28 MEMOIR ON COLOURED SHADOWS. 



in an iron forge J On illaniinating the pafteboard by the h'ght of a lamp and 

 that from the combuftion of culm in an iron forge, the (liadovV 

 arifing from the light of-the culm was bluifh, and that from the 

 lamp reddith. 

 In a glafs-houfe On illuminating the pafteboard by the light of a lamp and 

 burnt • '^^^ ^"^^"^ ^^® culm burnt in the furnaces of a glafs-houfe, where 



the brilliant flame of the working flues reddened that of a lamp, 

 the refult was fimilar to the preceding: the light from the 

 culnv produced a blue fliadow, and that of the lamp a reddifli 

 fhadow. 

 with a lamp and When the pafteboard is illuminated by the light of a lamp 

 "^° * and that from the combuftion of charcoal, the fliadow of the 



charcoal is blue, and that of the lamp red. 



The pafteboard illuminated by the light of a lamp and that 

 of charcoal urged by the large bellows in a chemical furnace, 

 fo as to produce a whitifli light as well as that violaceous light 

 fometime* obferved in the furnaces of a forge and in tall fur- 

 naces, conftantly afforded the fame refult. In thefe two cafes 

 the fliadow from the light of the charcoal was bluifli, and that 

 Pmbabillty that from the lamp reddifli. The identity of the colours of the 

 the colour of fliadows obtained in thefe three experiments with charcoal^^ 



the fliadows is • r, , r ,r^ - ^ 



produced by the "o^w'thftanding the colour of the flame was different m each 

 nature of the experiment, leads to an opinion that the refult depends on the 

 nature of the combuftible. Neverthelefs, to obtain more prO' 

 bability, we made furtber obfervations. We filled a chemical 

 furnace with charcoal, and having covered it with its dome 

 for the purpofe of comparing the fliadow of the dire6l light of 

 the violaceous flame arifing from the combuftion of the char- 

 coal, with that of the light of a lamp, we took notice of the 

 fhadows of thefe two lights at the moment when the flame 

 Singular change appeared at the fummit of the furnace. F6r a confiderable 



of colour in the ^j^^^ ^^ obferved that the colours of the fliadows were very 

 Ibadows* „ 



uncertain : fometimes the fliadow of the lamp was blue, and 



that of the flame red ; at other times the fliadow of the flame 

 was blue, and that of the lamp red. This alternate change in 

 the colours of the fhadows from blue to red, continued until 

 the charcoal, which was in the upper part of the dome, was 

 completely inflamed ; then the colours of the. two fliadows be- 

 came fixed, that from the flame of the charcoal became bluifli, 

 and that from the light of the lamp reddifli. 

 Repetition of As, from the obfervations of feveral perfons to whom thefe 



the expenm^t Jgf^l^^s ^gjg commui\icated, we were induced to believe that 

 y urnmg c ^^^ 



