32 Gee, Da/ton's Lectures and Lecture Illustrations. 



magnified real image, (2) by a concave mirror giving an 

 erect magnified virtual image, and (3) by a convex mirror 

 giving an erect, diminished and virtual image. Dalton 

 has written " object " and " image " against the crosses. 

 On the back of the diagram he has written " optical 

 schemes." 



Sheet 44. 



A larger diagram (21* x 16 J") showing the production 

 of images by curved mirrors. Two cases are drawn, the 

 formation of an erect magnified virtual image by a 

 concave mirror, and the formation of an erect diminished 

 virtual image by a convex mirror. Each mirror has the 

 same focal length, and the size of the object in front of 

 the convex mirror is made equal to the image in the 

 concave mirror, and since their distances from the mirrors 

 are also equal, one diagram is the reverse of the other. 



Sheet 46. 



(2 1 J" x 17I".) Two diagrams, the upper one repre- 

 senting the experiment of Newton. Light from the sun 

 passes through a hole and falls on an equilateral glass 

 prism which produces a spectrum. The lower diagram 

 explains the well-known experiment, which Dalton 

 showed in his lectures, of a coin placed in a vessel in such , 

 a position that the coin cannot be seen until water is 

 poured into the vessel. 



Sheet 47. 



(17I" x jo-J".) Illustrates the use of a Wollaston's 

 prism as a Camera Lucida. The diagram shows the two 

 reflections from the faces of the quadrilateral figure that 

 are essential to prevent a reversed image. 



