1318 



Journal of Applied Microscopy 



bearing lever strike against an eccentric cam, which has twenty-five stops in it. 

 To diminish the wear and friction, the lever where it strikes the cam is furnished 

 with a steel wheel. To prevent the dislocation of the pawl it is made in the 

 form of a fork, the prongs of which fit over the edges of the toothed wheel, so 

 that the pawl cannot slip to either side. Third— To prevent the overthrow of the 

 wheel, which, in rapid section cutting, is apt to cause a greater feed and there- 

 fore sections of greater thickness than intended, a simple and effective brake has 

 been added, the tension of which is easily regulated. The brake consists of 

 two steel springs, each with a leather pad, which press against the rim of the 

 wheel by a set-screw; these pads may be pressed together more or less, thus 

 regulating their pressure upon the wheel between them. Fourth — A split nut has 

 been provided for the micrometer screw, the two pieces of the nut are 

 attached to levers, which work like pincers, so that by pressing the levers the 

 nut is opened and object carrier may be run forward or back rapidly without 



disturbing the screw ; by releasing the levers the nut closes, and as it closes 

 snaps into place automatically. The device is such that when the carriage is 

 run way back to the beginning of its excursion, the nut snaps into place of itself, 

 and the machine is ready to work. Fifth — The main wheel by which the machine 

 is worked, has been so carefully balanced that the microtome may be stopped at 

 any point, and will remain in the same position without change. 



There are other minor alterations, which do not call for special description. 

 The resulting apparatus produced by Messrs. Bausch & Lomb is a fine instru- 

 ment of precision, very convenient and satisfactory in use, and attractive in 



appearance. 



II. THE PRECISION MICROTOME. 



The original form of this instrument was found by long continued use to" 

 have certain minor defects, three of which caused inconvenience. Perhaps the 



