492 History of Luminescence 



not lost but may be again revived in its former splendour and that 

 by the most simple means "—for example, by adding excess salt, the 

 light goes out but may be revived by diluting with fresh water. 



Hulme noted, as Canton had also, that " Spontaneous Light is 

 rendered more vivid by Motion " (a result connected with the solu- 

 tion of additional oxygen when the water was stirred) and that 

 " Spontaneous Light is not accompanied by any degree of sensible 

 Heat, to be discovered by a Thermometer." He also studied the 

 effects of heat and cold on luminous fish, wood and the glowworm 

 and the effect of animal fluids. Fresh milk and blood serum allowed 

 luminescence of fishes for a long time but sour milk, urine, and bile 

 extinguished the light quickly. 



Hulme's second paper (1801) dealt with the effects of "various 

 aerial Fluids " on spontaneous light, both of fish and of wood. He 

 showed that neither a blast of air from bellows nor vital air (oxygen) 

 increased the luminescence as they did a fire and that azotic gas 

 (nitrogen, undoubtedly impure) , which is incapable of supporting 

 combustion, had no effect on the light of fishes that were already 

 luminous, although it prevented the development of the light. In- 

 flammable air (hydrogen) and fixed air (CO2) prevented both the 

 development of spontaneous light and also extinguished it when 

 emitted, but the light again revived quickly in " atmospherical air." 

 Sulphuretted hydrogen gas (H2S) and " nitrous gas " (from dilute 

 HNO3 and Cu) both extinguished the light quickly and irreversibly 

 (some reversion in HoS) . A vacuum also put out the light but it 

 returned quickly in the air. 



Hulme came to the conclusion from these experiments that the 

 light is a " constituent principle of marine fishes " and the " first 

 that escapes after the death of the fish." Such a statement was quite 

 in line with the Newtonian conception of light as made up of ma- 

 terial particles. Humphry Davy (1778-1829) also, in 1803, after re- 

 ferring to the materiality of light, attributed the light of dead fish 

 to a light substance becoming free at a certain period of decay. 



The conflicting results and conclusions of all these men at the 

 end of the eighteenth century illustrate the difficulty of reaching 

 generalizations regarding relatively simple phenomena. The fact 

 that they were handicapped by impure gases and other chemicals 

 partly explains the difference in results. Although certain bio- 

 luminescences do not require oxygen,*^ the luminescence of the 

 glowworm, luminous bacteria, luminous fungi and phosphorus all 

 depend on the presence of molecular oxygen and might be called a 

 " slow " combustion. Boyle (1667) made the first discovery of the 



*° The ctenophores, a relation discovered by the author in 1926. 



