122 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



tubes is alternately V-shaped and flat, and the clamping arrangements 

 are entirely independent. The illuminating apparatus is an arc lamp 

 and parallelising system mounted on a brass tube fixed to the swinging 

 tail-piece. The arc lamp is described in this Journal, 1898, p. 170. 

 The entire instrument lests on three le veiling-screws supported by 

 thick lead disks on the surface of a stone table which is carried on brick 

 supports above the concrete foundation. 



Keichert's New Combined Apparatus for Drawing 1 , Projection, and 

 Photomicrography. — This apparatus (tig. 26) is principally adapted fol- 

 low powers (6 to 80 diameters) and can be worked with various forms 

 of the incandescent light (petroleum, spirit, gas). It answers the pur- 

 poses of drawing with magnifiers, photomicrography, and the projection 

 of lantern slides. It is supplied in three combinations : — (1) As a 

 drawing apparatus consisting of a stand fitted with stage capable of 

 moving up and down, condensing lenses in front of the light, mirror 

 inclined at 45°, condensing lens above the stage, Welsbach spirit-lamp 

 fitted with reflector, lens-carrier adjustable by raok-and-pinion, two 



Fig. 20. 



lenses magnifying 6 and 12 diameters ; (2) as a photographic camera, 

 double dark slide, and focussing screen ; (3) as a projection apparatus, 

 with frames for lantern-slides and projection-lens adjustable by rack-and- 

 pinion. 



Keichert's Small Photomicrographic Apparatus. — This apparatus, 

 (fig. 27) is made with the guide-rods hinged, so as to be used vertically 



