THE MICROSCOPE STAND 119 



It will be seen from the illustration that the attachment con- 

 sists of two pieces, one screwing on to the body-tube of the 

 microscope, and including the vertical illuminator (D), and the 

 other fitting into the standard substage or understage and held 

 in place by the screw H. 



Light from any desired source is projected into the prism A 

 and reflected into the prism B, and from thence to the prism 

 C and again into the vertical illuminator, where the light is 

 reflected, by the thin glass reflector D, downwards through the 

 object glass to the metal surface to be examined. 



A removable lens is fitted at G which can focus the iris dia- 

 phragm (F) upon the object and enables all extraneous light to 

 be cut ofi; a holder (E) for light filters and ground glass is 

 placed inmiediately behind the iris diaphragm and enables the 

 diaphragm to be used as the light source. The iris diaphragm and 

 ground glass can be moved so that it can be focussed upon the 

 object, thus giving so-called " critical " illumination. 



The reflector in the vertical illuminator is readily removed for 

 cleaning or replacement. A thin glass and a thicker parallel 

 glass, a green glass and a ground glass are supplied with each 

 instrument. 



For geology and mineralogy the illuminator wiU also be found 

 of value in the examination of polished specimens of ores and rooks. 

 The fact that objectives of different powers can be used and 

 focussed without interfering with the adjustment of the light is 

 of special importance in the examination of opaque metaUiferous 

 minerals. 



The bench metallurgical microscope (Fig. Ill) has no pillar and The bench 

 base. It has a limb carrying the body with the usual coarse and fine ^^oai 

 adjustments fixed to a large square stage. This stage is carried on miorosoope. 

 four levelling screws one at each corner of the stage. The micro- 

 scope can be stood upon a table or bench and used in the ordinary 

 way with specimens placed on the stage, or it may be placed on a 

 large metal or other surface, and the surface examined by focussing 

 the object glass down through the aperture in the stage. To render 

 this microscope convenient for metallurgical work a metal filament 

 electric lamp is attached to the illuminator and is provided with a 

 pair of light-tight tubular covers. It moves up and down as the 

 microscope is focussed, thus allowing the instrument to be focussed 

 without interfering with the Ulumination. The prism illuminator 

 is supplied with this microscope because it is more suitable for 

 low powers and almost equally good for high powers. This in- 

 strument is useful for many other purposes, including the Brinnel 

 test, in which case a scale is fitted into the eyepiece. The electric 

 filament lamp can be used on any voltage from 100 to 250 volts, 

 and on direct or alternating currents. It is troublesome to use a 

 lamp of low voltage which requires accumidators, but for those 

 who have 6- or 12-volt accumulators suitable lamps can be supplied. 



