Manchester Memoirs, Vol. lix. (191 5), No. \%. 31 



Sheet 38. 



(9 J" x I7i".) Probably used to illustrate the law of 

 inverse squares. It consists of four blackened squares 

 having the relative areas of 1 : 4 : 9 : 16. White lines 

 are used to divide the larger squares into areas equal to 

 the smallest square. 



Sheets 39 and 40. 



The first is a small diagram (16" x 10") showing the 

 method of the formation of the image of an object (a 

 Latin cross) by a plane mirror. The second is like the 

 last but larger (21" x 16"). 



Sheet 41. 



(17" X 21".) Two plane mirrors lettered A and B 

 are inclined at an angle of 30 . Between them are two 

 objects, a x and a 9. The multiplication of the images 

 of these objects is represented, there being eleven images 

 of each. Dalton has marked the manner of the forma- 

 tion of each image. Thus one of the images of the x 

 is marked 



" 1 b by a by b by a by b ", 



a and b referring to the mirrors A and B. 



Sheet 42. 



(21 J" x 1 7 J".) Multiplication of the images of a candle 

 flame by a single plane mirror, due to the reflection from 

 the front and back surfaces of the looking glass. The 

 formation of seven images is represented. 



Sheet 43. 



A small diagram (16" x 10") probably for use in small 

 lecture classes. It shows the formation of images of 

 Latin crosses (1) by a concave mirror giving an inverted 



