the Mercury unit of Electrical Resistance. 

 The resistances, calculated by means of the formula 

 #== 7 (W 1 + w) — w, 

 are collected in the following Table : — 



Table VII. 



171 



Tubes. 



7. 



8. 



10. 



12. 



13. 



14. 



15. 





millims. 



millims. 



millims. 



millims. 



millims. 



millims. 



millims. 



7 





2602-56 



1541-66 



165281 



1636*60 



1419-99 



1525-39 



8 



191818 





1541-67 



1652 86 



1636-88 



1420-28 



1524-93 



10 



1918-49 



2602 60 





1653-15 



163715 



1419-88 



1525-87 



12 



1918-55 



2602-33 



1541-51 







1637-04 



141983 



1525-54 



13 



1918-58 



2602-27 



1541-49 



1652-62 





1419-79 



1524-87 



14 



1918-39 



2601-94 



1541-97 



165309 



163711 





1525-70 



15 



1918-59 



2603-52 



1541-53 



1652-92 



1637-62 



1419-96 





Mean ... 



1918-43 



2602 54 



154164 



1652-91 



1637-07 



1419-96 



1525-38 



Calcul.... 



1918-32 



2602-37 



1541-80 



1652-84 



1636 82 



142004 



1525-61 



The vertical columns contain the resistances of the various tubes 

 compared with those which stand in the first column. 



At the bottom I have added the means of the observed resist- 

 ances, and set under them the calculated values. 



The differences between the single observations are not more 

 than can be attributed to errors of observation, in some cases 

 increased, and in others diminished by the individual errors of the 

 measuring-apparatus. 



By reason of their very different values, the tubes 3, 5, and 11 

 were compared separately. The results are as follows : — 



Table VIII. 



Tubes. 



a. 



b. 



W 2 . 



Resistance. 



Observed. 



Calculated. 



3 



509-2 

 509-0 

 509-1 



490-8 

 490-8 

 490-8 



536-32 



556-33 



556-47 



Mean ... 



5091 



490-8 



5 



415-25 



415-2 



415-20 



584-55 

 584-55 

 584-55 



27311 



193-89 



193-97 



Mean ... 



415-22 



584-55 



11 



493-95 

 493-85 

 493-90 



505-9 



505-85 



505-95 



4487-45 



4381-00 



4382-18 



Mean ... 



493-90 



505-90 



