and Laboratory Methods. 



1319 



most serious of them was the HabiUty of the automatic feed to get out of order 

 unless great and constant care was taken in the use of the machine. The sec- 

 ond defect was the wear on the ways, which took place chiefly in the middle, and 

 very little or not at all at the ends, so that the carriage was liable to bind at 

 the end of a longer excursion than usual. A third defect was that the object 

 holder could be lowered only by the slow process of turning the micrometer 

 screw backwards. Messrs. Bausch & Lomb have sought to remedy the first 

 defect by a new feeding device, which cannot be clearly described without spec- 

 ial illustrations. The general principle is to have a lever bearing a pawl, which 

 moves the toothed wheel ; the backward motion is so arranged that the pawl is 

 lifted free from the wheel altogether, but at the end of the backward motion the 



pawl is brought into place against the wheel again, by an action of the lever. 

 For this purpose the lever is hinged in its middle, so that its outer arm can 

 bend independently in one direction without displacing the whole lever. The 

 motion of the outer arm is utilized to bring the pawl into place against the 

 toothed wheel. This wheel is provided with five hundred teeth, each tooth 

 equaling a feed of one micron. It is also, to prevent overthrowing, supplied 

 with a brake similar to that on the wheel microtome. Of the new automatic 

 feed it is proposed to publish a separate account, with figures, on another occa- 

 sion. The second defect, that of the ways, has been obviated very simply by 

 shortening the ways themselves so that the whole of the ways will be worn 



