Jl-xe 8, 1883.] 



♦ KNO\A/LEDGE ♦ 



339 



fetched cause may tend to considerably influence and 

 modify tish and tishing — viz., how the pollution of rivers 

 can be obviated and turned to account. In the shed are 

 exhibited specimens of nativi> guano, precipitated from 

 sewage by a peculiar nii.\ture termed a li c ; the precipita- 

 tion is most perfectly effected, and all noxious substances 

 are dissipated ; the result of tliis is, that clear water flows 

 off, freed from all injurious materials. Some of the water 

 thus procured is shown to be perfectly harmless to tish in 

 tanks and aquaria. 



In conclusion, this narrative will be followed by a series 

 of descriptive illustrated papers on the natural history 

 exhibits. We propose to coniuicnce with the lowest forms 

 of life, and to progress to those of higher organisation. In 

 doing so we must obviously visit widely-separated stations 

 in the E.xhibition buildings, seek out and collect kindred 

 specimens, and study them systematically. 



Dr. Ramsay H. Traqiair, M.D., F.R.S., Director of the Naiurnl 

 History Jlnsenin, Edinburgh, is now delivering a course of Iccturis 

 (/re.) on the " Strneture and Clussification of Fishes." The fii-tt 

 lecture was given on the otli, and further lectures will be delivercil 

 at -1 p.m., on Tuesdays, Thursdays, and Fridays hereafter, till 

 June 29. 



PROF. HUGHES ON M.\G>'ETISM. 



By W. Si.in-<:o. 



PRESSMEN were wont to say of speeches made by 

 Mr. Lowe (Lord Sherborne) that they were so full 

 of points, each essential to the rest, that to eliminate any 

 of them for the purpose of condensation were well-nigh 

 impossible. A similar difficulty presents itself to any one 

 who ventures to epitomise the paper on " The Cause of 

 Evident Magnetism," read by Prof. Hughes at a meeting 

 of the Society of Telegraph Engineers on Thursday week. 

 The paper contains matter that is certain to evoke the 

 greatest interest in the minds of all who have hitherto 

 given any, even the slightest, attention to magnetism. The 

 chairman went so far as to say that nothing in magnetism 

 so interesting in description, or so perfect in demonstra- 

 tion, had been l)rought before the scientific world since the 

 time when Qllrsted made public his great discovery con- 

 cerning the relations between magnetism and electricity. 

 These discoveries were of themselves sufficient to make 

 telegraphy practicable, but whether or not Prof. Hughes' 

 labours will affect the applications of magnetism to every- 

 day life is matter of conjecture. It seems to lae 

 more likely that the science rather than the art (or 

 the application of the science) will reap the reward. 

 At the commencement of his paper, the Professor 

 details the chaotic work and theories of previous experi- 

 mentalists. Coulomb, Poisson, Ampire, De la Rue, ilatteuci, 

 Page, .Joule, and Maxwell. He does so in order to show 

 that they all " admit of the inherent polarity of the mole- 

 cule " ; but, he further observes, " the induction balance at 

 once shows that they are erroneous in the most important 

 part, for my researches have proved that neutrality is per- 

 fectly symmetrical, that there is no case of neutrality where 

 the axes of the molecules are turned indifferently in all 

 directions, and that we cannot obtain perfect neutrality 

 except when the molecules form a complete closed ciroiit of 

 attraction." Upon this basis, experimentally treated. 

 Professor Hughes draws the following conclusions : — 



1. That each molecule of a piece of iron, steel, or other mafrnetio 

 metal is a separate and independent magnet, having its two poles 

 and distribution of magnetic polarity e.tactly the same as its total 

 evident magnetism when noticed upon a steel bar-magnet. 



2, That each molecule, or its polarity, can be rotated in lithor 

 direction \ipon its axis by torsion, stress, or by physical force such 

 as niacnetisni and electricity. 



3. That the inherent polarity or magnetism of each molecule is a 

 constant quantity like gravity ; that it can neither be augmented 

 nor destroyed. 



i. That when we have external neutrality, or no apparent nmg- 

 netisni, the molecules, or their polarities, arrange themselves so as 

 to satisfy their mntnal- attraction by the shortest path, and thus 

 form a complete closed circuit of attraction. 



5. That when magnetism becomes evident, the molecules or 

 their polarities have all rotated symmetrically in a given direction, 

 producing a north pole if rotated in that direction as regards the 

 piece of steel, or a south pole if rotated in the opposite direction. 

 Also, that in evident magnetism, we have still a symmetrical 

 arrangement, but one whose circles of attraction are not completed 

 except through an external armature joining both poles. 



G. That we have permanent magnetism when the molecular 

 rigidity, as in tempered steel, retains them in a given direction, 

 and transient magnetism whenever the molecules rotate in com- 

 parative freedom, as in soft iron. 



Space will not permit me to give even a bare enumera- 

 tion of the various admirable and ingenious experiments 

 performed to demonstrate these deductions, but the pith 

 of them all is I imagine in the third and fourth paragraphs, 

 the others following as an almost natural sequence. Prof. 

 Hughes has been materially assisted in his ettbrts to over- 

 come previously - received notions of coercive force and 

 neutrality, by his recent experiments on the effects of 

 torsion, and by his invention of the induction balance. In 

 demonstrating the principle of "inherent" magnetism, the 

 professor maintains that a "bar of iron or steel, being held 

 in the earth's magnetic field of infinite size compared with 

 the bar, and infinitely homogeneous, cannot deflect or 

 weaken its surrounding field." " We cannot," he says 

 further on, " either by induction, conduction, or concen- 

 tration, produce a greater force in another body of similar 

 displacement or size, otherwise we could easily create power 

 from a feeble source. Thus the enormously greater mag- 

 netic power observed in iron than the same column of air 

 which it displaces must be due to the indirect polarity of 

 its molecules." This polarity he ascertained in a certain 

 piece of wire to be " l.'),GOO times greater than the column 

 it displaced." The effects of torsion are most remark- 

 able. Torsion is capable of doing anything that can 

 be performed by heat or by vibration. This was shown 

 in many ways. A piece of iron, after being slightly niag- 

 netised, was Vjy its means demagnetised. A piece of iron 

 held in the magnetic dip was highly magnetised. A piece 

 of untempered fine cast drill steel illustrated " superposed " 

 magnetism in a remarkable manner. The wire, one milli- 

 metre thick, had two entire turns or twists to the right, 

 and was then magnetised by passing it over the north pole of 

 a magnet. It was then subjected to two turns to the left, 

 and passed over the south pole of a magnet. When free 

 from torsion the wire exhibits perfect neutrality, but when 

 twi.sted either to the right or left polarity is evident. One 

 of the prettiest experiments of the evening was with the 

 aid of such a piece of wire. None of the apparatus was 

 remarkable for its costliness, the most elaborate piece con- 

 sisting of two footless wine-glasses, four penny bar-magnets, 

 and a short piece of thin steel. The steel was movable in 

 a horizontal plane over the bar magnets, and was therefore 

 polarised. 



If moved far enough in either direction, it struck one of 

 the glasses, producing a musical sound. The superposed 

 magnetic wire on being brought near the piece of steel and 

 twisted alternately to the right and left, repelled and 

 attracted it, and caused it to strike the glasses with 

 unerring distinctness. The effect was niarvellou.s, and 

 Prof. Hughes may be pardoned for taking a little pride to 

 himself for showing " the first direct transformation of 



