38 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXII.) 
over the result. As the crystal is shorter the distance n diminishes, all the other 
phenomena remaining' the same. A crystal 0*7 of an inch long, but thicker than the 
last, had for its maximum n distance 1*7 inch. A still shorter crystal had for its 
maximum n distance 1*1 inch. In all these cases variation of the force of the mag- 
net caused no sensible change. 
2620. Variation in that dimension of the crystal coincident with the rnagnecry- 
stallic axis affected the n distance : thus, increase in the length of the magnecrystallic 
axis diminished the distance, and diminution of it in that direction increased the 
distance. This was shown in two ways ; first, by placing a second prismatic crystal 
by the side of the former in a symmetric position (2636.), which reduced the n 
distance to between 1*76 and 2 inches ; and next, by employing two crystals in suc- 
cession of the same length but different thicknesses. The thicker one had the smaller 
n distance. 
2621. Variation in the depth of the crystal, i. e. its vertical dimension, did not 
produce any sensible effect on the n distance : nor by theory should it do so, until 
the extension upwards or downwards brings the upper or lower parts into the con- 
dition of raised or depressed portions (2617.)- 
2622. Variation in the form of the poles affects the n distance. As they are more 
acute, the distance increases ; and as they are more obtuse up to flat-faced poles 
(2463.), the distance diminishes. 
2623. With the shorter crystals, or with obtuse poles, it is often necessary to 
diminish the power of the magnet, or else the crystal is liable to be drawn to the one 
or other pole. This, however, may be avoided by employing a vertical axis which is 
confined below as well as above (2554.) ; and then the difference in strength of the 
magnet is shown to be indifferent to the results, or very nearly so. 
2624. These effects may probably be due to the essential difference which exists 
between the ordinary magnetic and the magnecrystallic action, in that the first is 
polar, and the second only axial (2472.) in character. If a piece of magnetic matter, 
iron for instance, be in the magnetic field, it immediately becomes polar (i. e. has 
terminations of different qualities). If many iron particles be there, they all become 
polar ; and if they be free to move, arrange themselves in the direction of the axial 
line, being joined to each other by contrary poles ; and by that the polarity of the 
extreme particles is increased. Now this does not appear to be at all the case with 
particles under the influence of the magnecrystallic force; the force seems to be 
altogether axial, and hence probably the difference above, and in many other results. 
2625. Thus, if four or more little cubes of iron be suspended in a magnetic field 
of equal force (2465.), they will become polar; if also four similar cubes of cry- 
stallized bismuth be similarly circumstanced, they will be affected and point. If the 
iron cubes be arranged together in the direction of the equatorial line, they will form 
