OF MICROSCOPIC OBJECTS. 15S 



Coinciding with this opening is a brass tube, fixed in the 

 under side of the table (if it may be termed so). This tube 

 is so cut at the bottom as to take a fine screw. Another 

 screw is also placed at the sanoe end of the " table," which 

 works at right angles to this, so that any substance in the 

 tube may be wedged firmly by working this last screw. To 

 use this instrument, the piece of wood or other object of 

 which a section is required must be placed in the tube, 

 when, by turning the screw underneath, the wood is raised 

 above the brass plate more or less as wished, and by using 

 the screw at the end, it is held firmly in the same position. 

 With a flat chisel the portion of the object which projects 

 above the surface of the brass plate may now be cut off, and 

 by means of the bottom screw another portion may be 

 raised and treated in the same manner. As to the thickness 

 of which objects should be cut, no proper directions can be 

 given, as this differs so greatly that nothing but experience 

 can be any guide. The same thickness can be obtained by 

 working the screw underneath in uniform degrees, the head 

 being marked for this purpose ; and where the substance to 

 be cut is very much smaller than the hole in the brass plate, 

 it may be wedged with cork. 



*As this instrument is peculiarly adapted for cutting 

 wood (though used for other substances, as before men- 

 tioned), I shall notice a few particulars concerning this 

 branch of sections. It may here be remarked, that to 

 obtain anything like a true knowledge of the nature of 

 wood, it should be cut and examined in at least two direc- 

 tions, across and along. The piece of wood is often placed 

 in spirits for a day or two, so that all resinous matter may 

 be dissolved out of it ; it must then be soaked in water for 



* M. Mouchet, in order to avoid all danger of "beards" in cutting 

 wood sections, procured a knife with a semicircular blade. This was 

 fastened at the end upon a flat plate, in order to rerolve, as we may 

 call it, the handle being long enough to give leverage for any required 

 power. The wood supporter being placed in a favourable position, 

 the knife is easily brought round, nd the section cafe by a circular 

 act'on. 



