64 Remarks on the Confirmation given hy 



posal ' for a fortnight,' a yV^h, ' similar, though perhaps slightly 

 superior, to the celebrated immersion yV^^) signalized by Dr. 

 Woodward,' but which they were 'unwilhng to dispose of on 

 account of its excellence.' " 



I think it is only fair to the reputation of Messrs. Powell and 

 Lealand_,to state that I assigned no reason for this unwillingness, 

 and in justice to them I may be permitted to quote the whole pas- 

 sage, thus (page 67) : — 



" In face of these observations with the best glasses, I presume, 

 in existence (Powell and Lealand's own rV^h, ivliich I think they 

 are unwilling* to dispose of, and their new sJ^th immersion, made 

 expressly for the writer), I may make bold to predict that a double 

 set of beading will also be observed on the Angulatum, Rhomboides, 

 and other difficult diatoms." 



It will be interesting to find that Colonel Woodward succeeds 

 in photographing the double sets of beading described in the Feb- 

 ruary number, with the admirable glass now in his possession, made 

 by Mr. Tolles. The Formosum will assuredly yield its secrets to so 

 excellent and artistic an instrument. 



I have very little doubt that if anyone be willing to offer Messrs. 

 Powell and Lealand double the price of their -pV^h — the same as 

 charged for Tolles' immersion y^th, by Mr. Stodder, $175, or 347. 

 sterling — they would be able to produce a glass proportionately 

 improved in some of the minor details. It would truly be unphilo- 

 sophical to believe that the best glass is absolutely so perfect as to 

 admit of no further improvement. 



Dr. Woodward's known courtesy towards those who happen to 

 differ from him, will, I am sure, excuse my pointing out to him 

 this passage of his as conveying more than I intended. 



One remarkable fact was noticed by me on the 7th November 

 last: that the beading on the Degeeria domestica Podura was 

 perfectly distinct moistened with water, though usually difficult of 

 observation in this condition. 



The colours of the beading on several wetted insect scales were 

 of a fine sapphire, blue, and red, when most distinctly defined ; thus 

 again verifying the importance of the " colour test." 



Notwithstanding the bold denials by persons insufficiently in- 

 formed as to the existence of errors in our best glasses of the old 

 fashion, it is gratifying to observe that strenuous efforts are now 

 made to improve them by new constructions. The capabilities of 

 Titanic optical glass, specially manufactured, encourage the hope 

 that not only the secondary spectrum will vanish, but also the 

 spherical residuary aberration. 



* I was informed that as it was a glass made by Mr. Powell, junior, he 

 wished to keep it for his own use. But it did not seem relevant to make known 

 this reason. 



