210 Permanence of the Rutherfurd Photographic Plates. 



Table of Errors of the Cylinder. 



Observer Davis. 



Observer Jacoby. 







Spider Line. 









Spider 



■ Line. 





scale. 





Dir't. 



Rev'd. 



Dir't. 



Eev'd. 



Final Mean, 



325 



— 0.0014 



+0.0002 



E 

 0.0012 



4-0.0005 



— c" 



).ooo5 



320 



— 



.0015 



• — 



.0004 







.0003 



— 



.0006 



— 



.0007 



315 



— 



.0005 



+ 



.0005 







.0010 



--[- 



.0005 



— 



.0001 



310 



+ 



.0003 





.0000 







.0006 



— 



.0002 



— 



.0001 



305 



+ 



.0003 



— 



.0001 







.0005 



— 



.0013 



— 



.0004 



300 



+ 



.0002 



+ 



.0002 



+ 



.0018 





.0000 



+ 



.0006 



295 



+ 



.0004 



+ 



.0004 



+ 



.0005 



+ 



.0008 



+ 



.0005 



290 



— 



.0005 



— 



.0012 



+ 



.0006 



— 



.0003 



— 



.0004 



285 



+ 



.0014 



+ 



.0004 







.0008 



+ 



.0009 



+ 



.0005 



280 



— 



.0009 



— 



.0006 







.0001 



— 



.0002 



— 



.0004 



275 



+ 



.0005 



+ 



.0008 



+ 



.0007 



— 



.0001 



+ 



.0005 



270 



+ 



.0010 



— 



.0008 







.0004 



— 



.0002 



— 



.0001 



265 



+ 



.0010 





.0000 



+ 



.0006 



— 



.0002 



+ 



.0004 



260 



+ 



.0013 



4- 



.0004 



+ 



.0004 



+ 



.0004 



4- 



.0006 



255 



+ 



.0005 



+ 



.0003 



+ 



.0001 



— 



.0004 



+ ■ 



.0001 



250 



+ 



.0010 



+ 



.0008 



+ 



.0009 



+ 



.C004 



+ 



.0008 



245 



+ 



.0007 



+ 



.0002 



+ 



.0016 



+ 



.0005 



+ 



.0008 



240 



+ 



.0007 



+ 



.0013 





.0000 



+ 



.0008 



+ 



.0007 



235 



— - 



.0011 



+ 



.0001 



+ 



.0007 



+ 



.0004 





.0000 



230 



— 



.0005 



— 



.oooS 







.0005 



— 



.0001 



— 



.0005 



225 



— 



.0007 



— 



.0001 



+ 



.0002 



+ 



.0003 



— 



.0001 



220 



— 



.0011 



— 



.0008 







.0001 



+ 



.0012 



— 



.0002 



215 





.0000 



+ 



.0003 



+ 



.0003 



— 



.0013 



— 



.0002 



210 



— 



.0008 



— 



.0002 







.0012 



— 



.0004 



— 



.0006 



205 



— 



.0005 



+ 



.0002 







.0018 



— 



.0005 



— 



.0006 



The above results bear eloquent testimony to the precision with 

 which the measuring machine has been constructed. It must be 

 borne in mind that the above errors are not strictly errors of the 

 cylinder. They include the errors caused by any defect in the 

 way the casting that carries the plate follows the C3dinder. Re- 

 membering that VLwity in the fourth decimal place corresponds to 

 0.00005 millimetre, we see that in no case does the cj'linder error 

 amount to half a micron. We can, therefore, conclude that no 

 harm has been done by the omission of the cylinder errors in the 

 present research. Still the numbers in the last column aboA^e 

 show a prevalence of the negative sign at the beginning and end 

 of the column. This seems to indicate that a very slight curve 

 exists in the CA^inder. If it were desired to apply the corrections 

 here determined, it would be necessar}^ to appl}^ the above num- 

 bers with reversed sign to the observed screw reading obtained 

 in the bisection of the star. 



5. Having finished the description of the investigation of the 



