102 SUMMARY OF CURRENT RESEARCHES RELATING TO 



a considerable distance above the object, and it is tbis idea whicb 

 has governed the construction of the Briicke lens. 



" The lens has a very long focus, and the construction is that of 

 the Galileo telescope as applied to opera-glasses, but the amplification 

 of the objective is much greater than that usually obtained in opera- 

 glasses. The focus is about 6 cm., and the power three to eight times. 

 The latter power is obtained by lengthening the tube, by which means 

 the distance between the two lenses is much enlarged and the amplifi- 

 cation increased without inconveniently modifying the focus. 



" This lens may be used in place of the body of a compound 

 Microscope when it is desired to dissect or to find small objects, or it 

 can be adapted to a simple Microscope or lens-holder with from 3 to 

 8 cm. between the object and objective." 



Kiinckel d'Herculais devised a holder for the lens shown in 

 Fig. 15. By tightening the screw on the horizontal arm the "jaws" 

 are separated or closed. The arm can be lengthened if desired and 

 also raised or lowered by the rack and pinion. L is the place for the 

 lens and for doublets. 



The Model Stand.* — Mr. J. D. Cox discusses the changes that 

 have taken place in microscope-stands with a view of determining 

 which will be of permanent value and should form part of the features 

 of a complete stand, and thus summarizes the essential requisites 

 which ought to be embodied in every instrument intended for real 

 scientific use. 



1. A firm and rigid arm having the general character of the 

 Jackson model, carrying the body of the instrument, with coarse and 

 fine adjustments conveniently placed below the body, with perfectly 

 even and reliable motion. 



2. A firm ring as the basis of the stage, to which any form of 

 stage-plate, plain with clips, glass, or mechanical, may be adapted and 

 interchanged. Nearly every microscopist has work to do for which a 

 mechanical stage is almost indispensable, such as micrometric measure- 

 ments, and the systematic sweeping of a slide to make sure that every 

 part has been examined. There should be no rack and pinion move- 

 ment for revolving the stage as it can be better done with the fingers, 

 nor a centering adjustment unless the instrument is intended for 

 goniometry. The stage thin enough to allow the use of light of at 

 least 70'^ obliquity from the axis of the instrument. 



In regard to the requisite of reversibility for the stage, Mr. Cox 

 points out that in nearly every department of natural science (and not 

 for diatoms only) there is need of the occasional use of light of 

 extreme obliquity upon dry mounts and from the mirror alone, so 

 that an easily reversible stage is desirable. If, however, immersion 

 illuminators came to be used for dry mounts as well as those in 

 balsam f a reversible stage would not be necessary, as a ray incident 

 at 41° only would emerge at the maximum obliquity of 90°. 



3. A grooved bar — immovable and not swinging — for the support 



* Amer. Jour. Micr., vi. (1881) pp. 89-95 (4 figs.)- 



t Tliis should read " for dry objectives as well as immersion." Balsam mounts 

 are on the same footing as dry mounts when a dry objective is used. 



