'284 



MEMOIR ON COLOURED SHADOWS. 



as produced by 

 the meridian fun 

 at dilYcrent pe- 

 riods of the 

 year. 



35 produced by 

 difference of la' 



titude. 



Refult of the 

 obfervations. 



Every day from the firft of Nivofe to the firft of Meffidor, 

 the folar fhadow offers different tints, at the moment when 

 this luminary paifes the meridian. The firft days of Nivofe, 

 the flwdow is violet, a little blackifli; it increafes in blacknefs 

 daily to the firft Meffidor j at this period, the fliadow is violet- 

 black. 



If the coloured fliadow of the rifing fun is obferved on a 

 clear day, at the fame period, and in different latitudes, it 

 will be feen to vary from violet-blue to green, going from the 

 equator to the pole. 



The coloured fliadow obferved at the beginning of Nivofe, 

 at fun-rife, from Meflina to Skalhot in Iceland, is, atMeffina, 

 light indigo ; at Vienna and at Paris, blue, with a flight green 

 tinge; at London, Berlin, Copenhagen, Edinburgh, a more 

 diftinft green tinge ; at Peteriburg, a little more green j 

 finally at Drontheim and at Skalholt, a greenifti tint. 



At the fame period, at noon, the fliadow varies, between 

 Meffina and Skalholt, from black flightly tinged with violet to 

 violet. 



The comparifon of the colour of the fliadow of the fun, 

 with its fituation in the different places where it is obferved, 

 naturally leads to this firft conclufion, that it is different in 

 the ratio of the intenfity of its light, compared with that of 

 the atmofphere, in fact, the rifing fun, on the firft of Nivofe, 

 having a feeble light in comparifon with that of the atmof- 

 phere, the fliadow is a greenifli blue; as it rifes above the 

 horizon, the intenfity of its light increafes, and the fliadow 

 becomes blue, indigo, violet : finally, when the fun is on the 

 meridian, its light has acquired its greateft intenfity, and the 

 fliadow blackens, preferving neverthelefs a violet tinge. 



Comparing in the fame manner the colour of the fliadow 

 obferved each day of the year at Paris, as well as that ob- 

 ferved in each latitude on the fame day, it will be feen, that 

 it changes from green to violet-black, according to the inten- 

 fity of the light acquired by the fun ; and when in winter the 

 fun, being but little elevated above the horizon, appears red, 

 from the feeble light which penetrates the light mifts ejcifting in 

 the air, the folar fliadow is green, fometimes a fine grafs green. 



To fatisfy ourfelves vyljether the colour of the fliadow de- 

 light which is pended on the relation of the light compared to that of the at- 

 vaxied, niofphere, we placed the light of a lamp near a white furfaoe, 



illuminated folely by the light of the atmofphere j when this 



lamp 



Experiments 

 with an artificial 



