MAGNECRYSTALLIC CONDITION OF SULPHATE OF IRON. 
37 
^ vi. Note. — On the position of a crystal of sulphate of iron in the magnetic field. 
Received December 7, 1848. — Read December 7, 1848. 
2615. Though effects of the following nature are general, 
yet I think it convenient to state that I obtained them chiefly 
by the use of magnetic poles (224705 form of which is given 
in the plan and side view annexed (fig. 6.). The crystals submit- 
ted to their action were suspended by cocoon silk, so as to be 
level with the upper surface of the poles. 
2616. A prismatic crystal of proto-sulphate of iron was selected, which was nearly 
0‘9 of an inch in length, OT in breadth, and 0’05 in thickness; by examination the 
magnecrystallic axis was found to coincide with the thickness, and therefore to be 
perpendicular, or nearly so (2546.), to the plate. Being suspended as above described, 
and the magnet (22470 excited by ten pair of Grove’s plates, the crystal stood trans- 
verse, or with its magnecrystallic axis parallel to the axis of magnetic force, when the 
distance between the poles was 2’25 inches or more ; but when the distance was 
about two inches or less, then it stood with its length axial, or nearly so, and its 
magnecrystallic axis therefore transverse to the lines of magnetic force. In the in- 
termediate distances between 2 and 2*25 inches, the prism assumed an oblique 
position (2634.), more or less inclined to the axial line, and so passing gradually from 
the one position to the other. This intermediate distance I will for the present call 
n (neutral) distance. 
2617- If the poles be two inches apart and the crystal be gradually lowered, it 
passes through the same intermediate oblique positions into the transverse position ; 
or if the crystal be raised, the same transitions occur ; at any less distance the changes 
are the same, but later. They occur more rapidly when the crystal is raised than 
when it is lowered ; but this is only because of the unsymmetric disposition and in- 
tensity of the lines of magnetic force around the magnetic axis, due to the horse-shoe 
form of the magnet and shape of the poles. If two cylinder magnets with equal 
conical terminations were employed, there is no doubt that for equal amounts of 
elevation or depression, corresponding changes would take place in the position of 
the crystal. 
2618. These changes however are not due to mere diminution of the magnetic 
force by distance, but to differences in the forms or direction of the resultants of force. 
This is shown by the fact that, if the crystal be left in its first position, and so point- 
ing with the length axially, no diminution of the force of the magnet alters the 
position ; thus, whether one or ten pair of plates be used to excite the magnet, the n 
distance (2616.) remains unchanged; and even descending to the use of an ordinary 
horse-shoe magnet, I have found the same result. 
2619. Variation in the length of the prismatic crystal has an important influence 
Fig. 6. 
