L".»S SUMMARY OF CURRENT RESEARCHES RELATING TO 



MICROSCOPY. 



A. Instruments, Accessories, etc.* 

 (1) Stands. 



Swift and Son's " Improved Dick " Penological Microscope 

 (Khartum Model). j — The first Microscope of this type (fig. 30) was 

 built to the specification of G. W. Grabharn, Senior Geologist to the 

 Sudan Government, Khartum. Possessing all the features of previous 

 " Dicks," it provides also additional adjustments, and permits the use of 

 further apparatus of the greatest practical utility to mineralogists. It 

 is provided with a rack-and-pinion focusing substage with centering 

 movements, which carries a triple nose-piece for the different condensers, 

 an iris-diaphragm, and a rotating swing-out cell for stops. Any con- 

 denser with the R.M.S. standard screw can be used. The iris-diaphragm 

 fitted below the condenser serves not only to regulate the illumination 

 of the object, but also to cut down the cone of light in order to test the 

 refractive indices of minerals and mounting media. The rotating swing- 

 out cell carries stops for giving oblique and dark-ground illumination. 



(3) Illuminating and other Apparatus. 



Hutchinson's Universal Goniometer.^ — This instrument (fig. 31) 

 is a goniometer of the suspended type. It is intended for the examina- 

 tion of small crystals, and by its aid all the usual crystallographic mid 

 optical determinations can be carried out. It is specially adapted for 

 the following purposes :— (1) as an ordinary goniometer ; (2) as an 

 axial-angle apparatus ; (3) as a Hohlrausch total reflectometer ; (4) for 

 determining refractive indices by the prism method. 



A circle D, 5 in. in diameter, graduated to half degrees and reading 

 by a vernier to minutes, is supported by a stout bracket S, at a height of 

 10 in. above a base plate P, 11 in. square. The circle is provided with 

 a slow-motion attachment, and can be clamped by the screw E. A steel 

 rod, which can be clamped at any convenient position by the screw F. 

 passes through the centre of the circle and carries at its lower end the 

 centering and adjusting head shown at G. A loose collar, which can be 

 clamped to the rod by the screw R, gives the means of raising the 

 adjusting head and of again lowering it to its former position. 



A telescope A and a collimator C are securely clamped to the base- 



* This subdivision contains (1) Stands ; (2) Eye-pieces and Objectives ; (3) 

 Illuminating and other Apparatus ; (4) Photomicrography ; (5) Microscopical 

 Optics and Manipulation ; (6) Miscellaneous. 



f J. Swift and Son's Catalogue, 1914, pp. 17-8. 



J J. Swift and Son's Catalogue, 1914, pp. 28-9. 



