ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 103 



of the substage with centering screws and which may or may not be 

 fitted with rack and pinion movement. No illuminating apparatus to 

 be attached to the bottom of the stage proper. The diaphragm with 

 tapering nose so that it can be racked up close to the bottom of the 

 slide. 



4. The mirror-bar to swing on the optical centre of the instru- 

 ment above as well as below the stage, and to have a sliding extension 

 so as to increase the distance between the mirror and the stage without 

 changing the angle of the incident light. 



5. Such form of base as will permit the mirror to be swung 

 laterally when the instrument is in upright position. 



Mr. Cox objects to the substage and mirror-bar swinging together, 

 on the ground that it is then necessary to attach " the immersion 

 illuminators to the bottom of the stage by some special means, such 

 as bayonet catch, screw in the stage-well, &c.," and he advises that all 

 such apparatus should be used in the substage for which it was in 

 fact devised. He suggests and figures an attachment to carry an 

 immersion illuminator, consisting of a movable elbow-piece on a 

 slotted arm sliding on a pin that screws on the outer end of a short 

 right-angled dove-tail slide fitting into a corresponding bar cast on 

 the substage carrier that racks or slides on the fixed tail-piece. This 

 appears to us, however, a complicated way of applying a simple im- 

 mersion illuminator such as the hemispherical lens, and we cannot 

 see any objection to mounting the lens in a disk to fit into the stage- 

 well or the under surface of the rotating stage plate. 



For use with the Continental stands that are not provided with 

 mechanical stages, Mr. Zeiss mounts the lens in a disk of brass which 

 drops into the bevelled central stage opening, the plane face is then 

 flush with the surface of the stage. 



Denomination of Eye-pieces and Standard Gauges for same. — 

 The Committee appointed by the Council in October last to consider 

 the question of standard gauges for eye-pieces (and substages) duly 

 presented their report, which was thereupon ordered to be printed 

 and circulated amongst the members of the Council, and is now 

 under consideration. 



Subsequently to the report being made, the following circular 

 was received by some of the English opticians from a committee of 

 the American Society of Microscopists, unfortunately too late to be 

 laid before the Committee. 



" 1st Question. — Please give list of various eye-pieces or oculars for 

 the Microscope made by you, with construction (Huyghenian, ortho- 

 scopic, periscopic, &c., &c.), with the equivalent amplifying power of 

 each, at a standard distance of 10 English inches or 254 mm. 



2. Please state how you determine the amplifying power of your 

 eye-pieces. 



3. Do you consider it desirable that a uniform nomenclature 

 (with reference to amplifying power) of eye-pieces should be adopted 

 by makers of Microscopes ? 



4. Will you adopt such a nomenclature if decided upon by this 

 Society ? 



