>46 



NA TURE 



[July 4, 1901 



may be seen the "pit-head frame," with the winding pulleys, 

 which was erected by the students. 



The Technical Education Board of the London County 

 Council is offering facilities for boys who are leaving, or have 

 recently left, public elementary schools to enter upon a course of 

 training which will fit them to become gardeners. A school of 

 practical gardening has been established at the Royal Botanic 

 Society, Regent's Park, and is now attended by some thirty 

 boys, most of whom are holding scholarships from the Technical 

 Education Board. The boys at this school go through a three- 

 years' course, in which they have a thorough training in prac- 

 tical gardening and also receive instruction in elementary science 

 and botany. The scholarships offered by the Board are open to 

 boys between the ages of fourteen and sixteen, whose parents are 

 resident within the County of London and are in receipt of in- 

 comes not exceeding 250/. a year. The scholarships provide 

 free tuition for three years at the School of Practical Gardening, 

 and also a maintenance grant rising from 20/. a year to 25/. a 

 year. There is no examination for these scholarships, but 

 parents are required to sign a declaration to the effect that 

 they intend their sons to become practical gardeners. Full 

 particulars of these scholarships, together with application 

 forms, may be obtained from the secretary of the Technical 

 Education Board, n6 St. Martin's Lane, W.C. Application 

 should be made not later than Monday, July 15. 



SCIENTIFIC SERIAL. 



Annalen der Physit, June. — On the parameters in the 

 physics of crystals and on directed magnitudes of higher order, 

 by W. Voigt. — On the change of the conductivity of salt 

 solutions in liquid sulphur dioxide with temperature up to the 

 critical point. Electrolytic conductivity in gases and vapours. 

 The absorption spectra of solutions with iodine salts, by A. 

 Hagenbach. Various alkaline salts, chiefly iodides, were dis- 

 solved in dry liquid sulphur dioxide and the conductivities 

 measured at temperatures up to and just above the critical 

 point. These salt solutions behave as electrolytes, even up to 

 the critical point. The fact that polarisation occurs, shows that 

 the electricity is conducted in the solution by means of ions. 

 The temperature coefficients are negative between the limits of 

 the experiments (from 20" to 160' C. ), with the exception of 

 potassium iodide, which shows a maximum of conductivity at 

 about 90'. In the conductivity curves Ihe critical temperature 

 is clearly shown, although there is no absolute discontinuity at 

 this point. Some interesting observations were made on the 

 stale of the dissolved solid when the liquid w'as just above the 

 critical point, as after the meniscus had vanished the resistance 

 of the vapour differed according as the electrodes were in the 

 upper or lower portion of the tube, this difference disappearing 

 immediately on shaking the tube. — On the second law of 

 thermodynamics, by N. Schiller. — The thermodynamics of 

 saturated solutions, by N. Schiller. — On an improved method 

 for the preparation of photographic plates sensitive to the ultra- 

 violet rays, by V. Schumann, A detailed description of the 

 methods of preparing the emulsion, coating and drying the 

 plates, exposure and development. An e.xample is given show- 

 ing the increased length of spectrum obtained with these plates 

 as compared with an ordinary dry plate. — On a mechanical 

 representation of the electrical and magnetic phenomena in 

 bodies at rest, by L. Graetz. — On changes of weight during 

 chemical and physical changes, by A. Heydweiller. Various 

 chemical reactions were carried out in closed vessels, and in 

 certain cases slight changes in weight were observed which, in 

 the opinion of the author, were outside the range of possible 

 experimental error. — Researches on electrical discharge in 

 rarefied gases, by W. Wien. — Experiments on the influence of 

 capillarity on the velocity of outflosv of liquids, by C. Christian- 

 sen. — Communication to the knowledge of the physical 

 properties of silver mirrors, by C. Grimm. A study of the 

 electrical resistance of thin silver mirrors under varying 

 conditions of temperature, light, degree of polish, &c. — C3n a 

 new experiment in dynamics, by V. v. Niesiolowski-Gawin. — 

 On the behaviour of liquid dielectrics on the passage of an 

 electric current, by E. v. Schweidler. — Stroboscopic methods 

 for the determination of the frequency of alternation and lag of 

 a motor, by G. Benischke. 



