1824.] Proceedings of Philosophical Societies. 385 



concluded. This paper commences with some general remarks' 

 on the various causes to which the luminosity of the lampyrides 

 has been ascribed ; the explanation of Macartney and Macaire, 

 that the light they emit is a simple product of vitality, being 

 considered as the true one. Dr. Todd then proceeds to a mi- 

 nute account of the apparent source and characters of the light 

 in the several animals ; describing the manner in which its 

 emission is affected by solar and other light, by heat, and by 

 certain chemical agents respectively. In the Lampyris splendi- 

 dula, the light is of a fine topaz yellow colour, with a tinge of 

 green, and is extremely vivid within the compass of a few 

 inches, but does not extend its brilliancy far around : within 

 that space the hour may be seen on a watch by its means. Tha 

 light of the Fire-fly is of a pale yellowish tint, with continual 

 flashes of vivid light : its variations are not connected with the 

 motions of the insect's wings, nor are they produced, as some 

 have affirmed, by the frequent intervention of a membrane. 

 This animal may be seen shining in full moon-light ; which is 

 not the case with its congeners. Irritants excite the luminous 

 power in all cases, and disorganizing substances destroy it. 

 Dr. Todd concludes that this power is solely an effect of vita- 

 lity, and that the light may be considered as animal light; 

 being analogous to animal heat, which arises from a power of 

 separating heat from its combinations with matter. He adopts 

 the hypothesis that its principal use is that of guiding the male 

 insects to the female, in the season of sexual congress : the 

 males always approach any light; and sometimes even the 

 shining females of other species, until they come very near 

 them. The fact that the larvae and even the ova possess a de- 

 gree of the luminous faculty, Dr. Todd does not consider as 

 militating against this explanation ; for various organs are par- 

 tially developed in the earlier stages of many animals, which 

 are only to be used by them when arrived at their perfect state. 



A paper was also read, entitled, "A Comparison of the Baro- 

 metrical Measurement of Altitude with that by Trigonometry : 

 by Capt. Edward Sabine, FRS." 



This paper contains the details of a comparative measure- 

 ment of the height of an hill at Spitzbergen in July last, by the 

 geometrical and barometrical methods : the instruments em- 

 ployed in both operations, and in the latter especially, had been 

 prepared with more than ordinary care, and the observations 

 were conducted with an attention to every circumstance which, 

 it was conceived, might influence the strictness of the compa- 

 rison, and sufficiently repeated to diminish at least the sliejit. 

 but unavoidable errors of observation. In the geometrical de- 

 termination, the base, exceeding 2000 feet, was measured on the 

 frozen surface of a bay at the foot of the hill, from whence a 

 polished copper cone fixed on the summit was visible : the ho- 

 rizontal and vertical angles were observed by a repeating circle ; 



New Series, vol. vn. 2 c 



