198 THE BOOK OF THE LANTERN. 



piece of ice may show them exquisitely, while a second 

 portion shows them imperfectly. 



" Here we have a reversal of the process of crystallisation. 

 The searching solar beam is delicate enough to take the 

 molecules down without deranging the order of their archi- 

 tecture. Try the experiment for yourself with a pocket- 

 lens on a sunny day. You will not find the flowers con- 

 fused ; they all lie parallel to the surface of freezing. In 

 this exquisite way every bit of the ice over which our 

 skaters glide in winter is put together." 



One of the most interesting chemical operations to 

 witness is the development of a photograph, and even 

 experienced workers will say that they never tire of 

 watching the gradual unfolding of the wonderful image. 

 Those who have never before had the opportunity of watching 

 the effect of the developing fluid on the blank plate, are 

 delighted when first the operation is brought under their 

 notice. It is certainly an experiment which never fails to 

 interest an audience, when properly performed, as it can be, 

 in the optical lantern. But the operator mast not be 

 a novice in photography, or he will probably fail, for the 

 experiment requires experience, land great care in all 

 its stages. 



A gelatine bromide plate, such as is ordinarily used 

 for negative work,, is of no use whatever here, for the 

 film is too opaque for the purpose. A gelatine chloride plate 

 (such as that described on page 133) is the right thing to 

 employ. If we compare a bromide and a chloride plate side 

 by side in the dark room, we shall soon see that there is 

 little difficulty in distinguishing the one from the other. In 



