MEMOIR ON COLOURED SHADOWS. ^ 



the great I'ntenfity of the light of charcoal obtained by its com* charcoal in oxi- 



buftion in oxigen gas, might change or make fome variation ^^"8'^^» 



in the colour of the fliadows, we ignited the extremity of a 



piece of charcoal, and urged its combuftion by a jet of oxigen 



gas ; tlie gas was contained in a bladder, which was prefled ♦ 



by the arm; the light obtained was extremely brilliant. A with a fimllar 



white parchment, illuminated at the fame time by this light ^^ " ^' 



and that of a lamp, prefented two coloured fliadows; that 



from the light of the charcoal was blue, and that from the 



lamp red. 



From the experiments we have detailed it refults, that the Summary of the 



fliadow of thelight of hidrogen and of alcohol is reddifti, when ^^P"^"^^"'^ > 



that of the lamp is blue ; that the fliadow of the light of wood, 



of culm, of charcoal, is bluifli, and that from the light of the 



lamp is reddifli; and as hidrogen and alcohol contain lefs , 



carbon than oil— and dry wood, culm, and charcoal contain 



lefs hidrogen than oil ; it would feem that the blue and red whence It Is in- 



colours of the fliadows of the two artificial lights, bear a relation ^^\^^^ that the 



• I I r r colour of the 



to each other correfponding with the proportions of thefe two ihadows depends 



combuflibles ; that the light produced by a fubftance in which "" *^^ predomi- 

 hidrogen predominates, gives a reddifli fliadow, and that pro- gen ©r carbon." 

 duced by a fubftance in which carbon predominates, affords a 

 bluifti fliadow. 



Although our experiments appear to lead to that conclufion, 

 and we took great care to be certain that the red and blue 

 fliadows produced by the two lights were independent of the 

 rapidity of the combuftion and intenfity of the lights ; never- 

 thelefs, we dare not hazard the prefenting this refult as forming 

 a general law; we prefer waiting until time and new experi- 

 ments ftiall confirm or deftroy them. 



Recapitulation. 



FROM the obfervations and experiments related in this 

 memoir, it follows, 



l/.-That the fliadows formed by the dired light of the 

 fun and that of the atmofphere, vary from meadow-green to a 

 violet-black, in a gradation through the blue, indigo, and 

 violet ; and that this variation depends on the intenfity of the 

 light (of the fun) compared to that of the atmofphere. 



2d. That the fliadows formed in apartments by the light of 

 the atmofphere and reflected lights, may prefent all the prif- 



matic 



