STEEL, NICKEL, AND COBALT TUBES IN THE MAGNETIC FIELD. 



467 



to move at the instant the magnetic field was established or removed. The positive 

 sign means that the meniscus moved outwards along the capillary, showing an 

 increase of volume of the iron tube contained in the brass tube. The negative sign 

 means, of course, a movement in the opposite direction, indicating a decrease in the 

 bulk of the contained iron tube. When two numbers are entered side by side in 

 the third column, the first (in brackets) gives the greatest excursion in the indicated 

 direction made by the meniscus before it comes to its final position of rest after 

 removal of the magnetic field. 



Iron Tube A III., November 12th, 1897. 

 Apparent Change of External Volume ; Tube Plugged. 



Field. 



Field on. 



Field off. 



531 



-25 



(-23) +11 



403 



-29 



(-13) +19 



302 



- 30-5 



(-11) +22 



202 



-33 



(-*8) +27 



100 



-42 



(-1) +38 



A III., November 15th, 1897. 

 Change of Volume of Metal. 



536 



+ 18 



-34 



408 



+ 15 



-28 



308 



+ 14 



-24 



100 



+ 5-5 



-"s-5 



Thus, taking the very first result given above, we see that, when a field of 531 

 was established, the water meniscus in the capillary moved back 25 divisions of the 

 micrometer scale, and there came to rest. On removal of the field, the meniscus darted 

 back 23 other divisions, then turned and moved forward along the capillary, stopping 

 finally +11 divisions from the position it occupied just before the field was removed. 

 Its final position was therefore — 14(= —25 + 11) from that originally occupied just 

 before the field was established. 



Again, taking the first result of the experiment of November 15th, we see that 

 the establishment of Field 536 produced a forward motion of the meniscus through 

 18 divisions of the scale, but that, on the removal of the field, the meniscus moved 

 back through 34 divisions, occupying a final position —16 from that occupied before 

 the field was established. 



The results are the same for both directions of field. In every case the negative 

 reading is greater than the positive. In the experiment of November 12th, the 



