NOLLET ON LIGHTNING. 573 



ill sulphurous, mercurial and nitrous vapors, the particles 

 of which, rising and falling, are continually rubbing 

 against one another. The rubbing of the sulphurous 

 particles generates electric matter, which may lie quiet 

 until some chance shock develops the conditions for dis- 

 charge and explosion, and then the sulphurous and nitrous 

 vapors are burned, and there is besides a conduction of 

 electricity along the particles which are non-electric. 

 This is the substance of a long and somewhat obscure 

 dissertation which ends with the statement : 



"It appears, therefore, that the electric sparks which 

 through art may be excited are the same in material, 

 nature and mode of production as the lightning flashes 

 and strokes, and that the only difference exists in the 

 relative strengths and weaknesses of their operation." 



Such was the development of the idea in England and 

 Germany. In France, nearly two years later (August 9, 

 1748), Abbe* Nollet published a treatise on physics 1 in 

 which, in due course, he deals with the nature of light- 

 ning. He describes the " matter of thunder " as a u mix- 

 ture of exhalations capable of self-ignition on fermentation 

 or by shock, and the pressure of clouds which the winds 

 violently agitate and drive together. When a consider- 

 able portion of this mixture takes fire, it causes an ex- 

 plosion stronger or weaker according to the quantity or 

 the nature of the ignited materials, or according to the 

 obstacles which present themselves to its sudden ex- 

 pansion." He regards also the lightning-stroke as due to 

 an ignited gas which always rends the cloud like an ex- 

 plosive bomb. With this theory, however, he is not 

 satisfied, and merely gives it as the one which is generally 

 accepted. Then he adds the following oft-quoted passage: 



"If any one should take upon him to prove from a well- 

 connected comparison of phenomena, that thunder is in 

 the hands of nature what electricity is in ours, that the 

 wonders which we now exhibit at our pleasure are little 



1 Nollet: Le9ons de Physique. Paris, 1746, vol. iv., 315. 



