"Zn'^aUMirch^^sTo.] Roycil Microscoincol Society. 125 



only add that those who, Hke myself, have seen Dr. Pigott's 

 exhibition of the beaded scales of Lejpidocyrtus curvicollis and 

 Begeeria domestica, can only sincerely thank him for taking the 

 trouble to compel us to believe that a successful raid upon the 

 existing trace of spherical aberration is not a myth. 



The immersion lens, the "hydro-objective," has probably an 

 advantage in " the battle of the glasses " over the " pneumo- 

 objective," as pointed out by Dr. Pigott; and Mr. Koss has laid 

 us under further obligation by kindly adding immersion-fronts to 

 his |th and J^th in our possession. The high praise, however, 

 which is given to the immersion system will perliaps be received 

 with caution until more extended observations have been made 

 upon its powers. Yet all seem, at present, to admit that consider- 

 able advantages are gained by its use. The light is more abundant, 

 the colouring of natural objects more brilliant, the definition keener : 

 inferior glasses are frequently improved by its application : illumi- 

 nation can be more effectively employed with a less complex machinery 

 of stops, diaphragms, and condensers : above all, facility of construc- 

 tion seems to be indicated by the offer of the highest powers at the 

 lowest prices. This intimation comes from the Continent, — A -^^th 

 for fifty shillings ! Is such work possible at home ? Still we 

 have yet to learn, notwithstanding these acknowledged advantages, 

 whether there are any considerable drawbacks looming in the 

 microscopic future which may in some measure counterbalance the 

 employment of water refractions. Of one thing we may be sure, 

 that absolute perfection is unattainable. The ghost of aberration 

 will never be entirely exorcised even by cold water. It is there 

 — do our best — and after all our compensations for figure, as for 

 colour, there ever must be a little ghost of an error in all probability. 

 At the same time, I believe it to be reduced to the minimum visibile 

 when the colour test so strongly advocated by Dr. Pigott is fairly 

 exhibited on the stage. Thus the natural colours, for instance, of 

 the upper and lower rows of beads on the scale of Begeerici plumhea 

 seem, for the first time, to be brought out by Dr. Pigott's more 

 accurate balance of positive and negative aberrations. But this part 

 of the subject is extensive, and must be left for further research and 

 observations. 



It is proper to remark that Colonel Woodward has resolved the 

 19 th band of Nobert's lines with a Powell and Lealand's iVth immer- 

 sion. He is the only observer who has succeeded in resolving 112688 

 lines to the inch, with a power of 1000 linear. But these lines 

 present the same appearance as lines drawn about 112 to the inch 

 would afford at a distance of 10 inches, to the ordinary sight, — which 

 are evidently exceedingly close for numeration. No other powers 

 in Colonel Woodward's possession could resolve this 19th band, and 

 this is a strong fact in favour of the immersion system. But even 



