468 



Propagation and Intensity of Light. 



No. 53 645 



53646. 1 : 10. 



53 647. 1 : 5. 



53 649. 1 : 4. 



53 650. 1 : 2. 



53 651. 1 : 2. 



53.645. Photometer after Foucault, Figure (Chwolson II, Fig. 350), with observing tube 



In this photometer the screen is formed by a glass plate covered with dry milk, this arrange- 

 ment being very sensitive. 



53.646. Photometer after Ritchie, Figure (Fr. phys. Techn. II, 2, Fig. 3379 [II, Fig. 693]) 



In this apparatus observations are taken on two white surfaces inclined towards each other. 



s. d. 

 2. 8.0 



1. 4.0 



53.647. Demonstration Photometer after Eitchie-Weinhold, arranged for objective demon- 

 stration, Figure (W. D., Fig. 263 [249]) | 1. 2. 



53.648. Diffusion Photometer after Joly, Figure (W. u. E. phys. Prakt,, Fig. 131) . . 2. 0. 



The photometer consists of a screen, carrying in front of an aperture two small paraffin blocks 

 with the plane surfaces pressed on each other. The paraffin blocks appear equally bright when 

 illuminated to the same intensity and the partition joint disappears entirely. Absorption glasses run 

 be inserted at M. 



53.649. Photometer after Wheatstone, Figure (Gan.-Eein., Figs. 484 [485]) 1. 16. 



The apparatus consists of a spherical mirror moved in a curve by means of a set of wheels. 

 The luminous sources to be compared are reflected in the small mirror as two luminous points, which 

 shine as two curviform image* of different brilliancy when the mirror is rotated and when the illu- 

 mination is unequal. 



I 'I. 1212,1213, 1210, I'.Ml, 1214. 

 5931, 5932. 



