The " Colour Test " and Dr. Figott. 117 



achromatic systems behind the single front, they were abandoned 

 for commercial reasons for the more simple form.* Mr. Eoss ex- 

 plained to me at the time that his reason for adopting the " supjDle- 

 mentary " achromatic was in order to get rid of some of the reddish 

 tinge of the Podura markings, and approach nearer to the then 

 approved black-and-white style, conspicuous in what are sometimes 

 nicknamed " wishy-washy " glasses. At that time, though writing 

 scraps relating to microscope matters, I said nothing concerning 

 object-glasses, because information was entrusted to me that I had 

 then no right to divulge. I am of opinion that still further im- 

 provements may arise with a different quality of glass, and am in 

 daily expectation of receiving some crown now in manufacture, of a 

 new composition, having but little spectrum, or, in other words, 

 relatively of a very high refractive and low dispersive power ; and 

 where there are four elements of crown to be corrected by one of 

 flint, the advantages should be correspondingly great. If secondary 

 spectrum is to be corrected by any peculiar composition forming 

 the negative element, we should properly begin by having as little 

 of it to deal with as possible. I have long been aware of the Har- 

 court Titanium glass, but hitherto have not been able to obtain an 

 atom of it. 



After passing over the region of self-quotation and inverted 

 commas in Dr. Pigott's paper, a phrase appears in the following 

 sense : — " If anyone will give P. double price — the same as charged 

 by T., I have no doubt that P. would be able to produce a glass 

 proportionately improved." If Dr. Pigott really knows what the 

 aberration is, and the means of correcting it, he ought in the inte- 

 rests of science to state it, or persons inclined to criticize might 

 consider such sentences more appropriate for a trade prospectus 

 than a scientific paper. 



The mere assertion that there is a " certain residuary aberration " 

 is unsatisfactory, and seems to have been raised from the region of 

 phantoms, and its shadow-form is the result of a wrong interpre- 

 tation of structure from illusory headings. These Dr. Pigott has 

 great skill in displaying as a reality, enhanced by drawings made 

 by persons who may be clever in the ordinary use of the pencil, 

 but clumsy and inaccurate in the delineation of microscope subjects, 

 for the want of that knowledge of interpretation and discrimination 

 of structure which alone can constitute the micro-draughtsman an 

 artist ; and yet such persons were first employed on the plea that they 

 were free from prejudice ? 



* For the information of those possessing these particular ^ths, I may state 

 that I have found that by approximating tlie same front lens by the adjustment 

 that they also act as immersion lenses, the water film giving an advantage in 

 definition and increase of light. Mr. Ross was not aware of this at the time that 

 they were made, for the value of the immersion was not then known or altogether 

 ignored. 



