On atmospheric magnetism / Professor Faraday.

Michael Faraday

Date:: [1851]

Credit: On atmospheric magnetism / Professor Faraday. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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in Mr. Faraday’s paper in the Philosophical Transactions for 1851, Part I. Par. 2843, &c. Now this by the hypothesis is assumed to take place in the atmo- isphere. Supposing it all at mean temperature, the lines of force would have the direction determined by the arrangement of the Ipower within the earth. Then the sun’s presence in the east would jmake all the atmosphere in that region a worse conductor, and cause jit to assume the character of D ; and as the sun came up to and passed over the meridian and away to the west, the atmosphere under his influence would bring up changes in direction like those shown in either D or D; it would therefore manifestly set a needle in a given latitude in opposite directions as it passed by; and as evidently set two needles in north and south latitudes in opposite directions at the same moment of time. As the night came on and a temperature lower than the mean came up from the east and passed over, the lines of force would be inflected as in P or P., and a reverse variation of the needle to that which occurred before would now take place. That natural efi’ects of variation must be produced consequent upon the magnetic nature of oxygen and its daily variations of tem- perature is manifest; but whether they cause the observed variations, or are competent to do so, is a question that can only be decided after very careful enquiry. Observations are now made on the surface of the earth with extreme care in many places, and these are collated, and the average or mean result, as to direction and intensity I of the earth’s force, ascertained for every hour and season ; and also many remarkable, anomalous, and extra results evolved. A theory of ;the causes of any or all of these variations may be examined first by the direction which the varying needle does or ought to assume, and then by the amount of the variation. The hypothesis now brought forward has been compared with the mean daily variation for all the months in the year at north and south stations, as Toronto and Hobarton, and at many others near to and far from the Equator, ; and agrees in direction with the results observed far beyond what the author anticipated. Thus the paths described by the upper ends of free needles in the north and south hemispheres should be closed i curves, with the motion in opposite and certain directions, and so they ! are:—the curves described by needles in north or south latitudes should be larger in summer and smaller in winter, and so they are :— a night or cold action should grow up in the winter months, and such I is the case:—the northern hemisphere ought to have a certain pre- dominance over the southern, because of its superior temperature, and that is so:—the disposition of land and water ought to have an influence, and there is one in the right direction :—so that in the first statement and examination of the hypothesis it appears to be remarkably supported by the facts. All these coincidences are particularly examined into and stated in the Philosophical transactions already referred to. The next step will be to ascertain what is the

On atmospheric magnetism / Professor Faraday.

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