550 



NA TUBE 



\_April%, 1886 



The logarithmic decrement : 

 and diameter of the wire. 



independent of both the lenLjth 



"Effects of Stress and Magnetisation on the Thermo-electric 

 Quality of Iron." By Prof. J. A. Ewing, B.Sc, F.R.S.E., 

 University College, Dundee. Communicated by Sir William 

 Thomson, F.R.S. 



This paper comprises 'a revised version of one submitted to 

 the Royal Society in 1881, under the title " Effects of Stress on 

 the Thermo-electric Quality of Metals, Part I." (published in 

 abstract in Proc. Roy. Sec, No. 214, 1881), along with much 

 ■new matter. It deals principally with the cyclic changes of 

 thermo-electric quality which an iron wire undergoes when ex- 

 posed to cyclic variations of stress (described in the abstract of 

 the former paper), and with the relations of these changes of 

 thermo-electric quality to the changes of magnetism which also 

 occur as an effect of stress. Stress was applied by exposing 

 the wire to longitudinal pull by means of loads. The changes 

 both of thermo-electric quality and of magnetism exhibit that 

 tendency to lag behind the changes of stress to which in a pre- 

 vious paper (Proc. Roy. Soc, No. 216, 1881, p. 22) the author 

 gave the name kysUresis, and the effects are sufficiently similar , 

 in regard to the two qualities to suggest that the changes of I 

 thermo-electric quality occur as secondary effects of changes of 

 magnetism. To examine whether this is the case, simultaneous 

 measurements of the magnetic and thermo-electric effects of stress 

 on an iron wire were made, and also independent observations 

 of the thermo-electric effects of m.agnetisation, without change 

 of stress. A com.parison of these made it clear that stress 

 causes change in the thermo-electric quality of iron directly, 

 and not as a secondary effect of magnetisatioi\. If the wire 

 be completely demagnetised to begin with, and Icept clear 

 of all magnetisation during the application and removal of 

 stress, the presence of hysteresis is not less marked than 

 before. Experiments are given to show how the thermo-electric 

 effects of stress .are modified by the exi-tence of more or less 

 magnetisation in the wire ; and, conversely, how the thermo- 

 electric effects of magnetism are modified by the existence of 

 more or less constant stress. The influence of vibration in 

 destroying the effects of hysteresis is investigated, and also the 

 result of exposing the wire to the process of demagnetising by 

 repeated rapid reversals of a continuously diminishing magnetis- 

 ing force, and it is shown that this process acts in the same 

 way as vibration in destroying the effects of hysteresis. Residual 

 effects of hysteresis are studied, as, for exam)ile, the difference 

 which presents itself when a wire is magnetised after having 

 been loaded strongly and then unloaded down to a certain 

 constant state of stress, and, on the other hand, when the same 

 state of stress has been produced by simply increasing the load ; 

 and it is shown that these re'-idual effects are wiped out by 

 vibration or by demagnetising by reversals. With regard to the 

 effects of stress on thermoelectric quality it is shown that if a 

 somewhat soft wire be more and more strongly magnetised 

 these effects become more and more similar to tliose v\hich are 

 found when the wire is hard-drawn but not magnetised. .\ 

 few experiments were made with wires of silver, copper, lead, 

 magnesium, aud German silver, but in none of these was 

 hysteresis of thermo-electric quality with regard to load dis- 

 covered. 



Special attention is directed to a peculiar feature in the curves 

 by means of which the experimental results are exhibited. In 

 curves showing the relation of thermo-electric electromotive 

 force to lo.id, it is shown that any reversal from loading to un- 

 loading, and vice versa, causes an inflection in the curve, the first 

 effect of the new process being to continue the kind of change 

 of thermo-electric quality that was going on before. That this 

 is not due to any mechanical disturbance which the loading or 

 unloading produces is shown by the fact that it occurs in an 

 equally marked way after the molecules have been brought to a 

 condition of stable equilibrium by vibrating the wire before 

 beginning to load or unload. It is suggested that the effects of 

 hysteresis, described in the paper, have a possible relation to 

 the properties which Prof. Osborne Reynolds has recently shown 

 to be possessed by granular media. 



The experiments described in the paper are closely connected 

 with those which were c 'mmunicated to the Society in January 

 18S5, under the title " Kxperimental Researches in Magnetism," 

 and are now being published in the Pliilosophical Transactions. 

 They were conducted in the Physical Laboratory of the Uni- 

 versity of Tokio, in 1S81-83, partly with tlie help of one of the 

 author's Japanese students, Mr. S. Sakai. The results are 



given graphically, and are for the most part reduced to absolute 

 measure. 



