266 PKACTICAL PHOTO-MICKOGKAPHY 



an ordinary 3" x 1" microscope slip. Around this put a 

 metal ring with exactly parallel ends (such metal rings may 

 be obtained commercially in varying sizes and depths for this 

 particular purpose from Messrs. K. & J. Beck of Cornhill, E.G.). 

 the depth of the ring being greater than the height of the 

 specimen as it lies on the slip. Now place over the specimen 

 some plasticine, putty, or moulders' clay, or some similar 

 easily moulded material. Press down another slip on to the 

 top of this clay so that the object is enclosed between the two 

 slips, these being exactly parallel, and then remove the bottom 

 slip and the metal ring. The object will now be supported on 

 one slip with the polished surface in such a position that it can 

 be placed on the stage of the microscope. This method is simple 

 and inexpensive, and so far as the experience of the writer is 

 concerned, there are few objects that cannot be satisfactorily 

 mounted in this way. 



I -.- Various appliances are on the market for holding the specimen 

 and adjusting it exactly at right angles to the optic axis of 

 the microscope without the necessity of embedding it in the 

 manner described. Where fractured unpolished surfaces have 

 to be dealt with, or where the incidence of the light is required 

 to be varied to suit a particular spot in a specimen, these are 

 of considerable value. In general, however, the method of 

 embedding in some soft material is far more useful, as it admits 

 of variation to suit the class of specimen. 



If it is desired to preserve a polished surface for future use, 

 then the best preservative is a weak solution of celluloid in 

 amyl acetate. When this is very gently brushed or poured 

 over the surface, it quickly dries off, leaving an extremely thin 

 film which efficiently protects without materially interfering 

 with the corrections of an objective, should it be desired to 

 observe the object again without cleaning the surface. The 

 only advantage in using some of the devices which are made 

 for holding specimens is that they then do not require any 

 mounting ; they can in fact be removed from the device or 

 re-introduced at will. There is the disadvantage, however, 

 that on each occasion they have to be re-levelled, and in 

 practice this is often a much longer operation than it would be 

 to embed it again as first described. 



For very low-power work, where illumination by directly 



