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The thermal stresses in solid and in hollow circular cylinders concentrically heated
Nov., I922.] NOTES FROM NELA RESEARCH LABORATORIES.
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favorable conditions a wave-length of o.8 mm. has been observed. The known electric wave spectrum has thus been extended toward shorter waves by an interval of from two to three octaves. THE OPTICAL CONSTANTS OF CERTAIN LIQUIDS FOR SHORT ELECTRIC WAVES. By J. D. Tear.
[ABSTRACt.] IN crossing the hitherto unexplored region of the spectrum extending from the extreme infra-red to the shortest electric waves, the reflection and absorption coefficients and the indices of refraction of a number of liquids undergo unusual changes. A notable example is water which for ho. 3 mm. has an index near that for the visible region of the spectrum, but for h3 o mm. has a refractive index of 8.5, which is very nearly that for an infinite wave-length, i.e., the square root of the dielectric constant. Experiments, described in the preceding abstract, 1 are now in progress which, it is hoped, will ultimately make a more complete exploration of this region possible. With the present equipment and methods the optical constants of a number of liquids, i.e., water, glycerin, methyl and ethyl alcohol for the wave-lengths 4, 8, I I, I8, and 2 7 mm., have been determined. The refractive indices have been computed by the CauchyQuincke formula from measured values of the coefficients of reflection and absorption. A second approximate, though direct determination of the refractive index, has been obtained by measuring the combined reflection from both surfaces of a thin liquid layer floated on mercury. As the thickness of the layer is varied, interference effects cause the reflected energy to pass through a series of maxima and minima which give a direct measurement of the wave-length in the liquid which divided into the wavelength in air gives the refractive index. The results obtained by these two methods are in good agreement. T h e T h e r m a l S t r e s s e s in Solid and in H o l l o w Circular Cylinders C o n c e n t r i c a l l y Heateck CHARLESH. LEES. (Proc. Royal Soc.,
A 7.I2).--" The large differences of temperature which exist between the inside and outside of the heating or firingtunnels used in pottery and • E. F. Nichols and J. D. Tear, " Short Elecrtic Waves."
686
CURRENT TOPICS.
[J. F. I.
other works, and between the inner and outer portions of the concrete or masonry pillars supporting the floors of a building in which a fire occurs, make the thermal stresses approach the breaking strength of the materials and they are crushed or torn asunder." These stresses have hitherto been calculated only under the assumption of certain limiting simplifications. The author solves the problem in a more general way and shows " that for any temperature distribution, with any law of expansion, the stresses may be found by a simple graphical method so long as the variation of the elastic constants with the temperature may be neglected." After the problem has been solved the solution is applied to definite cases occurring in industry such as the putting out of service of a pottery kiln. " The sudden cooling of the interior of a furnace such as that described above will therefore subject the interior of the wall to tensile stresses in both longitudinal and tangential directions much above the tensile s[rength of the material, and radial cracks will be produced at the inner surface, which, since the stresses are equal in the two directions, will run indiscriminately longitudinally and tangentially. Through the kindness of Sir Robert Hadfield I have been able to inspect the walls of furnaces which have been in use for various periods at the Hecla Works, Sheffield, and I find that the above results are confirmed by experience." An explanation is furnished also of the cracks which exist within columns that have been subjected to fire and which do not show themselves at the surface. This paper will in the future be used in the design of structures. G. F. S.
The Dielectric C o n s t a n t of Mica. J. R, WEEKS, JR. (Phys. Rev., April, I922).--Eighteen samples of mica of twelve different grades were measured. For sheets without visible air films the value of the constant was found to range from 6.4 to 9.3. Sheets having included air films seemed to give values from 2. 9 to 5.6. Thin sheets split from the sample which had given 2. 9 were measured and the results varied from 6.6 to 8.4. Other similar experiments confirm the belief that the low results are to be attributed to the presence of air. Thus is probably explained the wide divergence between values of the dielectric constant of mica given in handbooks. ' G.F.S.
The Departure from Ohm's Law in Gold and Silver at High C u r r e n t Densities. P. W. BRIDGMAN. (Phys. Rev., April, 1922 ) . - A method has been devised of attaining current densities of 5,000,000 amperes per sq. cm. along with the possibility of correcting the resistance for the increase of temperature. With these high current densities the resistance was found to increase about I per cent., the proportional increase being larger in tlaick than in thin gold and also greater for gold than for silver. G.F.S.