NO. 1653, VOL. 64] 



SOCIETIES AND ACADEMIES. 



Royal Society, June 6. — " On the Elastic Equilibrium o» 

 Circular Cylinders under Certain Practical Systems of Load." 

 By L. N. G. Filon, M.A., B.Sc, Research Student of King's 

 College, Cambridge ; Fellow of University College, London ; 

 1 85 1 Exhibition Science Research Scholar. Communicated by 

 Prof. Ewing, F.R.S. 



The paper applies the equations of elasticity to the investiga- 

 tion of problems connected with the circular cylinder. The 

 solutions are symmetrical about the axis of the cylinder, and 

 are obtained as infinite series involving circular and Bessel's 

 functions. 



The three problems treated of are as follows : — 



In the first a cylinder under pull is considered, the pull not 

 being applied by a uniform distribution of tension across the 

 plane ends, but by a given distribution of axial shear over two 

 zones or rings towards the ends of the cylinder. 



This corresponds to conditions which frequently occur in 

 tensile tests, namely, when the piece is gripped by means of 

 projecting collars, the pull being in this case transmitted from 

 the collar to the body of the cylinder by a system of axial 

 shears. 



It is found that the stress is greatest at the points where the 

 shear is discontinuous, i.e. at the ends of the collar in a prac- 

 tical case. At these points it is theoretically infinite. For a 

 short cylinder the tensile stress varies a great deal over the 

 cross-section and the distortion of the latter is large. 



The second problem is that of a short cylinder compressed 

 longitudinally between two rough rigid planes, in such a manner 

 that the ends are not allowed to expand. It illustrates the 

 crushing of blocks of cement or stone between iron planes or 

 sheets of millboard. 



The greatest stress occurs at the perimeter of the plane ends 

 and the " strength " is less than two-thirds of the strength under 

 uniform compression. This result apparently contradicts the 

 fact that the strength of stone or cement, when tested between 

 lead plates, which allow of expansion, is very much less than 

 when tested between millboards ; but if we take into account 

 the consideration suggested by Unwin (" Testing of Materials of 

 Construction," p. 419) and corroborated by Prof. Ewing, that 

 lead, which flows easily, may not merely allow, but force the 

 expansion of the ends of the block, then it is shown that in tests 

 between lead plates the strength may be much less than between 

 millboards ; moreover, such tests are indeterminate. The mill- 

 board test should give consistent results, though really intro- 

 ducing too large a factor of safety. The change in the form of 

 the fracture noticed by Unwin is also confirmed by theory. 



The third problem is that of the torsion of a bar in which the 

 stress is applied, not by cross-radial shears over the flat ends, 

 as the ordinary theory of torsion assumes, but by transverse 

 shears over the curved surface. This corresponds to the case of 

 a shaft or axle twisted by a frictional couple. 



It is shown that the points of danger are those where the 

 applied shear changes discontinuously. At a distance from 

 these the solution rapidly degenerates into the ordinary type. 



Physical Society, June 2S. — Prof. Everett, F. K.S., vice- 

 president, in the chair.— A paper on the effect of a high frequency 

 oscillatory field on electrical resistance was read by Mr. S. A. F. 

 White. The object of this paper is to discover if the action of 

 light upon the electrical resistance of selenium can be imitated 

 by using high frequency electrical oscillations. It is found that 

 such oscillations permanently increase the resistance of selenium. 

 The effect of a rise of temperature is to increase the resistance 

 of a piece of low resistance and decrease the resistance of a piece 

 of high resistance. The effects of the field in a piece of high 

 resistance can be reversed by exposure to light or by reheating 

 and subsequent cooling. In the case of tellurium a high fre- 

 quency field temporarily decreases the resistance, as also does a 

 rise in temperature. Repeated heating and cooling of a piece 

 of tellurium permanently increases its resistance. It seems pro- 

 bable that all of the effects are due to rise of temperature 

 caused by minute sparks within the mass. The rise in resist- 

 ance by alternate heating and cooling may be due to the for- 

 mation of tellurides with the metal of the electrodes. The large 

 negative temperature effect of tellurium suggests that it might be 

 usefully employed in the detection of heat radiation. The 

 chairman expressed his interest in the paper and drew attention 



