June 28, 1900] 



NA TURE 



21 



feet. The Upper Peninsula is a region notorious for its much 

 lower gradient. The author discusses the various hypothesis 

 framed to account for the differences in the gradient. Among 

 these are the cooling action of Lake Superior, a survival of the 

 Ice Age coldness, and differences in the conductivity of rocks. 

 The author favours the last hypothesis.— Production of X lays 

 by a battery current, by J. Trowbridge. The installation of a 

 plant of 20,000 storage cells at the Jefferson Physical Laboratory 

 has enabled the author to obtain X-rays of exceptional brilliancy, 

 yielding negatives of great contrast. When the X-ray tube is 

 first connected with the battery terminals no current flows. It 

 is necessary to heat the tube, when it suddenly lights up. A 

 distilled water resistance of about 4,000,000 ohms is inserted in 

 the circuit. 



Annalen der Physik, No. 5.— Change of conductivity of gases 

 by a continuous electric current, by J. Stark. The resistance 

 of a gas conveying an electric current is highest near the 

 electrodes, owing to the accumulation of ions of the same sign in 

 this neighbourhood. It has another maximum near the middle, 

 but rather more towards the side of the anode. The resistance 

 is influenced by the heat developed at the electrodes, by the 

 kathode rays, and by the unequal speed at which the two kinds 

 of ions travel through the gas. — Objective presentation of the 

 properties of polarised light, by N. Umow. A beam of parallel 

 plane-polarised light is allowed to fall on various geometrical 

 bodies whose surfaces have peculiar optical properties, such as a 

 cone covered with fuchsine, a quartz plate, or a Babinet com- 

 pensator. The reflection or transmission of the light gives rise 

 to striking colour phenomena. Peculiar spiral effects are obtained 

 by sending the beam through an opalescent colophonium emul- 

 sion. — Magnetic screening, by II. du Bois and A. P. Wills. In 

 this portion of their work, the authors calculate and verify the 

 effect of a triple screen of iron for galvanometers. The external 

 diameters of the three .screens are 2*5, 43 and 8'0 cm. 

 respectively, and their thicknesses are 0*27, o*l8 and o'i8 cm. 

 The total theoretical " screening ratio," z.e. the ratio by which 

 the disturbing magnetic field is reduced, is 60 "2, and the observed 

 ratio s 64 "6.— Armoured galvanometers, by H. du Bois and 

 H. Rubens. Describes some galvanometers screened in accord- 

 ance with the results of the previous paper. — Rotating magnetic 

 flag, by G. Jaumann. A small magnet mounted like a flag on 

 a glass rod as an axis may be given a continuous rotation by im- 

 mersing it in mercury contained in a glass vessel surrounded by 

 a tight-fitting copper vessel, with a current traversing the body 

 of the mercury and returning through the copper vessel. The 

 work spent in overcoming the resistance of the mercury is 

 derived from the current itself. It appears as a counter E.M.F. 

 until the mercury rotates with the magnet. — Thermal deforma- 

 tion of balances, by T. Middel. Delicate balances show a con- 

 siderable change of .sensitiveness with the temperature. The 

 author shows that this is due to the bending of the beam of the 

 balance, owing to the unequal expansion of the upper and the 

 lower portion, and that is due to the unequal working of the 

 metal, the coefficient of expansion for cast brass being less than 

 that of rolled brass. — ^The additive character of atomic heats, by 

 S. Meyer. The author shows that in the case of twenty-six 

 oxides an excess of the sum of atomic volumes over the molecular 

 volume is accompanied by an excess of the aggregate atomic 

 heats over the molecular heat, and that a defect of atomic 

 volumes is accompanied by a defect of atomic heats in the 

 same manner. Boron and bismuth sesquioxides are the only 

 exceptions. 



Bulletin de f Academic des Sciences de St. P^tersbourg, vol. 

 viii. No. I. — Yearly report of the Academy. — A newly- 

 discovered Old Turkish inscription, by Dr. W. Radloff, pre- 

 liminary report. The inscription was discovered by Madame 

 Elizabeth Clements near Urga, and excellent reproductions of 

 it were made. Dr. Radloff found that it was made in honour of 

 the wise Toyukuk, father-in-law of Bilga-khagan, who was born 

 in 646 of our era. — On the elements of earth-magnetism at 

 Kamenets, Khotin and Odessa, by W. Dubinsky. 



