This paper is an extension and revision of a previous paper by Rosa and Cohen. It is now by far the most complete and thorough study of the subject that has yet been published. The authors have taken great pains to bring it thoroughly up to date, and have made a critical study of nearly all the recent papers on the subject. The comparisons of the results obtained by various authors and the invcstigations of the convergence of the various series that have been proposed have cleared up the whole...

Topics: inductance, Condensed matter, electronic structure, electrical, magnetic, and optical properties

specific heat and latent heat; Heat flow, thermal and thermodynamic processes

Topic: USA

The authors first give a complete proof of Maxwell's formula for the mutual inductance between concentric coaxial solenoids of equal length. They then deduce Roiti's formula very simply by means of Maxwell's equations. The formulae of Gray, Searle, Himstedt, and Cohen are discussed. Cohen's formula is very laborious to evaluate, but it is useful in the special cases where the other formulae converge slowly, and when it is necessary to test their accuracy. The authors point out that Russell has...

Topics: electromagnetic induction, Electrical instruments and techniques

electrical conductivity; Medical and biomedical uses of fields, radiations, and radioactivity; health physics

Topic: USA

The two formulae employed by Coffin give results in very close agreement, and the only question remaining is whether the two closely-agreeing formulae are as accurate when applied to the coil in question as they appear to be. In deriving the formulae the current is supposed to be uniformly distributed over the surface of the cylinder, whereas the coil is actually wound with 661 turns of round wire having a diam. of 0.0634 cm. and insulated by a covering 0.0030 cm. thick. The author shows that...

Topics: electromagnetic induction, Electrical instruments and techniques

The specific heat of chemically pure copper between 0 degrees and 50 degrees C. has been redetermined with precision on account of its importance in some determinations of the mechanical equivalent of heat which are being undertaken, the thermal capacity of the copper in these experiments amounting to 1 or 2 % of the whole. A new method is adopted in which 50 m, of copper, wire 2.5 mm. in diam. serves the fourfold function of being the test specimen, the calorimeter itself, the heater, and the...

Topics: specific heat and latent heat, Heat flow, thermal and thermodynamic processes

Formulae for the self and mutual inductances of straight wires and rectangles are to be found in various books and papers, but their demonstrations are usually omitted, and approximate formulae are often given as though they were exact. The author derives the expressions very simply from Laplace's formula instead of using Neumann's formula, and thus gives a much better physical view of their meaning. He also deduces some interesting new formulae. The assumption is made that the magnetic field...

Topics: inductance, Condensed matter, electronic structure, electrical, magnetic, and optical properties

The object of the investigation is the determination of the monochromatic emissivity for a wave-length lambda = 0.65 mu, and the total emissivity of iron oxide formed by heating iron in air. Several methods were tried, but the only one giving satisfactory results was that of the "microscopic melts." A small sample of the oxide is placed on a Ni or Pt strip heated electrically. Upon the oxide are placed minute pieces of sodium chloride, sodium sulphate, and gold. At the instant of...

Topics: rays and radiation, Heat flow, thermal and thermodynamic processes

When it is desired to determine the resistivity of a fairly large portion of earth extending to a considerable depth, and it is not possible to disturb the portion of the earth to be measured, the following method is applicable. Four holes, 1, 2, 3, 4, are made in the earth approximately uniformly spaced in a straight line. The diam, of the holes is not more than 10% of the distance /b a/ between them, and all holes extend to approximately the same depth /b b/, usually that depth at which we...

Topic: measurements and use of instruments/ B8000 Power systems and applications

The authors have adapted (1) the continuous-flow calorimeter, and (2) the vacuum-jacketed (Dewar flask) calorimeter to the determination of specific heats of liquids over a temperature-range of a few degrees in the interval between -35 degrees and 20 degrees , measurement of temperature being made by Pt-resistance thermometers, and heat being supplied electrically and measured accurately by the potentiometer method. By the use of the flow calorimeter an accurate determination of the...

Topics: measurements and use of instruments, specific heat and latent heat, Heat flow, thermal and...

A very thorough examination is made of the various formulae which have been proposed from time to time for calculating the mutual inductance of two circular coils of rectangular section. Numerous numerical calculations are made by the various formulae. It is pointed out which are the most accurate and where some of them fail. New formulae are deduced which are more convenient in special cases. Curves are drawn showing the relative accuracy of various formulae for particular coils at varying...

Topics: electromagnetic induction, Electrical instruments and techniques

Topics: inductance, Electrical instruments and techniques

A description of electromagnet moving-coil galvanometers for measurements on alternating currents and a presentation of the theory of their action. From the equations of motion of a coil carrying an alternating current in an alternating magnetic field it is shown that the deflection thetas = GE cos [ beta /(RU)], where G is the rate of change with the deflection of the effective value of the flux, E the effective value of the impressed e.m.f., beta the angle of lead of the impressed e.m.f....

