120 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



observer's eye, to suit which, changes have to be made in the distance of 

 the paper which give rise to distortions. 



His new camera (fig. 10) has two mirrors, one C silvered, and the other 

 a of clear glass, and both set at 45°. The observer looks at the object 

 through the unsilvered mirror, and at the same time by reflection from 

 the two mirrors sees the drawing paper z. There are two convex lenses, 

 one & in a vertical plane between the two mirrors, and the other d in 

 a horizontal plane between the object and the unsilvered mirror. The 

 camera and stage slide on a graduated vertical rod (fig. 11), the feet of 

 which rest on the drawing paper, and the positions of the camera and 

 stage are so arranged that the object and the paper are at the foci of the 

 two lenses. Consequently an eye accommodated to infinity sees both 



Fig. 10. 



Fig. 11. 



object and drawing clearly. To regulate the illumination of the two 

 images, smoked glasses are used. A spectacle glass /can, if necessary, 

 be placed in the eye-piece to correct to infinity the eye of the observer. 

 To avoid parallactic displacement of the images a diopter g is fitted in 

 the eye-piece above the spectacle glass. The author gives tables of the 

 necessary lenses and distances of object and drawing plane for different 

 magnifications. For diminutions, the positions of object and drawing 

 plane are reversed. 



Besides the capability of accommodation to the state of the observer's 

 eye, the apparatus possesses the advantage that for weak magnifications 

 a large field of view is obtained. 



Finally the author points out how the use of weaker convex lenses 

 may enable the observer to dispense with the concave glass used for 



