ART. VIII.-On Fixing Magnetic Phantoms; by Prof. J. THE name phantom was given by M. de Haldat* to the figures which are obtained when iron filings are thrown upon a sheet of paper or a pane of glass placed over a magnet. This physicist fixed these images by producing them upon a sheet of paper coated with starch or prepared with gelatine. This process certainly enables us to obtain the general form of the phantoms, but all physicists can see that it suppresses the details. I was more particularly struck with this fact on a recent occasion, where I sought to fix the phantoms of some new electro-magnetic combinations; I therefore propose another method, which is here briefly given; it is very simple and succeeds perfectly. The paper upon which the phantoms are to be fixed is "waxed" paper. A sheet of this is placed over the poles of the magnet in question, and kept in a horizontal position by means of a screen placed between the paper and the magnet. Then proceeding in the usual manner, when the image is fully developed, a hot brick is held above it, or the warm lid of a crucible, which is preferable because it is lighter, and easily managed with the tongs. They must not touch the paper, but only be brought within the distance necessary to fuse the wax. As soon as this happens, which is easily perceived by the glistening appearance produced, the brick is withdrawn. Meanwhile the current does not cease its activity, nor the filings lose their arrangement, in which position the whole solidifies so well that the fixed image does not at all differ from the phantom of the magnet in activity. This result is explained as follows. By capillarity the melted wax penetrates the masses of filings, very much as water penetrates a heap of sand; the heat of the brick facilitates this, by preventing the solidification of the wax, and as the temperature is not sufficiently elevated to sensibly affect the magnetism developed, the phantom, after the solidification, and in the most minute details, preserves the same arrangement which the iron filings had, while they were free to obey the action of the magnet. A condition indispensable to success, is, that the stratum of wax has a sensible thickness, so that it may suffice for the agglomerations, since these absorb melted fatty matter, even to saturation. That this force of absorption is very energetically exercised, may be perceived after the cooling, since the paper about the agglomerations is deprived of wax, and differs thus in appearance from those parts where capillarity has not been exercised. It is therefore possible to preserve to the phantoms the * Memoir before the Academy of Stanislas, p. 43, for the year 1839-1840. relief which has before been sought in vain, and what will be still more useful, to give permanence to the sort of molecular arrangement which the filings take, when exposed to magnetic influence. Instruction can hardly fail to be derived from the use of these means, by aid of which it will be possible to study the figures more advantageously, which are, in some sense, the visible expression of the force animating bodies endued with polarity developed by magnetism.* Nancy, March, 1860. ART. IX.-On some Questions concerning the Coal Formations of North America; by LEO LEsquereux. Continued from Vol. xxviii, p. 21. Geographical Distribution of the Coal Flora. To follow the plan exposed in the first part of this memoir (Silliman's Journal, No. 82, July, 1859, p. 21) I should have to examine now the nature of the coal-flora, that is, the anatomical and chemical constitution of the coal plants, first comparing between themselves the groups of species of plants from which the matter of the coal is a compound, and then examining how this vegetation is related to the plants living at this epoch. The distribution of the coal plants, either geographical or stratigraphical, is a question accessory to the former. Nevertheless, it has become now of a greater importance, since it touches upon a problem which is at present discussed by the authority of the highest scientific names. I allude to the theory of the origin of species by Mr. Darwin. It evidently concerns the great problem of the inmost nature of man, and thus forces every naturalist to seek, in the sum of facts gathered up by his researches, either confirmatory or contradictory evidence of views which cannot but preoccupy his mind. Thus it is apparently advisable to change the order of examination of the flora of the coal measures of North America, studying it now in its stratigraphical and geographical distribution, and leaving for another opportunity the discussion concerning the nature of its vegetation and the specific and generic value of its representatives. This note is extracted from a work now in press and which will soon appear, entitled, Electro-magnets and Magnetic adhesion, and accordingly treats of electromagnets and their application to locomotion upon railways, with the design of increasing the adhesion of locomotive engines. To the experiments which we made public in 1853 (v. this Jour., [2], vol. xvi, p. 337), we shall add new ones which allow us to expect a speedy solution of this problem, so important to railroads. In regard to electro-magnets, we will only say at present, that we shall mention a great number of new species, which have compelled us to invent a new classification and a nomenclature based upon the principles of the natural method. We have also to make known a great number of new facts respecting the laws and properties of electro-magnets, to say nothing of what we wrote upon this point in 1853 (v. Am. Jour., [2] vol. xv, p. 381, and vol. xx, p. 100). J. N. I shall not attempt in any way either an exposition or a critical examination of the views of the celebrated English author. This task has already been admirably fulfilled in a former number of this Journal.