17t) THE AMERICAN MONTHLY. [June, 



E, which slides over the projecting tube which holds the bull's- 

 eye \ens. 



There is sometimes use for an extra shade, A ; this slides inside 

 the main shade and entirely cuts off all reflection from the eyes. 

 The latest production is a sand-bath attachment, which consists 

 of a ring, B, adjustable on the main upright, and a pan, C, for 

 holding the sand. This can be used for all purposes to which 

 the ordinary sand-bath is adapted, as for warming slides in pre- 

 paring or hardening balsam mounts. The apparatus is very 

 compact, and when packed in its case occupies but a space of 

 4 in. X 4^ in. X 9 in., thus adapting it for the microscopist who 

 needs a portable lamp. 



The price of the lamp is $5.25, extra shade 25 cents, sand-bath 

 75 cents, blue glass 35 cents, ground glass 50 cents ; total $7.00. 



The Star Microscope. — Messrs. Williams, Brown & Earle, 01 

 Philadelphia, recommended their Star Microscope, which has fine 

 and coarse adjustments, i-inch eyepiece, i-inch objective, a 

 double mirror and diaphragm ; and sells at $20. The same stand 

 fitted with an additional objective (;^-inch) costs $37.50. This 

 instrument is made by R. & J. Beck, of London, and pays a 

 dutv of 40 per cent. It nevertheless sells at about the same price 

 as domestic instruments of the same grade. The objective and 

 eyepiece are the same as fiuMiished with higher grade instruments. 

 To the substage can be fitted all ordinary accessories, like con- 

 denser, polariscope, and illuminator. The base is filled with lead 

 and the stand not likely to be overturned by accident. Great 

 delicacv of focusing is claimed for this instrument, and its fine 

 adjustment doubtless makes it somewhat superior to all which 

 lack a fine adjustment. 



MICROSCOPICAL MAMPULATION. 



Micrographic Projection. — It has been said, in reference to 

 the necessary absence of " ilepth of definition" in the micro- 

 scope, that more perfect impressions of objects in relief may be 

 obtained by rocking the microscope tube to and fro. It is, 

 however, by no means an easy method of building up a correct 

 mental image of the magnified object. Naturally the sug- 

 gestion presents itself that visual persistence might be made use- 

 ful. But to give the object or the lenses a reciprocating motion 

 of the necessary frequency would appear to be an almost ab- 

 surdly impractical device. In a scientific toy which has been 

 recently described, it is claimed that the property of persistence of 

 vision has b^en usefully applied But in this instrument, which 

 is a projecting microscope, it is the screen that is made to 

 reciprocate in the optical axis, bv a mechanical arrangement, fairly 

 good of its kind. The screen, which is of an optical dispersive 



