INVERTEBEATA, CRYPTOGAMIA, MICROSCOPY, ETC. 957 



times ; and the fourth and tiftli carry two other lenses of low magni- 

 fying power (7 and 3 times), the former having a jointed attachment 

 to allow of the lens being placed in any position. 



The arm carrying the Microscope is ordinarily turned away from 

 the stage to the left of the observer, while the other arms which are 

 not in actual use are placed forwards so as to be out of the way, but 

 are at once available when required. 



The inventor claims the following as the special advantages of the 

 instrument : — 



(1) The stage is entirely free for work, nothing being in the way 

 of the observer's hands or head on the side at which he stands. 



(2) It allows of a particularly rapid and convenient change of 

 powers ; and 



(3) The preparation need never be moved from its place during 

 work, and thus a great saving of time is effected. 



Ward's Improved Microtome. — At the November meeting of the 

 Society, an improved form of microtome was exhibited and described 

 by Mr. F. H. Ward. It is a modification of the one introduced by 

 Stirling, from which, however, it differs in the indicator. The thick- 

 ness of the section is indicated by means of a screw having thirty-six 

 threads to the inch, to which is attached a wheel containing thirty-five 

 notches upon its circumference ; into these notches a spring catch 

 falls in rotation as the screw is turned. This S2)ring is attached to a 

 metal plate through which the screw works, but which is prevented 

 from turning round with the screw by a brass rod fixed into the base 

 of the microtome. 



The bottom of the well is removable, and is retained in place by 

 two bayonet catches. When removed from its fitting, the bottom is 

 separable into two halves so as to release the screw. The continuity 

 of the thread in the internal screw is maintained in the two halves 

 when in position by means of two metal pegs on the face of one half 

 accurately fitting into holes on the face of the other. The object of 

 this contrivance is, that when the screw has been turned round to its 

 extreme limit, by a slight backward turn the bottom of the well is 

 removed, the two halves separated and the screw is set at liberty, thus 

 avoiding the wear to the thread and the sjiring catch, which must 

 inevitably result from rapidly turning the screw in the reverse direc- 

 tion through about two inches of its length. 



A thick plate of glass, with an aperture the size of the well,, 

 covers the upper brass plate, and slides into position by means of a 

 dovetail on each side. 



Matthews' Section-cutting Machine.* — Dr. John Matthews has- 

 contrived a machine for making sections of such substances as bone, 

 hard wood, ivory, nut, and other materials which are too hard to be 

 cut with the section knife, and not of a nature to require the lapidary's 

 wheel. 



The carriage holding the saw runs smoothly yet firmly betweeir 

 friction rollers, and derives its reciprocating motion from a crank, 

 * 'M. Jouni. Sci.,' i. (1879) p. 823. 



