860 



SCIENCE. 



[N. S. Vol. V. No. 127. 



with, clean, fresh oil. The micrometer 

 screw should be oiled with porpoise oil, 

 which will last for months. For the other 

 parts a light parafifine oil may be used. I 

 have found that which is known to the 

 trade as Xo. 40 suitable. 



3. All the permanent adjustments must be per- 

 fectly set. Of the permanent adjustments 

 there are two which require more or less 

 constant attention : First, the movable gib, 

 by which the carriage is held against the 



affine plate to the movable carriage there is 

 a triple clamp, so constructed as to allow 

 independent movements in three directions. 

 The three screws of the clamp must all be 

 tightened, and novices must remember that 

 a metal screw cannot be tightened with the 

 first turn, but that after a minute or so it 

 can be tightened a little more. The knife 

 is held by two screws, which must also be 

 doubly tightened to ensure the knife being 

 firmly held. In my experience with stu- 



iimi«0> 



vertical way ; that gib should fit as tightly 

 against the way as is compatible with the 

 fi'ee running of the apparatus. If this is 

 not done no satisfactory sections can be ob- 

 tained, because the action will be irregular. 

 Second, the split-ring around the neck of 

 micrometer screw must be tightened sufli- 

 ciently to prevent any back-lash, but not 

 enough to make the screw hard to turn. 



4. All the changeable adjustments must be 

 absolutely firm. In order to attach the par- 



dents, it seems to me that about nine-tenths 

 of the failures to get satisfactory sections 

 are owing to the neglect of the proper 

 clamping either of the knife or the object- 

 holder, or both. 



5. Avoid cutting on days when the sections 

 become highly electrified. Everyone who has 

 done much section cutting of objects im- 

 bedded in parafiine has encountered the 

 difficulty of handling sections which have 

 been electrified during the cutting, for the 



