OBSERVATIONS OF MAGNETIC PH/ENOMENA.
FOB this volume, and for others which we hope are to follow it, we are indebted to Baron HUMBOLDT and the late Duke of SUSSEX. Previous to 1838, a letter from the great naturalist to the Duke, in his capacity of President of the Royal Society, on the subject of Magnetic Observatories, excited much attention in the European world of science. Mainly to the influence of his Royal Highness with the English Ministry of that time, and to his zeal in the cause, are to be attributed the institution of Colonial Magnetic Observa- tories, and the fitting out of the Antarctic expedition under Captain JAMES CLARKE Ross, of which magnetic observation was one of the main objects. The Observatory at St. Helena was completed, and the instruments moved into it, in August 1840; that at Toronto, in September 1840; that at Van Diemen's Land, in October 1840; and that at the Cape of Good Hope, in April 1841. This was esta- blishing magnetic observations on a scale in some degree commen- surate with the interest such a maritime power as Great Britain has in them, and with due promptitude. Let all parties have their fair share in the honour, though justice requires more particular notice of those who first moved in the matter.
It is not necessary to go deeply into the subject in order to show the importance of this measure. Everybody knows that Captain JAMES Ross has actually ascertained the site of the North Magnetic Pole, and ascertained within a very limited possible range of error the South Magnetic Pole. Everybody who has visited the Adelaide Gallery is aware of the intimate relation that has been shown to subsist between the electric fluid and magnetic phmnomena. There are two or three facts, known or asserted, which, taken in connexion with these, will suffice to show the deep stake this country has in promoting magnetic observations, even if love of science and pride in forwarding it were left out of the question. A first fact is the local connexion between the Aurora Borealis (and the Aurora Australis) and the magnetic. pole ; a second is the alleged disturbance of the magnetic needle during appearances of the Aurora ; a third is the tendency of common clouds in calm weather to assume a direc- tion coincident with that of the magnetic needle ; and a fourth is the fact, that what before sunset seems a congeries of clouds, is occasionally found after sunset to be in reality the Aurora. All these facts direct us irresistibly to the inference, that the agent
(whatever it be) that produces the electric phEenomena, is the same with that which produces the magnetic phienomena ; and that this agent determines the currents of the atmosphere, and the assembling and dispersing of clouds ; that the thunder-storm and the Aurora are mere manifestations of the activity of an agent, which creates
meteors, lends new properties to metals, and in short seems to in- fluence, uphold, and impel all nature. In discovering the nature of this agent and the laws of its operation, safety will be afforded to
the traversers of the terrible ocean immeasurably beyond what has been conferred by the knowledge of the tendency to point North and South which it imparts to the magnet.
HUMBOLDT, ERMAN, LAMONT, SABINE, and other magneticians, have within the present century wonderfully extended and corrected
the views entertained of magnetic action. But the observations required to furnish data for a sound magnetic theory must be ex- tensive and protracted far beyond what individuals can accomplish.
Governments like those of England and Russia, which with ample means at their disposal combine territorial possessions extending through widely distant regions, alone are competent to the task. Russia has set the example : England has worthily followed, and we trust will soon better it.
The quarto now before us is only part of a volume to be devoted to a peculiar class of observations. We shall assume that the reader is aware that a periodical change takes place in the direction of the magnetic needle, not only from year to year, but in a lesser degree from hour to hour. What was once called the diurnal oscil- lation of the needle does not, as was once supposed, consist in a simple movement from one extremity of the range and back, but in an alternate progression and retrogression. One great object of magnetic expeditions, and of simultaneous observations at distant magnetic observatories, is to obtain a correct notion of the manner in which this perpetual quivering (analogous, we might say, to the flickering of the Aurora) manifests itself over the whole surface of the globe. In the course of observations instituted for this pur- pose, naturalists have become aware of inequalities both of time and intensity in the motions of the needle. These disturbances in magnetic action recur, though whether at regular or irregular in- tervals is as yet uncertain, and are sometimes so strong as to have suggested to HUMBOLDT the phrase "magnetic storms." It is to
the observations relating to these "storms" that the volume now before us is devoted. Colonel SABINE in his preface says—" As the
principal interest of the observations made during periods of mag- netic disturbance appears likely to proceed from their being viewed in connexion with similar observations made simultaneously in other parts of the globe, it has been considered desirable to separate the observations made at such times from those which are made daily at stated intervals, and to print them in a volume by themselves."
As the present fasciculus only contains the observations of 1840-41, while the volume, when completed, will embrace the observations from 1840 to 1845 inclusive, and as some elements of the ob- servations at Van Diemen's Land, St. Helena, and the Cape of Good Hope, are still wanting, it would be premature to expect any important conclusions. The precautions taken for insuring accu- rate observations, and the arrangement and care for accuracy in the publication of their results, are alone as yet open to animadversion. From the statements of Colonel SABINE, we incline to believe that every precaution has been taken to man the observatories suffi- ciently; and the arrangement of the work, and (as far as our in- spection has yet carried us) the accuracy of the tabular statements, are worthy of his high scientific character. Though Colonel SABINE justly remarks, that, while the obser- vations at many stations yet remain to be published, "it would be obviously premature to attempt to trace any one single disturbance through the various modifications with which it may have mani- fested itself in various parts of the globe," he appears to be pretty decidedly of opinion that "a cursory examination of these tables is
sufficient to show that some connexion exists between the dis- turbances of principal magnitude at Toronto and those at Van Diemen's Island." These stations are nearly at opposite ex- tremities of a diameter of the globe ; and it is therefore not ex- cessively sanguine to anticipate that our observers are on the eve of discovering an important magnetic law.
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