Royal Microscopical Society. 173 



IV. — The Magnifying Power of the Microscope. 

 By Count Castracane. 



" Surirella gemma may truly be called a touchstone for a high-power 

 objective. I do not think that it has been clearly defined as yet." — 

 John Mayall, ' Q. J. M. S.,' Jidy, 1869. 



The following pajDcr, which I have just received from Fano (Italy), 

 will answer, I hope satisfactorily, the above-quoted remark. It is an 

 original, yet unpublished, MS. of Count Castracane. I did my best 

 to translate it faithfully from the Italian. That being my native 

 language, it may easily be presumed I understood it right enough, 

 though it might be a quite different case with my not home-made 

 English. However, the benevolent reader will easily overlook any 

 un-English phrase for the sake of the valuable matter. 



P. J. Gagliardi. 



Count Castra-CAne's Paper. 



{Bead before the Eoyal Miceoscopical Society, March 1, 1871.) 



Far from wishing to sit down as judge on the controversy, which 

 lately sprung up between the illustrious American micrographer, 

 Charles Stodder, and Dr. Hagen, of Cambridge College, U.S., about 

 American microscopes and their respective value, I simply beg to 

 offer them some suggestions, whilst I shall bring forward a few 

 facts, wherewith I am perfectly acquainted by my own experience ; 

 these I hope will serve, better than any other argument, to clear 

 up the mooted question. 



Mr. Stodder* maintains against Dr. Hagen: — 1. That the 

 Surirella gemma given by Hartnack with flat hexagonal markings 

 is simply a theoretical diagram of the said diatom. 2. That the 

 hexagons were not probably seen, but with Tolles' xV^li by Mr. 

 Bicknell. 3. That Mr. Hartnack himself did not see those 

 hexagons but with his No. 10 (xV^li), and did not succeed in show- 

 ing it to more than two distinguished micrographers. 4. That Dr. 

 Eulenstein failed to see those hexagons with Nos. 10, 11, and 12, 

 nay, even with the best of Ross, and the most powerfully con- 

 structed up to this time, the sV^li of Powell and Lealand. 



In regard to the Surirella represented by Mr. Hartnack, in 

 his special memoir on this subject, with oblong hexagons {oblong 

 I think is a more exact expression in this case, than flat), I may 

 say that since the 7th March, 1869, I had myself the occasion of 

 treating this subject, in a short memoir, where I tried to set right 

 what I deemed wrong.t There, speaking of the difference between 



* Sec 'Montlily Microscopical Jcurnal,' Nov., 1870. 



t See ' Atti dell' Academia del Nuovi Lincei,' § iv. Su I'utio delle Liuee 

 di Nobert, etc. 