Topics: apparatus and instruments, measurements and use of instruments, Condensed matter, electronic...

A method of testing instrument transformers by means of ordinary commercial testing instruments is described. It has to be remembered that from the practical point of view we need only take account of these errors in ratio or phase angle which produce a visible error in the reading of the indicating wattmeter. A wattmeter is taken and used in such a way that differences in ratio or phase angle of the transformer being tested and a standard transformer may be most readily detected. The method is...

Topics: transformers, rotary converters and boosters, measurements and use of instruments/ B8300 Power...

A full account giving all details.

Topic: apparatus and instruments/ B8000 Power systems and applications

As a result of the investigation of various liquids for use as standards in the calibration of viscometers of several forms, it is concluded that mixtures of 20, 40, and 60% ethyl alcohol in water (by weight), and solutions of 20, 40, and 60% of surcrose are the most suitable. Tabulated values of the viscosities and fluidities of these liquids from 0 degrees to 100 degrees C. at intervals of 10 deg. C. are given. From the curves of fluidities given it is considered that, owing to their simple...

Topics: viscosity, General Physics

The author first gives Weinstein's and Stefan's formulae for the self-inductance of a circular coil of wire of rectangular section. The method of calculating the correction for the self-inductance of insulated round wire is next considered, and Maxwell's correction, which has been re-computed by Chree, is adopted. Maxwell stated that the geometrical mean distance of two squares side by side is 0.99401 times the distance between their centres. The author, by calculating on the lines laid down by...

Topics: electromagnetic induction, measurements and use of instruments, Electrical instruments and...

The most obvious method of directly determining the inductance of a coil is that originally proposed by Joubert, and consists in first determining the impedance of the coil and then finding the ohmic resistance of the wire and the frequency of the current employed. In a variation of this method, described by Gray, a non-inductive resistance is placed in series with the coil whose inductance is to be measured, and an alternating current passed through both. By means of an electrometer the...

Topics: measurements and use of instruments, Condensed matter, electronic structure, electrical, magnetic,...

After a consideration of the meaning of plastic as compared with viscous flow, the author goes on to describe experiments made to determine the laws governing the former. The different types of viscous and plastic flow are discussed theoretically. In the case of mixtures, according to circumstances the viscosities of the components may be additive, the fluidities may be additive (a special case of this is the suspension of solid in a fluid), or slipping or seepage may take place to modify the...

Topics: elasticity, viscosity, General Physics

In magnetic measurements made at the Bureau of Standards it has been found that the heating effect of the current, employed to produce fields of 100 to 300 gauss, changes appreciably the value of the induction for a given field. The usual practice, when an accuracy of 1 % is desired, has been to immerse the coil in an oil bath maintained at a constant temperature of 25 degrees . The object of the present investigation is to determine the magnitude of the temperature effect and to see whether it...

Topics: magnetism, Magnetic properties and materials A4100 Electricity and magnetism, fields and charged...

Methods of measuring very high resistances are discussed, diagrams being given showing how they may be applied to the measurement of volume resistivity and surface resistivity. The volume resistivities of more than 60 materials are tabulated. The effects of humidity of the air, temperature, and the magnitude and time of application of the impressed voltage, are discussed. The surface resistivity is shown to be due to a surface film, usually of water or oil, on the insulator. This is generally...

Topics: dielectric materials, insulation and insulators, Condensed matter, electronic structure,...

The freezing-point of mercury was determined by means of resistance thermometers calibrated at 0 degrees , 100 degrees , and the sulphur boiling-point (444.6 degrees at normal pressure). Various precautions were observed to avoid errors due to impurities in the mercury, conduction along the leads, and the heating effect on the thermometers of the measuring current. The mean value - 38.873 degrees C. was obtained for the freezing-point, the max. deviation of any determination from the mean being...

Topics: freezing, melting and boiling points, Heat flow, thermal and thermodynamic processes

The temperature-entropy diagram is much inferior to the Mollier diagram for the quantitative solution of problems in steam-turbine design. Willard Gibbs suggested using a surface with entropy, pressure, and total heat as co-ordinates; the Mollier diagram is a projection of this surface on the pressure plane, and thus has entropy and total heat as co-ordinates. The total energy equation for steady motion of a liquid is given, and the conception of total heat, which is sensibly equal to...

