BASIS OF ANIMAL PHOSPHORESCENCE. 1 1 I 



Under "Thermal Observations" the authors proceed : "To 

 give an idea of the amount of heat at our disposition for experi- 

 ment, and of the actual minuteness of the radiation which pro- 

 ceeds from even the most luminous tropical insect, we may say 

 that if that rate of radiation from a lamp-black surface I square 

 cm. in area, which represents the amount of heat necessary to 

 raise I gram of water to i centigrade, in i minute (i.e. one 

 small calorie), be taken as unity, then the luminous radiation of 

 the fire-fly's heat, per square cm., of exposed luminous surface, 

 as we have found, is about 0.0004 calorie in 10 seconds, and the 

 total luminous radiation from the most powerfully illuminating 

 light spot of the insect (the abdominal one) will not exceed 

 0.00007 calorie in the same time. But a small portion of this 

 could fall upon the bolometer, and that which actually reached 

 'it during the time (10 seconds) required for each observation was 

 sufficient only to affect an ordinary mercurial thermometer 

 having a bulb I cm. in diameter by rather less than 0.00000023, 

 or by less than 1/400000 of one degree centigrade" (pp. 108, 

 109). 



" Resuming, then, what we have said, we repeat that nature 

 produces this cheapest light at about one four-hundredth part 

 of the cost of the energy which is expended in the candle-flame, 

 and at but an insignificant fraction of the cost of the electric 

 light or the most economic light which has yet been devised ; 

 and that finally there seems to be no reason why we are for- 

 bidden to hope that we may yet discover a method (since such 

 a one certainly exists and is in use on a small scale) of obtain- 

 ing an enormously greater result than we now do from our 

 present ordinary means for producing light" (p. 112). 



The light emitted by the living organism differs very much 

 in color in different animals, and even in the same animal at 

 different periods ; green has been noticed in the glow-worm, 

 fire-flies, some brittle-stars, centipedes, and annelids ; blue is 

 seen in the Italian fire-fly ; blue and light-green are the pre- 

 dominant colors exhibited by marine animals ; the beautiful Gir- 

 dle of Venus, some species of Salpa, and Cleodora appear red ; 

 Pavonaria and other gorgonids are lilac ; and one hemiptera, Ful- 

 gora, is said to emit a purple light. One very remarkable 



