60 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 stage 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 great convenience, but scarce- 

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

 ranged 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 weight 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 nose-piece and perhaps the easiest to use, 

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

 simply a disc of tinted glass placed abovethe eyepiece and 

 at an ang-le 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 eyeisplaced above 

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

 ing- paper placed immediately 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 light in each lamp will 

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

 paraffin with a }4\n. wick. A cardboard screen can easily 

 be made to go 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 fiat re- 

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

 to the table. If a regular microscope lamp be bought it 

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