68 5
favorable conditions a wave-length of o.8 mm. has been observed. The known electric wave spectrum has thus been extended toward shorter waves by an interval of from two to three octaves. THE OPTICAL CONSTANTS OF CERTAIN LIQUIDS FOR SHORT ELECTRIC WAVES. By J. D. Tear.
[ABSTRACt.] IN crossing the hitherto unexplored region of the spectrum extending from the extreme infra-red to the shortest electric waves, the reflection and absorption coefficients and the indices of refraction of a number of liquids undergo unusual changes. A notable example is water which for ho. 3 mm. has an index near that for the visible region of the spectrum, but for h3 o mm. has a refractive index of 8.5, which is very nearly that for an infinite wave-length, i.e., the square root of the dielectric constant. Experiments, described in the preceding abstract, 1 are now in progress which, it is hoped, will ultimately make a more complete exploration of this region possible. With the present equipment and methods the optical constants of a number of liquids, i.e., water, glycerin, methyl and ethyl alcohol for the wave-lengths 4, 8, I I, I8, and 2 7 mm., have been determined. The refractive indices have been computed by the CauchyQuincke formula from measured values of the coefficients of reflection and absorption. A second approximate, though direct determination of the refractive index, has been obtained by measuring the combined reflection from both surfaces of a thin liquid layer floated on mercury. As the thickness of the layer is varied, interference effects cause the reflected energy to pass through a series of maxima and minima which give a direct measurement of the wave-length in the liquid which divided into the wavelength in air gives the refractive index. The results obtained by these two methods are in good agreement. T h e T h e r m a l S t r e s s e s in Solid and in H o l l o w Circular Cylinders C o n c e n t r i c a l l y Heateck CHARLESH. LEES. (Proc. Royal Soc.,
A 7.I2).--" The large differences of temperature which exist between the inside and outside of the heating or firingtunnels used in pottery and • E. F. Nichols and J. D. Tear, " Short Elecrtic Waves."
686
CURRENT TOPICS.
[J. F. I.
other works, and between the inner and outer portions of the concrete or masonry pillars supporting the floors of a building in which a fire occurs, make the thermal stresses approach the breaking strength of the materials and they are crushed or torn asunder." These stresses have hitherto been calculated only under the assumption of certain limiting simplifications. The author solves the problem in a more general way and shows " that for any temperature distribution, with any law of expansion, the stresses may be found by a simple graphical method so long as the variation of the elastic constants with the temperature may be neglected." After the problem has been solved the solution is applied to definite cases occurring in industry such as the putting out of service of a pottery kiln. " The sudden cooling of the interior of a furnace such as that described above will therefore subject the interior of the wall to tensile stresses in both longitudinal and tangential directions much above the tensile s[rength of the material, and radial cracks will be produced at the inner surface, which, since the stresses are equal in the two directions, will run indiscriminately longitudinally and tangentially. Through the kindness of Sir Robert Hadfield I have been able to inspect the walls of furnaces which have been in use for various periods at the Hecla Works, Sheffield, and I find that the above results are confirmed by experience." An explanation is furnished also of the cracks which exist within columns that have been subjected to fire and which do not show themselves at the surface. This paper will in the future be used in the design of structures. G. F. S.
The Dielectric C o n s t a n t of Mica. J. R, WEEKS, JR. (Phys. Rev., April, I922).--Eighteen samples of mica of twelve different grades were measured. For sheets without visible air films the value of the constant was found to range from 6.4 to 9.3. Sheets having included air films seemed to give values from 2. 9 to 5.6. Thin sheets split from the sample which had given 2. 9 were measured and the results varied from 6.6 to 8.4. Other similar experiments confirm the belief that the low results are to be attributed to the presence of air. Thus is probably explained the wide divergence between values of the dielectric constant of mica given in handbooks. ' G.F.S.
The Departure from Ohm's Law in Gold and Silver at High C u r r e n t Densities. P. W. BRIDGMAN. (Phys. Rev., April, 1922 ) . - A method has been devised of attaining current densities of 5,000,000 amperes per sq. cm. along with the possibility of correcting the resistance for the increase of temperature. With these high current densities the resistance was found to increase about I per cent., the proportional increase being larger in tlaick than in thin gold and also greater for gold than for silver. G.F.S.