236 O^ SPONTANEOUS INFLAMMATIONS. 



pencil of the miniature painter. The colours of thefe flower- 



nice ornaments, which are red, green, brown, fky-blue, and 



while, are pure and lively. The delineations pervade the 



whole fubftance, and upon a broken part h is feen by mere 



infpeftion, that thefe delicate figures have been formed of 



parallel giaffy fibres of various colours, conglutinated by means 



of gentle fufion. 



Coloured plate ^g (he drawings given by Count Caylus afford but a very 



fpecimen. j'mperfe^i idea of that ipgenious enamel-painting, I fubniit here 



a delineation of the larger of my two fpecimens. Fig. 1, 



Plate XUl, reprefents it in its true fize; Fig. 2 exhibits it 



magnified. 



Invention of On this occafion the following paflage from a letter of 



Meyer to multl- ^ Kaftner *, concerning an invention of the celebrated 



p'y copies or ' o 



paintings. Tobias Mayer, may well deferve a place here. '* Mayer 



polTefled the art of making a number of perfedly firailar copies 

 of a painting. He compounded his pidure of coloured wax- 

 crayons, in the fame manner as a prifm may be compofed of 

 thinner prifms of the fame length. Every tranfverfe cutting 

 afforded then a copy." Meyer might probably have been led 

 to this method of imitation in wax, from the infpedion of a 

 mufaic work of the kind here defcribed. 



II. 



On Spontaneous Injiammatinns. By G. C. Bartholdi, Pro- 

 Jejfor of Pliyfic and Chemijiry. 



(Concluded from Page azo. ) 



4-. The Fermentation of Animal and Vegetable Sub0ances, 



Heat from fer- Jl HE greater part of animal and vegetable fubftances, when 

 mentation. [hey ftill retain humidity, and arei accumulated into large 



malTes, enter into fermentation, a change in their compofition 

 is efFefted, and they frequently heat to the point of inflamma- 

 tion. It is thus that magazines of hay, of turf, of flax, of 

 hemp, flacks of bay or flraw, heaps of linen-rags in paper- 

 mills, Sfc. take fire fpontaneoufly, 



♦ Allgemeine Ceograjjhifche E^hemeridettf by Zach, 1798. 



