43ff Notices respecting Neio Booki. 



ferent mannef in which thev receive the electrical po-' 

 larilies; or in which ihcir parts become capable of com- 

 niunicatinii attractive or repellent powers to other matter; 

 Nonconductors appear to receive polarities, only with 

 great difficiiitv, but retain them for a lone; while, and present 

 probablv a number of different alternations of poles, within- 

 a small space, and cannot be affected to any great distance. 

 Imperfect conductors receive polarity with more facility, 

 but present fewer alternations, and preserve their electri- 

 cities for a shorter time. Perfect conductors are easily 

 afiected throughout; biit present at most only two' 

 poles, and the powers rapidly destroy each other. The 

 difficulty with which nonconductors receive polarity, is- 

 shown in- the pbaenomena of charging thick and thin 

 coated plates of glass and nnca. Ihetinn plates are capa- 

 ble of being charged much more highly than the thick 

 ones, and the accumulation on the opposite surfaces is 

 much greater. Rarefied air or gaseous matter, is much 

 more susceptible of receiving polarities, than dense air or 

 gaseous matter ; and hence, the electrical spark will pass 

 much further through rarefied air or light gases, than 

 through dense air or heavy gases ; it passes nuich further 

 likewise in gases, than in nonconductnig fluids." 



The terms quantity and hitcnsitij of electricity are ad- 

 mitted to be rather vague, although useful ; but if we consi- 

 der the former in its natural sense of volume or measure, 

 and the latter as indicating an increased impetus, we majr 

 form suflicienlly definite ideas from these expressions. 

 Thus, for instance, where the quantity of eleetriciiy in any 

 conducting body is not altered^ but the intensity is, the 

 Jatter is always in proportion to xht diminution of the dis- 

 charging surface ; hence the more the surface is diminishec) 

 the more the electricity is rendered intense. In this re- 

 spect, it mav be said to be condensed or concentrated, and 

 the more condensed, the greater its intensity. This is 

 further confirmed by the author's observation, that " whcii 

 verv small condurtinsr surfaces are used for conveying verv 

 large quantities of electricity, they become ignited ; and of 

 the different conductors that have been compared, charcoal 

 is most easily heated by (Voltaic) electrical discharges, 

 next iron, platina, gold, iheti copper, and lastly zinc. The 

 phaenomena of electrical ignition, whether taking place in 

 siaseons fluid or solid bodies, always seem to be the result 

 of violent exertion ai the electrical attractive and repellent 

 powers, which may be connected with motions of the par- 

 ticles of the substances affected." Here Sir H. adduces 



anoihcr 



