MEMORANDA. 209 



•001; and I have but little doubt that Amphipleura pellucida 

 may be found to take rank, in point of striation, as the alpha 

 ■md omega of the lineated diatoms. Mr. T. G. Rylands, I 

 lelieve in the ' Microscopical Journal/ for October, 1859, 

 ery correctly observes, " Having seen Amp. fiellucida with 

 tansverse lines much more distant than the 130 to "001" 

 bserved in that species by the Hull microscopists." 



In the same Journal an article appears from Mr. Sollitt, 

 /ho estimates the number at 130, along with several other 

 aicroscopists ; but no allusion is in any place made to the 

 existence of any coarser striation. 



It is hence evident, from the frequent occurrence of lower 

 numbers, that even Amphipleura pellucida cannot be taken 

 as any test of the quality of a high-power objective, since 

 the striation may be seen, in some instances, with the £th, 

 the ith, the |th ; and, I think, a T 4 oth objective might even 

 resolve some of the same ; with a ^th I can readily resolve 

 some into squares of 60 or 70 in •001". 



My attention to the subject was first arrested through a 

 beautiful slide presented to me by George Norman, Esq., of 

 Hull, in which I accidentally found one Acus measuring 42 

 striae in -001", the length of which was -0041". Having 

 also a gathering of the same, I subsequently put up a few 

 slides and found several others, one or two upon a slide of 

 similar measure, with others somewhat finer, and quite suffi- 

 cient to satisfy myself that a comparative coarse striation, 

 compared to 130, was by no means an exception ; and that, 

 could all the gathering be fairly resolved, I know not how 

 far might rather even constitute the rule, and the very fine, 

 perhaps, the exception. 



I am apprehensive that the 130 to '001" is not legitimately 

 arrived at ; that to half and quarter is not a fair means ; that 

 vision and judgment are not matured upon this point, through 

 want of proper objects of comparison ; and that microscop- 

 ists, generally, are not yet masters of the relative develop- 

 ments between Nobart's test-plate and the lined diatoms; 

 as, for example, whether 60 lines on the diatom are seen in 

 exact degree with 60 upon the test-plate, so as to decide the 

 question of the term of visibility. — Wm. Hendry, Sui'geon, 

 Hull; June, 1860. 



