HARDWICKE'S SCIENCE-GOSSIP. 



87 



III damp situations tlie light is observed to be more 

 vivid. 



The fact that the light increases with individuals 

 as we approach the equator, would lead us to expect 

 a rise of temperature would intensify the luminosity 

 of our species : indeed it does, but extremes of heat 

 and cold extinguish it. 



It shines more in tepid than in cold water ; agita. 

 tion of the fluid, electricity, and oxygen likewise 

 increase the luminosity. Such non-supporters of 

 combustion as hydrogen, sulphuretted hydrogen, 

 nitrous, sulphurous, and muriatic acid gases, and 

 carbonic anhydride extinguishe it. 



Insomecasesit has actually been heard to detonate 

 when placed under hydrogen. 



Prom some of these facts Spallanzaui concluded 

 that it is a compound of hydrogen and carburetted 

 hydrogen gas. It is right to mention that many of 

 these results have been denied ; one author afiirm- 

 ing that when placed in vacuo the light disappears, 

 although restoration takes place on renewed ex- 

 posure to the air ; and that carbonic anhydride, 

 previous to total extinction, excites it; another, 

 that electricity produces no effect on it. 



If tiie matter were always extracted from the 

 animal, the results would most likely agree ; it is 

 not just to experiment on the living beetle, for tota^ 

 extinction of the light may be the result of instinct 

 rather than that of the chemicals employed. 



Paraday took great interest in the glow-worm. 

 When a youth he made some experiments upon 

 some found at Geneva. The luminous matter cut 

 out of one preserved its quality for three days. I 

 should think decomposition liad set in before this, 

 although it has been stated that the light ceases as 

 soon as that change takes place. If produced by 

 respiration, why should one sex be almost devoid of 

 it? How could it be suddenly extinguished? Why 

 should not the light be of the same intensity at all 

 hours of the night, and at all seasons of the year ? 

 And, surely, if it were a case of chemical combination 

 more or less heat would be evolved, which does not 

 appear to be the case. Leaving these questions 

 unanswered, we will proceed to speculations on the 

 ■icse of the light. 



Poets have theorized on this subject as well as 

 naturalists. Vincent Bourne has written some verses 

 on the glow-worm, in which he says : 



" Perliaps indulgent Nature meant, 

 By such a lamp bestow'd, 

 To bid the trav'Ier, as he went. 

 Be careful where he trod." 



This beetle is several times mentioned by Shakes- 

 peare. Hamlet's ghost declares 



" The glow-worm shows the matin to be near. 

 And 'gins to pale his uneffectual fire." 



It would be interesting to know at what hour of 

 the night it really does cease to shine. 

 Shakespeare allows it to shine for a longer period 



than does Gilbert White, who remarks that they 

 appear "to put out their lamps between eleven 

 and twelve." In the comedy of "A Midsummer 

 Night's Dream," Titania, addressing the fairies, in 

 allusion to the humble-bee, says : — 



" And for night-tapers, crop their waxen thighs, 

 And Ught them at the fiery glow-worm's eyes." 



The light, as we have shown, does not proceed 

 from the eyes, which are comparatively small in the 

 female, nor does the luminous portion possess more 

 caloric than the rest of the body, but, as Words- 

 worth says, it is quite a " harmless ray." 



Some have imagined that as the glow-worm does 

 possess the power of extinguishing its flame, it is 

 to protect itself from nocturnal animals. But 

 Swainson has very properly objected that "the 

 owls and the goat-suckers are the only nocturnal 

 birds which feed after sunset ; but the former live 

 upon much larger insects .... while the latter 

 always seek their game at a much higher elevation 

 in the air than phosphorescent insects ever ascend 

 to," (" Habits and Instincts of Animals," p. 3GG.) 



In Dr. Paley's " Natural Theology " (c. xix.) we 

 find the following : "Two points seem to be agreed 

 upon by naturalists concerning it ; first, that it is 

 phosphoric ; secondly, that its use is to attract the 

 male insect." 



These two very points naturalists are now most 

 M«settled about. Its composition and its use 

 are not known. Gilbert White, in " Hero and 

 Leander," was evidently of Dr. Paley's contem- 

 poraries' opinion. Louis Piguier and Professor 

 Blanchard do not doubt in the least that this is the 

 use of the light. There are certainly objections to 

 it. It does not apply to many marine hermaphro- 

 dite animals. Why should they necessarily per- 

 petuate the species by night ? The insect has been 

 seen abroad during the day. The male would not 

 require a light, nor the pupae, larvae, and eggs. 

 Other insects find each other perfectly well in the 

 dark, and why should this species be bereft of the 

 instinct ? 



On the other hand, the male beetles have been 

 observed to fly to a lantern, and an entomological 

 friend of mine has seen them flying around the 

 modern lamp-post. That moths and other beetles 

 frequently do the same thing is certainly a serious 

 objection. 



In the male, again, the eyes are constructed for 

 forward and downward vision; the organs are 

 large, as if to adapt them for the absorption of 

 rays of light. 



It cannot be meant to steer the animal through 

 the dark, as the light is behind. If we wished to 

 make use of a lantern by night, we should not hang 

 it beneath our coat-tails ! If it were a means of 

 defence, it would possess electrical or poisonous 

 properties : it does not appear to be gifted with 

 either. 



