«0 THE AMERICAN MONTHLY [Feb 



make measurements it is only necessary to note the num- 

 ber of arbitrary divisions in the eyepiece micrometer cor- 

 responding- with the object to be measured, and then to re- 

 place this object on the stag-e by the stage micrometer,and 

 note the exact measurements which correspond to those 

 taken in the eyepiece. There are other forms of micro- 

 meter, but the above is simple and inexpensive, and quite 

 satisfactory for most purposes. 



Nose-Pieces. — These are a g-reat convenience, but scarce- 

 ly a necessity. One or two opticians have latterly so ar- 

 rang-ed their objectives that they are all nearly in focus 

 when rotated on the nose-piece. Under any circumstances 

 however, do not use a triple nose-piece, to say nothing- of a 

 quadruple one, as the weig-ht of three objectives is quite 

 sufficient to put a severe strain upon the fine adjustment. 

 The cost of a double nose-piece varies from $2.75 upwards. 

 The cheapest no«e-piece and perhaps the easiest to use, 

 is the one known as "Beale's Neutral Tint Reflector." It is 

 simply a disc of tinted g"lass placed above the eyepiece and 

 at an angle of 45 deg-s. to the optic axis. To use it, how- 

 ever, the microscope should be placed in the horizontal po- 

 sition, which is not always possible. The eye is placed above 

 the disc of glass, and looking- down throug-h it on the draw- 

 ing- paper placed immediatel}' beneath, the microscopical 

 image can then be readily traced. 



Illumination. — This is easily done if two lamps are used, 

 one for the microscope as usual, and one to illuminate the 

 paper. A little adjustment of the lig-ht in each lamp will 

 then be all that is necessary. The lamp itself should be 

 paraffin with a ,'2 in. wick, A cardboard screen can easily 

 be made to g-o round it. The excellent and often elaborate- 

 ly fitted lamps sold by opticians are, of course, very con- 

 venient, but are only absolutely necessary for those who 

 do much work. Their great convenience is in the readiness 

 with which they may be raised or lowered, and the flat re- 

 ceptacle for the oil, that enables them to be brought close 

 to the table. If a reg-ular microscope lamp be boug-ht it 

 should certainly be of this form, and capable of rotation. 



