« ZurückWeiter »
hail. The latter left behind a dense smoke, that was not even moist. In these phenomena, Mr. Espy's steam-power is entirely wanting ; for he certainly will not ask us to believe, that the vapor was condensed, and that an ascending force, varying from two hundred and forty to seven hundred and twenty feet a second, * existed in the spout, and yet that no drops of rain should be thrown from its summit. Here, again, we have very striking phenomena, that are to be accounted for upon other principles than those of Mr. Espy's theory. His neglect of the influence of electricity, also, which he regards as only accessory and secondary, is, in our judgment, a fatal defect. His theory aims at a complete explanation of all the wonderful changes of the atmosphere, without a passing notice of this mighty agent. We are not aware, that there is any detailed description of a tornado, in which it does not appear to take an active part ; and several of those the most minutely and accurately portrayed, such as the tornado seen from Nice by M. Michaud,t those of Châtenay, I Natchez, and Providence, exhibit its presence in so striking a manner, that it is difficult to imagine their production by other means. Dupré quotes the accounts of two tornados, which ravaged the vicinities of Pas-de-Calais on the 6th of July, 1822, and Trèves on the 25th of June, 1829, in both of which, the whirling motion and electrical agency are distinctly marked. He introduces them to teach the student the nature of these terrible storms. § Lamé also adopts Peltier's theory of the electrical origin of tornados. || Mr. Espy subsequently qualifies his opinions to this extent ; that he would not be understood to say that electricity has nothing to do with this phenomenon” ; but still he regards “ the dynamical agency, necessarily resulting from the diminished weight of a suddenly formed cloud,” as the prime cause,
" both in order and effect. I
We have yet stronger reasons for believing, that the action of electricity alone can account for the formation of hail.
Nicholson's Journal, Vol. I. 583. As described by M. Peltier. § Traité Elémentaire, p. 368, Vol. I. Il Cours de Physique, 2d ed. Vol. III. pp. 98, 100.
í Espy, p. 370. — The philosophic view of the electrical origin of torna. dos is ably presented by M. Peltier, “Sur Trombes,” and by Dr. Hare of Philadelphia, in his reply to Professor Oersted of Copenhagen, in Reid's Appendix.
A particular kind of crackling is frequently heard before the descent of hail, attributed by some meteorologists to electrical discharges, a thousand times repeated, the hail-stones being strongly and differently electrified. On the approach of hail, the atmospheric electrometer affords another proof; the electricity is found not only to change in intensity, but to pass from positive to negative, and vice versa, ten or twelve times in a minute. * Hail has been observed to fall from a cloud, that had previously discharged rain, when it encountered another cloud rushing towards it with great violence, and producing thunder. Some of the most beautiful provinces of France and Italy have been subject to periodical visitations of desolating hail storms, which have demolished the labors of the husbandman and vine-grower, and converted the bloom of summer, or the riches of autumn, into dreariness and sterility. Some places, from frequent catastrophes of this kind, have obtained the designation of “hail countries." Mr. Murray f relates several instances in which fields in these districts have been perfectly protected from the fatal consequences of these storms by conductors, or paragrêles. The hail cloud has carried its ravages to the very borders of the enclosure thus guarded, and, becoming harmless within the sphere of attraction of the paragrêles, has passed over it without injury, whilst it continued its work of destruction upon the adjoining plain, which had no means of disarming the cloud of its electricity.
We have still more important testimony from M. Lecoc, professor of natural history at Clermont-Ferrand, whose philosophic ardor carried him into the very laboratory of nature, when engaged in her mighty operations. He ascended the mountain of Puy-de-Dôme during a storm, and remained in the clouds which were pouring down rain and hail alternately. He observed, that both hail and rain, especially the former, were precipitated inmediately after a flash, and seemed to be a consequence of the lightning. Another fact, bearing on our argument, was remarked, that the hail cloud was low. Mr. Espy, it will be remembered, in his theory, requires, for the phenomenon of hail, a lofty cloud and great ascending force in the spout, to raise the drops of condensed vapor to its summit, and discharge them into the cold air where they are congealed. M. Lecoc saw two distinct beds of clouds, separated by clear atmosphere. It was only when these clouds, brought near each other by contrary winds, were imposed one over the other, that the hail was formed. The flash invariably preceded its descent, and it always fell from the lower cloud. M. Lecoc was able to determine the height of these clouds, some of which were beneath his station. One was only twelve hundred metres, or about two thirds of a mile high.* The motion of the clouds is adverse to Mr. Espy's theory. They approached, overlaid, and passed beyond each other, retaining their full shape, and did not, according to his supposed law, converge to a space of general congregation, and there appear to rise. Mr. Espy's column, also, was variously scattered by the conflicting winds, and yet clouds were fornied, and successive storms followed their conjunction. M. Arago testifies, that he has more than once seen clouds, from which hail would in a few moments have escaped abundantly, cover as with a thick veil the whole extent of a valley, whilst the neighbouring hills enjoyed at the same time a pure sky, and agreeable temperature.f According to Von Buch, it rarely hails on mountains, owing to the low elevation of the clouds from which hail descends. Finally, the illustrious Lamé, in unqualified language, ascribes to electricity alone the generation of hail. I
* Mr. George Harvey's Treatise on Meteorology, - Encyclopedia .Met. | Treatise on Atmospheric Electricity, by John Murray, F. S. A., &c. &c.
pp. 131, 135.
