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Gravitation anisotropy in crystals
NOTES
FROM
THE
U. S. B U R E A U
OF STANDARDS.*
GRAVITATION ANISOTROPY IN CRYSTALS# By Paul R. Heyl.
[A~STRACT.] EINSTEIN'S theory of gravitation is based upon a fundamental postulate which he calls thq principle of equivalence, and which asserts that gravitation and inertia are identical in nature, and hence indistinguishable. This, if true, is of the greatest theoretical importance, for gravitation has steadily refused to show any kinship to other physical phenomena. Einstein's justification for this postulate was found in the gravity pendulum experiments of Newton and Bessel, and the torsion pendulum experiments of E6tv6s, the results of which established to a high degree of precision (about I part in 2oo,ooo,ooo) that the inert mass and the gravitational mass of a body were proportional, or, in other words, that gravitation is independent of the nature of the matter acted upon. A still more delicate test of this postulate is possible in a crystal of one of the non-isometric systems; for in such a crystal every known physical property (except inertia, and possibly weight) varies with the axial direction in the crystal. It is therefore an interesting question whether, in such a crystal, gravitation will be found to align itself with inertia or will show some variability which will classify it with the great majority of physical phenomena. If, for example, such a crystal be weighed in different axial orientations with respect to the earth (which may be done with great precision) and any difference in weight be found in the different positions, Einstein would be wrong. T o test this point, crystals weighing a kilogram or more were thus weighed, the specimens coveringall five non-isometric crystalline systems. The precision reached, in nearly every case, was one part in a billion (lO9). T o this degree of precision no difference in weight was detected; the results have failed to prove Einstein wrong. * Communicated by the Director. Scientific Papers, No. 482, price ten cents. 691
692
U.S.
BUREAU OF STANDARDS NOTES.
[J.F.I.
Incidentally, this work has shown the practical possibility of using the gravity balance to a precision of I part in Io 9 even when the swing of the beam must be stopped and the object turned through a considerable angle. This improved precision was reached by the use of the almost neglected Poynting clamp, which permits the arrest of the beam and the changing of the load without raising the knife-edge or altering the state of flexure of the beam. A precision of about the same order was attained by Majorana in I92o. In this work it was not necessary to arrest the beam or to touch the load. The next best record (in work of a somewhat different kind) at the International Bureau of Weights and Measures is 7 parts in Io 9. THE PREPARATION AND PROPERTIES OF PURE IRON A L L O Y S : IV. D E T E R M I N A T I O N O F T H E C R I T I C A L R A N G E S OF P U R E I R O N - C A R B O N A L L O Y S BY T H E T H E R M O ELECTRIC METHOD? By J. F. T. Berliner.
[ABsa~ACr.] THE object of this investigation was to determine the critical ranges of pure iron-carbon alloys by means of the thermoelectric method. The material used was a very pure series of iron-carbon alloys prepared at the Bureau of Standards. For the purpose of this work the steel specimens were cold drawn to wires of about o.o 7 cm. diameter. The method used was practically the same as that employed by Burgess and Scott in 1916 (see B. S. Sci. Paper No. 296 ) which was a modification of that of Le Chatelier's. The steel wire specimen had each of its ends welded to the hot junction, of a platinum; platinum-rhodium thermocouple. The thermocouple gave the temperature at the ends of the wire, while the platinum wires of each thermocouple were used as leads from the specimen and gave the e.m.f, reading. The thermo-eleetrie power was measured at intervals of 2 ° C. from room temperature up to II5O ° C. The temperature difference between the ends of the wire specimen was usually less than 12 ° C. 2Scientific Papers, No. 484, price five cents.
FROM
THE
U. S. B U R E A U
OF STANDARDS.*
GRAVITATION ANISOTROPY IN CRYSTALS# By Paul R. Heyl.
[A~STRACT.] EINSTEIN'S theory of gravitation is based upon a fundamental postulate which he calls thq principle of equivalence, and which asserts that gravitation and inertia are identical in nature, and hence indistinguishable. This, if true, is of the greatest theoretical importance, for gravitation has steadily refused to show any kinship to other physical phenomena. Einstein's justification for this postulate was found in the gravity pendulum experiments of Newton and Bessel, and the torsion pendulum experiments of E6tv6s, the results of which established to a high degree of precision (about I part in 2oo,ooo,ooo) that the inert mass and the gravitational mass of a body were proportional, or, in other words, that gravitation is independent of the nature of the matter acted upon. A still more delicate test of this postulate is possible in a crystal of one of the non-isometric systems; for in such a crystal every known physical property (except inertia, and possibly weight) varies with the axial direction in the crystal. It is therefore an interesting question whether, in such a crystal, gravitation will be found to align itself with inertia or will show some variability which will classify it with the great majority of physical phenomena. If, for example, such a crystal be weighed in different axial orientations with respect to the earth (which may be done with great precision) and any difference in weight be found in the different positions, Einstein would be wrong. T o test this point, crystals weighing a kilogram or more were thus weighed, the specimens coveringall five non-isometric crystalline systems. The precision reached, in nearly every case, was one part in a billion (lO9). T o this degree of precision no difference in weight was detected; the results have failed to prove Einstein wrong. * Communicated by the Director. Scientific Papers, No. 482, price ten cents. 691
692
U.S.
BUREAU OF STANDARDS NOTES.
[J.F.I.
Incidentally, this work has shown the practical possibility of using the gravity balance to a precision of I part in Io 9 even when the swing of the beam must be stopped and the object turned through a considerable angle. This improved precision was reached by the use of the almost neglected Poynting clamp, which permits the arrest of the beam and the changing of the load without raising the knife-edge or altering the state of flexure of the beam. A precision of about the same order was attained by Majorana in I92o. In this work it was not necessary to arrest the beam or to touch the load. The next best record (in work of a somewhat different kind) at the International Bureau of Weights and Measures is 7 parts in Io 9. THE PREPARATION AND PROPERTIES OF PURE IRON A L L O Y S : IV. D E T E R M I N A T I O N O F T H E C R I T I C A L R A N G E S OF P U R E I R O N - C A R B O N A L L O Y S BY T H E T H E R M O ELECTRIC METHOD? By J. F. T. Berliner.
[ABsa~ACr.] THE object of this investigation was to determine the critical ranges of pure iron-carbon alloys by means of the thermoelectric method. The material used was a very pure series of iron-carbon alloys prepared at the Bureau of Standards. For the purpose of this work the steel specimens were cold drawn to wires of about o.o 7 cm. diameter. The method used was practically the same as that employed by Burgess and Scott in 1916 (see B. S. Sci. Paper No. 296 ) which was a modification of that of Le Chatelier's. The steel wire specimen had each of its ends welded to the hot junction, of a platinum; platinum-rhodium thermocouple. The thermocouple gave the temperature at the ends of the wire, while the platinum wires of each thermocouple were used as leads from the specimen and gave the e.m.f, reading. The thermo-eleetrie power was measured at intervals of 2 ° C. from room temperature up to II5O ° C. The temperature difference between the ends of the wire specimen was usually less than 12 ° C. 2Scientific Papers, No. 484, price five cents.