On i^ohured Shadows. 39 



shone upon by the light will assume a pale red colour, without 

 there being any shadow; if the object-glass is red, the light will 

 make the place where it falls appear of a greenish blue. 



The following facts come also in support of Mr Trechsers 

 fundamental opinion. 



1*^, The natural bluish shadows are more distinctly observed 

 in winter, with an overcast sky and a hazy atmosphere. Now, 

 in these circumstances, the blue light predominates, on account 

 of its greater refrangibility. According to Mr Zschokke's hy- 

 pothesis, the shadows projected in this blue light would not be 

 blue, but red or orange; it is seen, on the contrary, that the 

 blue tint which they really have, comes from the reflection of 

 the predominant blue light of the day. 



9>d^ If this bluish shadow be illuminated by the yellowish hght 

 of a burning candle, it assumes, at the very moment, a yellowish 

 tint. 



3J, On the other hand, the black or greyish shadow of the 

 light of a candle assumes a blue colour, whenever some rays of 

 the light of day are made to fall upon it. This is Rumford's 

 experiment. 



4^/^, If there be placed behind the shadow projected by this 

 day light when it is weak, an object painted red, yellow, or any 

 other colour, the shadow immediately assumes a tint similar to 

 that of the object which sent reflected light to it. 



5th, The shadows coming from the interception of the light 

 of a candle, are always of a more or less deep black, provided 

 there has been only one candle burning ; they appear yellowish 

 when two are hghted, of which the one shines upon the shadow 

 produced by the interception of the light of the other. 



" It is easily seen,*" says Mr Trechsel, " that there can be no 

 question here of the inflection of the light in the shadow, either 

 according to the ordinary explanation of this phenomenon, or 

 according to Mr FresnePs theory of interferences ; for, 1^^, The 

 coloured shadows are homogeneous, and not composed of alter- 

 nate bands; ^dly. They are obtained of any breadth that one 

 pleases ; ^dJy, They preserve, in general, the same colour, al- 

 though they change their intensity at each variation produced in 

 the distances which separate the plane that receives the light, 

 the opaque body and the source of light.'" 