We must terminate here our hurried examination of Mr. Espy's theory. Though it makes use only of principles of acknowledged validity, and is simple and elegant in the combination of them, we conclude, that their application is, in many cases, and with regard to the most interesting particulars, erroneous both in mode and degree. The actual phenomena of nature, .the rotation of the winds in storms, the whirling motion of the tornado and water-spout, and the existence of these phenomena unaccompanied by the evidences of Mr. Espy's only cause of aërial disturbance, the terrible power of electricity, are not accounted for, or even recognized. How far he may find it necessary to modi
Comptes Rendus, Vol. II. p. 324.
Mr. Harvey's Treatise. # Vol. III. p. 95. The formation of hail has been twice proposed by the French Academy, as the subject of an essay to receive the first mathematical prize, without success.
and Loomis [April, fy it hereafter, we shall not undertake to decide ; " but whatever may be the result, the merit of having first noticed this tendency of the liberated caloric must be conceded to Mr. Espy, and never can be disregarded as unimportant in any correct theory of storms." *
We have already had occasion to point out several inaccuracies of Mr. Espy, which seriously affect his character as a teacher of science. We should fail in duty to our readers, if we were to pass over some other errors, that have fallen under notice in the course of our investigation. In 1831, Mr. Espy declared, that he had found, by repeated experiments, that the dew-point descended before rain. At that time, he advanced a different hypothesis concerning rain, based upon the independent motion of the particles of aqueous vapor,
which he derived from Dalton's “ Constitution of the Atmosphere." His present theory requires, that the dewpoint should rise before rain ; accordingly, he tells us, that the air becomes highly charged with aqueous vapor before the cloud begins to form. The philosopher is allowed to alter, or abandon his hypotheses, and should be ready to do so, when he finds them inconsistent with facts ; but the facts themselves are not, we conceive, equally flexible and convenient.. On two occasions, Mr. Espy specifies the height of the clouds, and furnishes the data by which his computations are made. One of these clouds he pronounces eleven, and the other, fourteen, 9 miles high, and he adds, (what ought to be very gratifying to our pride to know,) that the steam power of the clouds in the United States is much greater than it is in Great Britain. These astonishing altitudes so far exceeded any thing in the table of Crosthwaite, the actual measurements of Riccioli, or the observations of Humboldt and Dalton, that we were induced to repeat his calculations. We have too great a. reverence for the
*“ Espy's Theory of Storms,” by Professor Peirce. Cambridge Miscellany, No. 3. Mr. Meikle, of Edinburgh, claims the honor of having anticipated Mr. Espy in his theory ; (see Edin. New Phil. Jour., Vol. XXIX.) For the proof, he refers to the “ London Quarterly Journal of Science" for April, 1839, and to the article “ Hygrometry,” in the “ Encyclopædia Britannica.” We have examined this question ; and after observing, that Mr. Meikle's merit, or rather demerit, consists in having very imperfectly copied from Dalton, or Daniell, a single idea concerning the latent heat of vapor, we dismiss the claim with contempt.
† Journal of the Franklin Institute, for April, 1831.
mother country, step-mother though she be, to rejoice in any such unfair advantage over her ; we were, therefore, pleased to discover, that our formulæ reduced these ambitious elevations to four miles in the first instance, and to two and a half (!) mīles in the last. In the first case, we counted the sunset from the setting of the upper limb; but if Mr. Espy dated from the centre, as he probably did, the cloud would come down to less than three miles. In the latter case, we made allowance for the refraction and sun's semidiameter, without which any pretence to accuracy is frivolous. Mr. Espy assigned to these clouds velocities of forty-eight, and one hundred and twenty, miles an hour, respectively. We find the velocities to be eleven and thirty-two miles an hour. *
The style of Mr. Espy's book demands some criticism. He has made an apology in the preface, (and one was needed,) for its ill sorted incongruities, and useless and costly repetitions. We will not, therefore, dwell upon this defect. Neither will we charge him with occasional injustice to Mr. Redfield.f Neither will we reproach him with his insufferable conceit and bad grammar, in calling his work “the beginning of our knowledge on the causes of Storms." I after Dr. Franklin had discovered the law of progress of our northeast storms, and Mr. Redfield had established the law of rotation of the West India hurricanes, and Colonel Reid had published his valuable compilation of facts and observations, enriched by his comments. Neither shall it subdue our gravity, that Mr. Espy has been pleased to style himself, by implication, the Archimedes § and Newton | of meteorology ; or that he considers the modern chemists, who first discovered the latent heat of vapor, as holding the same relation to him, that the ancient mathematicians, who made the sections of the cone, may be supposed to have to Newton, Kepler, and La Place. I
These things our charity can overlook. But his indecorous rudeness to a name iħlustrious in the annals of science imposes upon us a duty, which we hasten to perform. In
* Mr. Espy, in his work, changes the altitude of the first of these clouds to ten miles, and its velocity to forty-five miles. The data iemain un. changed. pp. 49, 50.
Philosophy of Storms, Preface, and pp 58, 60. # Ibid., Introduction, p. 5.
§ Ibid., Preface. || Ibid., p. 438.
Ibid , pp. 24, 25.