16 [May, 1841. 



Prof. Johnson suggested that the exterior wrappings might not 

 have heen originally saturated with bitumen, but that they had 

 been applied while clean to the mummy wrapped in the interior 

 saturated folds ; and that by slow, insensible transmission, the 

 clean folds had, with the volatilized bituminous matter, become in 

 a manner photogenic, and capable of being turned yellow by the 

 influence of light as soon as the jars were opened. He con- 

 ceived this explanation of the phenomenon by the known agency 

 of light on resinous and bituminous substances, more satisfactory 

 than that which had been previously offered, and which ascribed 

 it to the mere presence of air admitted on opening the jar. He 

 suggested that the latter explanation Avouid have had more plau- 

 sibility if the jar had really been hermetically sealed, and air 

 tight; which,- from its texture, being that of coarse unglazed 

 earthenware, and particularly from the covering of its mouth 

 being a still more coarse unburnt mortar, could not be presumed 

 to be the fact. 



Dr. Goddard admitted the action of light, in explaining the 

 phenomenon in question ; but as he supposed the cloth to have 

 been originally of a yellow or brownish colour, such as it assumes 

 on being removed from the jar, he considered the presence of 

 bitumen not necessary to the change. He cited, in illustration, 

 the Cartoons of Raphael, which, having faded in a moderately 

 lighted room, were subsequently restored to their original colours 

 by exposure to the sun's rays. 



Some further observations ensued on the action of light, and 

 its effects in bleaching resins. 



