200 



MEMORANDA. 



ment of the traversing-plates, &c, will exhibit them. We 

 have then merely to place the one we wish to subject to an 

 enormous power at the end of the " pointer." Change the 

 powers (which, by means of the nose-piece, is done literally 

 in the twinkling of an eye), bring down the high power to 

 focus, and instantly we see the tiny speck (which before 

 seemed sticking on the point of the needle in the centre of 

 the field), now swelled out so as to fill the entire field, and in 

 many cases far beyond its limits ; so that we must " traverse" 

 it, and examine part at a time. 



Oh, it is admirable ! and the velocity with which it may be 

 done must be seen to be duly appreciated. Let any doubtful 

 amateur call on me, and bring his circle-finder, his angle- 

 finder, or his graduated plate-finder, &c, &c, and I will 

 undertake to convert him to the nose-piece finder in a very 

 short time, and so perfectly, that he will not have the least 

 desire to fall back upon any other. 



Indeed, it would be a very amusing contest to see a meet- 

 ing of several sharp-eyed and nimble-fingered microscopists 

 trying their finders against time ; each using, of course, the 

 same object, and timed by the same observer from the second- 

 hand pointer of a watch; the watchman saying, "Now," 

 when the operator was to commence his search, and the 

 searcher exclaiming, " Found !" the instant he had centred 

 the object, and brought it to focus with the high power. In 

 order, however, to give & plate-man some idea of the superior 

 speed of the nose-piece finder, I will give a single example. 



I took a slider of fossil animalcules, the part containing 

 the objects exposing a circle of full seven tenths of an inch 

 in diameter ; the whole of that extent being crammed with 

 debris of various kinds, among which is a very fine specimen 

 of that beautiful object, the Craspedodiscus elegans of 

 Ehrenberg. Placing this slider on the stage, and focusing it 

 with a one-eighth, I began to " traverse" the circle ; and I 

 may truly say, with as much care as if anxious to exhibit the 

 object to a waiting friend, whose time was " almost ex- 

 pired," &c. 



After spending full five minutes in vain, I reversed the 

 nose-piece, thus applying the inch and half; and I found 

 that I could focus the objects, find out the desired one, 

 move it to centre, reverse the nose-piece, and bring the one- 

 eighth to focus, within ten seconds. In a subsequent trial 

 I did the same in six seconds, or the time in which one can 

 moderately count ten. 



I do not believe that any one of the methods usually 

 employed can be made to equal this. 



But here an objector may say, " Well, "but after all, this 



