Knowledofe. 



With which is incorporated Hardwicke's Science Gossip, and the Illustrated Scientific News. 



A Monthly Record of Science. 



Conducted b\- Wilfred Mark Webb, F.L.S., and E. S. Grew, M.A. 

 OCTOBER, 1912. 



FURTHER REiMARKS ON THE TRUE STRUCTURE 

 OF THE DIATOM X'ALVE. 



r.v T. E. SMITH. 



(Continued from pag 



OrK knowledge of the secondary structure of objectives, and under conditions of illumination 

 diatoms mav be said to date from a few vears after such as are abi;olutel\- essential if the full aperture 



the advent of the 

 oil-immersion objec- 

 tive, inore especially 

 from the epoch- 

 marking paper, 

 already alluded to, 

 read by Messrs. 

 Nelson and Karop 

 before the Ouekett 

 Club m 1886". The 

 first oil immersions 

 showed no improve- 

 ment upon the water 

 immersions, due to 

 the splendid pitch 

 to which these last 

 had been brought in 

 this country. In the 

 interval, however, 

 between 1878 and 

 1886, the N.A. of 

 the oil - iiTimersion 

 had been worked up 

 to 1-43 by Messrs. 

 Powell and Lealand ; 

 Mr. Nelson became 

 the owner of one, 

 and hence the paper : 

 " On the Finer 

 Structure of certain 

 Diatoms." In the 

 introduction the authors sav : 

 certain Diatoms with the finest 



Figure 404. Coscinodiscus asteroniphalus. Objective used. Swift 

 and Son's one inch of 0-30 N.A., orthochroniatic plate, no screen. 

 ni,agnification three hundred and fifty diameters, exposure ten minutes. 



and, therefore, re- 

 solving power, of 

 these glasses is to be 

 utilised, some details 

 of structure are 

 I nought into view 

 which are otherwise 

 quite invisible, and, 

 so far as we know, 

 have not hitherto 

 been correctly des- 

 cribed or properly 

 figured. Acting on 

 this belief, we have 

 \entured to bring 



fore \our notice 

 some short obser- 

 vations, accompanied 

 bv careful drawings, 

 recently made on a 

 few well-known 

 forms." 



This was but the 

 first of a splendid 

 series of observa- 

 tions, continued by 

 Mr. E. M. Nelson 

 right down to the 

 present time. Others, 

 of course, have 

 followed, and as Dr. 



On examining Dallinger said in the last edition of Carpenter 

 oil - immersion (1901): "The nature of the delicate markings with 



