riioroMicROCK.M'iiY .i\n i rciixicii. .u/cwo.sro/'K loi 



ciiUM'iiii'nt siip(>t)rt lor a li-iis. In tin- truatmeiit of most tr.iiis- 

 [Kirt-nt mounts an illuminating ili-\ice termed a substage condcnstr is 

 neressiiry, the microscope then forms a very necessary adjunct to 

 low -power work. 



Medium-power work always rei|uires the use of a microscope, and 

 because rigidity in mounting anil accuracy in adjustment are \ery 

 necess.iry to correct rendering of the image, some sort of a stand is 

 pro\ided on which the microscope and a suital)le illuminating train 

 are mounted. Usually this stand takes the form of a narrow wooden 

 or metal table supported by substantial metal legs. The table 

 carries an optical bench which in practice is a metal bar or rail of 

 special and rugged construction upon which the optical parts, the 

 illuminant and the camera are mounted and are capable of adjust- 

 ment so that they may be aligned optically. The description neces- 

 siirily, meets generalized conditions. There is, however, a great 

 similarity in the product of different makes of equipment and they all 

 follow the same conventional lines, improvements in one make quite 

 often being met by similar changes on the part of other makers. 



There is no very well defined line between medium-pow-er and high- 

 power apparatus so far as the stands are concerned, but when it 

 comes to real precision apparatus the choice in equipment is limited 

 to possibly two or three makes. The difference is to be found in the 

 quality of the optical parts and in the general stability of the assembly. 

 A skilled technician may produce remarkable medium-power results 

 with quite ordinan,' apparatus but no amount of training and skill 

 can make good in high-power work for the actual shortcomings of an 

 objective. Given a really good objective the skilled operator may 

 use an inferior type of stand and secure very fine results, but he will 

 be working under a considerable handicap and his work will not be 

 consistently good because lack of the right sort of apparatus is apt 

 to introduce variations in illumination, focusing, or adjustments 

 which will prove ruinous to good definition. 



Thus far consideration has been given to apparatus capable of 

 yielding a magnified image of some tangible sort of a specimen, but 

 there is an entirely different form of microscopic equipment which 

 reveals the presence of particles beyond reach by all other known 

 means of microscopic vision; reference is made to the ultra-microscope. 

 This instrument is not ordinarily provided with photographic ap- 

 paratus although with certain classes of work and under favorable 

 conditions it is possible to reprotiuce the image photographically. 

 Both liquids and solids may be studied by this means but in each 

 case the specimen must be capable of transmitting light. 



