78 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of illumination is adjusted to give the best effect. The illuminator 

 can be fitted with a permanently attached metallic filament lamp, which 

 reduces to a minimum the trouble of setting-up and adjustment. Further, 

 it enables metallurgical work to be done on an ordinary Microscope. 



Wychgram's New Low-current Microscopical Lamp.* — E. Wych- 

 gram points out that a microscopist's lamp should satisfy the following 

 requirements : — Stability and compactness, with light-control ; applica- 

 bility both to optical bench and to work-table ; maximum light-produc- 

 tion with minimum energy- consumption ; simplicity of construction 

 and of eventual repairs ; absolute invariability of the position of the 

 light-spot. The author points out that all these requirements are only 

 satisfied by the use of right-angled carbons, the horizontal crater carbon 

 lying in the optical axis. Even in such lamps of small dimensions the 

 invariability of light-spot can be depended on. Automatic action com- 

 bined with applicability either to optical bench or to work-table is not so 

 easily attained, and, so far as the author knows, is only attained by a 

 new form of Leitz lamp, which has, furthermore, the advantage of 

 extreme compactness. This new Leitz lamp consists of a plane-sided 

 rectangular box containing the rackwork for the carbon-holders. The 

 positive carbon is moved forward parallel to the upper surface and lies 

 horizontally in the optical axis : the negative carbon is vertical and 

 parallel to the front surface. Behind the box and secured to it is a 

 clock-work, which, although of equal thickness, is half as large as the 

 lamp-box : it is worked with a pendulum with a hair-spring and simple 

 escapement, and can be delicately regulated. The clockwork is controlled 

 externally so that the approximation of the carbons equals the velocity 

 of carbon consumption. The gearing is large and strong, and the risk 

 of magnetic attraction of the steel parts appears to be insignificant. A 

 small hand-wheel regulates the coarse adjustment, the combustion of the 

 lamp, and the length of the arc, exactly as in the Zeiss-Wenle lamp. 

 Some of the lamp data are :— Current intensity, 4-5 amp. ; length of 

 positive and negative carbons, 15 cm.; thickness of positive carbon, 

 8 mm. ; ditto of negative, 6 mm. ; combustion duration, 2 hours ; perio- 

 dicity of clockwork, 8-10 hours ; focal length of condenser lens, 75 mm. ; 

 weight of lamp without foot, 1'36 kgm. ; thickness of pillar for rider, 

 10 "8 mm.; minimum distance at which the lens yields an image of 

 crater, 80 cm. 



The lamp is easily equipped with a U-Y filter and can, therefore, be 

 adapted to luminiscent investigations. 



New Safety Device for High-power Lenses and Cover-glasses. 

 This instrument (fig. 11) was exhibited and described by C. E. Heath 

 at the November Meeting last year.f A gives the plan and elevation ; 

 B shows it in use on an ordinary stage ; C is a modified form as adapted 

 to an open mechanical stage. In use the apparatus is placed over 

 the objective threads and the lens screwed home. The tube is then 

 racked up till the chain can be slipped over the milled head so as to 



* Zeitschr. wiss. Mikrosk.,xxx. (1913) pp. 203-5. 

 t See this Journal, 1913, p. 644. 



