704 RECORD OF CURRENT RESEARCHES RELATING TO 



D is a stage with spring clips for fixing the preparation whose 

 gpectrum is to be compared. The comparison-prism is brought up 

 before one half of the slit by the lever p. The screw / regulates the 

 width and g the length of the slit ; when the latter is opened as wide 

 as possible, the central portion of the field is free ; so that the upper 

 part (B C) being turned back, the Microscope may be used in the 

 ordinary way. The screw h (underneath the tube C) serves to adjust 

 the scale. This is to be fixed before commencing, so that the Fraun- 

 hofer line D coincides with " 589. The parallelism of the scale with 

 the spectrum is secured by turning its frame i. The mirror h throws 

 light on the comparison-prism, and I on the scale. 



The microspectroscope is inserted in the tube of the Microscope 

 like an ordinary eye-piece, and is fixed in the required position by an 

 attachment screw beneath A. When the object to be examined is of 

 considerable dimensions, no objective need as a rule be used on the 

 tube, otherwise as low a one as possible. As a variation in the dis- 

 tance between the scale and the lens o would alter the value of the 

 divisions of the scale, very short-sighted or long-sighted observers 

 must use proper spectacles (or have a spectacle lens placed on B) to 

 produce a medium distance of vision in order to see the lines and 

 numbers on the scale with perfect sharpness of definition. For exact 

 focal adjustment of the spectrum, the eye-glass is movable beneath the 

 collar B. It must be so fixed that the Fraunhofer lines in the spec- 

 trum of daylight plainly appear along with the scale, and on moving 

 the eye there should be no ajipearance of parallactic displacement 

 towards the division lines. 



Ross's Improved Microscope (Plate XVI.). — Since this instru- 

 ment was first exhibited to the Society * several improvements have 

 been made in the details of the construction by which the stand is 

 rendered more serviceable as a practical working instrument. 



The vertical pillar supports have been adopted for the main limb, 

 an alteration which permits the free use of the swinging substage 

 with the Microscope in a vertical position, a point of special importance 

 for work with fluid preparations. 



For central light the substage can now be clamped in the optic 

 axis, and the illumination exactly centered by means of the usual 

 centering screws. 



For convenience in using low powers — when the substage con- 

 denser may be dispensed with — the substage itself may be entirely 

 removed, the mirror alone then serving as illuminator ; for this 

 purpose the focus of the mirror has been shortened, and means have 

 been provided for more readily adjusting it to any required position. 



The mechanical stage, with rotatory motion in azimuth and the 

 facility of being inverted, has been considerably altered by the intro- 

 duction of phosj)hor-bronze metal'in the parts liable to flexure, and the 

 stage has been rendered one of the most rigid and at the same time 

 thinnest yet made. The modifications in the construction of the 

 stage, though making but little change in its general appearance, are 

 specially imjiortant in detail. 



* See this Jouriiiil, i. (1S7S) pp. 1G3 and 197. 



