8. 9. 10. On some observed changes in Vorticella; by A. H. Tuttle. Remarks on a Standard of Powers for Microscopical Objectives and Eye On the Microscopic Structure of Eozoon Canadense; by E. Bicknell. 3. On the relation of the Auroras to Gravitating Currents; by PLINY EARLE CHASE, Professor of Physics in Haverford College. (Read before the American Philosophical Society, May 5th, 1871.) -Prof. Loomis's observations of the number of auroras in each month of 1869 and 1870 (Amer. Jour. of Science, III, S., i. 309), are specially noteworthy, both because of the careful accuracy of the observer, and because they are the first published observations. which furnish satisfactory data for an approximate determination of the laws of auroral distribution. If the auroras are, as is now generally believed, luminous manifestations of terrestrial magnetism, it seems reasonable to look to them for some additional evidence upon the question of the relation between magnetic and gravitating currents. endell and Bloxam have already pointed out some resemblances Messrs. Baxbetween hyetal and magnetic curves (see Proc. A. P. S., x, 368), and if analogous resemblances can be traced between hyetal and auroral curves, they will be interesting and suggestive. I have not found the similarity between the annual distribution of rain-falls and of auroras sufficiently striking to impress any one who has not made a special study of the causes of resemblance and difference. But, as I have repeatedly urged, currents are subject to an increased number of disguising disturbances, in proportion to the sluggishness of their motion, and the time which is consequently required for their formation or change. We may very reasonably look for analogies between the daily and the annual auroral or magnetic curves, of a character for which we could hope to find no parallel in wind, rain, or ocean-current curves. If we desire, therefore, to find evidence of the joint influence of solar expansion and gravitating equilibrium, we should look where it is most likely to be found, and to the best of the observations which may be supposed to be fairly comparable. There are similar variations of solar attitude, and consequently increasing and diminishing solar force, in the day and in the year, but the effects of these variations upon the precipitation of vapor, are more likely to be shown in their greatest simplicity by the means of observations at different hours of the day than at different seasons of the year. I know of no published observations of this character at New Haven, but there are some extending over a long series of years at Philadelphia, and at Greenwich, the curves at each station indicating minima of rainfall at noon and midnight, and maxima in the morning and evening. The difference of longitude between Philadelphia and New Haven being less than 24, it is not likely that there is any material difference in the daily rain-curves at the two places. In order to make the curves fairly comparable, both in regard to the times and the magnitudes of deviation, I treated the auroral observations in the same manner as those of rainfall (Proc. A. P. S., x, 526). Both in the magnetic and in the hyetal phenomena, the greatest effects accompany the greatest atmospheric changes, But in the magnetic disturbances the principal maxima occur in the spring of the year and the morning of the day, while the gen eral evaporation is increasing, whereas, in the daily rains at Phila delphia, the principal maximum occurs in the afternoon, wher evaporation is diminishing. I have, therefore, compared the mid winter ordinate of the auroral with the noon ordinate of the rain curve, and the midsummer auroral with the midnight hyetal or dinate. The auroral observations and the normal ordinates, of the accompanying curves, are given in the following table. I presume no one will doubt that the condensation of vapor, which is repre sented by the rain curve, is occasioned by the simple operation of gravitation in blending currents of different temperatures, and i see no reason for postulating any different law for the development of electricity and magnetism in the aurora. Comparative Table of Auroras and Rainfalls. IV. MISCELLANEOUS BIBLIOGRAPHY. 1. War and the Weather, or the Artificial production of Rain; y EDWARD POWERS, C.E.-The object of this little volume is to how that rain can be produced by human agency, particularly by eavy discharges of artillery; and a large number of cases are ited in which great battles have been followed by speedy rain. ix cases of this kind are cited which occurred during our war with Mexico in 1846 and '47; nine cases of battles or skirmishes re cited which occurred in 1861 in the war of the rebellion, and hich were followed by rain at no great interval; forty such cases re cited for 1862; thirty for 1863; twenty-eight for 1864; and ix for 1865. Eighteen similar cases are also cited from among he great battles which have occurred in Europe during the past entury, making a total of 13 cases. The author thinks that if hese facts are insufficient to convince, it would be vain to expect o do so with a greater number of cases. To this argument it may be replied that throughout the region om which his examples are mainly collected, rain falls upon an verage once in three days, and probably a little more frequently; o that from the conclusion of one rain to the commencement of nother, the interval is on an average but little over two days. ow battles are not usually commenced during a period of rain; enerally not till some hours after the conclusion of a rain. Rain ught then generally to be expected within about one day after he conclusion of a battle. Now the argument of Mr. Powers is me in this point. He takes no precise account of the length of he interval between the conclusion of a battle and the commenceent of rain; nor does he show that this interval is less than it ould be if the battle had no influence in the production of