April 2 2, 1886] 



NA TURE 



597 



Fig. 2. The gas entered by the inner tube, which passed down 

 to the surface of the mercury, and the outer tube was connected 

 with tlie gas-burner placed under tlie (J's'i^P^tl heating-tube. 

 Thus a rise of mercury in the regulator reduced the supply of 

 gas to the burner. The cross-section of the Hat glass bulb at the 

 common surface of the mercury and volatile liquid was large 

 compared with the cross-section at the upper end of the regu- 

 lator ; thus nearly all the increase in height due to expansion of 

 the volatile liquid and vapour takes place at the upper end of 

 the regulator, and the level of the common surface of the 

 mercury and volatile liquid remains nearly constant. 



The most interesting part of the apparatus is the arrangement 

 for compensating for the variation of atmospheric pressure. 

 With this object a barometer in tlio form of a bent tube is fixed 

 at F. To simplify the explanation we will suppose that the 

 atmospheric pressure diminishes by an amount equal to a head 

 of one inch of mercury ; this will cause the mercury in the open 

 end of the barometer to rise half an inch. If the regulated gas- 

 flame is to be extinguished when there is a constant pressure on 

 the volatile liquid, then the tube E must be raised one inch ; thus 

 it must move in the same direction as and twice the amount of 

 the exposed surface of the mercury in the barometer. To 

 accomplish this the upper part of the regulator was attached to 

 a board turning about a horizontal axis. A. A gas-bag was 

 placed between the projecting end of this board and a fixed 

 tjoard, B. The board turning about A was so weighted as to 

 tend to close the bag. The nozzle of the bag was connected to 

 the gas-main, and a branch pipe led to a small tube, c, passing 

 down the open end of the barometer. This small tube was fixed 

 by a bracket to the movable board half-way between the upper 

 end of the regulator and the pivot a. Now if the mercury rises 

 in the open end of the barometer it closes the tube c, and the 

 gas from the main passes into the bag, forces the boards apart, 

 and raises both the upper end of the regulator and the tube c, 

 until the escape restores the equilibrium. The flexible india- 

 rubber connections in the glass tubes allow the necessary move- 

 ment to take place. This arrangement is of interest, as the 

 pressure of the gas-supply is the motive-power for automatically 

 moving a piece of mechanism in a required manner. 



The apparatus was kept in action for fourteen days without 

 readjustment, but the stirring of the water was discontinued at 

 night. The thermometer was read about ten times a day, and 

 from July 18 to August I the extreme readings were 30°'90 C. 

 and 30° 86 C. The greatest change of temperature during any 

 day was o°'04 C, the least observed change during any day was 

 o°'oi C, and the longest period during which no change was ob- 

 servable was from 12.30 p.m. on July 20, to i p.m. the following 

 day. At night, when the stirring was discontinued, the variation 

 of the temperature was greater, but it settled down to its normal 

 amount shortly after the stirring began. In a properly-con- 

 structed comparing-room the change of temperature would have 

 been less. On one occasion the barometer rose rapidly, nearly 

 half an inch in twenty-four hours, and during this time the tem- 

 perature of the water did not vary perceptibly. If the baro- 

 meter had not been attached to the regulator, this change of 

 pressure on the volatile liquid would have produced a change of 

 o°"l4 C. in the bath. 



The apparatus was roughly made in an experimental form, 

 but the results were highly satisfactory. There were no doubt 

 errors in the readings of the thermometer. Sir William 

 Thomson, in his .article on "Heat" in the " Encyclopcedia 

 Britannica," describes an error which may be introduced owing 

 to the mercury in the stem of a thermometer remaining at rest 

 whilst slight changes of temperature are occurring, and then 

 moving suddenly into a new position, where it again remains at 

 rest. This phenomenon was observed in the very delicate 

 thermometer used. 



The variation of temperature due to the expansion of the 

 mercury in the bai-ometer and regulator was perceptible, and 

 agreed roughly with the amount arrived at by calculation. Very 

 small errors were also probably introduced by the following 

 causes : the sticking of the mercury in the regulator and the 

 barometer ; variation of the gas-pressure ; imperfections in the 

 mechanism and of the vacuum in the barometer. There can, 

 however, be little doubt that the errors produced by these and 

 other causes could be reduced to an inappreciable amount, and 

 if the apparatus were placed in a room of fairly constant tem- 

 perature, remarkable results could be obtained. 



