view that the fol- 

 lowing experiments were made. 



I provided a small galvanometer which could be used with facility 

 on the sea beach. At first I used a wire 300 yards long, but as I 

 found the effects disturbed by the wire getting wet, and thus form- 

 ing one of the plates of the couple, I preferred to use short wires, 

 well coated with shell lac, and kept quite dry. Two wires of 6 

 yards each were connected with the galvanometer, and attached, one 

 to a slip of zinc, the other to a slip of copper ; these formed a gal- 

 vanic couple capable of being adjusted with the utmost facility, with 

 the plates 12 yards apart, down to near contact. 



The galvanometer, screwed to a wooden spear, was fixed in a mea- 

 dow on the bank of a clear slow-running stream. When the plates 

 were thrust into the moist soil, as near together as they could be put 

 without touching, the indication was 12°, from which it did not change 

 on increasing the distance betwixt the plates to 12 yards. When 

 the pieces of zinc and copper were removed to the clear water of the 

 stream, the galvanometer rose to 38°, and kept its place steadily 

 without reference to the distance the electricity had to pass through 

 the water. The galvanometer was next carried to the sea beach, and 

 placed among some rough stones by the edge of a pool of sea water. 

 On thrusting the plates of the couple betwixt the stones into the in- 

 terstices which were filled with wet sand the deflection was 40° ; 

 and by varying the distances of the plates from near contact to 12 

 yards there was no change. Like results were obtained in fine sand 

 and in pools of sea water. In making these experiments the galva- 

 nometer cannot alway be got to the same point exactly, but by care- 

 ful repetitions, I satisfied myself that the distances betwixt the 

 plates had no connection with the variations noticed. The low de- 

 flection obtained in the moist earth is due to the small quantity of 

 water retained in the soil. 



The galvanometer, and its plates and wires, were carried home to 

 be excited by water in an earthenware vessel ; depth of water 1^ 

 inches. The plates, when near in contact, indicated 30° ; on gradu- 

 ally increasing their distance, the galvanometer indication fell, until 

 it stood at 10°, with an interval of 15 inches betwixt the plates. 

 Here, from a change of distance of only 15 inches, there is a loss of 

 more than two-thirds of tiie electricity ; while the same apparatus 

 excited 1)y water, resting, in connection with the wet materials of tlie 

 earth, shewed no loss of electricity when the distance of the plates 

 was increased 20 times as much. The depth of the water in the 



