APPENDIX. 



287 



represented on the paper by a space of half an inch, this 

 interval is magnified as many times as the j^V^th of an 

 inch will go into half an inch, that is to say, 500 times ; 

 and every other object under similar conditions is magni- 

 fied to a like extent. 



Fig. 34. 



Lines of stage micrometer viewed with an ocular-micrometer. 

 The finer lines are those of the stage micrometer ; about eighteen of the lines of 

 the ocular micrometer are comprised in oue of the larger intervals between 

 them, so that if these intervals represent _^_ inch, the subdivisions of the 

 ocular micrometer will represent l_._ inch. 



The enlargement thus obtained may be determined 

 once for all for each objective, the same ocular being 

 used and the tube being drawn out to the same extent 

 say, to the full length in each case, and scales may be 

 made representing the intervals between the micrometer 

 lines under the different powers. For purposes of measure- 

 ment it will then only l)e necessar} 7 to compare the pro- 