IIOKACF. Darwin 



SCIENTIFIC SERIALS 



yotirnal of the Russian C/itmual ami Physical Society, vol. 

 xviii., fasc. ii. — On the analysis of platinum ores, by F. Willm. 

 All former methods of the separation of noble metals, though 

 sufficient for technical purposes, are considered not exact for the 

 scientific determination. Electrolytic method is recommended. — 

 On the thermic effects of the replacement of hydrogen by 

 bromine in the aromatic compounds, by E. Werner. — On 

 cholanic and bileanic acids, by P. Latchinoff. Both having been 

 obtained from cow's bile and formula; proposed for the former 

 CjsHjsO; 4- iH.O, and for the latter CosH^^Og -t- iHjO.— 

 Contribution to the theory of the influence of the decomposition of 

 a body due to heat or to mechanical influences, on its magnetism, 

 by P. Bakmetieft". — Thermo-electrical researches, by the same 

 author. The starting-point for these researches being the fact 

 observed by the author, that the thermo-electro generative force 

 in the metal rods, which serve as thermo-elements, undergoes 

 variations under the influence of the contraction or expansion of 

 the rods parallel to those of magnetism in the same metals and 

 from the same causes. 



Rtiuliconti del Reak Iitituto Lombardo, February 18.— State 

 of public instruction in Italy, by Prof. A. Amati. In general 

 the results here tabulated of an inquiry into the present state of 

 instruction throughout the peninsula show that the number of 

 unlettered is in direct proportion with that of the criminal 

 classes. — On a phenomenon of intermission in the sense of 

 hearing, by Prof. A. Raggi. It is shown that under certain 

 conditions regularly recurring sounds strike the auditory faculty 

 in rhythmically recurring waves of greater and less intensity. 

 The phenomenon is regarded as the direct result of perception, 

 the reflex act represented by the awakened attention not being 

 produced with a uniform degree of energy continued throughout 

 the duration of the stiinulus, the lack of uniformity being itself 

 due to the feeble degree of excitement. — Note on a simple and 

 obvious, but not hitherto noticed deduction from Ta)lor's 

 formula in infinitesimal analysis, by Gian Antonio Maggi. — 

 Remarks on a normal metamorphosis of the scented violet due 

 to the presence of the larva of Cecidomyia destructor, by Dr. S. 

 Calloni. 



SOCIETIES AND ACADEMIES 



London 



Royal Society, March 25. — " On the Changes produced by 

 Magnetisation in the Length of Iron Wires under Tension." 

 By Shelford Bidwell, M.A., LL.B. Communicated by Prof. 

 F. Guthrie, F.R.S. 



In a paper communicated to the Royal Society about a year 

 ago, the author discussed the results of certain experiments 

 made by Joule in relation to the efTects of magnetism upon the 

 dimensi' ins of iron and steel bars. 



It is well known that the length of an ir>.n rod is in general 

 slightly increased by magnetisation. Joule enunciated the law 

 that the elongation is proportional in a given bar to the square 

 of the magnetic intensity, and that it ceases to inci-ease after the 

 iron is fully saturated. The author's experiments, made with a 

 greater range of magnetisini; forces and with thinner rods than 

 those used by Joule, showed that if the magnetising current 

 were gradually increased after the so-called saturation point of 

 the iron had been reached, the elongation, instead of remaining 

 at a maximum, was diminished, until, when the current had 

 attained a certain strength, the original length of the rod was 

 unaltered, and if this strength were exceeded, actual retraction 

 was produced. 



Joule also found that when the experiment wis performed 

 upon an iron wire stretched by a weight, the magnetic extension 

 was in all cases diminished, and if the weight were considerable, 

 magnetisation caused retraction instead of elongation. From 

 these facts he appears to have formed the conclusion that, under 

 a certain critical tension (differing for difterent specimens of 

 iron, but independent of the magnetising force), magnetisation 

 would produce no eft'ect whatever upon the dimensions of the 

 wire. In one of his experiments a certain iron wire loaded 

 with a weight of 408 lbs. was found to be slightly elongated 

 when magnetised ; the weight was then increased to 740 lbs., 

 with the result that magnetisation was accompanied by a slight 

 retraction. In both cases the magnetising currents varied over 

 a considerable range, and the smaller ones were without any 

 visible effect. Commenting upon these results, Joule conjectured 

 that "with a tension of about 600 lbs. (which number is roughly 



