134 E AMBLES OF A NATUKALIST. 



mirable discoveries on the properties of light had 

 pre-eminently fitted him to grapple with this subject. 

 The disinterested zeal of these three men led to 

 the rapid attainment of numerous valuable results. 

 MM. Arago and Fresnel, by following the plan 

 suggested by Rumford, gave a most unexpected 

 degree of perfection to the lamp with a double 

 current of air. They constructed an apparatus 

 having four concentric wicks, which were supplied 

 with oil by clockwork, and whose illuminating power 

 was so great that a single wick was equivalent to 

 twenty-two of the best Carcel lamps. Fresnel re- 

 placed Borda's mirrors, in which the light is concen- 

 trated by reflection, by lenses which the rays traverse, 

 and which throw them by refraction into the desired 

 direction. 



The best polished surface absorbs very nearly half 

 the quantity of light which strikes it. The other 

 half alone is reflected, and is therefore the only part 

 that can be made available. In traversing a glass of 

 moderate thickness, the same quantity of light is 

 only diminished by about one twentieth of its ori- 

 ginal amount. These well-known facts led in Eng- 

 land to the employment of glasses resembling those 

 which are used for ordinary lenses. The adoption 

 of this form rendered it necessary to use glasses of 

 considerable thickness, in consequence of which the 

 light experienced even more diminution in traversing 



light, not as an emission from luminous bodies, but as produced by 

 the vibration of an universally diffused agent, which we designate 

 under the name of ether. According to this theory, the phenomena 

 of light and of sound closely resemble one another. 



