Magnetism, i. 30 periodic and secular variations of, i. 30 probably stand in some periodic connection with the solar spots, i. 30, 31 probable cause of terrestrial magnetism, i. 31 difference between magnetic and electric currents, i. 33 relations between the force of magnetism and the atoms of matter, i. 75 all substances either magnetic or diamagnetic, i. 75 proof of the connection between the magnetic forces and crystalline structure, i. 76 conduct of amorphous and isomorphous substances under magnetic influence, i. 76 action of magnets upon matter most powerful in the line of maximum density, i. 76 conditions of the position which crystals take with regard to the magnetic force, i. 76 magnetic changes in the relations and distances between the ultimate atoms of matter, i. 77 effect of magnetism on the stratified appearance of the electric light, i. 78 causes of the polarity of a magnet, according to Ampère, i. 80 action of magnetism on the stratified discharges of electric light, i. 82 illustration of the action of magnetism and electricity on light, i. 90 Maiden’s hair fern, structure and habitat of, i. 359 Malaxis paludosa, or bog malaxis, structure and mode of reproduction of, i. 400 Malic acid, chemical combination forming, i. 97 Manchineel, poison of the, i. 426 Manganese, peroxide of, relative weight of the atoms of oxygen and metal in, i. 99 atomic weight of, compared with that of hydrogen, i. 100 peroxide of, combination forming, i. 104 Manihot, or Cassava, food obtained from the, i. 426 Marasmius Oreades, spawn of, i. 262 Marattia salicina used as food, i. 365 Marattiaceæ, characters of the group, i. 364 Marchantia polymorpha, structure, development, fructification, and habitat of, i. 317-320 Marchantiaceæ, characters of the order, i. 317 Mars, the planet, spectrum of, i. 158, 161 Marsh-gas, i. 118 amount of absorption of radiant heat by, i. 41 Marsilea, characters of the genus, i. 372 Marsileaceæ, or Rhizospermæ, characters of the tribe, i. 371 Matonineæ, characters of the group, i. 344 Matter, molecules of, i. 2 agency of electricity in the chemical composition and decomposition of, i. 32 decomposing and elective power of, i. 35 Mauve, Dr. Hofmann’s discovery of the aniline colour, i. 122 at first made from orchil, i. 124 derived from guano, i. 125 Mediterranean sea, zones of algæ in the, i. 259 foraminifera, the ooze in the bed of the, ii. 51 Medusæ, form and structure of, ii. 91