"The following explanations will account for some of the arrangements, the reasons for which are not obvious at first sight. It is very difficult to make wood slide on wood without adhesion and consequent jerking. After many unsuccessful experiments, I found white-pine would run smoothly over a surface covered with tinfoil. The unusual length of the object-plate renders it much more manageable than the ordinary ones. The arrangement of the lever not only gives extreme accuracy and delicacy to the fine adjustment, but, the screw being independent of the rest of the instrument, the focus does not change when the hand is lifted from it, as it does in many microscopes. The wick-tube of the lamp is so placed that it can be brought close to the object, and is at the same time at such a distance from the achromatic condenser as to give light enough without heating it to any extent which might injure the glasses. The wires by which the tube is moved are a little above the level of the cradle, so as to admit of a slight rocking motion of the tube. The delicacy of the coarse adjustment is such, that the use of the fine adjustment may very often be dispensed with. "This instrument cost between three and four dollars. I have been so well pleased with its performance, that I have ordered one to be made of brass and iron, with a hollow pillar instead of the tripod, with several modifications, but the same general arrangements. Such an instrument may cost about ten dollars, and would offer some advantages over a carefully constructed one of the cheaper materials, which, however, would do good service. I hope to have the opportunity of showing a more nicely executed instrument, of the same general form with this, at a future meeting of the Academy, and if it meets the approbation of microscopists, I shall request a competent workman to make them at the lowest rate he can afford, for those who are disposed to try a new and somewhat peculiar piece of mechanism. "Many will at first object to the vertical stage, in the belief that fluids cannot be conveniently examined in the position this requires. I believe this objection is of little importance. Capillary attraction, which holds mercury suspended in a fragment of thermometer-tube, is surely enough to support any watery fluid and its contents between two plates of glass, if the film of fluid is thin enough. Currents there will often be, and currents there constantly are on a perfectly horizontal stage, unless various precautions are taken, which I shall not here stop to indicate. I have found no practical difficulty in examin. ing any fluid I have tried, with its contents, whatever they might be. At the same time, neither this nor any other bulky instrument can be a substitute for a simple, portable, vertical instrument, with a horizontal stage, and mirror below it, to be employed with the low powers. It is an adjunct to it, performing all the difficult tasks which the small "comet-seeker" indicates and leaves unfinished. The new instrument can be employed with the lowest powers; most conveniently by using a secondary stage, consisting of a piece of sheet brass bent at right angles, and carrying two springs on its outer vertical surface to hold the object-plate; this secondary stage being placed on the lampshelf. But every microscopist requires a portable instrument which will be sufficient for all powers below the one-fourth inch objective or its equivalent. For twenty dollars or a little more, he can get such an instrument with two eye-glasses and two objectives. Let him add twelve dollars to this, and he can obtain, in addition, the highest objective of the French makers. With the addition of an instrument like that I have shown, he will have at his command a sufficiently complete series of powers, and the means of employing common and achromatic light in every degree of intensity and obliquity, with a brilliancy of effect and a convenience in application which I will venture to compare with those of much more costly instruments. If he can obtain the more perfect and expensive objectives of Mr. Spencer or the best London makers, he will be able to bring out all their powers, and need not fear to subject them to the trial of defining the most difficult test objects." Professor Horsford made some additional remarks on the subject of the late explosion of burning-fluid at Salem. On further consideration, he was of opinion that the ascent of heated air above the stove would cause currents of air to descend by the sides of the pantry, and flow towards the stove; and that the vapor of burning-fluid would be thus carried towards the fire, and ignition consequently ensue. He also offered an explanation of several other cases of explosion of burning-fluid to which he referred. NOTE. THE statutes of the Academy authorize the Corresponding and Recording Secretaries "to publish in an octavo form such of the proceedings of the Academy as may seem to them calculated to advance the interests of science." As the matter to be published in this volume consisted in part of papers referred by votes of the Academy to the Committee on Publications, the duty of publication seemed to have devolved in part upon that committee. This volume has accordingly been published by the Corresponding and Recording Secretaries and the chairman of the Committee on Publications. The abstracts of remarks made at the meetings of the Academy, which are printed in small type, or included within quotation-marks, have not been copied from the records of the Academy's proceedings, but furnished, at the request of the Recording Secretary, by the Fellows respectively by whom the remarks were made. The following abstracts should also have been included within quotation-marks: Professor Horsford's, pp. 238, 239, and pp. 295, 296; Professor Peirce's, pp. 256, 257; Mr. Alger's, pp. 263, 264; Mr. Desor's, p. 282; and Dr. W. F. Channing's, pp. 282, 283. An Index to Volume I. follows the Index to Volume II.; but it is printed so that it can be easily separated from this volume and bound up with the volume to which it belongs. May 24, 1852. ERRATA. Insert "as observed" before "at Castle William," sixth line from the bottom of page 259. Instead of a dash before "potash," page 271, eighth line from the bottom of the page, substitute a comma after that word. Substitute a period for the note of admiration on page 285, twelfth line. The experiment exhibited by Mr. Guyot, and described on page 284, where it is credited to Professor Snell, is identical with that performed by M. de Maistre in 1832, of which an account is given in Peltier's work, "Des Trombes," page 11. INDEX TO VOL. II. N. B. New genera and species are in Italics. A. ABBOT, J. H. Facts in electricity, 252. New experiment in Hy- Acartia, gen., Dana, 10, 25. laxa, D., 26. limpida, D., 26. negligens, D., 26. Africa, configuration of, 265. AGASSIZ, L. On the fossil Cetacea of the United States, 4. Investi- Agatea, gen., Gray, 323. violaris, Gray, 324. Air, influence of, in the action of water upon lead, 86. Alcohol, importance of, for light, 319, 322. Aldebaran, occultation of, 258. ALGER, FRANCIS. On crystals of gold from California, 246. On Sigillaria, 263. |