522 RECORD OF CURRENT RESEARCHES RELATING TO 



raise or lower the beam of light untler oblique illumination, he moves 

 this beam out of the optical axis of the instrument to either one side 

 or the other ; whereas by the new plan the beam is raised and lowered 

 in the axis of the instrument. Any one who will work with oblique 

 light on the one system or the other, will at once perceive the ad- 

 vantage and practical utility of it. Instead of the character of the 

 illuminator being changed by the increased or decreased propor- 

 tion from the one side or the other, it remains perfectly the same. 

 The only value of these contrivances for the use of oblique light 

 rests in their perfect accuracy ; and anything that leads thereto is 

 a step in advance. If there is any advantage in accuracy, as it 

 must be considered that there is, the Grubb, the Zentmayer, and the 

 Tolles-Blackham plans are only accurate for viewing an object on a 

 slide of a definite thickness ; any variation throws them out at once, 

 whereas, by the new plan, the rotation can readily be made exact for 

 an object mounted on glass of any thickness. 



Jaubert's Microscopes.* — It may be new to many microscopists 

 to learn that, some years ago, M. Jaubert, optician, of Paris, proposed 

 to mount — and did actually mount — the Microscope limb, carrying the 

 optical body, on a joint that permitted its inclination to either side. 

 If a suitable object were placed some distance above the level of the 

 stage, the optical body could be inclined so as to view it from one side 

 of its horizon to the other, or even beyond. The side-inclination of 

 the stage can only be regarded as a tentative process of examining the 

 object from side to side, when comjjared with M. Jaubert's method. 

 Not that the general adojition of M. Jaubert's idea is to be approved, 

 but when we ai'e seeking the best means of making a special examina- 

 tion, we must take cognizance of apparatus that has already been 

 designed for that purpose. 



M. Jaubert is also said to have made and published, and pro- 

 visionally patented in England, a practical binocular Microscope, 

 before either Professor Eiddell's or Mr. Wenham's, or even Sir Charles 

 Wheatstone's binocular projects were published. 



Sidle and Poalk's Acme Microscope.! — This Microscope, shown 

 in Fig. 39, is the first cheap instrument that we have seen with a swing- 

 ing substage. 



The general form of the instrument hardly needs any description, 

 but it may be mentioned that the stage is made of two thin, circular 

 brass plates, the upper one (shown in the lower left-hand corner) 

 fitted to turn upon the lower, so that the object can be rotated in the 

 field of view. The stage can be centered. The upper plate can be 

 removed, and two spring clips attached to the lower one, either above 

 or below, thus making a stage for use with oblique light. The aperture 

 in the stage has a standard-screw thread, to receive various accessories 

 for illumination when it is desired to have the mirror move indepen- 

 dently of them, and also to afi"ord a means of mounting the selenite 

 so that it can be revolved without turning the Nicol prism. 



♦ 'Engl. Meoh.,' xxxi. (1880) p. 135. 



t 'Am. M. Mlcr. Journ.,' i. (1880) p. 8 (1 fig.). 