* I shall merely expose the facts that appear surely ascertained by a long and careful exploration of the coal-fields of North America, leaving the naturalist-philosopher to take from these facts any conclusion that may appear just to him. It is a mite only. But the monuments of humanity, like the mountains of limestone, are built by the slow accumulation of minute remains. The botanical paleontology of the coal-period and the succession and variation of species in the different strata of the coalmeasures, cannot be studied with more advantage and with more chances of reliability than in the coal-fields of the United States. Their immense area, the uniformity of their generally unbroken stratification, the facility of ascertaining in many localities the order of this stratification, the numerous exposures of coal banks, not limited to a particular district, but opened and worked now at distant points over the whole area of the coal-fields; all this affords to a systematic exploration such advantages as cannot be found in any other country of the world. Moreover, my explorations of the coal-fields of North America have been favored by peculiar circumstances. Connected at different times, during ten years, with the geological surveys of the states of Pennsylvania, Kentucky, Indiana, Arkansas and Illinois; called to survey for comparison the coal-fields of Ohio and part of those of Virginia; constantly limiting my researches to botanical palæontology, I have thus, I suppose, collected on the distribution of the coal-plants in North America, more materials and more reliable accounts than geologists may be able to get at for a long time to come. The first important question in regard to the coal-plants of America is what is their relation of forms with the plants of the same formation in Europe? The comparison of the coal flora of both continents has never been made except on few and insufficient data.+ Except two, all the genera of fossil plants of the coal-fields of America are represented in Europe. One of them is the remarkable Whittleseya elegans of Dr. Newbury, a flabellate, apparently short pedicillate, cuneiform-oval and truncate leaf, found hitherto always detached from the stem. It evidently differs from the genus Cyclopteris by its simple straight nervation and by its up * Vol. xxix, p. 1. + I have attempted it formerly, in my palæontological report of the Geological State Survey of Penn., delivered January 1st, 1854, but only published five years afterwards. As I have been denied the privilege of reviewing and correcting my manuscript before its publication, I cannot consider myself accountable for the errors, and especially for the deficiency of conclusive data, which may be found in it. per margin being horizontally truncate and regularly wavy-denticulate by the percurrent and slightly emerging nerves. The typical affinity of this plant is unknown. It is perhaps more related to Cordaites or even to Salisburia than to a fern. The second genus peculiar to the American coal-flora is my Scolopendrites, represented, like the former, by a single species; Scolopendrites dentata Lsqx., of which fragments only have been found. The name has no relation to the nervation of the leaf, but to its outline. This leaf is apparently five to six inches long, more than an inch broad, lanceolate, deeply cut by obtuse somewhat regular teeth and marked by a few very thin distant nervules, emerging from a narrow medial nerve in an acute angle, scarcely arched and forking twice. Both these genera represent peculiar types to which no form of the European coal-flora can be compared. I could also mention as a peculiar type of our coal-flora Crematopteris Pennsylvanica Lsqx., a thick stem or branch, on both sides of which short, lanceolate, obtuse, thick leaflets, without any trace of nervation, are pinnately attached. The single specimen which I have found of this plant was not well preserved enough, and it would be unsafe to consider the species which it represents as having been seen in its true form and full development. If we admit the generic distribution of the fossil plants of the coal, as it has been established by Brongniart in his Tableau des Genres, (certainly the best that has been attempted either before or after him) all the European genera, even the undefined genus Aphlebia, (Sterbg.) have representative species in the coalfields of America. From the nomenclature of Göppert and Corda, a few European genera, it is true, are hitherto without representative species in our coal-fields. But these genera, established on the form and the position of fructification, always very difficult to identify from even the best preserved specimens of fossil ferns, may be represented by some species of our Sphenopteridea and Pecopteridee. These genera, viz., Rhodea Sternb., Trichomanites Göpp., Steffensia Göpp., Beinertia Göpp., Diplaxites Göpp., Woodwartites Göpp., are no peculiar types. Thus, considering their generic distribution, the coal-plants of Europe and of North America show very little difference indeed. But in examining the species separately and comparing them on both sides of the Atlantic, the number of forms peculiar to America appears much larger than it was at first supposed, and thus the vegetation of our continent, at the epoch of the coal formation and considered in its whole, is far more different than it has been supposed heretofore. It would be too long and tedious, perhaps, to take one by one and compare all the American species with those of Europe, SECOND SERIES, VOL. XXX, No. 88.-JULY, 1860. mentioning the identity, the relation, or the difference of each of them. I will therefore give in a table the number of species of each genus, belonging either to North America or to Europe, or common to both continents, and complete this general view by a few remarks on some of the species, apparently the most interesting, by predominance of number, of typical form or by a peculiar distribution. * In this enumeration, I count the species named as new ones in a catalogue published in 1853 by Dr. Newberry (Nos. 8th and 9th of the Annals of Science of Cleveland). As the species have not been described and did not come under my examination, they are still doubtful and separately marked by a *. 5 2 5 12+9* 37 17 0+1* 0 2 0 0 1 10 11 0 4 2 1 + 1* 4 0 |