Topic: steam engines/ B8230E Steam power stations and plants

After giving a brief review of previous determinations of the latent heat of fusion of ice, the authors describe in detail their investigation of this constant by two independent calorimetric methods. The first of these is the ordinary method of mixtures, the temperature measurements in which are made by means of sensitive Pt-thermometers, and the corrections inherent in the method very carefully determined; the second is an electrical method, in which the electrical heating serves to reduce...

Topics: specific heat and latent heat, Heat flow, thermal and thermodynamic processes

Modern instrument transformers have such good characteristics that it is not easy to determine their constants by using wattmeters or watt-hour meters in both primary and secondary circuits. The small differences to be measured are masked by errors of measurement, and such a method is not applicable to high voltages or large current-ranges. A modern induction watt-hour meter, however, can be used to determine /b difference/ in ratios and /b difference/ in phase angles between two voltage- or...

Topics: measurements and use of instruments, transformers, rotary converters and boosters/ B8300 Power...

The densities of copper sulphate-sulphuric acid solutions of varying concentrations have been determined at 25 degrees and 40 degrees . The concentrations of the solutions varied from 50 gm, to 300 gm. of total solute per kg. of solution. Within the range studied the density of the solutions is approximately a linear function of the concentration. The densities of solutions of equal-weight (not equivalent) concentrations of copper sulphate (CuSO/sub 4/5H/sub 2/O) and of sulphuric acid are...

Topics: solution and solubility, Physical chemistry

This paper is supplementary to previous papers on the subject published by the Bureau of Standards, and brings the list of formulae up to date. Butterworth's series formulae for the calculation of the mutual inductance of two parallel coaxial circles are compared with those given by others, and it is shown that they diminish the labour of computation. Butterworth's formulae for the mutual inductance of parallel eccentric circles are next considered, and various particular cases are given and...

Topics: inductance, Condensed matter, electronic structure, electrical, magnetic, and optical properties

The importance of the e.m.f. developed by the relative motion of the magnet and the winding of the galvanometer is pointed out and the general theory of the instrument is developed. The fundamental equation is stated and a solution is obtained giving the various working constants in terms of the intrinsic constants. The advantage of using a transformer with an instrument developing a relatively large back e.m.f. is shown. The double period sometimes observed is due to the system being...

Topics: measurements and use of instruments, Condensed matter, electronic structure, electrical, magnetic,...

In low-resistance standards capable of carrying large currents, the surfaces of the contacts through which the current enters and leaves must be large. In many cases the resistance depends, to some extent, on the manner in which the current leads are attached. In alternating-current measurements it is also necessary to know the inductance. The present paper points out the conditions which must be fulfilled in order that the resistance may be definite, or both the resistance and inductance be...

Topics: measurements and use of instruments, electricity and magnetism, Condensed matter, electronic...

This paper comprises a complete statement of previous formulae and includes the development of a more direct solution of the case where two parallel, coaxial, circular ceils are placed at such a distance that their mutual attraction or repulsion is a maximum. Methods for the application of the formulae, worked-out examples, and tables to facilitate calculation are given. The paper does not permit of a more detailed abstract.

Topics: electricity and magnetism, Condensed matter, electronic structure, electrical, magnetic, and...

A theoretical discussion is given to show the conditions which must be fulfilled in the construction of resistance coils in order that the phase angle shall be small and the change of resistance with frequency negligible. These principles are applied to the design of coils of different values, and specifications are given for the construction of coils of different denominations from 0.1 to 10,000 ohms.

Topics: measurements and use of instruments, Condensed matter, electronic structure, electrical, magnetic,...

It is shown that while the transformation ratio of current transformers usually decreases with increasing current, it may increase in individual cases or even attain a maximum. This ratio and the phase-angle at various loads can be accurately computed from the magnetic data of the core. The slope of the ratio curve can in general be qualitatively predicted from the value of the Steinmetz coefficient. But the iron losses, especially at low flux densities, cannot be accurately- represented by a...

Topic: transformers, rotary converters and boosters/ B8300 Power apparatus and electric machines

This paper gives the spectral transmission of various substances, especially coloured fluorite, light-filters, and coloured glasses. Some of the substances investigated provide a simple means for obtaining narrow spectral bands of radiant energy of high intensity and covering a wide range, without the employment of a spectroscope. By properly combining them it is possible, for example, to obtain a screen having narrow transmission bands at 0.38 mu, 0.5 mu, 0.55 mu, 0.7 mu, 0.8 mu, 1 mu, and 2.2...

