292 
MR. joule’s introductory RESEARCH ON THE 
distances of 2 and 6 inches. They are all however reduced to the latter distance by 
means of the data derived from the comparison of the action of the wire electro- 
magnets at the respeetive distances. 
In the adjoining’ Table, all the results except the last six were obtained at 2 inches 
distance, and the observations are divided by8'96, the relative attraction at 2 inches 
to that at G inches, called unity; the first recorded magnetic set was deduced from 
the mean of thirty-six experiments on the attraetion at 2 inches distance. The mean 
deflection amounted to no more than ’247 of a minute of a degree, and as the error 
incident to any single observation is from 1 to 2 minutes of a degree, it follows that 
no great reliance can be placed on this first result. 
Table III. 
Attraction, at 6 inches, of wire electro-magnet, 5^ inch diameter, wrapped with 
21 feet of wire. 
No. of experi- 
ments forming 
the mean result. 
36 
32 
18 
20 
9 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
6 
Intensity 
of 
current. 
Total change of 
magnetism by re- 
versal of current. 
•00441 
•0086/ 
•0195 
■0391 
•0568 
•0787 
•08061 
•0848 V0841 
•0870 J 
•O9O8I 
'llll ^963 
•0992 J 
•10191 
:1!!85 p*"' 
•1089 J 
•1134^ 
•1151 >•1156 
•1184 J 
•4372 
1-2919 
•00072 
•00145 
•00377 
•00929 
•01528 
•02657 
•02798 
•02998 
•03220 
•03529 
•03976 
•04570 
•04413 
•04573 
•04838 
•05338 
•09969 
•05972 
•10190 
•06622 
•14570 
•19320 
•29710 
•32810 
•38750 
•52980 
Magnetic set. 
•00001 
•00010 
•00029 
•00152 
•00330 
•00782 
•00855 
•00939 
•01001 
•01228 
•01488 
•02090 
•01809 
•01904 
•02047 
•02355 
•06240 
•02835 
•06580 
•03269 
•09900 
•14220 
•21420 
•22900 
•24760 
•26400 
Total change 
minus 
magnetic set. 
•00071 
•00135 
•00348 
•00777 
•01198 
•01875 
•01943 
•02059 
•02219 
•02301 
•02488 
•02480 
•02604 
•02669 
•02791 
•02983 
•03729 
•03137 
•03610 
•03353 
•04670 
•05100 
•08290 
•09910 
•13990 
•26580 
Set divided 
by square of 
current. 
Total change 
minus set, divided 
by current. 
•934 
•5161 
1-352/ 
•763 
•994 
1-023 
1-263 
1-3161 
1*306 >1-315 
1-323/ 
1- 489'/ 
2- 124 
1-838 J 
1-8341 
1- 871 L-40 
2 - 000 
5-262 J 
2-205^ 
4-967 >3-168 
2-332 J 
1-293 
•158 
•178 
•198 
•211 
•238 
•2411 
•243 >-246 
•255 J 
•253 ] 
■^^9 ^-256 
•250 f 
•262 J 
•2621 
•2fi7 • 
•S5 
•342 J 
•2771 
•314 >-291 
•283 J 
•320 
•206 
2 
4 
From the results of the above Table, it appears that, through the range of electrical 
intensities from ’0065 to ’0841, the set of the wire electro-magnet is proportional to 
tlie square of the cuirent; that fi-om the latter intensity to -1060 the set increases 
with much greatei’ rapidity, varying at one point with the 6th or 7th power of the 
