DISCOVERT BY EXAMINING PECULIAR TRUTHS. 495 



crystals of zinc obtained by electro-deposition sometimes 

 emit light spontaneously, and also when struck. I have 

 several times tried to obtain this effect, without suc- 

 cess ; and if it is a fact, it is worthy of investigation. 

 I have also been informed that a voltaic circuit completed 

 through a permanent steel magnet at one of its poles 

 yields a much larger spark than when similarly completed 

 through a bar of unmagnetised steel. The statements, 

 that the solar spectrum yields a single line, slightly more 

 refrangible than those of sodium, and belonging to a 

 new elementary body ; that the upper region of the sun's 

 corona gives a green line belonging to a new substance 

 of less specific gravity than hydrogen ; and that the same 

 substance yields three green lines in auroras in the upper 

 region of our atmosphere, are other peculiar phenomena, 

 well worthy of investigation. 



6 Many before' Jenner ' had witnessed the cow-pox, and 

 had heard of the report current among the milkmaids in 

 Gloucestershire, that whoever had taken that disease was 

 secure against small-pox. It was a trifling, vulgar ru- 

 mour, supposed to have no significance whatever, until it 

 was accidentally brought under the notice of Jenner. He 

 was a youth, pursuing his studies at Sodbury, when his 

 attention was arrested by the casual observation made by 

 a country-girl who came to his master's shop for advice. 

 The small-pox was mentioned, when the girl said, " I 

 can't take that disease, for I have had cow-pox." The ob- 

 servation riveted Jenner's attention, and he forthwith set 

 about inquiring and making observations on the subject,' 1 

 which led to the discovery of the process of vaccination. 



c. By investigating unexplained phenomena observed 

 in manufacturing and other operations. The discovery 



1 Self -Help, by S. Smiles, p. 88. 



