Notes. 397 



Personally, I have found that the new amplifier yields especially 

 good results when employed in conjunction with a Powell y 1 ^ in. 

 oil immersion of measured N.A. 1*27, this lens being provided 

 with collar adjustment. With the combination specified, 13 '18 

 revolutions of the micrometer drum equal ygW * n -> an( l tne defini- 

 tion proves remarkably sharp, both with a large solid axial illu 

 minating cone and also with oblique light from a wide-angled oil 

 immersion condenser. By the latter arrangement I have been 

 enabled not only easily to " step " and count the tranverse stripe 

 on A. pcllucida running at 94,000 to the inch, but have also suc- 

 ceeded in " stepping " those of an extremely finely marked small 

 species of Nitzschia (mounted in realgar), which count 112,000 to 

 the inch. The last proved a very delicate and difficult task, owing 

 to the faint resolution obtainable by lamplight. 



Although primarily intended for micrometrical purposes, the 

 new amplifier would doubtless prove most useful for students' 

 stands, if mounted on an arm so as to allow it to be brought into 

 working position through a slot cut in the body of the instrument. 

 In this manner a great increase of magnifying power could be 

 quickly and easily obtained, and the resultant slight disturbance 

 of the objective correction would be quite negligible, and indeed 

 not discoverable, when the Microscope is set up in the ordinary 

 rough-and-ready fashion inculcated in the medical schools, while 

 more careful manipulators could readily obtain really critical 

 images with a little skill in the adjustment and choice of the 

 objectives employed. To many workers also who prefer shallow 

 eye-pieces, yet do not possess objectives of very high initial magni- 

 fying power, the new arrangement would probably be welcome. 



Through Mr. Nelson's kind permission I am enabled to annex 

 hereto the formula of the new amplifier. 



Formula of Amplifier. 



Plano-concave Borosilicate glass v = 64 • (0 • 144 No. 5, Jena 



Catalogue). 

 Ptadius of concave = 1*0. 

 Diameter =0*7. 

 Focus = 2-0. 



Thickness at centre = 0*05. 

 Measurement is in inches. 

 Plat side of lens to face objective. 



