Magnetism

There are no lines of force!

Great has been the fame of the lodestone and of amber in the writings of the learned: many philosophers cite the lodestone and also amber whenever, in explaining mysteries and things beyond man’s understanding by means of the lodestone as a sort of Delphic sword and as an illustration of all sorts of things. Medical men also (at the bidding of Galen), in proving that purgative medicines exercise attraction through likeness of substance and kinship of juices (a silly error and gratuitous!), bring in as a witness the lodestone, a substance of great authority and of noteworthy efficiency, and a body of no common order. Thus in very many affairs persons who plead for a cause the merits of which they cannot set forth, bring in as masked advocates the lodestone and the amber. But all these, besides sharing the general misapprehension, are ignorant that the causes of the lodestone’s movements are very different from those which give to amber its properties; hence they easily fall into errors, and by their own imaginings are led farther and farther astray. For in other bodies is seen a considerable power of attraction, differing from that of the lodestone, in amber, for example. Of this substance a few words must be said, to show the nature of the attachment of bodies to it, and to point out the vast difference between this and the magnetic actions; for people still continue in ignorance, and deem that inclination of bodies to amber to be an attraction, and comparable to the magnetic coition.
— William Gilbert (1540-1603), De Magnete [All About Magnets], 1600

One loadstone appears to attract another in the natural position; but in the opposite position, repels it and brings it to rights.
— William Gilbert (1540-1603), De Magnete [All About Magnets], 1600.

But when I tried all these things, I found them to be false: for not onely breathing and belching upon the Loadstone after eating of Garlick, did not stop its vertues: but when it was all anoynted over with the juice of the Garlick, it did perform its office as well as if it had never been touched with it.
— William Gilbert (1540-1603), De Magnete [All About Magnets], 1600

Take the stone on which you have designated the poles, N and S, and put it in its vessel so that it may float …
— William Gilbert (1540-1603), De Magnete [All About Magnets], 1600

Lines of force can cross space, like gravity and electricity. So space has a magnetic relation of its own, and one that we should probably find hereafter to be of the utmost importance in natural phenomena.
— Michael Faraday (1791 – 1867), lecture to the Royal Society, about 1850,

For the complete determination of the magnetic force of the earth in a given place three elements are required: the declination, or the angle between the plane in which the magnet lies and a meridian; the inclination of its direction to the horizontal plane; and in the third place, the intensity…

The method which was used in this investigation consists in the observation of the time in which the same magnetic needle makes the same number of oscillations in different places, or of the number of oscillations made in the same interval of time. The intensity is set proportional to the square of the number of oscillations in a given time.
— Johann Karl Friedrich Gauss (1777 – 1855), writing in 1841.

At the centre of the card is a metal thimble holding a jewel with a conical hole, which rests on the supporting pivot. A jewel such as a small ruby is used for pivots in the compass, in the best watches, and in the best pivoted electrical instruments, because it is very hard and does not wear out. Underneath the card is fixed not one magnet, but eight, held by an arrangement of threads which makes the north point of the card point to the magnetic north.
— E. N. da C. Andrade and Julian Huxley, Forces at Work, Blackwell, 1934.

In January 1981 … we undertook an expedition to New Zealand and Tasmania to search for magnetotactic bacteria and to test the hypothesis. The sites were chosen because they are ecologically diverse and share many physical characteristics with New England, such as absolute latitude, magnetic field strength and climate. Moreover, the magnetic inclination in New Zealand and Tasmania has the same absolute value as it has in New England, although it has the opposite sign.
— Richard Blakemore and Richard B. Frankel, ‘Magnetic navigation in bacteria’, Scientific American December 1981.

[They] had been set together, side by side, to work on the problem of deducing the characteristics of German magnetic mines laid at sea, especially the sensitivity and polarity of the firing mechanism. The data from which the characteristics were to be deduced were the reports of our minesweepers as they exploded the mines, with the positions of the explosions being reported as ranges and bearings from the minesweepers.
— R. V. Jones, Most Secret War, Hamish Hamilton, 1978.

Field reversals, occurring roughly every million years, are the most dramatic of the wide range of phenomena exhibited by the earth’s magnetic field. And the next reversal on Earth may not be so far away: if the current rate of decay of the Earth’s dipole component is maintained, it will vanish in less than 2000 years’ time.
— Jeremy Bloxham, ‘Evidence for asymmetry and fluctuation’, Nature, 322: 13, 1986

I am the Knower of the field in everyone, Arjuna. Knowledge of the field and its Knower is true knowledge.
— Bhagavad Gita, 13:2, in the translation of Eknath Easwaran, Arkana Books, 1985.

We know that the magnet loves the lodestone, but we do not know whether the lodestone also loves the magnet or is attracted to it against its will.
— Unknown Arabic physicist, 12th century.

If the experiments are completed within a short time, and if the needle which is used is made of hardened steel and carefully magnetised, no considerable loss of its power need be feared …
— Karl Friedrich Gauss (1777 – 1855), writing in 1841.

In treating of magnetism, a distinction is made between permanent and variable magnets; we regard, for example, a magnet of hard steel as a permanent magnet, and a magnet of soft iron as a variable one. Were the distinction between the two classes perfect (which is, however, as little the case as that between conductors and insulators in electricity), the magnetism of a permanent magnet could only investigated through its effects, while that of the variable magnet might be investigated through its causes as well as its effects. At all events, even though the distinction is not perfect, the variable magnet is more favourable to a complete examination of the nature of magnetism than the permanent one …

Now it is known that the investigation of the magnetism of a magnet through its effects (produced on other bodies) leads us to the knowledge of the ideal distribution of the magnetic fluid on the surface of a magnet, regarding which Gauss has proved, that as far as the explanation of phenomena is concerned, it answers completely to the true internal condition of the magnet. In many investigations it is a great advantage to find a way furnished by the ideal distribution towards the simple and complete union of all the observed actions, without the necessity of making any hypothesis regarding the interior of the body; more particularly when the causes of these actions remain unknown and are still to be investigated.
— Wilhelm Eduard Weber (1804 – 1891) Poggendorff’s Annalen, lxxxvii, translated in the Scientific memoirs, edited by Tyndall and Francis, 1853.

You will find an index to this blog at the foot of this link. Please be patient: I am pedalling as fast as I can.