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



531 



The Steel Tubes. 



No. 



Length. 



External 



Internal 



Volume of 



Diameter. , 



Diameter. 



Bore. 



I. 



45-7 cm. 



3-84 cm. 



•635 cm. 



16-7 c.c. 



II. 









•953 



32-9 



III. 



• • » 







1-270 



59-06 



IV. 



.1. 







1-588 



91-94 



V. 



.4. 





, . 



1-905 



128-63 



VI. 









2-222 



166-55 



VII. 



-•-•• 







2-696 



243-51 



3 



• ■ ■ 





• • 



1-27 



61-93 



5 



• ■ • 



1 





1-905 



127-95 



7 



... 







2-540 



227-45 



The Nickel Tubes. 



No. 



Length. 



External 



Internal 



Volume of 



Diameter. 



Diameter. 



Bore. 



I. 



47 cm. 



4'2 cm. 



•635 cm. 



17-43 c.c. 



II. 







•953 



33-57 



III. 



t •• 





.. 



1-270 



59-77 



IV 









1-588 



95-81 



V. 



• • • 







1-905 



136-35 



VI. 



... 





, . 



2-222 



173-72 



VII. 







, . 



2-540 



228-6 



1 









•635 



17-88 



4 



... 







1-588 



87-58 



7 









2-540 



224-47 



The volume of each bore was measured by weighing the mercury which exactly filled 

 the tube, when cap and capillary were fitted to it as in the magnetic experiment (§ 7). 



§ 6. The Magnetic Field. — The magnetic field was established by means of a 

 magnetising coil built up of six similar coils of stout copper wire capable of conveying 

 a current of ten amperes. Very rarely, however, did the current exceed three amperes. 

 The coils were made to order for the present series of experiments. They were distin- 

 guished by numbers, and were arranged one over the other so as to give as uniform a 

 field as possible in the axial core. The order of arrangement is shown in the following 

 table, which also gives the resistance and number of turns on each coil : — 



Coil. 



Turns. 



Eesistance 



No. 4 



1771 



4-75 ohm 



„ 6 



1756 



4-«3 „ 



» 5 



1769 



4-90 „ 



„ 3 



1765 



4-97 „ 



2 



1757 



4-80 „ 



„ 1 



1770 



4-97 „ 



Between No. 5 and No. 3 a secondary coil was inserted, by means of which, in 

 connection with a ballistic galvanometer, the total induction across the middle section of 

 the core could be measured. This necessitated these two coils being a little further 

 apart than any other contiguous pair. The field at the middle point of the axis, due to 

 one ampere flowing through the coils for various symmetrical combinations of these, 

 was calculated according to the well-known formula. 



