216 POPULAR LECTURES .LVD ADDRESSES. 



the other hand, to supply the counter-channels by 

 which pure science may exercise its perennially 

 beneficial influence on practice. 



Time would fail me to give any such statement 

 as would include a large part of the subject upon 

 which I have touched ; I shall therefore confine 

 myself strictly to one point, and that is the science 

 of terrestrial electricity. I have advisedly, not 

 thoughtlessly, used the expression " terrestrial 

 electricity." It is not an expression we are accus- 

 tomed to. We are accustomed to ".terrestrial 

 magnetism ; " we are accustomed to " atmospheric 

 electricity." The electric telegraph forces us to 

 combine our ideas with reference to terrestrial 

 magnetism and atmospheric electricity. We must 

 look upon the earth and the air as a whole a 

 globe of earth and air and consider its electricity, 

 whether at rest or in motion. Then, as to terres- 

 trial magnetism, of what its relation may be to 

 perceptible electric manifestations we at present 

 know nothing. You all know that the earth acts 

 as a great magnet. Dr. Gilbert, of Colchester 

 made that clear nearly 300 years ago ; but how 



