162 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXX.) 
upon the torsion wire ; — thus, a crystal of tourmaline, which in air hung with the 
weight of 40‘4 grains upon the wire, would in water hang with the weight of 27‘3 
grains, and in phosphorus with the weight of only 15’5 grains. As this variation 
would slightly change the value of the torsion degrees, compensating weights of pure 
copper were added at the lower end of the torsion wire (3369.), ?. e. 5*7 inches above 
the place of the crystal and magnetic poles. 
3373. Bismuth crystal . — A piece of uniformly crystallized bismuth was reduced to 
the form of an octagonal prism, the height of which was 0*45, and its average 
diameter about 0‘28 of an inch ; its weight was 77 grains. When suspended per- 
pendicularly its magnecrystallic axis was horizontal, and therefore set in the magnetic 
field, which existed between the flat faces of the pole-pieces (3368.) fixed at the 
distance of 1 inch apart. The torsion suspender was, in this case, a bundle of ten 
cocoon silk fibres, only 5 inches in length. The temperature was 68° Fahr. The 
torsion between the upsetting points was as follows, for four different media, differing 
much in their magnetic relation : — 
Air 2250 
Absolute alcohol 2269 
Water 2230 
Saturated solution of protosulphate of iron . . 2234 
In another set of experiments, carbonic acid gas was compared with alcohol and 
water, and the result was the same in it as in them. 
3374. Desiring to include a highly diamagnetic medium in the list, I employed 
phosphorus ; but, as the heat required to melt it is competent to change the magnetic 
force of the bismuth crystal (3399.), it was requisite to compare it with water at a 
like temperature : — this was done, the temperature of 160° Fahr. being chosen. The 
results came forth as follows torsion force in water 1945°; in melted phosphorus 
1950°; and are therefore to be considered alike. 
3375. The liquids employed as surrounding media were contained in wide thin 
glass tubes, placed within the copper trough against which the magnetic poles rested 
(3368). Much care was requisite in the use of phosphorus. This substance was 
covered with water, and when the bismuth was passed through the water into the 
phosphorus, although it did not wet with phosphorus, still the latter acted slightly 
upon it, producing a few minute bubbles of adhering gas. These were not found on 
after occasions, when the same crystal was employed. It was also necessary that 
the phosphorus should be perfectly clean and good. Films soon form in it, and 
more especially at the contact of the phosphorus and the covering water ; and these, 
clinging to the suspending wire, embarrass the vibrations of the immersed crystal 
and render them uncertain; the least portion of burnt phosphorus makes these films 
abundant. Whenever they appeared, fresh clean phosphorus was employed. 
3376. From these results and from many others not described, it follows that the 
differential magnecrystallic force, i. e. the relations of the magnetic force in different 
