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needle of inclination, and ought consequently to diverge from all sides; a circumstance unfavorable to their union in perspective at the magnetic zenith. But it is not proved that the radiation has always for center the magnetic pole; it may very well have another central point, as was the case during the observation I made on the 18th of October. On that occasion, in fact, the ring could not have been completely visible if it had had for center the magnetic pole. Besides, this variation of position is more in conformity with the manner in which the electric charges operate, and with the peculiarities observed in the local appearances of polar light.*

Returning to the lights observed around the elevated peaks of the Spitzbergen, I ought to say that this phenomenon has been noticed before. The learned philologist of Finland, Cashen, witnessed it in his journeys to Siberia, and his description of it exactly accords with what I have myself observed. Similar light has been seen in South America above the peaks of the Cordilleras, and in several other localities mentioned by M. Delleman. The Archives des Sciences physiques et naturelles (tome xxxi, p. 15) contain an article by M. H. de Saussure, in which are described a great number of phenomena, belonging, without doubt, to the same category. But it is in the arctic regions, above all others, that we find circumstances most favorable to observations of this kind, and it is much to be desired that future expeditions will undertake them.

If we seek for the reason why the clouds of the upper latitudes discharge themselves under the form of polar light, and not that of thunder and lightning, we find it in the permanent humidity of the air. The hygrometric observations, made during the expedition of the Sophie, show that the air is constantly saturated with aqueous vapors, which condense frequently into clouds, more rarely into rain. It is clear that this stratum of humidity, a good conductor of electricity, determines a slow discharge. If between the poles of an electrical machine, not sufficiently near together to produce a discharge, we project, by means of an atomizer, some water in spray, we see the discharge under the form of brilliant rays. It is the same in a glass cylinder in which the air has been rarified by several strokes of a piston, a rarefaction sufficient to produce a mist. The discharge, which at first appears as a

*The author remarks here that the appearance of polar light is always accompanied by a dark segment, through which the stars are visible. He mentions in this connection the experiment of M. de la Rive, who, in transmitting the discharge of an induction coil through very rarefied air, proved the existence of a very remarkable dark band near the negative electrode. The author cites an experiment made by himself in the presence of M. Edlund, during which he obtained by means of an electrophorus, in a tube of very rarefied air, a bluish light, followed by a dark band strongly marked around the negative electrode, and a kind of crown of rays around the positive electrode. In the phenomenon of polar light, the earth constitutes the negative electrode, the rarefied air of the higher regions of the atmosphere the positive electrode, and the dark segment bears a strong resemblance to the dark band of the preceding experiment.

spark, is gradually transformed into a luminous current, exhibiting the ordinary colors observed in polar light.

The more the relative degree of the humidity of the air increases an augmentation, which at the surface of the earth proceeds from the equator to the poles, the more easily the electric discharge acts under the form of polar light. But there may be a limit beyond which the humidity is so great that the discharge takes place without the accompaniment of light. Such would seem to be indicated by the table prepared by M. Loomis, of the geographical extension of polar light; according to which there must be a zone, comprised between the 68th and 76th degree of latitude in Europe, and between the 50th and 64th in America, in which the greatest number of phenomena of polar light are produced. This very interesting peculiarity has been proved by observations made during our expedition; at Spitzbergen the polar light always appeared to the south, while at a lower latitude, the 69th degree, it appeared at the zenith or to the north.

I now return to the question of spectral analysis; and for the moment notice only the mobility, so marked, of the light of the yellow ray, which seems to indicate a discontinuous luminous source which is evidently formed by an infinite number of sparks, succeeding each other in rapid succession.

As to the crackling or rattling noise which accompanies the appearance of polar light, I cannot say anything positively, since, on the occasions when I made my observations, the combined noise of the sea and the wind was of such a nature as to drown the faint crepitation of an electric discharge. It is very probable that such a noise can be heard under certain circumstances, for instance when the discharge takes place at a minimum height, and also when it is made between small particles of ice, which produce longer, and consequently stronger, sparks than those formed between particles of water. As these circumstances which are necessary for the production of this sound rarely occur, we can understand why observers do not agree in regard to the fact of its exist

ence.

Some remarks upon the memoir of M. Lemström, by Professor De la Rive.

I find in the observations made by M. Lemström, in the polar regions, such a complete confirmation of the views I have expressed on several occasions in regard to the cause and explanation of polar auroras, that I cannot refrain from noticing very briefly some of the points upon which observation and theory completely agree. I have generally found myself in accord with observers, whether such as Parry, Franklin and Ross, or Bravais and Martins; it is rather between the theorists and myself that there has been occasionally some difference. I ought to thank M. Lemström for the pains he has taken, on every occasion, to mention my experiments, and the consequences I have deduced from them, the accuracy of which he has confirmed.

M. Lemström proves by a great number of facts, supported by incontestable reasoning, that polar light is due to atmospheric electricity, of which he has proved the presence in the polar regions, often in the region of clouds, and sometimes even nearer the earth. He shows, as I have done, that this light is the consequence of electric discharges, which in these regions, constantly pervaded with humidity, operate in a slow, continuous manner, instead of instantaneously by shocks producing lightning, as takes place in equatorial regions and middle latitudes.

