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PROFESSOR HELE-SHAAV AND MR. ALFRED HAY 
solution not for a single cylinder of the given cross-section placed in a magnetic 
field, but of a whole row or grating of such cylinders, the distance apart of anv 
two neighbouring cylinders being equal to the breadth of the liquid film. 
Fig. 11 gives the solution for an elliptic cylinder similar to that in fig. 10, but 
having a permeability of 20. In fig. 12 we again have a cylinder of the same 
cross-section, but of permeability equal to 1000. On account of the great depth of 
the elliptic wall, the lines crossing the ellipse appear to be almost entirely obliterated : 
notwithstanding this fact, they emerge on the other side, preserving their identity 
and not mixing with the body of the liquid. The distortion of the lines close to and 
on the inner side of the elliptic boundary is in this case very strongly marked, and 
well illustrates one of the difficulties encountered in attempting to imitate the 
effects of highly permeable bodies. 
An interesting feature, well-known as a result of theoretical deductions, is clearly 
brought out by a comparison of the three diagrams, viz., the gradual decrease in the 
angle made by the external lines with the normal to the ellipse as the permeability is 
increased. Thus in fig. 11 this angle of incidence of the lines is quite large at certain 
points of the elliptic boundary; it is greatly reduced in fig. 10, and in fig. 12, for 
which the permeability is 1000, it is practically zero. 
It will be seen that the refraction of the lines in fig. 11 is very sharp—the “ weir 
effect ” being extremely feeble. No trouble was experienced on this account in any 
of the diagrams so long as the permeability did not exceed about 100. 
Figs. 13 and 14 (Plate 15) are a set relating to circular cylinders of permeability 
2 and 100 respectively. They illustrate clearly the well-known theoretical result 
that, on account of the shape of the cylinder, large changes of permeability produce 
only relatively slight changes in the magnetic induction through the cylinder. 
In fig's. 15—20 we have a set of diagrams which will be found interesting in con- 
nection with the important question of magnetic shielding—a subject which has 
recently attracted a good deal of attention. Fig. 15 is a diagram corresponding to 
the case of a hollow circular cylindric shield surrounding a solid cylinder, both 
cylinders having a permeability of 100. Fig. 16 relates to a hollow cylinder whose 
cross-section is bounded by two confocal ellipses. As shown in the mathematical 
appendix, the field produced inside such a cylinder is uniform if the original 
impressed field is uniform. Fig. 17 (Plate 16) represents the effect produced by a 
double cylindrical shield ; it is one of the earliest diagrams obtained by us, and the 
permeability is so extremely low that, even with the double shield, the field in the 
innermost space is comparable with the undisturbed field. It would correspond to a 
highly-saturated double cylindric shield in a field of very great intensity. Figs. 18, 
19, and 20 have a more practical interest, the permeability being 100 in each case. 
In fig. 18 we have a double cylindric shield, with a solid cylinder of iron placed con¬ 
centrically in the innermost space; the powerful shielding effect on the central 
cylinder is sufficiently evident. Fig. 20 shows the effect produced by a triple con- 
