MEMORANDA. 305 



The l-i2tli is Powell and Leland's^ the remainder were 

 made by A. Ross. 



It will be observed that with the exception of the l-8tli, 

 which ought to be about '125^ every objective has less than 

 its nominal focus, notwithstanding which all have not their 

 nominal power ; for by Mr. Ross's catalogue the l-6th should 

 give 320, and the l-12th 600 diameters. He calls the power 

 of the 2-inch 20, which gives a power of 4 to the eye-piece ; 

 but if we apply this number (4) to the l-6th we find that 320 

 is the proper power of the l-8th, and that the so-called l-8th, 

 with a power of 420 assigned to it, is something less than a 

 1-lOth. 



This to me appears very unsatisfactory, and although M. 

 Thury observes in a foot-note that " Les opticiens Anglais 

 semblent ne se faire aucun scruple de ces petites surprises, 

 par la raison que les objectifs content d'autant plus qu'ils 

 ont une distance plus courte et qu^ainsi le constructeur 

 donne plus qu'il ne promet ; entre deux exces, celui la est as- 

 surement le meilleur. . . . C'est celui dont nous avons 

 le moins le droit de nous plaindre,'^ it seems to me it would 

 be best to call a spade a spade. As to the gain to the cus- 

 tomer, if I want a glass of a certain power, what satisfaction 

 is it to be told that, although I have not been supplied with 

 what I asked for, I have got more for my money than I had 

 any right to. An argument of that kind would be simply im- 

 pertinent, and such as no man with the reputation of our 

 best makers would, I think, use. But the fact remains, that 

 they do make " les petites surprises," as my l-4th, l-6th, and 

 l-8th are perpetually reminding me. 



But these little " surprises" may do the makers themselves 

 injury in a way they little expect. It may happen that a 

 good honest glass is compared with another of the same 

 nominal power but of less pretension, and may fail to show the 

 same objects, the consequence of which is that the work would 

 be said to be '' falling off." I say this is possible because it 

 has happened to me. If I had an opportunity of getting at the 

 true focal length of the " new and improved" l-4th,'^ I should 

 probably find why it is not better than the old one, but I 

 have not had that opportunity. 



It must not be supposed from the foregoing that I am 

 finding fault with the ivorkmansMp of my microscope. On 

 the contrary, I feel bound to say that I consider the finish of 

 everything that I have seen from Featherstone Buildings as 

 second to none, and I believe that everything about my 

 microscope is (like the stand) A 1. Nevertheless, I should 

 * Bought by a friend on my recommendation. 



