662 SUMMARY OF CTJKRENT RESEARCHES RELATING TO 



fication of about five times the initial magnifying power of the objective 

 employed, and when fully extended gives ten times the initial power of the 

 lens. The outer cardboard tube is fastened to an upright piece of wood 

 which is clamped to the baseboard by thumb-screws at any point of its 

 extension. The focusing screens of grey glass and plain glass with ruled 

 lines, slide in grooves at the back of the upright piece of wood. The double 

 back is the well-known Tylar patent metal one, which is cheap and 

 efficient. This back is not a fourth of the cost of the wooden ones, and 

 is free from the objectionable sticking of the slide due to the warping of 

 the wood. The focusing is effected by a rod which runs down the right- 

 hand side of the camera, a string passes round this and over a pulley 

 on the other side of the board, taking a turn round the milled head of the 

 fine-adjustment screw. This string is kept tight by a piece of elastic. 

 The feet of the Microscope fit into blocks fastened on the baseboard. 



Mr. Nelson especially recommends the aplanatic lens No. 127 in Zeiss's 

 catalogue, power 6, as a focusing glass, and says that " the whole of the 

 apparatus, viz. camera. Microscope, and lamp, is produced at a cost less than 

 is usually paid for a camera alone. It is not a makeshift which is only 

 capable of doing fairly good work, but it is proved by practical experience 

 to be equal to the highest class of work. The Campbell differential screw 

 fine-adjustment will be found peculiarly serviceable for photomicrographic 

 work, as it is slow and free from spring, which is the bane of every geared- 

 down fine-adjustment." * 



PhotomicrograpMc Camera for the Simple or Compound Microscope.f 

 — Dr. P. Francotte's camera is intended specially for Mayer's simple Micro- 

 scope, but can be used with any instrument in a vertical position. Low 

 powers only are used. In form the camera is merely a pyramidal box with 

 four sides. The topmost side carries a quarter-plate frame (9 x 12). The 

 lower one is fitted with a brass tube by which it is arranged in the Micro- 

 scope. By means of three screws, exact centering is perfectly obtained. 

 A frame with ground glass serves for the superficial point and the regulation 

 of light, and for the exact point a frame with transparent glass and a single 

 lens of low power is used. The frame for the sensitized plates is double, 

 and is supplied with two intermediate arcs, the one for a glass 6x4^ 

 (quarter plate cut in two), the other for a quarter plate cut in four. With 

 Steinheil's lens and monochromatic light, beautiful cliches of entire sections 

 of larvae of Salamander, &c., 15-18 mm. in length, were_ obtained. The 

 images were 9-11 cm. long. The sections were stained with picrocarmine 

 and the plates used were those obtained from Attout-Taillefer or those of 

 Monckoven or Beernart sensitized for red rays by quiuoline blue (cyanine). 



The apparatus also gives good results with the compound Microscope, 

 with or without the ocular. 



Focusing in Photomicrography. — The inconvenience of focusing by 

 means of long rods has been attempted to be obviated in several ways. 

 One method, by the substitution of a piece of white paper for the ground 

 glass, viewing the image from an opening at the side, was described in this 

 Journal, 1886, p. 841. 



To accomplish the same object, Dr. B. Benecke | inserted a telescope 

 with a right-angled prism in the front part of his camera (fig. 188), by 

 means of which the image on the screen of white paper at the other end of 



* Cf. Engl. Mech., xlv. (1887) p. 213. 



+ Bull. Soc. Belg. Micr., xiii. (1887) pp. 149-51. 



j ' Die Photograpliie als Hilfsmittel Mikroskopischer Forschung,' 1868, pp . 74-5 



(1 fig). 



