14 Modern Microscopy 



stop-pin, against which the slide can be set), the special 

 feature would be at once in the field of view. These 

 divisions can also be used for roughly measuring objects, 

 the modus operandi of which is given in the instructions for 

 the measurement of objects, page 114. 



If a mechanical stage be selected, it should be a good 

 one, for if badly made it is far less convenient than a plain 

 stage ; also the frictional parts should be sprung, and 

 fitted with adjusting screws, so that compensation may be 

 made for wear and tear. 



Attachable Mechanical Stages. — In recent years a 

 variety of mechanical stages, which can be attached to or 

 removed from an ordinary plain stage microscope, have 

 been introduced. Some of these possess merit, but, taken 

 as a whole, they are inaccurate in working, and at their 

 best are not for one moment to be compared with the 

 mechanical stage, which has been built as an integral part 

 of the microscope, and no microscopist who wishes to do 

 himself and his work full justice should entertain such a 

 fitting. , 



For some reason, Continental manufacturers have never 

 fitted their instruments with the mechanical stage as it is 

 understood in England, but have always recommended 

 and arranged for the adaptation of an attachable stage. 

 Where mechanical movements are found to be an essential 

 for certain work, and from reasons of inconvenience or 

 impracticability the plain stage cannot be exchanged for a 

 proper mechanical one, then, and then only, should the 

 attachable form be resorted to. 



Plain Stages.— The stage of the microscope shown on 

 page 8 has two flat springs only, to hold the object in 

 position on the surface, and the movement of the object 

 is effected by the fingers. For cursory examinations this 

 answers every purpose ; but where systematic work is to be 

 done something more is needed, and this, when a mechani- 

 cal stage is not provided, should take the form of a bar 

 reaching completely across the stage and sliding in a 



