ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 101 



arranged so that the operator could focus directly on to the sensitive 

 layer. The stop apparatus was synchronous with the descent of the 

 film, and was -placed in the luminous beam before the beam reached the 

 preparation. Thus in the intervals of rest the moving particles were no 

 longer submitted to the action of the light and heat of the electric arc. 

 The whole apparatus was operated on an optical bench whose very mas- 

 sive support eliminated vibrations as much as possible. Moreover the 

 apparatus could be arranged at a variable distance from the Microscope. 

 In order to get exactly the illusion of movement seen in the ultra- 

 microscope, the cinematographic views must be taken at normal rate, that 

 is to say at the rate of sixteen photographs per second, thus giving a 

 pose of ^V sec - f° r eac h image. The quantity of maximum light, the 

 film-sensitiveness, the pose time, being quantities almost fixed, the 

 magnification must be varied in order to get the images with optimum 

 illumination. The best results for photographs of blood and its parasites 

 were obtained with a Zeiss 4 mm. apochromat, No. 4 projection ocular, 

 and a film at 0*28 metre from the ocular (plate II.). A magnification 

 of about 280 diameters was thus obtained. In order to get a quantitative 

 measure of the movements of the particles, a rod beating seconds 

 intercepted the luminous ray and thus provided a scale of observation. 

 The author made some very interesting comparative studies of those 

 small mobile blood particles known as Muller's hsemokonies, which were 

 easily counted by this method. 



Crabtree, J. H. — Formation and Photomicrography of Crystals. 



[A useful article on the method of production, of illumination, and photo- 

 micrography of crystals ; is well illustrated.] 



Knowledge, vi. (1909) pp. 411-14 (10 figs.). 



(5) Microscopical Optics and Manipulation. 



Methods of Determining the Amount of Light Scattered from 

 Rough Surfaces.* — W. F. Barrett, having been consulted in connection 

 with a case of " ancient lights," found it desirable to devise some trust- 

 worthy methods for determining the amount of light scattered from 

 large rough surfaces such as the wall of a house. The word " scattered " 

 is to be taken in the sense of " irregularly reflected." Ordinary photo- 

 metric methods are inapplicable in the case of large surfaces. The 

 author devised the two following methods. 



Method A. — This consists of a rapidly revolving opaque disk with a 

 transparent sector which can be altered in size, and whose angular 

 magnitude can be measured (fig. 13). It can be driven by hand, a 

 simple speed-gear being all that is necessary. It is placed at a given 

 distance between the reflecting surface, which is illuminated by the sun 

 or strong artificial light, and the photometer. The width of the sector 

 is altered until equality of illumination between the reflecting surface 

 and a standard source of light is obtained, as shown by some transmission 

 photometer such as Bunsen's, Joly's, or Lummer and Brodhun's. If 

 the scattered light is coloured, as from a brick building, a wedge of 

 suitably coloured glass, or a coloured gelatin film of increasing thickness 

 is gradually interposed in front of the standard light until a similar tint 

 is obtained. 



* Soi. Proc. Roy. Dublin Soc, xii. (1909) pp. 190-7 (3 figs.). 



