Things not generally Known. 



velocity of the light of frictional electricity, we are disposed, 

 in accordance with Wheatstone's ingeniously-conducted experi- 

 ments, to regard the lowest ratio in which the latter excels the 

 former as 3 : 2. According to the lowest results of Wheatstone's 

 apparatus, electric light traverses 288,000 miles in a second. 

 If we reckon 189,938 miles for stellar light, according to Struve, 

 we obtain the difference of 95,776 miles as the greater velocity 

 of electricity in one second. 



From the experiment described in Wheatstone's paper (Phi- 

 losophical Transactions for 1834), it would appear that the hu- 

 man eye is capable of perceiving phenomena of light whose 

 duration is limited to the millionth part of a second. 



In Professor Airy's experiments with the electric telegraph 

 to determine the difference of longitude between Greenwich 

 and Brussels, the time spent by the electric current in passing 

 from one observatory to the other (270 miles) was found to be 

 0-109", or rather more than the ninth part of a second; and 

 this determination rests on 2616 observations : a speed which 

 would " girdle the globe" in ten seconds. 



IDENTITY OF ELECTEIC AND MAGNETIC ATTRACTION. 



This vague presentiment of the ancients has been verified 

 in our own times. " When electrum (amber)," says Pliny, "is 

 animated by friction and heat, it will attract bark and dry 

 leaves precisely as the loadstone attracts iron." The same 

 words may be found in the literature of an Asiatic nation, and 

 occur in a eulogium on the loadstone by the Chinese physicist 

 Knopho, in the fourth century: "The magnet attracts iron 

 as amber does the smallest grain of mustard-seed. It is like a 

 breath of wind, which mysteriously penetrates through both, 

 and communicates itself with the rapidity of an arrow." 



Humboldt observed with astonishment on the woody banks of the 

 Orinoco, in the sports of the natives, that the excitement of electricity 

 by friction was known to these savage races. Children may be seen to 

 rub the dry, flat, and shining seeds or husks of a trailing plant until 

 they are able to attract threads of cotton and pieces of bamboo-cane. 

 What a chasm divides the electric pastime of these naked copper-co- 

 loured Indians from the discovery of a metallic conductor discharging 

 its electric shocks, or a pile formed of many chemically-decomposing 

 substances, or a light-engendering magnetic apparatus ! In such a 

 ch ism lie buried thousands of years, that compose the history of the in- 

 tellectual development of mankind. Humbvldt's Cosmos, vol. i. 



THEORY OF THE ELECTRO-MAGNETIC ENGINE. 



Several years ago a speculative American set the industrial 

 world of Europe in excitement by this proposition. The Mag- 

 neto-Electric Machines often made use of in the case of rheu- 

 matic disorders are well known. By imparting a swift rotation 



