VOL. XC.] PHILOSOPHICAL TRANSACTIONS. 637 



nated. The next evening it appeared still very lucid ; as also on the succeeding 

 night. — Exper. 4. The experiment was reversed. Half a dr. of the salt being dis- 

 solved in 2 oz. of water, had herring-light mixed, so as to be made very luminous. 

 On the addition of 2 dr. more of the salt, the lucidness was instantly destroyed ; 

 but the light was again recovered, by pouring 8 oz. of cold water on the extin- 

 guished luminous fluid. The revived light was very vivid the next evening. — 

 Exper. 5. Two oz. of sea-water were illuminated with mackerel-light, and then 

 extinguished by adding 2 dr. of common salt. The light was again restored, by 

 diluting the solution with 8 oz. of cold spring water. 



n. B. If the illuminated liquid be uncommonly brilliant, it may sometimes 

 require more salt to extinguish the light completely, than is here specified ; in that 

 case, the measure of water for dilution must be always calculated in exact propor- 

 tion to the weight of salt employed. 



Section 6. Spontaneous Light is rendered more vivid by Motion. 



The truth of this proposition is proved by 2 experiments in which the liquid 

 became more luminous on being shaken or stirred. 



Section 7. Spontaneous Light is not accompanied with any Degree of sensible 

 Heat, to be discovered by a Thermometer. 



The truth of this proposition is proved by 5 different experiments made on dead 

 herrings, dead mackerel, rotten wood, &c. 



Section 8. The Effects of Cold on Spontaneous Light. 



The Light of Fishes. — Exper. 1. Five small gallipots, containing 3 pieces of 

 soft-roe of herring, and 2 of the herring itself, all very luminous, were placed in 

 a frigorific mixture, composed of snow and sea-salt ; in about an hour and a half 

 the light was quite extinct, and the bodies totally frozen. The gallipots were then 

 removed into a vessel of cold water, that their contents might be gradually thawed; 

 which being done, they all recovered their pristine luminous state. The pieces 

 were afterwards observed to shine during 3 succeeding nights. — Exper. 2. A small 

 phial, containing 3 or 4 drams of liquid impregnated with light, was placed in a 

 frigorific mixture. As the liquid froze, its lucidness gradually diminished ; and 

 when it quit© congealed the light perfectly disappeared. The phial was then taken 

 out, and put into cold water, at about 49° temperature, that the ice might be gra- 

 dually liquified ; after which, the whole fluid became as luminous as before. 



The Light of shining Wood. — Exper. 3. A fragment of shining wood was put 

 into a small wide-mouthed phial, which was plunged into a frigorific mixture. As 

 the cold affected the wood, the light gradually faded, and at last was totally im- 

 perceptible. The phial was then taken out, and placed in water at about 62° ; by 

 this change of temperature, the frozen wood gradually thawed, and then regained 

 its former lustre. 



The Light of Glow-worms. — Exper. 4. A small phial, containing a luminous 

 dead glow-worm, was exposed to the cold of the frigorific mixture ; as the cold- 

 ness penetrated the phial, the light diminished, and at length was totally extinct. 