He shows, with truth, that terrestrial magnetism, to which an exaggerated importance has been attributed, in the production of polar light, has only a very secondary part in this phenomenon. This part consists simply in giving to the luminous electric jets a certain direction they can follow because of their flexibility, which depends upon whether the medium through which they pass is gaseous. In support of his views in this respect, he refers to my experiments, by which I have demonstrated this influence, and the law by which, according to Plucker, it is governed. One very essential point upon which M. Lemström insists, and which has been noticed by several observers, particularly by Bravais, is that the crown formed in some cases by the rays of polar light is very far from having always for center the magnetic zenith; that is to say, the vertical line passing through the magnetic pole of the earth. In fact, although the formation of this crown depends upon the directing influence of the magnetism upon the electric currents which form the luminous jets, and is not, as M. Lemström very well proves, a simple effect of perspective, it must also depend upon the direction of the passage of the electric discharges through the atmosphere, a direction which itself changes with the conductibility more or less variable of the different atmospheric strata, so that the united effect of these two influences ought to give to the rays a curvature and a position which cannot always be the same.

In short, the electric discharges which take place in the polar regions between the positive electricity of the atmosphere and the negative electricity of the terrestrial globe are the essential and only causes of the formation of polar light-light, whose existence is independent of that of terrestrial magnetism, which only imparts to it a certain direction, and in some cases a movement. These views I have always maintained in opposition to those who think they find in terrestrial magnetism, or rather, in the currents of induction which it can develop, the origin of polar light.

I will not dwell upon various interesting circumstances, such as the presence of a dark segment at the base of the luminous arcs of the aurora borealis, in which M. Lemström sees, as I do, an analogous effect to the dark band produced at the negative electrode, in electric discharges through rarified air; or such as the influence of particles of ice suspended in the atmosphere, which I have also noticed. I will confine myself to one point which, I confess, had completely escaped me, and

which is of great importance. Although, in my theory, the terrestrial currents which result from the electric discharges, the cause of polar light, ought to be directed from the north to the south, some are observed, either in the telegraph-wires or in their action upon the needle of the compass, which have a contrary direction, that is from the south to the north. The former, it is true, are much the more numerous and the more intense; but still the latter are apparent from time to time. M. Lemström attributes them to the currents of induction, and the elec tro-motive force which accompanies always the production of an electric spark, as M. Edlund discovered. He considers in fact, and with reason, the electric discharges which constitute polar light, as a series of an infinite number of sparks, and in this fact found a satisfactory explanation of the existence of currents in an opposite direction from that of the principal current, which is from north to south.

The perusal of M. Lemström's article, while confirming me in the theoretical views I have advanced in regard to polar auroras, has shown me that there still remain many points to be explained of this interesting subject, especially in what concerns the propagation of electricity in air more or less damp, and reduced to a very low temperature and the influence of a very strong magnetism upon the electric discharges taking place under these conditions. I intend to pursue the subject with diligence.

ON A DOMINANT LANGUAGE FOR SCIENCE.

BY ALPHONSE DE CANDOLIE,
Of Geneva, Switzerland.*

At the period of the Renaissance, Latin was the language employed by all the learned men of Europe. It had been carefully preserved by the Romish Church; and not one of the modern languages presented, at that time, a sufficiently rich literature to become its rival. But at a later period the Reformation disturbed the unity of the Romish influence. Italian, Spanish, French, and English gained successively regular idioms, and became rich in literary productions of every kind; and at last, eighty or one hundred years ago at most, the progress of science caused the inconvenience of the use of Latin to be felt. It was a dead language, and, in addition to that, was wanting in clearness, owing to its inversions, to its abbreviated words, and to the absence of articles. There existed at that time a general desire to describe the numerous discoveries that were being made, and to explain and discuss them without the necessity of seeking for words. The almost universal pressure of these causes was the reason for the adoption of modern languages in most sciences, natural history being the only exception. For this, Latin is still employed, but only in descriptions-a special and technical part, where the number of words is limited and the construction very regular. Speaking truly, what naturalists have preserved is the Latin of Linnæus, a language in which every word is precise in meaning, every sentence arranged logically, clearly, and in a way employed by no Roman author. Linnæus was not a linguist. He knew but little even of modern languages, and it is evident that he struggled against many difficulties when he wrote in Latin. With a very limited vocabulary and a turn of mind which revolted equally from the periods of Cicero and the reticence of Tacitus, he knew how to create a language precise in its terms, appropriate to the description of forms, and intelligible to students. He never made use of a term without first defining it. To renounce this special language of the learned Swede would be to render descriptions less clear and less accessible to the savants of all nations. If we attempt to translate into the Latin of Linnæus certain sentences in modern floras, written in English or German, we quickly perceive a want of clearness. In English, the word smooth applies equally to glaber and **The fifth chapter of the Histoire des sciences et des savants depuis deux siècles, 8vo, Genève, 1873. London, Dulan. Translated by Miss Miers, by permission of the author. Ann. & Mag. N. Hist., ser. 4, vol. xi.

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