CHAPTEE II. 

 OPTICAL CONSTRUCTION. 



IN the former part of this' book we have dealt exclusively 

 with the stand, or mechanical means of employing the 

 various optical accessories, and important as it is that 

 those details shall be very efficient, it is, if anything, 

 still more so that the eyepieces, objectives and illuminat- 

 ing apparatus shall be of the most perfect description, 

 properly adapted and intelligently employed, as on the 

 optical combinations depend the results that are to be 

 obtained with the stand ; and although care and trouble 

 may enable a person to use a bad stand, no good stand can 

 ever compensate in any way for bad objectives. It requires 

 a deal of practice and a long apprenticeship to learn to 

 use the microscope to the utmost advantage, but the more 

 it is understood the greater will be the appreciation of it. 



MAGNIFYING POWER. 



It is often supposed by the novice that magnification is 

 dependent on the size of the instrument, and a large one is 

 frequently described as a very powerful one. This is quite 

 an error. Given similar eyepieces and objectives, the same 

 magnification is obtained on a small microscope as on a 

 large. It is entirely dependent on the two optical parts, 

 the objective and the eyepiece, or ocular. Under the head 

 of ' Objectives ' in the makers' catalogues it will be noticed 

 that the powers are expressed as 1-inch, -J-inch, J-inch, etc. 

 This does not indicate the distance at which they focus on 



