'292 Mr, Charles Tomlinson on 



audience is as follows : my lecture room is illuminated by 

 a branch of two gas lights. A large screen is placed six or 

 seven feet from, and parallel to the gas lights. One of the 

 gas lights is provided with a small wire frame fitted for the 

 reception of a piece of stained glass ; the screen is thus 

 illuminated by the coloured light, and also by the other 

 burner — two separate shadows of the body, or any opaque 

 object, are therefore cast, the one being complementary to 

 the other.''^ 



In this class may also be included coloured silks, moreens, 

 cottons, (fee, provided they are sufficiently thin, (or the 

 illuminating object sufficiently intense) to transmit the 

 light either of the sun or of an argand lamp. Windows 

 provided with red moreen curtains present favourable 

 opportunities for observation : if the sun be shining on the 

 window, and these curtains be drawn, a quantity of red 

 light will illuminate the ceiling, and a shadow falling upon 

 it will be green. So also in Mons. Meusnier's experiment, 

 where the sun shone through a hole in a red curtain, the 

 image of the luminous spot was green. If green, blue, 

 yellow, &:c. curtains be employed, the spots will be red, 

 orange, indigo, &;c. A disk of coloured glass with a hole 

 in the centre is an interesting and useful article for experi- 

 ments of this kind, the glass being easily pierced by means 

 of a common awl kept well moistened with oil of tur- 

 pentine. 



22. Class 3rd. The flames employed have been the 

 white, red, green, blue, purple and yellow fires, and signal 

 lights ; as also the less vivid, but equally efficacious, flames 

 obtained by solutions of the various salts in alcohol. In 

 most cases, the colours of the flames are not homogeneous, 

 and the complementary shadows are modified more or less, 

 by the presence of other colorific rays ; but where one 

 colour is in considerable excess, there is no difficulty in 

 procuring the complementary shadows. I have adopted a 

 very useful mode of testing the true colour of the shadow, 



* The advantage of this arrangement is, that the shadows are of a size sufficient 

 for a large audience to judge of and appreciate. It is obvious, that a similar 

 arrangement can be adopted with two lamps, or two candles. There must be two 

 sources of light, one of which is to afford coloured light, and tlie other to illuminate 

 the coloured shadow. 



