206 Permanence of the EiUherfurd Photographic Plates. 



is, however, credited to Leman and Thiessen in the report 

 of the Aichungs Kommission. The millimetre lines were de- 

 termined by comparison with a standard centimetre whose sub- 

 divisions had been previously carefully examined. The details 

 of the present scale investigation, as well as those of an indepen- 

 dent investigation which has been undertaken at Columbia Uni- 

 versity, are reserved for a separate publication. The present de- 

 termination Avas made in such a way that the mean millimetre of 

 the scale is taken as the standard millimetre. Consequently, the 

 division ei'rors for the two end lines of the scale are zero. The 

 following table contains the division errors, the positive sign in- 

 dicating that the interval between the zero line and the line in 

 question is greater than the number of millimetres indicated by 

 the number attached to the line. Consequently, in measuring with 

 this Sfale,we must add to distances obtained directly the correc- 

 tion given in the following table, in order to obtain what we would 

 haA^e got if all the spaces of the scale were equal to the mean mil- 

 limetre space. 



Table of Division Errors op the Scale. 



Line 



Corr. 



Line 



Corr. 



Line 



Corr. 



Line 



Corr. 



Line 



Corr. 





mm. 





mm. 





mm. 





m.m. 





mm. 



o 



.000 



27 



+.004 



53 



+.002 



79 



+.004 



105 



+.002 



I 



— .001 



28 



+ .002 



54 



+.004 



80 



+.004 



106 



+ .002 



2 



— .001 



29 



+.002 



55 



+.003 



81 



+ .004 



107 



-i-.002 



3 



— .001 



30 



-f.003 



56 



+.004 



82 



+ .004 



108 



+.002 



4 



.000 



31 



+ .003 



57 



+ .005 



83 



+ .004 



109 



+.002 



5 



.000 



32 



+ .003 



58 



+ .005 



84 



+ .003 



no 



-j-.ooi 



6 



.000 



33 



+ .002 



59 



+ .005 



85 



+ .003 



III 



.000 



7 



.000 



34 



+.002 



60 



+.004 



86 



+.001 



112 



.000 



8 



— .001 



35 



+.003 



61 



+.004 



87 



+ .004 



113 



.000 



9 



— .001 



36 



+.003 



62 



+.004 



88 



+.002 



114 



+.002 



lo 



+ .001 



37 



+.003 



63 



+.006 



89 



+ .003 



115 



+.001 



II 



-|-.oo2 



38 



+.002 



64 



+.005 



90 



+.003 



116 



+.001 



12 



+ .001 



39 



+.003 



65 



+.004 



91 



+.004 



117 



+.003 



13 



+.001 



40 



+.002 



66 



+.C06 



92 



+.002 



118 



+.001 



14 



.000 



41 



-)-.ooi 



67 



+ .004 



93 



+.002 



119 



+.003 



15 



+.001 



42 



+.001 



68 



+.003 



94 



+.002 



120 



4-. 002 



i6 



+.001 



43 



+.002 



69 



+.005 



95 



+.002 



121 



+.002 



17 



.000 



44 



-|-.0O2 



70 



+ .005 



96 



+.002 



122 



+ .002 



i8 



.000 



45 



-(-.002 



71 



+.005 



97 



+.002 



123 



+ .002 



19 



+ .001 



46 



-|-.002 



72 



+ .004 



98 



+•002 



124 



+.003 



20 



+ .001 



47 



+ .002 



74 



+.004 



99 



+.002 



125 



+.002 



21 



+.001 



48 



+ .002 



74 



+ .004 



100 



+.002 



126 



+.003 



22 



+.001 



49 



+ .003 



75 



+.003 



lOI 



+ .001 



127 



+.002 



23 



.000 



50 



+ .003 



76 



+.005 



102 



+.001 



128 



-j-.OOI 



24 



+.001 



51 



+ .OL>3 



77 



+ .005 



103 



+ .001 



129 



+.003 



25 



-|-.03I 



52 



+.003 



78 



+ .004 



104 



-|-.ooi 



130 



.000 



26 



+ .002 



















