1076 RECORD OF CURRENT RESEARCHES RELATING TO 



it, beiug firmly fastened to the limb. Tlie ring may be clamped in 

 any position by a screw passing through the base of F, and the stage 

 may be clamped in any position by M. The projections at N (and M) 

 afford bearings for the stage to move upon and diminish friction. 



The stage is thin enough to admit oblique light up to 134°. 



(2) Congress (neiver form). — Mr. Bulloch writes : " I have recently 

 made several improvements and additions to the stand. 



" As originally intended, the front end of the centre of the substage 

 passed through and supported the stage support or saddle-piece ; but 

 for the finer work of measuring angles of aperture as Dr. Blackham 

 does, any connection between substage and stage would cause the 

 object to move to one side when the substage was swung from one 

 side to the other ; as now made there is no connection between sub- 

 stage or mirror and the stage ; the stage is fixed to the limb by an 

 angle-piece quite independent of the swinging arms, which I consider 

 an imi)()rtant improvement. (Cf. Figs. 140 and 141.) 



" I have also improved the arrangement of the pinion box ; the 

 slide of the coarse adjustment is now provided with a V piece on each 

 side of the rack-work, and these fit into corresponding slots : they act 

 as guides to the movement and add to the steadiness. I have also 

 added guide pieces outside the pinion box, that travel with the fine 

 adjustment on the sides of the limb. (Cf. Figs. 140 and 141 : they are 

 shown above and below the large milled heads on the limb.) 



" In the end of the tube is the new broad-gauge screw (the ' Dr. 

 Butterfield broad-gauge screw '), 1^ inch in diameter, for low-power 

 objectives of extra high angle. In this screw are two separate 

 nose-pieces containing the Society screw — one is for the binocular, 

 which must have diaphragms, so that the full benefit of high angle is 

 lost ; the other has a clear aperture, the diameter of the Society 

 screw. 



" At the upper end of the slide of the tube is a scale reading to yi^ 

 of an inch, and the slow-motion screw reads to yoVo' ^^ ^^^^ working 

 distance of objective can be measured. 



" There is also what I call a new adaptation of the Gillett 

 diaphragm, which can be used close up to the object, or when using 

 the hemispherical lens can be swung close round it. The Woodward 

 prism and also the hemispherical lens are specially fitted to the 

 imder part of the stage support, so that the stage can be revolved in 

 the axis without altering the position of the hemisphere." 



Of the points mentioned in Mr. Bulloch's letter, we must certainly 

 agree with him as to the importance of making the attachment of the 

 stage substantial and rigid, as may doubtless be done by screwing it 

 to the limb by an angle-piece. If it were desired to have a second 

 stage adapted — say a small diatom stage — it would be quite possible 

 to provide convenient means for changing the stage, and at the same 

 time to ensure that either stage should, when in position, be exactly 

 at right angles to the optic axis. 



Still later Mr. Bulluch has modified the stand to make it more 

 especially applicable for the examination of diatoms. The stand is 

 shown in Figs. 140 and 141, the latter being a representation of the 



