THE INFLUENCE OF MATTER UPON LIGHT, 163 



purified turpentine, is burnt, gives a flame which emits 

 most of the rays found in sunlight. Spirit of wine 

 mixed with water, warmed and ignited, gives only yellow 

 rays ; add nitrate of strontian and they become red ; but 

 nitrate of barytes being mixed with the fluid, they are 

 changed to green and yellow ; salts of copper afford fine 

 blue rays, and common salt intense yellow ones. Many 

 of these coloured rays and others can be produced in 

 great power by the use of various solid bodies introduced 

 into flame. This has not been sufficiently pointed out 

 by authors ; but it is clear from experiments that light 

 requires the presence of matter to enable it to diffuse its 

 coloured glories. How is it that the oxygen and 

 hydrogen flame gives so little light, and with a solid 

 body present, pours forth such a flood of brilliancy ? 



The production of artificial light by electrical and 

 chemical agencies will necessarily find some consideration 

 under their respective heads. There are numerous 

 phenomena which connect themselves with luminous 

 power, or appear to do so, which, in the present state of 

 our knowledge, cannot come immediately under our 

 attention. We are compelled to reserve our limited 

 space for those branches of science which we are enabled 

 to connect with the great natural operations constantly 

 going on around us. Many of these more abstruse 

 results will, however, receive some incidental notice 

 when we come to examine the operation of the combined 

 physical forces on matter. 



We see in light a principle which, if it has not its 

 source in the sun, is certainly dependent upon that 

 luminary for its manifestations and powers. From that 

 " fountain of light " we find this principle travelling to 

 us at a speed which almost approaches the quickness of 

 thought itself; yet by the refinements of science we 

 have been enabled to measure its velocity with the 

 utmost accuracy. The immortal poet of our own land 

 and language, in his creations of Ariel, that " tricksy 



