OF MICROSCOPIC OBJECTS. 137 



included in any of the former chapters, but would have left a 

 most interesting branch untouched had it been neglected. There 

 is another subject also which should not be passed by viz., the 

 production of minute pictures which serve as objects for microscopic 

 examination. I may here mention that as this manual is simply 

 to enable the young student to prepare and mount his objects, 

 the photography of magnified objects has evidently no place here. 



Few slides caused so much astonishment as these minute 

 photographs when first exhibited ; small spots were seen to con- 

 tain large pictures, and a page of printed matter was compressed 

 into the one-hundredth part of a square inch. It would be im- 

 possible in this place to give the inquirer any instruction in the 

 manipulation of photography, so it must be assumed that he al- 

 ready knows this. 



We will first consider the process performed by artificial light. 

 The collodion employed in photographing generally shows as 

 much structure when magnified as is found in linen of moderate 

 texture; but this is not always the case, as some samples bear 

 much enlargement without any of this appearance. It is evident 

 that a structure so coarse would make it entirely unfit for these 

 minute pictures, as all the small markings would be destroyed, or 

 so interfered with that no great enlargement would be practicable. 

 To obtain almost structureless collodion is not an easy matter, and 

 a clever practitioner in this branch of photography states that he 

 knows of no method to accomplish this with certainty, but he 

 himself tries different samples until he falls upon a suitable one, 

 which he then lays aside for this object. A beneficial effect is 

 often derived from keeping the collodion awhile, but this is not 

 always the case. The slides should be chosen of an equal thick- 

 ness, so that when focussed upon one no re-adjustment may be 

 necessary for the others. The glass should, of course, be free 

 from any roughness, scratches, or other imperfections, and of first- 

 rate quality and colour. 



The microscope must then be placed in a horizontal position, 

 and the eye-piece removed, the stage having a small clip upon it 

 to keep the prepared plate in position. The negative must then 

 be supported at a distance from the end of the microscope tube 

 from which the eye-piece was withdrawn. The distance will, of 



