MICROMETERS FOR COVERING GLASS 



441 



One of the continuous aims of the working microscopist is to 

 save or utilise to its utmost his time. Complicated measurements and 

 calculations are to be avoided where possible, and a very beautiful 

 and ingenious instrument, capable of being used as a meter for 

 cover-glass, has been devised by Mr. J. Ciceri Smith, of 61 Hatton 

 Garden, London. It is a perfect direct-reading micrometer, and i& 

 constructed to take measurements in thousandths of an inch, and 

 may be used in gauging the thickness of microscopical glass, metal 

 and other sheets, balls 

 for bearings, needles, 

 wire, &c. Its advan- 

 tages over the ordinary 

 micrometer consist in 

 the measurements 

 being automatically 

 and accurately re- 

 corded in clear figures 

 on the index, thus 

 avoiding the strain on 

 the eyes caused by 

 reading the fine lines 

 on the old form of 



gauge; in there being no liability to errors through miscalcula- 

 tions, and in its being possible to take any number of various 

 readings with ease, accuracy, and rapidity. We illustrate this appa- 

 ratus in fig. 374. 



As in the ordinary decimal gauge the glass or other article to be 

 measured is placed between the ' anvil ' (or hexagonal nut) and the 

 face of the spindle, the thimble being rotated in either direction 



FIG. 373. Zeiss's cover- glass tester. 



FIG. 374. Mr. J. Ciceri Smith's direct-reading micrometer. 



until the required adjustment is obtained, the exact measurement in 

 decimal parts of an inch being at the same instant automatically and 

 accurately recorded on the index, these readings responding in either 

 direction with the most delicate movements of the screw. 



To avoid the screw being unduly strained, the spindle is rotated 

 by friction from the cuter spring-tight thimble, the inner thimble 

 being rigidly fixed to the spindle. Hence it is impossible to strain 

 the screw, since as soon as the pressure becomes too great the spring 