March iS. — "On the Properties of Matter in the Gaseous 

 and Liquid States under Various Conditions of Temperature 

 and Pressure." By the late Thomas Andrews, M.D., LL.D., 

 F.R.S. Communicated by the President. 



The following are the general conclusions to which this in- 

 quiry has led : — 



(i) The law of gaseous mixtures, as enunciated by Dalton, 

 is largely deviated from in the case of mixtures of nitrogen and 

 carbonic acid at high pre-sures, and is probably only strictly 

 true when applied to mixtures of gases in the so-called perfect 

 state. 



(2) The critical point of temperature is lowered by admixture 

 with a permanent gas. 



(3)- When carbonic acid gas and nitrogen diffuse into each 

 other at high pressures, the volume of the mixture is increased. 



(4) In a mixture of liquid carbonic acid and nitrogen at 

 temperatures not greatly below the critical point, the liquid 

 surface loses its curvature, and is effaced by the application 

 of pressure alone, while at lower temperatures the nitrogen 

 is absorbed in the ordinary way, and the curvature of the 

 liquid surface is preserved so long as any portion of the gas 

 is visible. 



Linnean Society, April i. — Sir John Lubbock, Bart., 

 President, in the chair. — Mr. J. G. Balier exhibited Scolopen- 

 driuut Devalyi, a new species of fern discovered by tlie Abbe 

 Devalyi in the province of Yunnan. — Dr. F. Day showed pho- 

 tographs of the fully-grown skulls of Salmo salar and S. fario, 

 in proof of the marked cranial differences existent in the very 

 adult stages of the salmon and the trout. — A paper was read, 

 botanical observations made in a journey to the Naga Hills 

 (between Assam and Munipore), by Mr. C. B. Clarke. Writing 

 from Kohima, a station 4750 feet altitude, he says the country 

 above 5000 feet is nearly all jungle, and that the predominant 

 plant-groups, such as the Commelinacece, Rubi, Senecio, and 

 ferns, besides others, are nearly all identical with those growing 

 in Sikkim, while, on the contrary, many Kh.asi plants are con- 

 spicuously absent. Various kinds of oaks form forests around 

 Kohima, and the alder is abundant, the latter occasionally 

 having an enormous trunk. The Nagas pollard the alder at 

 6 feet from the ground, and cut the innumerable sprouts for fire- 

 wood. Two rare species of Dyospyros were observed. The 

 flora is altogether rich and interesting, though there are few 

 new species. Mr. Clarke gives an account of his ascent of 

 Jakpho, a mountain-peak 99S0 feet high, and about 10 miles 

 distant from Kohima. Lomaria i^laiica, a rare fern in Khasia, 

 is here jjlentiful, rhododendrons are plentiful at 8500, and the 

 ridge at the top is clothed with dwarf bamboo. The levels 

 5000 to 7000 feet on Jakpho are mostly forests of shrubby Strobi- 

 lanthes 6 to 12 feet higli, just as in Sikkim. There are several 

 laurels, and Ilex Ai]uif\iliuin exists as a tree 30 to 40 feet high. 

 The Convolvulacere are prominent up to 5000 feet. — The fir^t 

 part of a lengthened technical communication, " Index Florae 

 Sinensis," or an enumeration of all the plants known from China 

 proper, Formosa, the Corea, and the Luchu Islands, together with 

 their synonymy and distribution, was spoken to by the authors, 

 Messrs. F. B. Forbes and W. B. Hemsley. — Afterwards a paper 

 was read by Mr. H. N. Ridley, on the freshwater Hydrochar- 

 ideie of Africa. Among many new species described is Boctia 

 exseria, obtained by Sir John Kirk on the borders of the Zam- 

 besi in i860. — The Secretary read a communication, on the 

 vegetation of the Arctic regions, by M. Buysman. The author 

 remarks that the flora of Greenland is decidedly Scandinavian 

 in character. Almost all the plants are also found in Lapland, 

 but, notwithstanding the proximity of America, few belong to 

 that continent, while Asiatic Arctic types are rare. Some 378 

 species of phanerogams and cryptogams compose the Greenland 

 flora. Of these, over 200 are found on the eastern coast, only 

 7 of them being absent on the western shore, while 170 species 

 are recorded from the west, these being absent on the east. 

 Nova Zemlya and the Island of Waigatz together possess 290 

 species, and Spitzbergen 1 17 species. The author enters into 

 particulars regarding the special plants peculiar to the seaboard, 

 and such as are cultivated by the inhabitants both in the open 

 air and under cover. He remarks that the long and continuous 

 summer sunlight, and at times intense heat, have much influence 

 on the vegetation, and counterbalance the dark severe winter 



