632 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



16 oz. The water used in general for the experiments, was pure spring water, 

 drawn up from under ground by means of a pump ; and it was always employed 

 cold, unless otherwise expressed. 



Section 1 . The Quantity of Light emitted by Putrescent Animal Substances, is 

 not in Proportion to the Degree of Putrefaction in such Substances as is com- 

 monly supposed ; but, on the contrary, the greater the Putrescence, the less is the 

 Quantity of Light emitted. 



The truth of this proposition is proved by 7 different experiments, made partly on 

 dead herrings and partly on dead mackerel. The light which they emitted dimi- 

 nished after the 2d or 3d day, and was nearly extinct on the 4th or 5 th day. 



n. b. In experiments of this kind, for the production of light, the fishes should 

 always be gutted, the roes taken out ; and the scales, if any, carefully removed. 

 As the roes are likewise very productive of light, they should be preserved. 



Obser. 1 . These experiments clearly prove, that light begins to be emitted by 

 marine fishes, before any signs of putrefaction appear: they likewise demonstrate, 

 that as soon as a great degree of putrescence has taken place, the luminous pro- 

 perty of the fishes is destroyed, and the light extinguished. 



Obser. 2. In the instance of light proceeding spontaneously from animal flesh, 

 recorded by Aquapendente, the flesh emitted light before any sensible putrescence 

 had taken place, the meat being hung up in the larder for use. In that also men- 

 tioned by Bartholin, in l641, the flesh must have been fresh and sweet, for it was 

 not intended to be dressed till the next day. Mr. Boyle, in his report of light 

 issuing from flesh, expressly says, that neither he, nor any of those who were 

 about him, could perceive in it any offensive smell, whence to infer any putrefac- 

 tion; the meat being judged very fresh, and well conditioned, and fit to be dressed. 

 And lastly Dr. Beale, in his account of a luminous neck of veal, says, that when 

 it was dressed, on Feb. the 27th, some of the neighbours, who saw it shining, 

 were invited to eat of it, and all esteemed it as good as they had ever tasted; that 

 a part of it was kept for Feb. 28th and 29th, in which time it lost nothing of its 

 sweetness. 



Obser. 3. Whenever I wish to obtain a plentiful supply of light from fishes, for 

 the purpose of experiments, I always endeavour to procure the freshest that can be 

 had: long experience and frequent disappointments have taught me to adopt such 

 a precaution. 



Section 2. The Light here treated of is a constituent Principle of some Bodies, 

 particularly of Marine Fishes, and may be separated from them, by a peculiar 

 Process ; may be retained, and rendered permanent for some Time. It seems 

 to be incorporated with their whole Substance, and to make a Part of it, in the 

 same manner as any other constituent Principle. 



Exper. 1. A fresh herring was split, or divided longitudinally, by a knife, into 

 2 parts. Then, about 4 dr. of it, being cut across, were put into a solution, com- 

 posed of 2 dr. of Epsom salt or vitriolated magnesia, and 2 oz. of cold spring water 



