14S 



SCIENTIFIC AGRICULTURE. 



January, 1922. 



Strong enough to break through the inter- 

 vening space, a violent spark occurs, but 

 if aUowed to leak off points, these charges 

 neutralize quietly without a spark. 



Accordingly in the summer of 1752, 

 within a few weeks of his great discovery, 

 he erected a set of lightning rods on his 

 own house, constructed of iron, with a 

 sharp point at the top and the bottom 

 extending five feet into the ground. 



f 



Attaching cable to ventilating shaft, New Centre 

 Block, Parliament Buildings, Ottawa. 



To the lightning rod he attached a 

 device that was connected with two bells 

 which rang when a current was passing 

 along the rod. Some of the observations 

 are best told in Franklin's own words : 

 *'I found the bells rang sometimes when 

 there was no lightning or thunder, but on- 

 ly a dark cloud over tlie rod; tluit some- 

 times, after a fla.sh of lightning, they 

 would .suddenly st^)p, and at other times 

 when they had not rung before, they 

 would, after a flash, suddenly l)egin to 



ring; that the electricity was sometimes 

 very faint, so that when a small spark was 

 obtained, another could not be got for 

 some time after. At other times, the 

 sparks would follow extremely quick- 

 1}'; and once I had a continual stream 

 from bell to bell, the size of a crow-quill". 



Europe was prepared for the news of 

 Franklin's discovery. In 1751 a manus- 

 cript entitled "New Experiments and 

 Observations in Electricity, made at Phi- 

 ladelphia, in America", was sent by him 

 to a friend in London, who realizing the 

 importance of the paper had it printed in 

 pamphlet form. It set forth Franklin's 

 conviction that lightning was an electric 

 discharge. The pamphlet was sent to men 

 of science throughout Europe. One of 

 them, M. Delibard. erected an iron rod 

 100 feet high on a tower in his garden, and 

 during a thunderstorm on May 10th 1752, 

 nearly two months prior to Franklin's kite 

 experiment, he was rewarded by finding 

 electric sparks given off at the foot of the 

 rod. Three days later this was reported to 

 the Academic des Sciences of Paris, at a 

 special meeting called for the pui"pose. The 

 experiment was weak in one respect — the 

 observers were inexperienced. The occur- 

 rence really took place in M. Delibard 's 

 absence and Avas observed by one of his 

 servants, who summoned the prior of the 

 village, followed by other inhabitants 

 equalh' inexperienced. Hence, though they 

 all Avitnessed the display there was some 

 hesitancy on the part of scientists to ac- 

 cept the result as conclusive. But when 

 Franklin "s report of his kite experiment 

 arrived, all doubt was swept away and 

 Franklin himself heralded as one of the 

 most noted scientists of the world, in re- 

 cognition of which he was elected to hon- 

 orary membership in most of the scientific 

 societies of Europe. 



For 150 years the history of the light- 

 ning rod was a checkered one. Its first 

 blow was in France, where it was attacked 

 by Abbe Nollet, their most noted electri- 

 cian, and a man in high favour at the 

 French court. He used his great influence 

 in all quarters, and the clergy generally in 

 France, Italy and other Catholic countries 

 opposed tlie "heretical rods". In England 

 there was a strong faction against the use 

 of rods. Gradually, however, they gained 