Vol. viii. No. 2.— On the rapid motion of the line of the 

 absides in the system of o' Gimini, by A. Byelopolsky. — On 

 the spectroscopic determination of the movements of 7 Virginis, 

 by the same. — Aurora borealis observed at Pavlovsk on 

 December 20, 1897, by V. Kuznetsoff, with two photographs. — 

 Hydrobiological researches at the Sebastopol Biological Station, 

 by A. Ostrooumoff. 



Vol. viii. No. 3. — On the attempts at reproducing cometary 



NO. 1600, VOL. 62] 



phenomena by means of experiments, by Th. Bredikhin (in 

 Russian). The recent results obtained by photography per- 

 mitted us to obtain most exact reproductions of cometary forms. 

 They .«.timulated the desire of producing theories of comets, and, 

 I as far as the author knows, five different theories were proposed 

 lately ; they differ essentially in their fundamental principles. 

 No great comets having appeared lately, the earlier drawmgs, 

 made by previous astronomers, necessarily must be taken into 

 account. Bredikhin found it necessary, therefore, to system- 

 atically discuss the facts which relate to the variety of forms of 

 comets, and the passages from the one form to another. These 

 facts can be ignored by no theory, and the author consequently 

 analyses those criteria which must be applied to each theory of 

 the comets. — On the way of building magnetic observatories, 

 by H. Wild. — Description of a very rare case of Craniopagus 

 parielalis, by J. Ziematzky (plate). — On the influence of the 

 terms of third order in the perturbations function of the move- 

 ment of the earth round its centre of gravity on the formulae of 

 nutation, by A. Ivanof (in French). The author gives a new 

 formula for reducing the length of the second pendulum for any 

 geocentric latitude. 



Vol. viii. No. 4. — Ephemerid of the comet of Encke from 

 June I to July 31, 1898, by A. Ivanoff.— On the differences of 

 the horizontal intensities of earth magnetism obtained from 

 observations of the unifilar and the bifilar theodolite, by 

 H. Wild.— Positions of 104 1 stars of the star-cluster 5 Messier, 

 deduced from photographs, by Madame Shilow. Full list, 

 compiled from careful measurements made on photographic 

 plates. 



SOCIETIES AND ACADEMIES. 

 London. 

 Royal Society, May 31.—" The Crystalline Structure of 

 Metals." Second Paper. By Prof. J. A. Ewing, F.R.S., 

 and Walter Rosenhain, B.A. 



The investigations described in this paper deal principally 

 with the phenomena of annealing. The first section of the 

 paper describes experiments made in the hope of observing 

 under the microscope the process of recrystallisation in strained 

 iron. This attempt to watch the process of recrystallisation 

 failed, although the experimental diificulties of keeping a 

 specimen under microscopic observation while it was being 

 heated were successfully overcome. The specimen was electri- 

 cally heated in a vessel with a thin glass or mica window, and 

 the microscope-objective was kept cool by directing a strong 

 blast of cold air on it and on the surface of the window. 



The next section of the paper deals with the changes of 

 crystalline structure which go on in lead and other metals at 

 comparatively low temperatures. The authors' attention was 

 directed to this by noticing that a piece of plumber's sheet 

 lead, when etched with dilute nitric acid, exhibits a strikingly 

 crystalline structure, with large crystals. The character of 

 this appearance led the authors to the view that a slow process 

 of annealing or recrystallisation was at work in such lead at 

 ordinary atmospheric temperatures, and the authors have satisfied 

 themselves that this is the case. The method of investigation con- 

 sisted in taking a series of micro- photographs, at low magnifica- 

 tions, of certain marked areas in the surface of a specimen, in 

 order to watch the change which went on through lapse of time, 

 or after application of some thermal treatment. 



When a piece of cast lead is severely strained by compression, 

 the originally large crystals, after being considerably flattened, 

 are driven into and through one another, so that the etched 

 surface of a strained specimen presents a fine grain, whose 

 crystalline nature only becomes apparent under considerable 

 magnification (80 to 100 diameters). A piece of lead severely 

 strained in this way, and kept for nearly six months in an 

 ordinary room without any special thermal treatment, was 

 found to be undergoing continuous change during that time. 

 A series of photographs of this specimen, taken at intervals 

 during the six months, show that a great number of the small 

 crystals have grown larger at the expense of their neighbours. 

 In similar specimens which have been kept at 200° C, the 

 growth has been much more rapid and more pronounced. The 

 rate of growth is a function of time and temperature, but some 

 specimens show much more rapid changes than others under 

 similar conditions of temperature ; in some cases five minutes' 

 exposure to a temperature of 200° C. is sufficient to alter the 



