66 MEMORANDA. 



It is true, this method destroys a few of your larger globes ; 

 but you can afford to lose them, as they are too large for the 

 microscope. 



You can examine the shells from time to time by a drop-tube, 

 letting a single drop fall on a glass slide placed horizontally on 

 the stage. An oblique light shows them best. — Thomas 

 Furlong, 10, Sydney Place, Bath. 



Further Notes on Finders.— At the conclusion of a letter on 

 " Finders'^ (inserted in your Journal for last July), I en- 

 deavoured to impress upon opticians the desirableness of 

 directing more attention to the subject of the Binocular 

 Microscope than they have hitherto done ; and it appeared 

 to me a singular coincidence, that the very number contain- 

 ing my suggestion should also contain what looked like a 

 precise answer to it. I allude, of course, to the intensely 

 interesting essay by ]\Ir. Wenham, at page 154 of the 

 ^Transactions.^ On reading that paper, I felt quite satisfied 

 that the ultimatum, or something very near it, had at length 

 been attained ; and immediately commenced a correspondence 

 with Mr. Wenham upon the subject. Nothing could possibly 

 exceed the kindness with which that gentleman took up the 

 matter ; even offering to send me his own instrument for 

 examination. But this I declined, as it was clear to me that 

 the mode he had adopted must answer. I, according, re- 

 quested him to supervise the adaptation of one of his prisms 

 to a double tube added to my miscroscope. 



And now that this has been done, and I have had time for 

 a fair and deliberate examination and trial of it, I should 

 consider myself very deficient in duty to my brother micro- 

 scopists, if I delayed another moment to recommend it to 

 them, as by far the greatest advance* that has been made 

 upon the instrument since the invention of achromatics. It 

 is, indeed, a very magnificent improvement. The comfort 

 (or, I may truly say, the luxury) of using both eyes equally, 

 when both are equally good, is very delightful ; but that is 

 not the only nor, indeed, the chief point of superiority. It 

 is the entire relief from all that unpleasant optical fatigue 

 produced by the old practice of using one eye at a time. With 

 the binocular arrangement the observer may go on hour 

 after hour with perfect impunity, feeling no worse than if 

 he had merelv been reading a book through a binocular 

 hand-glass or a common pair of spectacles. But after long 

 use of the one-eyed tube, it is not so. It produces more 

 or less feeling of pain, confusion, megrims, giddiness, &c., 

 and, in the course of years, is pretty sm'e to effect some 



