17^ THE AMERICAN MONTHLY. [Juno, 



E, which slides over the projecting; tube wliich holds the Inill's- 

 eye lens. 



There is soiiietiines use for an extra sliatle, A ; this slides inside 

 the main shade and entirely cuts oil" all reflection tVoni the eves. 

 The latest proiluction is a sanil-bath attachment, which consists 

 of a ring, B. adjustable on the main uprij^^ht. and a pan, C, for 

 holdinjj the sand. This can be used for all j^urposes to which 

 the cirdinarv satul-bath is ailapted. as for warminy; slides in pre- 

 paring or hardening balsam mounts. The apparatus is very 

 compact, and when packed in it.s 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 

 7^ cents, lilue glass 25 cents, ground glass 50 cents : total $7.00. 



The Star Microscope. — Slessrs. Williams. Hrown & Earle.oi 

 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 adilitional objective (^-inch) costs $27.50. This 

 instrument is made l)y R. (S: 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 furnished with higher grade instruments. 

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

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

 and the stand not likelv 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. 



MICROS! OPKAL )IAMIH LATION. 



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

 the necessarv absence of "depth of definition" in the micro- 

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

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

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

 mental image of tiie magnified object. Naturally the sug- 

 gestion presents itself that visual persistence n)ight be made use- 

 fid. 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 ])roperty 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 theoptical axis, bv a mechanical arrangement, fairly 

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



