On the force between two coaxial single layer helices carrying current

General Description ◽

Physical Laboratory ◽

The following is an abstract of a paper bearing the above title which is being printed in the Collected Researches of the National Physical Laboratory , vol. 24. The detailed calculations are very long and of interest to only a few persons. The result, however, is of importance to all interested in the absolute measurement of an electric current; it seemed desirable therefore to put it on record, to give a general description of the method employed with its limitations, and to indicate where full particulars may be found.

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

Comparison of the acceleration due to gravity at the National Physical Laboratory, Teddington, the Bureau International des Poids et Mesures, Sèvres, the Physikalisch-Technische Bundesanstalt, Brunswick, and the Geodetic Institute, Potsdam

10.1098/rspa.1952.0135 ◽

1952 ◽

Vol 213 (1114) ◽

pp. 408-424 ◽

Cited By ~ 7

Keyword(s):

Absolute Value ◽

Geodetic Institute ◽

Physical Laboratory ◽

The values of gravity at these stations have been compared by means of pendulum observations with Invar invariable pendulums. The observed differences of gravity from the National Physical Laboratory are: B. I. P. M. -256·73 ± 0·49 mgal P. T. B. + 68·68 ± 0·49 mgal Bad Harzburg - 15·68 ± 0·49 mgal The accuracy of the measurements is not so great as has been achieved once or twice previously with the same apparatus, mainly because the changes in the lengths of the pendulums were greater than usual. These differences have been combined with German pendulum observations and with gravimeter comparisons with the following results: Value of gravity at N. P. L. on the Potsdam system: 981196·29 ± 0·3 mgal. Differences between sites of absolute determinations of gravity: N. P. L. - B. I. P. M. +256·45 ± 0·3 mgal N. P. L. - P. T. B. - 68·98 ± 0·3 mgal P. T. B. - Potsdam - 8·95 ± 0·4 mgal ( g at Potsdam = 981274 mgal.) The effects of these results on gravity surveys based on Cambridge and on the absolute value of gravity are indicated.

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

On the determination of the absolute unit of resistance by alternating current methods

10.1098/rspa.1912.0094 ◽

1912 ◽

Vol 87 (597) ◽

pp. 391-414 ◽

Cited By ~ 4

Keyword(s):

Lower Order ◽

Alternating Current ◽

Mutual Inductance ◽

Electrical Circuits ◽

Physical Laboratory ◽

Absolute Measure ◽

The Absolute ◽

Set Up

1. Introductory .—Recently at the National Physical Laboratory we have constructed a standard of mutual inductance of novel type, whose value has been accurately calculated from the dimensions. This inductance has formed the basis for the determination of the unit of resistance in absolute measure by two different methods, in both of which alternating current is employed. Although there is no doubt that the accuracy attainable by these methods could be increased by greater elaboration of the apparatus used, the results already obtained seem to be of sufficient interest to warrant publication. It should be mentioned that the accuracy here aimed at was of a considerably lower order than that contemplated in the determination of the ohm by the Lorenz apparatus which is at present being carried out in the laboratory. For the experiments here described, no apparatus was specially constructed, but use was made of instruments which had already been designed and set up for the measurement of inductance and capacity. I shall first give a brief description of the standard inductance and then pass on to the methods and results. 2. Standard Mutual Inductance .—The design of the mutual inductance has already been described. The electrical circuits have the form and arrangement shown in section in fig. 1.

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

The absolute measurement of resistance by the method of Albert Campbell

10.1098/rsta.1937.0007 ◽

1937 ◽

Vol 236 (769) ◽

pp. 423-471 ◽

Cited By ~ 12

Keyword(s):

Electric Current ◽

Electrical Resistance ◽

Glass Tube ◽

Absolute Measurement ◽

Cross Sectional Area ◽

Precision Measurements ◽

Sectional Area ◽

Cross Sectional ◽

The Absolute ◽

London Conference

Throughout the last 25 years nearly all precision measurements of electrical resistance have been expressed in terms of the International Ohm, a unit which was defined by the London Conference of 1908 (Glazebrook, 1922-3) as follows : “ The International Ohm is the resistance offered to an unvarying electric current by a column of mercury at the temperature of melting ice, 14.4521 grammes in mass, of a constant cross-sectional area, and of a length of 106.300 centimetres". Any measurement in terms of this unit is dependent on experiments in which a glass tube, the dimensions of which have been accurately measured, is

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

Calculation of a primary standard of mutual inductance of the Campbell type and comparison of it with the similar N. P. L. standard

10.1098/rspa.1922.0047 ◽

1922 ◽

Vol 101 (711) ◽

pp. 315-332 ◽

Cited By ~ 5

Keyword(s):

Primary Standard ◽

Single Layer ◽

Alternating Current ◽

Mutual Inductance ◽

Secondary Coil ◽

Physical Laboratory

The standard mutual inductance devised and designed by Mr. A. Campbell and constructed in 1907-8 at the National Physical Laboratory has been one of the foundations of our alternating current measurements since that date. It will be sufficient here to note that the special feature in the design of the Campbell type of mutual inductance consists in a primary single-layer winding, so proportioned that the field due to it is practically zero over the region occupied by the secondary coil. By this means the dimensions of the secondary coil are rendered relatively unimportant, so that it may be an overwound many-layer winding, whereby a suitably large value of mutual inductance may be obtained.

