Things not generally Known. 



MUTUAL RELATIONS OF PHENOMENA. 



In the observation of a phenomenon which at first sight 

 appears to be wholly isolated, how often may be concealed the 

 germ of a great discovery ! Thus, when Galvani first stimu- 

 lated the nervous fibre of the frog by the accidental contact of 

 two heterogeneous metals, his contemporaries could never have 

 anticipated that the action of the voltaic pile would discover 

 to us in the alkalies metals of a silver lustre, so light as to 

 swim on water, and eminently inflammable ; or that it would 

 become a powerful instrument of chemical analysis, and at the 

 same time a thermoscope and a magnet. When Huyghens first 

 observed, in 1678, the phenomenon of the polarisation of light, 

 exhibited in the difference between two rays into which a pencil 

 of light divides itself in passing through a doubly refracting 

 crystal, it could not have been foreseen that a century and a 

 half later the great philosopher Arago would, by his discovery of 

 chromatic polarisation, be led to discern, by means of a small frag- 

 ment of Iceland spar, whether solar light emanates from a solid 

 body or a gaseous covering ; or whether comets transmit light 

 directly, or merely by reflection. Humboldi's Cosmos, vol. i. 



PRACTICAL RESULTS OF THEORETICAL SCIENCE. 



What are the great wonders, the great sources of man's 

 material strength, wealth, and comfort in modern times? The 

 Railway, with its mile-long trains of men and merchandise, 

 moving with the velocity of the wind, and darting over chasms 

 a thousand feet wide ; the Electric Telegraph, along which 

 man's thoughts travel with the velocity of light, and girdle the 

 earth more quickly than Puck's promise to his master ; the 

 contrivance by which the Magnet, in the very middle of a strip 

 of iron, is still true to the distant pole, and remains a faithful 

 guide to the mariner ; the Electrotype process, by which a 

 metallic model of any given object, unerringly exact, grows 

 into being like a flower. Now, all these wonders are the result 

 of recent and profound discoveries in theoretical science. The 

 Locomotive Steam-engine, and the Steam-engine in all its other 

 wonderful and invaluable applications, derives its efficacy from 

 the discoveries, by Watt and others, of the laws of steam. The 

 Railway Bridge is not made strong by mere accumulation of 

 materials, but by the most exact and careful scientific exami- 

 nation of the means of giving the requisite strength to every 

 part, as in the great example of Mr. Stephenson's Britannia 

 Bridge over the Menai Strait. The Correction of the Magnetic 

 Needle in iron ships it would have been impossible for Mr. 

 Airy to secure without a complete theoretical knowledge of 



