November 30, 1899] 



NATURE 



115 



possible photographic exaggeration of really minute differences 

 of intensity, and the difficulty of observations of such faint 

 phenomena. 



To this Prof. Keeler replies, " That the difference between 

 the plates is not sufficient to explain the irregularities found, 

 as the star images on both plates are equally intense ; the 

 differences in intensity are measured from point to point on the 

 same negative, not from one to the other ; the observations are 

 neither difficult or delicate, as the light given by the 36-inch is 

 quite sufficient for the purpose. 



A NEW ROCKING MICROTOME. 

 CERIAL section-cutting has sprung into such prominence 

 "^ during the last fifteen years, and has now become so 

 essential to almost every branch of biological research, 

 that we are apt to forget that we are still using, practi- 

 cally unmodified, one of the earliest invented automatic micro- 

 tomes. The Rocking Microtome designed by the Cambridge 

 Scientific Instrument Company was first put before the public 

 in 1885, within a short time of the appearance of the very earliest 

 of all automatic microtomes, that designed by Caldwell and 

 Threfall. The simplicity, efficiency and cheapness of the 

 former soon caused it to become both widely known and used 

 by all biologist^, and it may be doubted whether any instrument 

 has ever spread so rapidly and deservedly over so wide an area 

 as the familiar " rocker" which is now 

 a characteristic feature in all labora- 

 tories in which any branch of biology 

 is taught. 



Considering the number of years 

 which the microtome has been in use, 

 and the variety of purposes which it 

 has been made to serve, it is not sur- 

 prising that several small alterations 

 have been made in it from time to 

 lime ; none of these, however, have 

 affected the essential features of the 

 rocker, which remains the same in- 

 strument to-day that it was years ago. 



Recently the Cambridge Instrument 

 Company brought out an enlarged and 

 improved form to obviate what has 

 generally been regarded as the chief 

 defect of the "rocker," viz., the fact 

 that, owing to the principle upon 

 which this instrument is constructed, ~='; 



the cutting -surface was of a necessity 

 a curved one. This microtome, how- 

 ever, is too expensive to replace the 

 rocker for which, in spite of its curved 



cutting surface (a defect of no moment in most work), there 

 was and is still a great demand. The makers have, therefore, 

 set to work to remedy certain minor defects in the rocker, and 

 have, as a result, .placed what they consider to be a greatly 

 improved microtome on the market. 



The new microtome, as will be seen from the figure, is of 

 much the same form as the old design, and is built upon the 

 same principle, the chief difference being in the bearings of its 

 working parts, and in the addition of one or two new features. 



The foUowing advantages are claimed for the new model : — 



(i) Increased rigidity. 



(2) Impossibility of tearing sections on the upward movement 

 of the object. 



(3) Impossibility of cutting thick and thin sections. 



(4) Graduated arc for showing the thickness of the sections. 



(5) Catch for holding object alxjve the razor edge. 



(6) Improved method of fixing the cord. 



(7) New object-holder. 



Most of these are small but useful additions to the microtome, 

 which by themselves would call for no special comment. The 

 chief features presented by this instrument, and through which it 

 claims more than passing notice, are Nos. 2 and 3 in the above list. 



Every one who has had much experience in serial section- 

 cutting will at one time or another, no matter what automatic 

 microtome he was using, have found that the sections were 

 torn or lifted off the edge of the razor, and adhered to the 

 block of paraffin on the upward stroke. It is to obviate this 

 trouble that the modified rocker has appeared. 



AH possibility of this injury to the section is prevented in this 

 model by the fact that in the upward movement the object can- 

 not touch the razor, since^by means of an additional pawl 

 which at the end of the stroke turns the screw down by four 

 teeth on the notched wheel, the object is drawn backward 

 before the upward movement commences. 



This apparatus acts perfectly, but may possibly introduce a 

 new source of damage to the machine, viz., additional wear 

 to the notches on the toothed brass wheel. As one who has 

 used a rocker since its first appearance, I can state that the only 

 serious trouble I ever had with this instrument was due to the 

 wearing down of these teeth ; therefore, it seems to me that the 

 addition of a second steel pawl will cause these important 

 structures to wear away more'quickly. After all, is the occasional 

 displacement of the section in the upward movement due to a 

 defect in the older microtomes? Or is it not rather due to 

 carelessness on the part of the manipulator, a blunt razor, a 

 paraffin block with imperfectly trimmed edges, and the latter 

 not arranged parallel to the edge of the razor?' Personally, I 

 believe the operator is generally to blame, and that it is due 

 to a combination of the above mistakes on his part. But 

 even if it is so, we ought to thank the makers for trying to save 

 us from ourselves, and if the extra pawl will not wear the very 

 important teeth too much, it should prove a very useful addition 

 to the microtome, since even the most careful of us are apt to 

 err at times, and it is very trying to struggle with an object which 

 will not ribbon. 



Most of the bearings of the machine are based on a new de- 

 sign, which is said to reduce wear and friction. That at the 

 base of the big screw, as now spherical instead of conical, this is 

 believed to prevent the cutting of thick and thin sections. How 

 far this is a fact time only can tell, but a trial of the instrument 

 with very hard and trying objects gave highly satisfactory 

 results. 



The whole instrument is much more rigid than the old form, 

 and the addition of a Citch for holding the object above the 

 razor, the improved cord fixer, the graduated scale for showing 

 the thickness of the sections, and the new compact object- 

 holder provided with universal movement, will add much to the 

 utility of the machine. It is to be hoped, however, that the scale 

 will be quite accurate ; the divisions on the scale attached to the 

 machine (a rough model only), which has been examined, did not 

 appear quite equal, some giving two and some three teeth. 



It may be mentioned that the new microtome will be issued at 

 practically the same price as the old form, and sh.mld, with its 

 new additions, prove a boon to all biologists. M. F. W. 



CORRESPONDING SOCIETIES OF THE 



BRITISH ASSOCIATION. 



T^HE meetings of the Conference of Delegates of the Corre- 



•*• sponding Societies were held in the Mayor's parlour at 



the Town Hall, Dover, on September 14 and September 19. 



First Meeting. — The Corresponding Societies Committee of 

 the British Association were represented by Rev. T. R. R. 



NO 



1570, VOL. 61] 



