PHYSICS OF THE GLOBE. 1ST 



lightning by a given rod a circle whose radius is If times 

 the height of the rod above the building. 



An excellent paper on Lightning-conductors was read 

 before the British Association, by Mr. R. Anderson. He 

 states that so slow has been the march of progress since the 

 days of Benjamin Franklin, that lightning-conductors are 

 still wanting on at least half, and perhaps two thirds, of all 

 the public buildings, and on 95 per cent, of all the private 

 houses in Great Britain. The terrible losses occasioned by 

 lightning are due to three sources of neglect: first, not pro- 

 viding any lightning-rods at all ; second, not placing them in 

 the right position ; third, not having them regularly tested, 

 so as to ascertain their constant efficiency. Lightning-con- 

 ductors, he says, ought to be tested at least once a year. 

 Between three and four thousand pounds sterling were spent 

 in protecting the Houses of Parliament some twenty years 

 ago. Since that time they have never been tested, and there 

 is no guarantee whatever that a discharge of lightning may 

 not at any time fall upon the Queen's throne. The testing 

 should take place at regular intervals. 



The wonderful sensitiveness of Bell's telephone such that 

 it responds to induced currents of the strength of only the 

 one thousand-millionth part of a C. G. S. unit, or less gives 

 it great importance as an instrument of research in relation 

 to atmospheric electricity and terrestrial ground -currents. 

 Some observations made in Providence, II. I., have led to 

 the conclusion that by it the existence of a thunder-storm 

 may be detected when otherwise altogether invisible at the 

 station. 



The Edison microphone has even been applied successfully 

 to the observation of subterranean sounds produced by vol- 

 canic actions, and may evidently be further applied to what- 

 ever goes on in the earth and ocean. 



Mr. Henry Goldmark, of the Laboratory of Harvard Col- 

 lege, contributes observations upon the Effect of Temper- 

 ature on Atmospheric Electricity. He used Sir William 

 Thomson's water-dropping apparatus and his quadrant elec- 

 trometer. The observations were made in a room whose 

 temperature could be varied as desired. He found, first, that 

 even a very considerable change of temperature does not 

 have any great or marked effect upon the electric potential 



