Accessories. 61 



close to the table, and we should recommend glass in pre- 

 ference to metal, it being much cleaner, and the worker 

 can always tell when his oil is getting exhausted ; whereas 

 with a metal reservoir, unless careful reckoning is kept, in 

 the middle of some important observation the light will go 

 out from want of oil. A half -inch wick is generally found 

 to be sufficient. We strongly deprecate the use of glass 

 chimneys. They are always liable to get broken very 

 easily, and become a source of expense, in addition to which, 

 if away from town, there is a possibility of not being able 

 to get the right kind, and so work may be delayed. Far 

 better will be found the metal chimneys now made by 

 nearly all opticians, with a carrier for a 3 x 1 slip. It is 

 obvious that if the slip be broken it can be immediately re- 

 placed, it being part of the microscopist's average stock. 

 It is also desirable that the bar on which the lamp is 

 raised and lowered on the stand should be a square one. 

 If round in shape, the lamp is apt to swing round on the 

 stand and the whole lot topple over. This is an impossi- 

 bility, with the square bar. Such a lamp is shown in Fig. 

 21, by Swift and Son, and modifications of it can be obtained 

 at most dealers'. We have already referred to the methods 

 of using the lamp on page 52. 



The Nosepiece. 



Time-saving arrangements will 

 often be found useful in work, 

 and the nosepiece is one of 

 these. This is an arrangement 

 which is screwed into the nose- 

 piece of the microscope, and 

 carries two, three or four objec- 

 tives, each of which can in turn 

 be rotated into the optical axis, 



thus saving the necessity of un- 



,. ,. i FIG. 22. Triple Nosepfece. 



screwing an objective and screw- 

 ing another on in order to get a variation of power. In 



