318 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



SI 



7l\ 



*JLg 



pawl e takes, carried upon an arm d y the pawl being pressed against the 

 rachet- wheel by a small bent spring /. Tho arm d, which works loosely 

 upon tho spindle D, is kopt in its proper position by means of a washer ; 

 the extremity of tho arm is forked, into which takes a bent wire H, 

 fixed to a rod G, working horizontally in bearings. Within the bearings 

 the rod is surrounded by a spiral spring h. To ono end of the rod, be- 

 yond tho bearing, is a small hook i, to allow of the attachment of a cord, 

 which, passing over the small pulley I, is secured to a suitable treadle 

 beneath the table. Tho other end of the rod has a screw-thread with a 



thumbscrew i 1 for regulating 

 Fig. CI. an d limiting the horizontal 



motion or " play " of the rod. 



To the base plate A is fixed 

 a second pawl F, of such length 

 as to act upon the rachet-wheel 

 E at whatever height the latter 

 may be, the pawl being gently 

 pressed against the rachet-wheel 

 by the spring /. The upper part 

 of the vertical spindle I) has a 

 fine screw-thread, which works 

 in a metal disc screwed to the 

 base plate. The other extremity 

 of the spindle is plain, and 

 moves freely in a bearing 

 formed in a rigid bracket J, 

 which serves to keep the spindle 

 perfectly central relatively to 

 the tube &. The spindle ter- 

 minates at its upper extremity in a conical point o, upon the apex of 

 which is a plug m, which moves freely up and down in unison with the 

 vertical motion of the spindle. 



The mode of working the apparatus is as follows : — Having adjusted 

 the thumbscrew i\ the treadle is depressed, and by means of the cord n 

 attached to the rod G, the latter is drawn forward in the direction of 

 the arrow, a distance limited by the position of the thumbscrew i 1 , and 

 in this forward motion carries with it, by means of the wire H, the 

 arm d ; whereupon the pawl e takes into the rachet-wheel E and 

 rotates the latter a distance corresponding to one, two, or more teeth, 

 thus raising tho plug m and object to such a height as to allow of 

 a section being taken in accordance with the thickness desired. The 

 whole of the mechanism, it will be seen, is actuated by the depression 

 of the treadle, thus leaving both hands free to manipulate the knife, as 

 also to vary the position of the object. 



The author, in his specification,* further says : — " It is well known 

 that in preparing objects for microscopic examination, it is almost im- 

 possible, by the methods at present generally adopted, to obtain very 

 thin sections or slices of substances of a brittle or non-elastic nature. 

 This difficulty is, to some extent, due to the inability to utilise both 

 hands for manipulating the razor or section knife before referred to, 

 but with the improved apparatus above described, inasmuch as the 



1887, No. 9900. 



