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<\/a>\u201cThus far we have a mere collection of facts, and we might go on after the manner of the books, accumulating these to almost any extent.\u00a0But facts without an explaining theory will be but confusion.\u00a0We have a theory most fertile in its consequences.\u00a0Ampere, the discoverer of the 3rd<\/sup> fact is the author of a theory which explains all the facts of common magnetism and of electro-magnetism. The fact that currents passing the same way attract each other, and those passing opposite ways repel each other is an ultimate one. His hypothesis is that magnetism consists in currents of electricity. A magnet consists of currents of electricity revolving around the bar. When the S end of a magnet (fig 6) is brought near the S end of a second magnet, the currents turn in opposite directions whence the repulsion between them. When dissimilar ends are brought near to each other, these currents turn in the same direction whence their attraction. Ampere made hundreds of deductions from this theory, all of which he found to agree exactly with the facts. Professor Henry was the first in this country who studied Ampere\u2019s theory, and made some new deductions from it, and experiments proving them; owing to which it was that he was called to the Professorship in Princeton. If he has done anything for science, it has ever been by the proper use of a theory. Ampere supposes the currents flowing in the same direction, by their lateral action to carry along + rarify the electricity between, when by the external pressure so to speak, the magnetic bars are brought together. Again currents flowing in opposite directions crowd in the fluid + increase its pressure between them, when the bars separate. This theory was too fanciful to meet with much favor at first, but all the English philosophers have at length come to adopt it. If it is without analogy to any other theory, the facts + motions on which it is founded are also unlike any previously known phenomena. We need not suppose these currents to be constant, but to be set in motion by magnetizing the bar. In treating this subject, we shall take Ampere\u2019s supposition, endeavoring to get a clear idea of the consequences flowing from it.<\/p>\n Ampere\u2019s theory which explains all these motions, rests as we have seen on the one fact.\u00a0Currents in the same direction attract, in opposite directions repel, and the one hypothesis.\u00a0Around every atom of the magnet currents of electricity are moving at right angles to the magnets length.\u00a0The currents around the interior atoms (fig 5) neutralize each other\u2019s effects, and those around the exterior atoms produce as their resultant the currents around the magnet.\u00a0We say that these currents move around each atom of the magnet, because no matter into how many pieces we break a magnet, each portion still magnetic, ie. has these currents.<\/p>\n<\/div>\n The simple galvanometer is but such a magnetic needle, around which in the direction of its length is placed a coil of wire.\u00a0The least galvanic current in the wire turns the needle towards the position perpendicular to the wire.\u00a0The surrounding coil of wire should not be made too long, or there will be too great a retardation of the electricity, which is feeble.\u201d (William J. Gibson’s student notebook, 1842-1843)<\/p>\n Another student notebook by Henry Cameron dated four years later includes these notes on the same subject.\u00a0 It also includes brief notes on the ether components of Ampere’s theory:<\/p>\n “Ampere instead of accumulating facts as had been done in other branches of science, at once proposed a hypothesis and proceeded to verify it by deductions, and thus discovered new facts. VC. The theory it is true is fanciful, but the facts are strange and new.\u00a0This theory depends or rests upon one fact, and one hypothesis\u2014The fact\u2014that currents in the same direction attract\u2014in opposite repel.\u2014The hypothesis\u2014that magnetism consists in currents of electricity around each atom of the iron, and at right angles to the length of the bar.\u00a0This theory serves to explain a great many facts.\u00a0How the currents are generated VC his theory does not attempt to explain.\u00a0We shall endeavor to do it hereafter.\u00a0Thus unlike poles of magnets attract because when they are put together, the currents around them are then going in the same direction whereas if like are put together, the currents are opposite and repel.\u00a0VC.\u00a0If we break it are two poles.\u00a0VC. It also explains why the needle turns at right angles, because in that direction the currents around the needle are going the same way as that in the wire.\u00a0The magnetism of the earth is no longer an ultimate fact; but is referred to currents around the earth in the direction in which the sun moves.\u00a0We hope to be able to refer the developments of these currents to the influence of heat.\u00a0By this theory we are enabled to explain the dip of the needle VC.\u00a0Why do currents in the same direction attract?\u00a0We suppose that there is a plenum of the ethereal medium, and from the fact that we suppose it to pervade all space, the atoms must press with great force, upon one another, and consequently the elasticity is very great, it being a function of this pressure.\u00a0We infer great elasticity in this from the immense velocity in light, as sound in air.\u00a0When currents are induced in wires, something like the lateral action of air takes place, and a small degree of exhaustion between the wires allows the immense pressure without to be perceptible and hence the attraction is explained upon the chemical principles. it is mere pressure probably.\u00a0In the case of opposite currents, there is as it were a conflict VC hence repulsion.\u00a0But a slight degree of exhaustion of the ethereal medium is necessary to develop electrical phenomenon.” (Henry Cameron’s student notebook, 1846-7)<\/p>\n<\/div>\n The VC’s that dot these notes may mean “Vi coactus<\/strong>” which is Latin for “under constraint.”\u00a0This was historically used to indicate that one was forced to sign, which would make them a humorous addition by Cameron.<\/p>\n","protected":false},"excerpt":{"rendered":" Acceptance of the Theory Joseph Henry’s Explanation of the Galvanometer It is Ampere\u2019s theory that Professor Henry took to the lecture hall in order to explain the electromagnetic phenomenon displayed by magnets, currents, and of course, the galvanometer. An excerpt from William J. Gibson\u2019s notes on his lectures on the subject is as follows: \u201cThus … Continue reading “Henry’s Explanation”<\/span><\/a><\/p>\n","protected":false},"author":5,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"categories":[],"tags":[],"class_list":["post-3933","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/pages\/3933","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/comments?post=3933"}],"version-history":[{"count":6,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/pages\/3933\/revisions"}],"predecessor-version":[{"id":3942,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/pages\/3933\/revisions\/3942"}],"wp:attachment":[{"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/media?parent=3933"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/categories?post=3933"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/tags?post=3933"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}<\/a><\/a>