ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



329 



Fig. 55. 



is a useful auxiliary, as it is always at hand for purposes of small 

 magnification. 



Details of the other uses of the instrument are omitted here, as 

 scarcely falling within the proviuce of microscopy. 



An arc lamp " volta " is recommended as the best source of light. 



Combined Condenser and Polariser for Petrographical Microscopes.* 

 — Mr. W. L. Patterson's arrangement consists of a double lens con- 

 densing system, and a Nicol prism 

 mounted as shown in fig. 55. The 

 upper condensing lens is mounted on 

 a revolving arm, so that it may, at 

 the will of the operator, be instantly 

 thrown in or out of the optical axis by 

 a lever : a suitable stop being provided 

 for bringing it to a central position. 

 The lower lens is mounted at the 

 proper distance below the upper sur- 

 face of the apparatus, so that, when the 

 upper lens is moved out of optical axis, 

 the lower lens focusses upon the slide, 

 thus avoiding the necessity of re-focus- 

 ing the condenser system when chang- 

 ing from the double to single combina- 

 tion. The Nicol prism is mounted in 



a revolving sleeve with graduated collar, and a stop to indicate zero, or 

 the position when the prisms are crossed. 



The author claims the following advantages over other similar 

 contrivances: 



1. It is not necessary to increase the size or thickness of the Micro- 

 scope stage. 



2. The attachment is always in focus when one or both lenses are 

 used. 



3. Compactness and freedom from liability to disturbance while stage 

 or slide is being operated. 



(6) Miscellaneous. 



New Form of Loup-holderf — M. Malassez has aimed at producing 

 a portable and inexpensive loup-holder, of a nature such that a travelling 

 Microscope could be used as it stands. Fig. 56 shows one of his ar- 

 rangements. The weight of the loup and its holder is counter- 

 balanced by a fairly heavy ball sliding on a quadrangular stem, whose 

 extremity screws into the collar of the holder. The rackwork and 

 niicrometric screw of the Microscope are, as is readily seen in the figure, 

 available for focussing and adjustment. In order to be able to fit in 

 loups of different diameters, the inventor makes use of a kind of small 

 vice with parallel grip, actuated by a screw. The whole arrangement 

 allows to the worker great freedom of position, and especially secures 

 his face from contact with the apparatus. 



For the convenience of those who may prefer the loup-holder to be 



* Journ. App. Micr., 1901, p. 1155 (1 %.). 

 t Arch. Anat. Micr., 1900, pp. 424-8 (2 figs.). 



