214 History of Luminescence 



Alteration in the Ponderable Matter of Bodies," which included 

 phosphorescence, thermoluminescence, triboluminescence, and crys- 

 talloluminescence. As a chemist, Gmelin was not particularly con- 

 cerned with luminescences in which no chemical changes occurred. 

 The only reference to light development at a low temperature 

 as a result of " actual chemical combination " was the following 

 (p. 181): 



Hydrate of potash or soda produces light in combining with sul- 

 phuric, nitric, or concentrated acetic acid dropt upon it; baryta or lime 

 with water or one of the acids just mentioned; magnesia with sulphuric 

 or nitric acid. . . . 



The light must either have existed ready formed in one or both of 

 the combining bodies, and be merely separated by the act of combina- 

 tion, or it must be evolved during the combination of the ponderable 

 bodies out of imponderable elements contained in them. 



Gmelin attributed animal light to the fact (pp. 181-182) , 



that they eliminate a peculiar and in most cases liquid substance, con- 

 taining phosphorus or some other element, which combines, at common 

 temperatures, with the oxygen of the air or of water containing air, 

 producing a faint luminous appearance. Not only does the separation 

 of this fluid appear to depend upon the life of the animal, but its will 

 seems likewise to determine whether the fluid shall— partly by means of 

 the respiratory process— come in contact with the oxygen of the air, and 

 thus produce a development of light, or not. 



Regarding putrefying animal and plant material, Gmelin stated 



(p. 189): 



At a certain temperature, and in contact with moisture and oxygen 

 gas, a decomposition appears to arise in many dead animals, especially 

 in sea-fish, before the commencement of actual putrefaction,— producing 

 a glutinous substance, whose constituents are capable of burning in the 

 smallest quantity of oxygen, with a feeble light and scarcely perceptible 

 development of heat:— or may it not be supposed that the decomposition 

 is attended by the production of luminous infusoria? 



The suggestion of animalcules as the cause of light in meat and 

 fish comes very near the truth. Gmelin was presenting the work of 

 others, but the extraordinarily complete tabulation of luminous 

 organisms and luminous phenomena makes his article outstanding. 



Most of the nineteenth century textbooks on natural philosophy, 

 the present day physics, contain some references to luminescence. 

 One of these was the Course of Lectures on Philosophy and the 

 Mechanical Arts (1807) of Thomas Young, already mentioned in 



