202 MICROSCOPIC ILLUSTRATIONS; > 



7th. Method of observing Opaque Objects by Artificial 

 Light, either plain, condensed, or reverberated, by Silver 

 Cups. Use the mounting (No. 2), as before: close the 

 shutters of your apartment, if you mean to observe in this 

 way in the day-time : procure a telescope candlestick, or 

 one which has an arm moving up and down upon a bar, 

 so that it can be adjusted to any height as a candle burns 

 down (the sliding-tube of the pillar will, in some mea- 

 sure, serve this purpose, if you have not a proper candle- 

 stick), and get a wax taper, or, what is better, a piece of 

 old rushlight, to afford your illumination. Don't laugh ! 

 but do as I bid you : and, moreover, a pair of scissars, to 

 trim it. A piece of rushlight (please your worship) well 

 trimmed, gives a remarkably steady light, without flaring 

 or flickering, and is just as intense as that afforded by oil, 

 or tallow, or gas itself, burnt in any other way. The 

 intensity of the light is the thing wanted, not the quantity. 

 Perhaps a wax rushlight might be an improvement. Now 

 this rushlight, adjusted to the proper height, is to be 

 placed before your stage, and as near to your object and 

 object-glass as may be, without burning them : but you 

 must take especial care that its direct light does not get 

 into the body of the engiscope, or it will utterly destroy 

 all distinct vision : on this account it must be always 

 placed a little on one side of the objective : and if the 

 focus of the said object-glass is longer than half an 

 inch, it will be highly advisable to use a conical 

 shade (fig. 19), drawn over it, reaching almost to the 

 object itself; which will, moreover, always be some 



