30 THE ADDRESSES, LECTURES, ETC., OF 



important of these tests are carried into effect. It is unnecessary 

 for me to enlarge on the importance of electrical tests ; I would 

 only call to your mind that in the case of an Atlantic cable, a 

 single flaw a microscopic defect would vitiate the whole under- 

 taking. But I also hope to be able to prove to you that by a 

 proper system of electrical testing, the chances of such a flaw 

 remaining unobserved are infinitely small. 



G-ENEBAL LAWS. In dealing with the subject, we have to 

 operate chiefly with one of the forces in nature, that is the " elec- 

 tromotive force." We are taught, however, that the forces of 

 nature, such as heat, light, electricity, and chemical action, are 

 reducible to one and the same fundamental principle that is, 

 " mass in motion." If I take any weight, say one pound, and 

 raise it one foot high, I cause a tension between this substance 

 and the table, or the earth beneath it, which tension will call this 

 weight back to the table through the space of one foot, with a 

 force of one pound, and the power here represented is the foot- 

 pound or unit of force. In electrical science we have another 

 kind of tension, which is not gravity, but electro-motive force. 

 We have in each of these glass jars a porous jar containing proto- 

 sulphate of mercury. This proto-sulphate of mercury is composed 

 of sulphuric acid and oxide of mercury, and the oxide of mercury 

 of oxygen and metallic mercury. Inside this pot amidst proto- 

 sulphate of mercury is carbon, and outside the porous pot is zinc. 

 Now, zinc has a great 'affinity for oxygen, whereas carbon has. at 

 low temperatures, a very slight affinity for oxygen. The conse- 

 quence is that the zinc wants to combine with the oxygen and set 

 the mercury free. The sulphuric acid present is quite ready to 

 take up the oxide of zinc as soon as it is formed, and aids the 

 tendency of the zinc to separate the oxygen from the salt. A 

 tension is produced which results in chemical action and in motion 

 of the particles acted upon, which latter manifests itself either as 

 heat or, if the conditions admit of it, as electricity. The chief 

 condition necessary to produce the electric current consists of a 

 metallic connection between the carbon and the zinc, and it is 

 within this metallic connecting wire that the electromotive force 

 becomes manifest and applicable for our purposes. 



But it is quite permissible to represent electromotive force by 

 gravitation. I have here a diagram (Plate 2, Fig. 1) in which 



