ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 223 



(3) Illuminating- and other Apparatus. 



High-Angle Condenser Carrier for Petrological Microscopes.* — In 

 connection with their Petrological Microscope, Watson and Sons have 

 recently introduced a new arrangement for quickly removing the upper 

 portion of the condenser from the field of view without the removal of 

 the polariser or other apparatus. 



The upper portion of the condenser mount, containing the lens which 

 produces the high-angled convergence, is carried on a holder which is 

 fitted into the stage itself. This holder can be immediately turned on a 

 pivot so as to bring the condenser into the optical axis, or remove it 

 therefrom. When high-angled convergent light is required, the holder 

 is turned so as to bring the condenser to the centre of the stage — it is 

 then just below the surface. The polariser is then pushed upwards, and 

 in so doing lifts the condenser from its holder and carries it upwards to 

 the surface of the stage. When the condenser is not required, the 

 polariser is lowered until the condenser rests once more on its holder, 

 when it can be at once turned aside. 



Miller Sub-Stage Spark-Gap Lamp for the Microscope.f — T. I. 

 Miller has arranged this apparatus (fig. 31) for photographing thin sec- 



QQ 



Fig. 31. 



tions of minerals while fluorescing. It is not possible to give exact 

 dimensions of the apparatus, because these must vary with the require- 

 ments of the Microscope selected. A piece of vulcanite f in. thick and 

 about 1 in. wide, is made with a base for two metallic terminal balls each 

 ^ in. in diameter, and mounted on pins having a tapered point. These 

 pins are driven into holes drilled in the vulcanite. Two wires of thin 

 copper are then wound around the pins, and connected to the secondary 

 of a ^-in. induction coil. This " lamp " is fastened to the sub-stage of 

 the Microscope by machine screws, which loosely fit through the slots. 

 By this construction it is quite easy to adjust the spark to the centre of 

 field, or entirely out of field. The balls may be made of various metals, 

 and provided with tapering holes to fit the pins, thus making it easy to 

 use various metals whose spectra and effect on the mineral section are 



* W. Watson and Sons' Catalogue, 1906, p. 79. 



t Optical Instrument Monthly (New York) i. No. 3 (Aug. 1905) pp. 13-14 (3 figs). 



