PREFACE 



OUR aim in the preparation of this work on Optic Projection 

 has been to explain the underlying principles on which the 

 art depends, and to give such simple and explicit directions 

 that any intelligent person can succeed in all the fields of projec- 

 tion; and our hope is that the book will serve to make more 

 general this graphic art by means of which many persons can be 

 appealed to at the same time and in the most striking manner. 

 Furthermore we believe that this art has great, undeveloped 

 possibilities for giving pleasure, arousing interest and kindling 

 enthusiasm, in that it provides for the rapid demonstration of 

 maps, diagrams and pictures of all kinds, the structure and develop- 

 ment of animals and plants, many of the actual phenomena of 

 physics and chemistry, and finally scenes from nature and from life, 

 even with their natural motions and colors. 



The authors have received most generous aid from many indi- 

 viduals and many manufacturers; and most loyal service from 

 those who have helped to put the book in its present actual form. 



Manufacturers have not only answered our numerous questions, 

 but have put at our disposal valuable apparatus for experiment. 

 They have also loaned us electrotypes of their apparatus. 



We feel especially indebted to the Department of Physics of 

 Cornell University for the help given by different members of the 

 staff, and for the use of a research room and apparatus for the 

 numerous photometric and other determinations required. Pro- 

 fessor George S. Molcr of that department read over the manu- 

 script, and gave us many valuable hints derived from his experience 

 of over 40 years with all kinds of projection apparatus. 



While we have both joined in the preparation of the entire 

 work, each holds himself especially responsible for certain chapters 

 as follows: 



The senior author for 10 chapters (I-V, VII-X and XII). 



The junior author for 5 chapters (VI, XI, XIII-XV). 



SIMON HENRY GAGE, 

 October 4, 1914. HENRY PHELPS GAGE. 



