13 



5. When spontaneous light is extinguished by some bodies or sub- 

 stances, it is not lost, but may be again revived in its former splen- 

 dour, and that by the most simple means. 



These means are in general the greater or less degrees of impreg- 

 nation of the saline menstrua, which alternately extinguish and re- 

 vive the light at the option of the operator. 



6 . Spontaneous light is not accompanied with any degree of sen- 

 sible heat, to be discovered by a thermometer. 



7. Cold extinguishes spontaneous light, but not permanently, as 

 the substances mentioned in the third article ; since here the light 

 could be revived in its full splendour, by exposing the substance to 

 a moderate degree of temperature. 



8. The eighth section treats of the effects of heat on light when 

 in a state of spontaneous union. We gather from the experiments 

 here described, that in every substance there is a certain point of 

 temperature at which it acquires its maximum of lustre ; that this 

 varies considerably in various substances, the fishes, rotten wood, 

 and aqueous solutions, becoming dark at a temperature of between 

 96 and 110; while glow-worms retain their lustre until exposed- 

 to the degree of boiling water. Common water impregnated with 

 light, when by mere time and rest, without any considerable change 

 of temperature, it had become obscure, was soon rendered luminous 

 when gradually warmed by small and successive additions of warm 

 water ; but no sooner was boiling water added in any considerable 

 quantity, than the luminous appearance vanished, and was altogether 

 extinguished. 



It was here observed, that if heat be applied to the bottom of a 

 tube filled with illuminated water which has been some time at rest, 

 the light will descend in luminous streams from the top of the tube 

 to the bottom, and be gradually extinguished. 



9. In the ninth and last section we find a set of experiments on 

 the effects of spontaneous light when applied to the human body. 

 As to the living body, it was found that on touching the luminous 

 matter of fishes, the light adhered copiously to the fingers and dif- 

 ferent parts of the hands, remained very lucid for some time, but 

 then gradually disappeared ; whereas the same kind of matter being 

 applied to pieces of wood, stone, and the like, of the same tempera- 

 ture as the laboratory, continued luminous on these substances for 

 many hours. It might hence be inferred that the living body ulti- 

 mately absorbs the light ; but other experiments seem to contradict 

 this inference, it having been observed that a piece of shining wood 

 being placed on the palm of the hand, and a glow-worm being 

 breathed upon repeatedly, were both rendered more luminous, and 

 this for a considerable time. 



As to the animal fluids ; the crassamentum of the blood of healthy 

 persons, and also of some labouring under inflammatory diseases, re- 

 ceived indeed the light of a herring to a certain degree, but did not 

 retain it long : and when this coagulum had been kept for some time, 



