THE BOOK OP THE LANTERN. 227 



required dimensions, and having seen that that image is 

 as sharply focussed as possible, it will be as well if a slip 

 of sensitive paper, say, 1 inch wide, is first of all exposed 

 as a pilot. 



In the hurry and bustle incidental to, if not inseparable 

 from, every -day life, we all have a tendency to work too 

 much by rule of thumb, and it must be confessed that rule 

 of thumb often turns out very good results. But, in spite 

 of this, and of the old adage to the effect that an ounce of 

 practice is worth a pound of theory, we cannot afford to 

 give theory the go-by entirely. Theory is a useful servant, 

 but a bad master, for those patient, plodding creatures who 

 think of nothing else seldom turn out work which has the 

 stamp of genius upon it. Theory holds them down in her 

 rigid grasp, and they have not the pluck to try anything 

 or dare anything that seems opposed to her teachings. If, 

 on the other hand, theory be regarded as a reliable servant, 

 to be consulted when difficulties occur in practice, her 

 value will soon be recognised. 



These thoughts came into my mind once when watching 

 a young experimenter, who was endeavouring to make 

 some enlargements on bromide paper from small negatives, 

 by means of an oil lantern. The negative was placed 

 on the stage of the lantern, and its image was projected 

 upon the side of a wooden packing-case, which stood on 

 the table in front of it. My young friend was endeavour- 

 ing to make from his small negative (J-plate) enlarged 

 copies of different sizes ; and, to obtain the different sized 

 images, he had, of course, to move the focussing surface 

 either to or from the lens as the image was required to 

 Q 2 