the in; and in particular he takes no account of the cases unfavorable his theory, in which rain follows a battle only after a very long terval. In order to make the argument complete, a much more reful analysis of the facts is required. It should be determined om a comparison of a large number of cases, including all the attles within a particular circuit, what is the average interval etween a battle and the next succeeding rain, and it must then be own that this interval is less than it would be if the battle had › influence in the production of rain. The simplest mode of making the comparison may be the followg: Determine for all the battles occurring within a particular cuit what is the average interval between the conclusion of the in next preceding a battle and the commencement of the rain xt following it; and then determine for the same region the erage interval between two successive rains when no battle has curred. If the former interval should be found sensibly less an the latter, it would be reasonable to conclude that the battle d exerted some influence in accelerating the fall of rain. The ets collected by Mr. Powers are not digested in any such manner; d although we are inclined to the opinion that great battles do ert some influence in the production of rain, we do not think A that Mr. Powers has established his proposition in a satisfactor manner. With regard to the mode in which a heavy discharge of artillery might cause rain, we differ widely in opinion from the author d this book; but we are not fairly called upon to assign a reason why artillery firing causes rain until it has been shown that it does, x least sometimes, produce such an effect. We should be muci pleased if Mr. Powers, or some other person, would resume the discussion of this subject in accordance with a truly scientifi method. E. L. 2. Introductory Text-Book of Meteorology; by ALEXANDES BUCHAN, M.A., F.R.S.E., Secretary of the Scottish Meteorologica Society. 218 pp. 12mo, with 6 plates. Edinburgh and Londo 1870. (Wm. Blackwood & Sons).-Mr. Buchan takes the leai among the meteorologists and meteorological investigators d Scotland. This small and convenient text book takes up in orde the history and scope of Meteorology; Atmospheric pressure and its distribution over the globe-a subject which has been much elucidated through Mr. Buchan's labors; modes of observing and calculating temperature; solar and terrestrial radiation; distribution of terrestrial temperature and its relation to atmospheric pressure; moisture of the atmosphere; mists, fogs and clouds; rain, snow and hail; winds; storms; atmospheric electricity whirlwinds, and waterspouts; aurora borealis and terrestrial magnetism; ozone; optical phenomena; meteors; weather and storm warnings. Six of the plates contain an exhibition for the globe of the isobarometric and isothermal lines; one is a synchronous weather-chart of Europe for 2d Nov., 1863, at 8 A. M., and one s similar chart of the West Indies for 1st Oct., 1866, at 8 P. M. 3. Dominican Republic. Report of the Commission of I quiry to Santo Domingo, with the Introductory Message of the President, Special Reports made to the Commission, State Papers furnished by the Dominican Government, and the statements c over Seventy Witnesses: Commissioners, B. F. WADE President A. D. WHITE, S. G. HowE; Secretary, A. A. BURTON, Assistan Secretary, F. DOUGLASS. 298 pp. 8vo, with a map of the island. This volume contains reports from the Scientific view of the expedition, W. P. Blake, C. Wright and others. But the time at the island was too short for thorough exploration. 4. Sun-Pictures of Rocky Mountain Scenery, with a descrip tion of the Geographical and Geological features and some accoun of the Resources of the great West; containing thirty photo graphic views along the line of the Pacific Railroad, from Omah to Sacramento. By F. V. HAYDEN, M.D., U. S. Geologist, Pro Min, and Geol. in the University of Pennsylvania. 150 pp. 4t< 1870. New York: (Julius Bien). The character of this wor has already been stated in this Journal, and citations have bee made from its pages of important scientific observations. It i published in elegant style, the paper and printing being of th best kind; and the photographs excellent and highly interesting THE AMERICAN JOURNAL OF SCIENCE AND ARTS. [THIRD SERIES.] ART. XXXIX.-On some Phenomena of Binocular Vision; by JOSEPH LECONTE, Prof. Geol. and Nat. Hist., University of California.* VI. So-called "images of illusion;" and the theory of binocular relief. IN a very elaborate paper on binocular vision published in the Archives des Sciencest for Feb., 1871, which is itself but a succinct resumé of a much more extended memoir soon to be published, M. Pictet undertakes to establish on a firm basis the nativistic" theory which regards corresponding points as congental and the result of anatomical structure, as opposed to the empiristic" theory which regards them as the result of experi ence. After summing up the usual arguments and objections on each side, he proceeds, as he thinks, to prove the truth of the former theory by showing, first, a priori, the consequences which must flow from the admission of this theory; second, that the visual results of certain experiments are precisely what a priori reasoning leads us to expect; and third, that this theory, in the form in which he maintains it, explains all the more obvious phenomena of binocular vision. The one strikingly new thought in M. Pictet's memoir is the supposed existence of "images of illusion" in every act of vision. This it is which follows, he thinks, from the admission of the nativistic theory; it is this which he attempts to prove by all his experiments; it is by means of this that he solves all the * For previous papers on this subject see II, vol. xlvii, pp. 68, 153; III, vol. i, p. 33, and vol. ii, p. 1. + Arch. des Scien., nouv. per tome xl, p. 105. AM. JOUR. SCI.-THIRD SERIES, VOL. II, No. 11.--Nov., 1871. |