THE BOOK OF THE LANTERN. 235 



1 had occasion to obtain from some half-plate negativss 

 some copies of them on plates measuring 16 by 13. The 

 problem I put to myself was this, which is the quickest 

 and best way of accomplishing the work ? After some 

 consideration I determined to work with the limelight, 

 for the weather was dull and uncertain at the time I am 

 speaking of, and 1 thought that I would at once eliminate 

 one common source of error by adopting a mode of illumi- 

 nation which represents a constant quantity. This being 

 settled, I next thought over the different systems of en- 

 larging, and finally decided to try a new plan. 



I am so constantly using the lime-light for lecture 

 purposes, that a residue of oxygen is always at hand, 

 ready for any home experiment that I like to try ; other- 

 wise, I should, perhaps, have decided to carry out my plan 

 with some other illuminant. Fitting a blow-through lime- 

 jet to an experimental lantern with a 4-inch condenser, 

 and with a quarter-plate portrait lens as the objective, my 

 optical arrangements were complete. But a 4-inch con- 

 denser is clearly useless for projecting the image of a 

 negative nearly double its area. My first operation was, 

 therefore, to make some small positives on glass from the 

 negatives. This was easily done by fitting the negatives 

 into my copying apparatus, and using a quarter-plate 

 camera. The size of the resulting positives was just two 

 inches across ; smaller, it may be thought, than was abso- 

 lutely necessary. But, by this plan, I employed the best 

 part of the projecting lens, and there was no chance of any 

 falling off in sharpness at the margin of the pictures. 



The small positives were made with very great care, the 