THE GRAVITY METER AS A GEODETIC INSTRUMENT

Geophysics ◽

10.1190/1.1437572 ◽

1950 ◽

Vol 15 (1) ◽

pp. 1-29 ◽

Cited By ~ 18

Author(s):

George Prior Woollard

Keyword(s):

Base Stations ◽

Absolute Gravity ◽

Naval Research ◽

Absolute Value ◽

Office Of Naval Research ◽

Physical Laboratory ◽

The World ◽

Before And After ◽

A special Worden temperature compensated gravity meter having a range of 5,500 mgals, and a reading sensitivity of 0.1 mgal was used to tie together various primary gravity base stations around the world and to establish new stations. Air transport was used and in a 3 month period over 80,000 miles were flown. Thirty‐three pendulum stations were reoccupied involving a change in gravity of 3,800 mgals, and 125 gravity stations were established. The investigation demonstrated that this instrument could be used satisfactorily for long range geodetic work and the results appear to be the equal of good pendulum observations. Drift was corrected for on the basis of the drift rate established immediately before and after flights. Closures after correcting for drift averaged less than 0.4 mgals, and the closure for the world girdling loop was 0.33 mgals. The probable error based upon the gravity values at the reoccupied pendulum station was ±0.5 mgals. Reoccupation of the absolute gravity stations at the U. S. Bureau of Standards in Washington, D. C. and the National Physical Laboratory in Teddington, England, indicated an approximate 5 mgal error in these pendulum determinations. Indirect ties to the absolute gravity base in Potsdam, Germany, through the primary national gravity bases tied to it, indicated a 15 to 19 mgal error in the Potsdam absolute value. Most of the primary national gravity bases tied directly to Potsdam were found to agree among themselves to within 1 mgal, and the U. S. Bureau of Standards Absolute Base in Washington, D. C. to have a perfect connection within the limits of accuracy of the present measurements. This investigation was made under the auspices of the Office of Naval Research.

The Absolute Determination of Gravity at the National Physical Laboratory

Metrologia ◽

10.1088/0026-1394/5/4/008 ◽

1969 ◽

Vol 5 (4) ◽

pp. 141-142 ◽

Cited By ~ 8

Author(s):

A H Cook ◽

J A Hammond

Keyword(s):

Absolute Determination ◽

Physical Laboratory ◽

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

Comparison of the acceleration due to gravity at the National Laboratory, Teddington and the Bureau of Standards, Washington, D. C

10.1098/rspa.1940.0047 ◽

1940 ◽

Vol 175 (960) ◽

pp. 110-117 ◽

Cited By ~ 7

Keyword(s):

Electric Current ◽

Standard Error ◽

National Laboratory ◽

National Bureau ◽

International Union ◽

Recent Meeting ◽

Physical Laboratory ◽

The World ◽

Acceleration Of Gravity

For many years values of gravity all over the world have been obtained relative to that at Potsdam by observations with invariable pendulums. The value at Potsdam was determined by Kühnen and Furtwängler (1906) by Kater’s method and a standard error of 0.003 cm./sec. 2 was claimed for the result. Any error in the Potsdam value would involve an equal error in the related values all over the world. As the acceleration of gravity is involved in all measurements of force with the balance and thus in the unit of electric current and in such quantities as the velocity of an α -particle, it is important to know whether the accepted value at Potsdam has the accuracy claimed for it. A recent absolute determination by Heyl and Cook (1936) at the National Bureau of Standards, Washington, D.C., gave a result 0.020 cm./sec. 2 less than that obtained by comparison with Potsdam, whilst one by Clark at the National Physical Laboratory, Teddington gave 0.013 8 cm./sec. 2 less. The relative gravity connexion between Potsdam and Washington is strong, but those between Teddington and Washington and between Teddington and Potsdam are weak and indirect. Advantage has therefore been taken of the visit of the authors to Washington to attend the recent meeting of the International Union of Geodesy and Geophysics to make a comparison of the values of g at the places used for the absolute determinations at the National Physical Laboratory and at the National Bureau of Standards. It had been intended also to connect the National Physical Laboratory directly with Potsdam, but the outbreak of war has made it necessary for this to be postponed.