November 28, 1912] 



NATURE 



375 



tenable at the Royal College of Science, Dublin, shall 

 be offered for competition among Irish students of 

 science and technology in 19 13. 'Ihe scholarships are 

 of the value of 50/. per annum, and, in addition, 

 entitle the holder to free instruction during the asso- 

 ciate course. A teachership-in-training has similar 

 advantages except that the maintenance allowance is 

 2 IS. per week for the session of about forty weeks. 

 Candidates must be not less than sixteen nor more 

 than thirty years of age on June i, 1913, and will have 

 to satisfy the Department as to their knowledge of 

 English and of one other of the languages — Greek, 

 Latin, Irish, French, or German. The competition 

 will be confined to mathematics, experimental science, 

 and drawing. Applications for admission to the 

 examination must be made not later than April 30, 

 1913, on forms copies of which may be obtained 

 upon application to the Secretary, Department of 

 Agriculture and Technical Instruction, for Ireland, 

 Upper Mcrrion Street, Dublin, or to the Registrar, 

 Roval College of Science, Upper Merrion Street, 

 Dublin. 



SOCIETIES AND ACADEMIES. 

 London. 

 Physical Society, November 8. — Prof. A. Schuster, 

 F.R.S., president, in the chair.— H. R. Nettleton : A 

 method of measuring the Thomson effect. The dis- 

 tribution of temperature down a conductor conveying 

 an electric current and at the same time moving 

 uniformly through two fixed temperature sources is 

 investigated. The effect of the Thomson heat on the 

 distribution is exactly similar to the effect of a small 

 impressed velocity. This result was applied to mer- 

 cury to measure the Thomson effect by comparing the 

 alteration of temperature Afl^ at a point near the 

 middle of the gradient caused by reversing a current 

 of C amperes w-ith the alteration of temperature AS, at 

 the same point due to a flow of mercury of m grams 

 per second. Without any approximation as to emis- 

 sivity loss or magnitude of Joulian heat, 2Ca lms = 

 A9j/A9,, where s is the specific heat of mercury and a- 

 the specific heat of electricity. Working with currents 

 of from 4 to 9 amperes and with flows of different 

 magnitudes — but never exceeding i cm. per hour — 

 consistent values of o- were obtained, the value at 

 61° C. being — i'52 x io-° calories per degree Centi- 

 grade per coulomb. The thermo-junctions, which 

 were of iron and constantan, were fused through the 

 glass tubes with inappreciable distortion. — F. W. 

 Jordan : An improved Joule radiometer and its applica- 

 tions. The first part relates to improvements made in 

 order to convert the original Joule convection appa- 

 ratus into an instrument for the exact measurement 

 of small steady rates of evolution or absorption of 

 heat. These improvements consisted in (i) replacing 

 the badly conducting glass enclosure and cardboard 

 partition by others made of brass and copper ; (2) re- 

 placing the uncertain and variable magnetic control 

 of the movement of the vane in Joule's apparatus by 

 the elastic control of a quartz fibre ; (3) shaping the 

 channels, in w-h!ch the vanes moved, so that the 

 angular deflection of the vanes was proportional to 

 the rate of evolution of heat ; (4) reducing the size, so 

 that uniform temperatures of its various parts could 

 be maintained by f.^) placing the radiometer within a 

 concentric brass tube to exclude all extraneous heat 

 excepting that which might be directed through aper- 

 tures in its side towards the radiometer. The sensi- 

 bilitv of the instrument was measured and found to 

 be equal to o'.i;2 mm. per microwatt, as mesfsured on 

 a scale at a distance of one metre from the mirror. 

 NO. 2248, VOL. 90] 



Thus the instrument may be used for the measure- 

 ment of feeble oscillating currents. To convert the 

 apparatus into an instrument for the measurement of 

 radiant heat it is suggested that the radiant heat be 

 directed through a small rock salt or fluorite window 

 in the side of a compartment on to a thin blackened 

 metal disc supported centrally. Its use for the quick 

 measurement of the heat given out by radium is also 

 suggested. The second part relates to a suggested 

 method of measuring the Thomson effect with this 

 radiometer. The method hinges on an experiment 

 described by the author in N.wure, May 18, 1911. — 

 Miss A. Somers : Note on the attainment of a steady 

 state when heat diffuses along a moving cylinder. 

 The paper dealt with the case of a column of mercury 

 moving with uniform speed between two fixed tem- 

 perature sources. The differential equation for the 

 temperature within the column was stated and its solu- 

 tion given, and it was shown how the time of attain- 

 ment of a steady state could be obtained from the 

 latter. Dr. S. VV. J. Smith : Thermomagnetic study 

 of steel. Thermomagnetic measurements make it in- 

 creasingly evident that tlie magnetic properties of 

 steels are frequently those of mixtures of magnetic 

 substances, each possessing characteristic properties, 

 which contribute in a comparatively definite way to 

 the properties of the material as a whole. In the case 

 of a simple ferromagnetic substance, magnetising 

 fields can be found in which the permeability variation 

 with temperature is small except in the neighbourhood 

 of the critical temperature. In such fields there is a 

 marked peak in the permeability temperature curve 

 for the substance. The explanation of this peak sug- 

 gests that the phenomenon should be found common 

 to all ferromagnetic substances. The paper shows 

 that it is exhibited by the carbide of iron (cementite) 

 in annealed carbon steels. 



Mineralogical Society, November 12. — Anniversary meet- 

 ing. — Dr. A. E. H. Tutton, F.R.S., president, in the 

 chair. — Prof. W. J. Lewis : Ilmenite from the Lengen- 

 bach Quarry. Imbedded in the dolomite was found a 

 minute crystal, irregular in habit, showing the forms 

 no, loi , 100, 112, III, 275. The best readings were 

 obtained from pairs of faces of 10 1 and between them 

 and faces of a prism, the corresponding angles being 

 found to be 64° 47' and 57° 33' respectively. — Prof. 

 W. J. Lewis: Multiple twin of cassiterite. Three- 

 fold twinning is well and regularly developed on 

 opposite sides of the crystal, which consists of two 

 main portions with twin axes all in one plane, and 

 the triplets so formed are connected together in a 

 somewhat irregular way. Further, some of the in- 

 dividuals are twinned along pyramid faces inclined 

 to the general plane, so that the back of the crystal 

 is unlike the front. — Arthur Russell : An account of 

 the minerals found in the Virtuous Lady Mine, near 

 Tavistock. The following species were met with : — 

 Chalybite, in pseudomorphs after fluor and b^rytes, 

 termed respectively "boxes" and "slippers" by the 

 miners; marcasite in sheaf-like aggregates; mispickel 

 in two modifications ; anatase, on one crystal of 

 which w-as found a small crystal of brookite, the only 

 one seen Ijy the author from this locality. — Dr. A. 

 Hutchinson : Some graphical methods in crystallo- 

 graphy and crystal optics. Diagrams of expressions 

 involving sines, such as sinE = ;3sinV, are much sim- 

 plified by taking log sines for coordinates, the result 

 being a series of parallel straight lines. — Dr. A. 

 Hutchinson and W. Campbell Smith : Labradorite from 

 St. John Point, co. Dow-n. The large fresh crystals 

 of felspar, which occur in a basaltic dyke, have 

 physical characters — specific gravity 2'7o6, extinction 

 on 010 and 001 —23° and —11° respectively, refractive 



