I907.] EWELL— STUDY OF MODERN MICROMETERS. 189 



No. VI. Glass Scale by Zeiss. 



space. Relative Correction. 



First TO mm _ 0.2 micron. 



Second ^n mm +0.2 micron. 



Third To mm +0.7 micron. 



Fourth Tu mm —0.3 micron. 



Fifth tV mm — 0.4 micron. 



No. VII. Glass Scale by Powell and Leeland. 



Space. Relative Correction. 



First t'o mm +0.7 micron. 



Second i^u mm _ i.o micron. 



Third ^ mm -f 0.9 micron. 



Fourth ^ mm —0.5 micron. 



Fifth tV mm _ o.i micron. 



No. VIII. Glass Scale by Watson. 



Space Relative Correction. 



Firs t tV mm 4-0.5 micron. 



Second t^ mm —0.5 micron. 



Third tV mm -f- 2.9 micron. 



Fourth tV mm —1.7 micron. 



Fifth iV mm _ 1.2 micron. 



No. IX. English Scale on Speculum Metal by the late Professor 



W. A. Rogers. 



Space Relative Correction. 



First 1^0 inch -f 0.4 micron. 



Second j^o inch _ 0.6 micron. 



Third y^o inch —0.3 micron. 



Fourth T^o inch 4-0.7 micron. 



Fifth jio inch 4-0.4 micron. 



Sixth y^o inch _ 0.8 micron. 



Seventh y^o inch 4-0.2 micron. 



Eighth jio inch —0.3 micron. 



Ninth TTTo inch +0.1 micron. 



Tenth j^^ inch ^ 4-0.1 micron. 



No. X. Scale on Platinum Iridium, known as " Centimeter A " 

 the Standard of the American Microscopical Society. 



St ace. Correction (f tal). 



First tV mm -f 0.20 micron. 



Second tV mm +0.13 micron. 



Third tV mm 4- 0.84 micron. 



Fourth tV mm _ 0.60 micron. 



Fifth TH mm _ 0.44 micron. 



Sixth tV mm -f 0.22 micron. 



Seventh tV mm — 0.14 micron. 



Eighth tV mm -f 0.21 micron. 



Ninth t\t mm _ 0.02 micron. 



Tenth i^n mm 4- 0.18 micron. 



