PREFACE. IX 



name the instrument is already constantly called upon 

 to illustrate various subjects, and I venture to state 

 that its use will be greatly increased now that so 

 much attention is being paid to the art of photo- 

 micrography, by which enlarged pictures of micro- 

 scopic objects can be easily rendered available for 

 projection by means of the lantern. A large class 

 of students can thus at the same moment study the 

 structure of an organism which may be in reality 

 invisible to unaided sight by reason of its minute 

 size. 



But during the past few years, the number of those 

 who interest themselves in the lantern and its 

 capabilities has been vastly increased by the sudden 

 popularity of the art of photography. Amateur 

 photographers are now to be found in every town in 

 the kingdom, and they are beginning to find out that 

 there is no better method of showing their friends the 

 pictures which they have taken than by means of the 

 optical lantern. The same instrument, too, as it 

 offers a means of making permanent enlarged copies 

 of small photographs, serves with them a double 

 purpose. 



The introduction as illuminants of the hydrocar- 

 bons, under the name of petroleum, paraffin, kerosene, 

 &c., has also had its share in the recent development 

 of the optical lantern, for now a few pounds will 

 purchase a better instrument than was procurable at 

 any price twenty years ago. 



I . 



