Potatoe, found wild in South America, iv, 195. ----, fruitfulness of, iii, 381. ----, culture of, in France, xxvii, 176. ----, on the growth of, xii, 170. ----, precaution in planting, xxi, 159. ----, nutrition from, _E. Ives_ on, i, 297. ----, mode of preserving, vi, 200; xvii, 188. ----, how to boil, xxiii, 201. ----, used in steam engine boilers, vii, 193. ----, oil from spirits of wine of, xxviii, 386. ----, essential oil of, _A. Cahours_, xxxii, 382. ---- cheese, xviii, 395; xxiii, 202. ---- flour for bread, xvi, 391. ---- ----, detection of, in wheat, xvii, 173. ----, molasses from, _S. Guthrie_, xxi, 93. ---- starch, sugar from, _S. Guthrie_, xxi, 284. ----, Sweet, sugar in, xv, 285. ---- fly, cantharidin in, ii, 137. Potentilla supina, xiv, 114. Pot-holes, made by means of running water, in the Green Mountains, vi, 252. ----, near the Franconia Notch, xxxiv, 122. Potosi silver mines, xxiv, 233. Potstone, Middlefield, Mass., viii, 51. ---- of Greenland, xvii, 14. _Potter, C. E._, notice of a rocking stone, xxiv, 185.^f Pottery, analysis of, xv, 183. ----, notice of _A. Brongniart_ on, xxxi, 134. ----, ancient American, xxvii, 175. Powder of Cassius, purple, see _Cassius_. ---- of Balda, viii, 204. ---- mills, inflamed by the stroke of copper, xiii, 161. Powders, fulminating, see _Fulminating_. _Powell, B._, on the interference of light, xxxviii, 107. ----, on refractive indices, xxxviii, 107. ----, on the wave theory, xxxviii, 108. ----, on radiant heat, xl, 313. ----, on certain cases of elliptically polarized light, xliv, 171. ----, on the elliptic polarization of light, reflected from various substances, xlvi, 390. Power of horses, xxi, 167. Pozzuolana, iv, 373. Practical Tourist, review of, xxiii, 213. Prague, statistics of, ix, 184. Prairies, origin of, _R. W. Wells_, i, 331. ----, ---- and extension of, _R. Nutt_, xxiii, 40. ---- of the West, _C. Atwater_, i, 116. ---- and barrens of the West, _A. Bourne_, ii, 30. ---- of Alabama, _W. W. McGuire_, xxiv, 187; xxvi, 93. ---- formation of Opelousas an Attakapas, _W. M. Carpenter_, xxxv, 344. ----, observations on, _G. Jones_, xxxiii, 226;--dry prairies, 226; comparison with Holland, 228. ---- of Ohio, xxxiii, 230. ---- of Texas, _J. L. Riddell_, xxxvii, 212. ----, Hog-wallow, of Texas, notice of, xxxix, 211. Prase in Massachusetts, i, 344. ---- in Rhode Island, viii, 226, 230. ---- in Pennsylvania, viii, 238. Precession of the equinoxes, remarks on, vii, 323^f; viii, 132, 139.^f ---- ----, constant of, _O. Struve_, xlvii, 91. Precipitate, purple, of silver and gold, xxii, 198.