IN MAGNETISM AND ELECTRICITY. 
95 
expected that two magnets placed on the cylinder would have induced a double amount 
of magnetic force in the electro-magnet, whereas the force required to detach the sub- 
magnet was equal to a weight of 11'25 ozs., or was a little more than quadrupled. From 
a further comparison of the numbers contained in the Table, it will be seen that (within 
the limits and conditions of these experiments, and after making allowance for a certain 
degree of imperfection in them) the amount of magnetism induced in the electro-magnet, 
as measured by the weight required to separate the submagnet, is as the square of the 
inducing magnetism of the permanent magnets of the electro-magnetic machine. 
28. Experiments were then made for the purpose of ascertaining to what extent an 
alteration in the length and section of the wires surrounding the electro-magnet would 
influence the quantity of magnetism induced in it. The electro-helices were therefore 
coupled up so as to form a single circuit 200 feet in length (23), and its resistance was 
about four-tenths of that of the wire surrounding the- armature. The experiments were 
conducted in the same order as those in the preceding series, the thin cardboard being 
still interposed between the submagnet and the electro-magnet (24), and the following 
Table contains the results obtained. 
Table III. 
No. of magnets on cylinder. 
Weight, in ounces, required to separate 
submagnet from electro-magnet. 
Squares of magnetic force of 
magnet-cylinder. 
1 
5-00 
5 
2 
28*00 
20 
3 
76-00 
45 
4 
144-00 
80 
29. From a comparison of the numbers in this Table with those in Table II., it will 
be seen that the ratio of increase, as well as the amount of the magnetism induced in 
the electro-magnet, has been considerably augmented by an increase in the length of the 
electro-magnetic circuit. 
30. Experiments were also made with the submagnet in direct contact with the 
electro-magnet without the interposition of the cardboard, the arrangement of the 
electro-helices remaining the same as in the preceding experiments (28). The small 
scale-beam and stand were removed from the lathe-bed, and were replaced by a stronger 
apparatus of a similar construction. The results of these experiments are shown in the 
following Table. 
Table IV. 
No. of magnets on cylinder. 
Weight, in pounds, required to separate 
submagnet from electro-magnet. 
1 Squares of magnetic force of 
magnet-cylinder. 
1 
31-50 
31-50 
2 
98-00 
126-00 
3 
150-50 
283-50 
4 
178-50 
504 00 
