SECT, xxviii.j PHOSPHORESCENCE. 327 



together with the chemical rays that accompany them, 

 has the same effect with the less refrangible part of the 

 spectrum ; hence there can be no doubt that the most 

 refrangible and obscure rays of the spectrum excite phos- 

 phorescence, while all the less refrangible rays of light 

 and heat extinguish it. It appears, from the experiments 

 of MM. Biot and Becquerel, that electrical disturbance 

 produces these phosphorescent effects. There is thus a 

 mysterious connexion between the most refrangible rays 

 and electricity which the experiments of M. E. Becquerel 

 confirm, showing that electricity is developed during chemical 

 action by the violet rays, that it is very feebly developed by 

 the blue and indigo, but that none is excited by the less 

 refrangible part of the spectrum. 



Paper prepared with the sulphuret of barium, when under 

 the solar spectrum, shows only one space of maximum lumi- 

 nous intensity, and the destroying rays are the same as in 

 sulphuret of calcium. 



Thus the obscure rays beyond the extreme violet possess 

 the property of producing light, while the luminous rays have 

 the power of extinguishing it. 



The phosphoric spectrum has inactive lines which coincide 

 with those in the luminous and chemical spectra, at least, as 

 far as it extends ; but, in order to be seen, the spectrum must 

 be received for a few seconds upon the prepared surface 

 through an aperture in a dark room, then the aperture must 

 be closed, and the temperature of the surface raised two or 

 three hundred degrees ; the phosphorescent parts then shine 

 brilliantly, and the dark lines appear black. 



Since the parts of similar refrangibility in the different 

 spectra are traversed by the same dark lines, rays of the same 

 refrangibility are probably absorbed at the same time by the 

 different media through which they pass. Multitudes of 

 fish are endowed with the power of emitting light at pleasure, 

 no doubt to enable them to pursue their prey at depths where 

 the sunbeams cannot penetrate. Flashes of light are fre- 



