62 RemarJcs on the Confirmation given hj 



afterwards described this in the ' Philosophical Transactions ' * as a 

 nebulous yellow fog, \\hich no objective adjustments are able 

 to dissipate, p. 592; and from experiments therein detailed the 

 residuary lateral aberration was calculated to be 5-0 J- oo" of an inch. 

 The details sent us by Colonel Woodward now seem amply to 

 justify the following passage of my first paper, p. 304 : — 



" I know it is very difiicult to throw aside the creed and belief 

 of forty years, and I have hesitated a long time (seven years) to 

 bring forward my views, being perfectly convinced that a battle of 

 the glasses will have to be fought. 



" I point to the immersion lens as an irrefragable proof of the 

 deficiencies of the corrections of the old-fashioned glasses to grapple 

 with some of the exquisite difficulties of microscopic research, and 

 if my efforts shall in any way advance the excellence of defining 

 power, especially in the higher range of investigations, I shall feel 

 in the end amply rewarded ; my work has been earnest and sincere." 



The passage, however, which I wish particularly to call 

 attention to, now that the principle is better acknowledged and 

 understood, is in the April number, ' Monthly Microscopical 

 Journal,' 1870 : — 



" I have lately seen the Formosum beading coloured with red, 

 orange, yellow and blue. The beading has appeared wreathed 

 with a golden bronzing ; individual beads separated frota their 

 fellows appeared remarkably distinct. 



" Destruction of colour reduces the field to a spiritless picture. 

 (Dr. Woodward now says they cannot be seen at all on the whole 

 screen he employs unless they are made to appear red on a 

 greenish ground.) 



" Now, if we view diatoms en masse with the unaided sight, they 

 appear resplendent with a variety of prismatic hues when under a 

 strong light. 



" Yet these colours, so evident to the unassisted eye, en masse 

 vanish in achromatic vision : should these charming colours," I 

 then asked, " be destroyed " ? 



In a paper communicated last June to the ' Quarterly Journal 

 of Microscopical Science,' I made the followng deductions from the 

 observations there related : — 



. , . On referring to a diagram, I said the great bulk of 

 the rays, except the red or reddish yellow, converge accurately to 

 B, whilst the residuary rays of reddish orange converge to B, so 

 that we either in general get achromatism with residuary spherical 

 aberration, or reddish yellow rays when the spherical aberration is 

 destroyed. 



Spherical aberration, as detected hy the methods I have recom- 

 mended, disj^jlatjs itself in a colourless milkiness or whitish smoJce- 



* Vol. ii., 1870. 



