Sccr. XXV. HERSCHEI/S EXPERIMENTS. 231 



may therefore be regarded as an elastic system, the dif- 

 ferent parts of which are capable of receiving the tremors 

 of elastic media, and of vibrating in unison with any num- 

 ber of superposed undulations, all of which have their 

 perfect and independent effect. Here our knowledge 

 ends ; the mysterious influence of matter on mind will 

 in all probability be forever hid from man. 



A series of experiments by Sir John Herschel has 

 disclosed a new set of obscure rays hi the solar spec- 

 trum, which seem to bear the same relation to those of 

 heat that the photographic or chemical rays bear to the 

 luminous. They are situate in that part of the spec- 

 trum which is occupied by the less refrangible visible 

 colors, and have been named by their discoverer Parather- 

 mic rays. It must be held in remembrance that the 

 region of greatest heat in the solar spectrum lies in the 

 dark space beyond the visible red. Now Sir John Her- 

 schel found that in experiments with a solution of gum 

 guaiacum in soda, which gives the paper a green color, 

 the green, yellow, orange, and red rays of the spectrum 

 invariably discharged the color, while no effect was pro- 

 duced by the extra-spectral rays of caloric, which ought 

 to have had the greatest effect, had heat been the cause 

 of the phenomenon. When an aqueous solution of 

 chlorine was poured over a slip of paper prepared with 

 gum guaiacum dissolved in soda, a color varying from a 

 deep somewhat greenish hue to a fine celestial blue was 

 given to it ; and when the solar spectrum was thrown 

 on the paper while moist, the color was discharged from 

 all the space under the less refrangible luminous rays, 

 at the same time that the more distant thermic rays 

 beyond the spectrum evaporated the moisture from the 

 space on which they fell : so that the heat spots became 

 apparent. But the spots disappeared as the paper 

 dried, leaving the surface unchanged ; while the photo- 

 graphic impression within the visible spectrum increased 

 in intensity, the non-luminous thermic rays, though 

 evidently active as to heat, were yet incapable of effect- 

 ing that peculiar chemical change which other rays of 

 much less heating power were all the time producing. 

 Sir John having ascertained that an artificial heat from 

 180 to 280 of Fahrenheit changed the green tint of 



