ELECTRICITY. * 103 



but are necessary results of the sudden subversion of mole- 

 cular polarisation, or of a sudden or irregular vibratory move- 

 ment of the matter itself. We see similar effects produced 

 by sonorous vibrations, which might be called conduction 

 and non-conduction of sound. One body transmits sound ea- 

 sily, another stops or deadens it, as it is termed i. e. dis- 

 perses the vibrations, instead of continuing them in the same 

 direction as the primary impulse ; and solid bodies may, as 

 has been above observed, be shivered by sudden impulses of 

 sound in those cases where all the parts of the body cannot 

 uniformly carry on the undulatory motion. 



The progressive stages in the History of Physical Philoso- 

 phy will account in a great measure for the adoption by the 

 early electricians of the theories of fluids. 



The ancients, when they witnessed a natural phenomenon, 

 removed from ordinary analogies, and unexplained by any 

 mechanical action known to them, referred it to a soul, a 

 spiritual or preternatural power : thus amber and the magnet 

 were supposed by Thales to have a soul ; the functions of 

 digestion, assimilation, &c., were supposed by Paracelsus to 

 be effected by a spirit (the Archaeus) . Air and gases were 

 also at first deemed spiritual, but subsequently became invest- 

 ed with a more material character ; and the word gas, from 

 geist, a ghost or spirit, affords us an instance of the gradual 

 transmission of a spiritual into a physical conception. 



The establishment by Torricelli of the ponderable charac- 

 ter of air and gas, showed that substances which had been 

 deemed spiritual and essentially different from ponderable 

 matter were possessed of its attributes. A less superstitious 

 mode of reasoning ensued, and now aeriform fluids were 

 shown to be analogous in many of their actions to liquids or 

 known fluids. A belief in the existence of other fluids, differ- 

 ing from air as this differed from water, grew up, and when 

 a new phenomenon presented itself, recourse was had to a 

 hypothetic fluid for explaining the phenomenon and 



