INTRODUCTION 5 



The manufacturer naturally advertises the possibilities of his 

 apparatus as if he expected it to be used under the most favorable 

 conditions, and operated by men skilled in the use of optical instru- 

 ments, and the results to be judged by persons of experience who 

 do not expect the impossible. 



For example, if one reads the statements concerning the projec- 

 tion of pictures in books, photographs, postal cards and actual 

 objects, the impression would be very strong that the screen pic- 

 tures so produced were every bit as satisfactory as those of lantern 

 slides, and just as easily produced. In speaking with many 

 individuals we have found the belief is very general that with the 

 new apparatus nothing is simpler than to get good screen images 

 of objects, pictures, etc., with all their natural colors, and that the 

 expense of lantern slides can be wholly done away with. But we 

 have yet to find the actual user of such apparatus who found his 

 sanguine expectations fully realized. 



Modern opaque projection is marvelous in its accomplishments, 

 but what is gained in the use of actual objects, books, etc., is lost in 

 the relative dimness of the screen image, in the expense and diffi- 

 culty of managing the apparatus, and in the large electric current 

 needed to give even tolerable screen images. 



Judging from our observations the manufacturers have not fully 

 realized the lack of optical and mechanical knowledge and instinct 

 in many users of projection apparatus. Naturally, the user of the 

 apparatus wants results, and he wants the apparatus to give the 

 results without trouble. 



Perhaps the most striking, as also it seems to us the most easily 

 obviated defect, is, that with many parts of the apparatus, it is just 

 as possible to insert them in the wrong position as in the right 

 position. For example, in most of the apparatus we have examined 

 the condenser is so mounted that it can be put with either end 

 facing the arc lamp. So with many other parts, they can be put in 

 a wrong position just as easily as in a right position. 



In our opinion there are five fundamental rules in the production 

 of projection apparatus that the manufacturers should follow: 



