42 CORKESPONDENCE. 



he will do well to visit some of our Metropolitan Medical Schools, or 

 the Medical Microscopical Society, where I know he would have 

 ample opportunities afforded him of both seeing and learning that the 

 immersion system has much simplified the whole process of obtaining 

 high-power definition ; and that students are now able to examine for 

 themselves with a magnification of a thousand diameters, where for- 

 merly such magnification was scarcely practical, or only known as of 

 difficult achievement. 



Doubtless, if Mr. Brakey could see a fair comparison made be- 

 tween immersion objectives, as those of Hartnack, or some other 

 equally well-known maker, and the old or even modern dry objectives, 

 he would at once admit that there is not much room for a play of 

 fancy, " as in judging the merits of wine," and he might " exactly say 

 how much of the difference is really due to the immersion system," 

 both as to practical results obtained, economy of time (probably also 

 of money), and what is due to a previously settled " conviction." 

 I have the honour to remain, 



Your most obedient servant, 



Jabez Hogg. 



On Immersion Lenses. 



To the Editor of the ' Monthly Microscopical Journal.'' 



Sir, — As an Immersion of some years' standing I should like to 

 say a few words on behalf of myself and of certain of my fellow- 

 objectives. 



Your contributor on the Theory of Immersion suggests that we 

 have received undue praise for our merits, which he says are so in- 

 definite that he does not care to pledge himself either for or against 

 us ; he evidently inclines to the belief that the qualities claimed 

 for us, and on which we pride ourselves, are mainly imaginary. 



I think your contributor might well admit that not everyone, 

 save himself, who has seen and examined, is still unconvinced of our 

 high qualities of clearness and definition. In this I would ask him to 

 believe it possible that others besides himself and Mr. Wenham have 

 given serious attention to the subject of Immersion, and that some 

 have had quite as much and possibly more varied experience than 

 either of them in the use of Immersion lenses. I venture to say that 

 neither of them would presume to be of greater authority on the 

 Theory of Optics than Sir David Brewster or Amici, both of whom 

 declared in favour of the Immersion principle. Sir David (then Dr.) 

 Brewster, indeed, claimed to be the inventor of the first compound 

 microscope involving the Immersion principle : he describes it in his 

 ' Treatise on New Philosophical Instruments,' published at Edinburgh 

 in 1813 : while Amici not only spoke in favour of the principle, but 

 exhibited Immersion lenses made by himself, which he openly stated 

 would show minute structure that was invisible to the Dry Objective. 

 Since then, certain Paris opticians and others have given special 

 attention to the Immersion principle, and have not been sparing of 



