ELEMENTS OF MICROSCOPY. 123 



The stand has a wide, firm base. There is a rack and pinion 

 coarse adjustment, a differential-screw, or " Campbell " fine 

 adjustment, and the optical tube is so made as to lengthen or 

 shorten at the will of the worker, whilst the sub-stage is provided 

 with a tube to receive any optical apparatus for ordinary or 

 polarized light, which it may be desired to use. The instrument 

 has, in short, all the points of a sound, reliable stand at a 

 moderate price, and to intending purchasers of limited means we 

 can strongly recommend it. 



But many of our readers will wish rather to know how to make 

 the best of the instruments they have, than to be told of the 

 excellences of one which they have not, and we forbear to 

 expatiate at greater length on this portion of our subject. 



Proceeding to work, then, we suppose the microscope to be 

 put in position, with a lamp in front of it, and not at the left 

 hand side as is so frequently recommended in text books. The 

 edge of the flame should be directed toward the microscope, and 

 a flat burner is infinitely preferable to the argand or ring burners 

 so frequently employed. The size of the flame is not of material 

 consequence ; a half-inch paraflin-lamp wick, turned down until 

 the bright part is about half an inch in height, will be found to 

 yield excellent results when employed as we are about to describe, 

 and is preferable to all other means of illumination, except day- 

 light from a white cloud, when very low powers are employed. 

 With such a lamp and such a flame as above described, a perfectly 

 blinding amount of light can be obtained when properly managed. 

 For our own work we prefer to raise the microscope upon a 

 block of such height as will enable the flame to be placed in the 

 line of the axis of the optical tube, when the microscope is 

 incUned, and the " Nelson " body is so hung as to allow of this 

 being done without the block. As some of our readers, however, 

 may not be provided with a microscope which can be inclined, 

 and as the above method is only applicable with a sub-stage 

 condenser, we describe here a method which can be applied to 

 any stand. In any case the microscope should, if possible, be so 

 arranged as to height that the centre of the mirror is on a level 

 with the centre of the lamp flame. By this means the subsequent 

 manipulations are rendered much more simple, since so many 



