THE BOOK OF THE LANTERN. 11 



sing purposes, and that its chief expanding part is made 

 of folded leather (concertina bellows fashion). Now, why 

 should not the same arrangement be adopted for the 

 optical lantern ? We here require a similar extension of 

 the front of the instrument, in order to suit the foci of 

 the different lenses employed, and according to the dis- 

 tance and size of the picture which we wish to project on 

 the screen before us. Surely some arrangement of the 1 

 kind could be adapted to the lantern. If such a change 

 of construction were brought about, and with analogous 

 alterations in other parts, the weight of a double or triple 

 lantern would certainly be reduced to about one-third of 

 of what it is at present. It may, perhaps, take some time 

 for opticians to appreciate this view of the case, and there 

 may be good trade reasons for not making a change of 

 such a radical nature. I am not behind the scenes, and 

 so cannot tell. It might certainly be urged with some 

 truth that there is no need to be in a hurry to alter the 

 present type of lantern, seeing that lightness of construc- 

 tion may soon be brought about by the substitution of 

 aluminium for brass. The production of the former 

 metal is daily becoming cheaper, and as its weight, bulk 

 for bulk, is about one-third that of brass, and as it is 

 strong, not easily tarnished, and in other respects is suit- 

 able for the purpose of lantern construction, we may look 

 forward to its adoption in this service. 



Where a lantern is used for educational purposes it 

 requires certain additions which are quite unnecessary in 

 exhibition instruments. On the other hand, several 

 ornamental adjuncts which are desirable in the latter 



