On a disturbance of the earth's magnetism : in connexion with the appearance of an aurora borealis, as observed at Albany, April 19, 1831 / by Joseph Henry.

  • Henry, Joseph, 1797-1878.
Date:
[1832?]
Catalogue details

Licence: Public Domain Mark

Credit: On a disturbance of the earth's magnetism : in connexion with the appearance of an aurora borealis, as observed at Albany, April 19, 1831 / by Joseph Henry. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

    6/18
    needle had accidentally been placed contiguous to some ferru- ginous substance ; but on a most careful investigation, nothing could be discovered which would tend in the least degree to ex- plain the cause of the phenomenon. The experiment was made at the usual place, with the box containing the needle resting on a post permanently fixed for the purpose, in the Academy Park, at a sufficient distance from every disturbing object, and with the usual precaution of divesting the person of all articles of iron, such as keys, knives, &c. At about 9 o'clock in the evening, or three hours after the above observation, an unusual appearance was noticed in the southern part of the heavens, which was shortly afterwards recognized as an arch of the aurora. It was about 9 degrees in breadth, with the vertex of the arch 20 degrees above the horizon. At this time the northern part of the sky was covered with light fleecy clouds. At 45 minutes past nine, the clouds partially disappeared, and dis- closed the whole northern hemisphere entirely occupied with co- ruscations of the aurora, shooting up past the zenith, and appa- rently all converging to the same point. The actual formation of a corona might probably have been observed, but for a dark cloud which remained stationary a little south of the zenith. The idea for the first time now occurred to me, that this uncommonly bril- liant appearance of the aurora might possibly be connected with the magnetic disturbance observed at 6 o'clock ; and in order to test this, the apparatus was again placed on the post in the Aca- demy Park, and an observation made during the most active ap- pearance of the meteor. The result of the observation Mas, how- ever, entirely different from that anticipated; for instead of still indicating, as at 6 o'clock, an uncommonly high degree of magnetic intensity, it now showed an intensity considerably lower than usual. Observations were also made .on the 20th and 21st, but no dis- turbance was again noticed ; the intensity had resumed its former state. The following table exhibits the observed times of 300 vibra- tions, with the mean temperature and aspect of the weather during each observation :