260 Miscellaneous. 



may be cemented to the inner, by Canada balsam ; or left free, to 

 admit of adjustment to suit different observers. Prisms of other 

 form, with due arrangement, may be substituted. 



I find the method is applicable with equal advantage to every 

 grade of good lens, from Spencer's best sixteenth, to a common 

 three-inch magnifier ; with or without oculars or erecting eye-pieces ; 

 and with a great enhancement of penetrating and defining power. 

 It gives the observer perfectly correct views, in length, breadth and 

 depth, whatever power he may employ. Objects are seen holding 

 their true relative positions and wearing their real shapes. A 

 curious exception must be made. In viewing opake solid bodies, 

 with one eye-piece to each eye, depression appears as elevation, and 

 elevation as depression, forming a singular illusion. For instance, a 

 metal spherule appears as a glass ball silvered on the under side ; 

 and a crystal of galena, like an empty box. By the additional use 

 of erecting eye-pieces, the images all become normal and natural. 

 Match drawings of any solid object, made from each eye-piece, by 

 the aid of the camera lucida, when properly placed in the common 

 stereoscope, appear to stand out in natural relief. These, if engraved 

 and printed in the proper position with respect to each other, might 

 find an appropriate place in books on the arts and sciences. 



In constructing binocular eye-glasses, I use, for lightness and 

 economy, four pieces of common looking-glass, instead of prisms. 



With these instruments, the microscopic dissecting knife can be 

 exactly guided. The watch-maker and artist can work under the 

 binocular eye-glass, with certainty and satisfaction. In looking at 

 microscopic animal tissues, the single eye may perhaps behold a con- 

 fused amorphous or nebulous mass, which the pair of eyes instantly 

 shapes into delicate superimposed membranes, with intervening spaces, 

 the thickness of which can be correctly estimated. Blood-corpus- 

 cles, usually seen as flat disks, loom out as oblate spheroids. In 

 brief, the whole microscopic world, as thus displayed, acquires a ten- 

 fold greater interest, in every phase exhibiting, in a new light, beauty 

 and symmetry indescribable. — Silliman's American Journal, January 

 1853. 



University of La., New Orleans, Oct. 1, 1852. 



ON THE GENUS BIFRONTIA. 



Mr. MacAndrew has lately discovered Bifrontia Zanclcea of Phi- 

 lippi, in a recent state, off the coast of Madeira, and has presented 

 specimens of it to the British Museum. It has a high conical oper- 

 culum, with a spiral ridge hke the genus Torinia {Solarium variegatum, 

 Lamk.), which supports Dr. Phihppi's opinion that this genus is 

 probably allied to Solarium, Moll. Sicil. ii. 225. 



In the older specimens the outer whorls are separated from the 

 others, like the fossil species of Bifrontia found in the Paris formation. 



The animal is pellucid : and when it crawled up the glass, the 

 shell laid on one side, so that its flat side nearly touched the glass. — 

 J. E. Gray. 



