170 FE. H. Hall—New Action of Magnetism 
6th. Another series of observations with the test coil. 
7th. Another series of observations with the earth inductor. 
8th. Another determination of the direct action of the mag- 
ed on the Thomson galvanom 
as was usually the case, several series were to be hele: 
a the same plate in one day, for the purpose of using pri- 
mary currents of various strengths, the sensitiveness of the 
Thomson galvanometer was tested before each main series of 
observations and after the last. 
e mean of two values found for the sensitiveness of the 
Thomson galvanometer was of course taken to bé the sensi- 
tiveness during the series of observations fn eke a 
not found necessary to determine the strength of . — 
field more than twice during a half day’s iasevesio 
n working up these observations the tellowings “formula 
applies : 
2 
2 ktana 
rao o a? ae 
MV eS 
| eee Bre 
M, V, and E’ have been already ve me 
7460 — twice the in tegral area of the earth inductor divided by 
the integral area of the test coil. Twice the simple ratio of 
these two areas is taken, for the reason that the earth induc- 
tor coils are turned through 18 180° when use 
eT st Se emia intensity of earth’s magnetism at position of earth 
induct 
sin =a quantity relating to effect on the galvanometer used 
‘with test coil, produced by withdrawing the latter from the 
magnetic field. 
sin z=a similar aur relating to the galvanometer and the 
earth induc 
k = constant of ee galvanometer. 
a = reading of tangent galvanometer when measuring primary 
current through the metal strip. 
w = effective width of metal str ip. 
t = effective thickness of metal stri 
d= difference in readings on the Thomson galvanometer scale 
caused by rever _ rita ee in ne main experiment. 
= difference in readings on same scale caused by reversing 
~ gurrent in duiariintag berlaiti satan of the Thomson gal- 
vanometer. 
© = reading of tangent galvanometer when measuring current 
used to determine sensitiveness of Thomson galvanometer. 
