1042 General Notes. [December, 



tial to the best work of many freezing microtomes, and the char- 



The cutting knife is supported upun a circular plate, which screws 

 up and down around the object, the extent of its motion, and the 

 consequent thickness of the section to be cut, being indicated by 

 a pointer near its graduated edge. The best of workmanship is 



as to give excellent work. It' is evident' that the ' Hiscoc form' of 

 knife-carrier could be easily adapted to this instrument by those 



to one inch wide, and costs s 1 5.00. or with rubber tubes, clips and 

 tin pail. $15.50. A special size is being made for cutting much 



strume.iVcm'l). obtain lfr..:n \ R b ivlo ' • :i Massachusetts 

 avenue. Capitol Hill, Washington. D. C. ' 



Relatiox of Aperture and Power.— In the Journal of the 

 Roval Microscopical Society, Professor Abbe gives an elaborate 

 and exhaustive mathematical demonstration ' of the apertures 

 useful for va 



recited address on llu subject, at th • Montreal meeting ^ 

 A. A \ S He preferred moderat mgl s fo. most purposes, 



bug to the eves. It is useless to spoil a g< 

 ngto make -it a poar one-fourth. On the othc 



iier ail des than would be ad- 



■sliutt. j 1 n< !<- u_!l, thoig'i tlne-,.f Zis,, made from tl 



formulas of Professor Abbe, do not. (Conf. discussion 

 Manchester, Mic. Soc, in the Northern Jfieroseofist, Vol. 2, p 

 2^4-291.) 



Visibility of Fine Rulings.— Professor W. A. Rogers, in 

 piper before the A. A. A. S. considers Mr. Fasoidt first m the : 



