48 THE FAIRY-LAND OF SCIENCE. 
Here, again, invisible waves have been at work, and 
this time neither as light nor as heat, but as chemical 
agents, and it is these waves which give us all our 
beautiful photographs In any toyshop you can buy 
this prepared paper, and set the chemical waves at 
work to make pictures. Only you must remember 
Fig. o. 
Piece ol lace photographed during the lecture. 
to fix it in the solution afterwards, otherwise the 
chemical rays will go on working after you have taken 
the lace away, and all the paper will become brown 
and your picture will disappear. 
And now, tell me, may we not honestly say, that 
the invisible waves which make our sunbeams, are 
wonderful fairy messengers as they travel eternally 
and unceasingly across space, never resting, never 
tiring in doing the work of our world ? Little as we 
have been able to learn about them in one short hour, 
do they not seem to you worth studying and worth 
thinking about, as we look at the beautiful results of 
