The Microscope. 161 



THE PROPER CARE AND USE OF MICROSCOPE 



LENSES. 



BY WILLIAM WALES. 



However good the lenses of an instrument may be, they 

 will not do their best work except when properly cared for and 

 properly used. Yet I have met with reputable microscopists 

 who do not in practice appreciate this obvious truth. 



Let me show you how a lens is cleaned. My implements 

 are four, — an old, soft, silk handkerchief, a small stick of soft 

 wood, a phial of alcohol, and a watch-maker's glass of two 

 powers. 



I have here an eye-piece. I will first examine it with the 

 magnifying glass, by reflected light, to learn its condition. If it 

 be found to need cleaning, alcohol is to be applied with the 

 handkerchief. This liquid must not be allowed to touch the 

 lacquer ; but the cell which holds the lens will not be harmed 

 by it, since that has been burned black with acid. If, after the 

 cleaning, fibres from the cloth be found adhering to the lens, 

 they may be blown off by a quick breath. 



I have brought an objective which was sent to me to be 

 cleaned. I will attach it to an instrument, and will place under 

 it a slide of familiar diatoms. Now view the object through the 

 lens. It looks so obscure that you will all exclaim, " Well, this is 

 a very poor objective ; " whereas, it is of excellent quality, as 

 you shall presently see. In it are eight pieces of glass. The 

 back combination is composed of two crowns and the flint ; the 

 front, -of two crowns, with a flint between them. It has, prob- 

 ably, not been cleaned for twenty years. Suppose your watch 

 to have been thus neglected ! I will now clean this objective. I 

 begin the work by unscrewing the cells. I then moisten a part 

 of the handkerchief with alcohol, and, with the help, if needed, 

 of the stick of wood in reaching the corners, carefully clean each 

 combination, and I then screw each cell back accurately to its 

 place. The work is now finished, and I will attach the object- 

 ive again to the microscope, and will again ask you to view the 

 slide of diatoms through it. The dimness is now, you perceive, 

 all gone. Indeed, you can hardly believe it the same objective ; 

 and you have ocular proof that clearness is essential to the 



