LUMINOUS OWLS 65 



27. Luminous Owls and Other Luminous Animals and 

 Plants 



A correspondent lately described in a letter to a London 

 newspaper what he believed to have been " a luminous 

 owl," which was seen flying about at night in Norfolk. 

 He mentioned the well-known fact that the dense greasy 

 patch of feathers on the breast of the heron is said to 

 be luminous by many trustworthy observers. It is very 

 probable that it was some carnivorous or fish-eating 

 bird, which was thus seen in a luminous condition at 

 night. The occurrence is much more in accordance 

 with known facts than most people would suppose to 

 be the case. Light, even strong light, is produced by 

 many natural objects without the accompaniment of 

 heat. We usually expect not merely fire where there 

 is smoke, but heat in fact, great heat, where there 

 is light or flame. Yet there are many instances to 

 the contrary, and the word " phosphorescence " is used 

 to indicate a production of light without heat in 

 reference to the fact that phosphorus is luminous, 

 even when covered with water, although no appre- 

 ciable heat accompanies the light such as we are 

 accustomed to observe in ordinary " combustion " or 

 burning. 



There is more than one kind of phosphorescence. 

 We separate the phosphorescence which is due to the 

 oxidation of peculiar fatty matters in the bodies of 

 plants and of animals (such as glow-worms) from that 

 which is caused by the breaking or heating of crystals 

 (white arsenic and apatite), or by longer or shorter 

 exposure to the sun's rays (luminous paint), or by 

 radio-activity, or by electrical discharges in vacuum 

 tubes. 



The " luminous owl " of the above-mentioned corre- 

 spondent and the ]uminous breast of the heron probably 



