January, 1922. 



SCIBNTIP'IC AGRICULTURE. 



147 



Lieht 



gntnmg 



Rodi 



W. H. Day*, Secretary and Manager, Sliiun Manufacturing Co. of Canada, Ltd. 



No article of merit and usefulness has 

 suffered more from unscrupulous methods 

 than has the Lightning Rod. Perhaps none 

 is entitled to greater confidence. Certainly 

 none has a more solid foundation in scien- 

 ce. 



. Protection against lightning is an elec- 

 trical problem. Pew of the stories of 

 science are of more absorbing interest 

 than that of Franklin's discovery that 

 lightning is a discharge of electricity and 

 may be rendered innocuous by the light- 

 ning rod. 



For many centuries development in elec- 

 tricity \vas very slow. Static charges pro- 

 duced by friction were first discovered by 

 Thales, 640 B. C. in a piece of amber, 

 Greek electron, hence the word electricity. 

 They were mentioned again by Pliny in 

 70 A. D. but not till Dr. Gilbert's time, 

 1600 A. D., was any extended and concen- 

 trated investigation devoted to the sub- 

 ject. Thi_s English physician and physicist 

 discovered that not only amber but all 

 solids, if properly manipulated can be 

 electrified by friction. Forty years later 

 Otto von Guericke of Magdeburg invented 

 the first ''electrical machine", consisting 

 of a sulphur ball mounted on an axis and 

 turned by a crank, the friction being ap- 

 plied by the hands rubbing on the ball. 

 Considerable charges could be produced 

 by it. All the leading scientists of the day 

 experimented with it and improved forms, 

 and at least two suspected the identity of 

 the electric spark and the lightning dis-^ 

 charge, viz, Francis Hauksbee mildly in 

 1709 and Stephen Gray emphatically in 

 1720. Twenty five years later the Leyden 

 jar was discovered by which large charges 

 could be accumulated and violent flashes 

 produced. This was soon incorporated in 

 the electric machine. Experimenting 

 spread even to the "New World" where 

 on July 4th, 1752, Franklin, by means of 

 a kite sent up in a thunderstorm, proved 

 directly and absolutely that lightning is 

 produced by a discharge of electricity. 



Franklin's scientific knowledge was not 

 gained in University but by his own pri- 

 vate study and was marked by his out- 

 standing characteristic of being practical. 

 Consequently, the discovery of the rela- 

 tion between lightning and electricity led 

 at once to his applying three of the laws 

 of this science in an endeavour to control 

 lightning. They are : 



* Formerly Professor of Physics at the 

 Ontario Agricultural College. ' 



steeple -jacks at work ixrotecting' Northwest 

 Tower, New Centre Block, Parliament Build- 

 ings, Ottawa. 



1. Electricity is transmitted most easily 

 along metals. 



2. Electricity leaks off points (disco- 

 vered by Franklin) . 



3. When two opposite charges of elec- 

 tricity exist they attract each other if 