Topics: absorption (light and heat), spectra

Coffin quoted a formula for the mutual inductance of two coaxial solenoids, which he attributed to Kirchhoff. The author, having found by trial that the formula gave obviously erroneous results, was led to investigate where it was wrong. Using a method suggested by Himstedt, the complete solution of the problem is obtained in terms of complete and incomplete elliptic integrals. The formula agrees with the elliptic integral formula given by Russell, when an algebraical slip in the latter's...

Topics: electromagnetic induction, Electrical instruments and techniques

Topics: inductance, Electricity and magnetism, fields and charged particles

In the first part of this paper the construction and measurement of some standards are described. Each inductance coil consists of a single layer of wire wound on a nearly perfect circular cylinder of marble. This latter was ground on a Poole grinder as used to shape the rolls or calendars employed in paper machinery. The cyclinders are remarkably perfect, the max. variation in the diam. being 0.0013 cm. On one of the standards the wire was singly wound, the winding being divided into three...

Topics: electromagnetic induction, measurements and use of instruments, molecular physics, matter and...

The Arsem vacuum furnace previously used was slightly modified, and arrangements were made to sweep out the smoke from the heated oxides which affects the optical pyrometer readings. The materials as a rule are charged into the ring space between an outer and an inner tube; some gas (hydrogen, nitrogen, etc.), is passed down the inner tube, into which the pyrometer is sighted. The tubes are made of graphite or of tungsten, the latter being moulded in graphite. The pyrometer lamps were...

Topics: freezing, melting and boiling points, materials properties, Heat flow, thermal and thermodynamic...

By his method of grouping similar terms Runge has greatly simplified harmonic analysis. The object of this paper is still further to lessen the labour of analysing curves and more especially to facilitate the analysis of alternating current waves. The arrangement of the calculation is given in detail for three special cases, namely, for 6, 12, and 18 measured ordinates per half-period. Useful equations are also given for checking the accuracy of the results obtained. Numerical examples are...

Topics: physics, General Physics

Describes the construction of 4 mercury units of resistance at the Bureau of Standards, Washington. A number of tubes of Jena glass were procured and 4 others of "Verre dur," but the latter have not yet been used, although their calibre factors are somewhat less than those of the Jena tubes. The respective lengths, calibre factors, and masses of mercury contained by the tubes at 0 degrees 3C are as follows:- Table no. Length Calibre factor Mass of mercury at 0 degrees C 1 95.08231 cm...

Topics: electrical conductivity, measurements and use of instruments, Condensed matter, electronic...

One of the most carefully constructed standards of self-inductance in the world was made by Frohlich in 1897. It consists of a large marble ring of rectangular section wound with a single layer of fine silk-covered wire. Frohlich calculated the self-inductance on the assumption that it was the same as for a current sheet the thickness of which was equal to the diam. of the bare wire. He found that L = 0.10199063 henry. The author has previously pointed out that the assumption that a winding of...

Topics: inductance, Electrical instruments and techniques

The first part of this paper gives an account of the principles underlying the operation of total radiation pyrometers and describes some representative types. Some 20 instruments were examined in the course of the research, including the various forms of Fery, Foster, Thwing, and Brown pyrometers. A considerable portion of the paper is devoted to the examination of the sources of error met with, and to the description of methods of eliminating or correcting these. The principal errors noticed...

Topics: thermometry, pyrometry and calorimetry, Heat flow, thermal and thermodynamic processes

electrical conductivity; Medical and biomedical uses of fields, radiations, and radioactivity; health physics

Topic: USA

The small 500-volt Crocker-Wheeler bipolar dynamos, capable of giving 0.22 amp. as a maximum, are belt-driven by a 2-h.p. motor, the armatures being connected in series, thus giving 5,000 volts, and the fields in parallel, the latter being excited from a separate circuit. By means of a speed controller the voltage may be held constant, between 3,000 and 5,000 volts, to within 1 per cent. For gas-conductivity work requiring about 1 milliamp. a continuously variable resistance of about 5 megohms...

Topics: apparatus and instruments, Condensed matter, electronic structure, electrical, magnetic, and...

The object of the investigation was the determination of the spectral visibility curve of the average eye, 130 subjects being tested, of whom 7 were known to be colour-blind. The distribution of energy in the source of light used, a cylindrical acetylene flame, was determined with great care, and visibility curves extending from 0.46 mu to 0.74 mu were obtained by using a ficker photometer. Observers experienced little difficulty in making settings with this instrument, but wide variations were...

Topic: vision

Accurate determinations of the heat of combustion of a solid may be made by means of a calorimetric bomb of one of the several recognised types. In order to make it possible for different laboratories to express results of calorimetric determinations on a uniform and comparable basis, it was deemed desirable to determine accurately the heats of combustion of some chosen substances which can be reproduced with the requisite degree of purity, and which can be used for calibrating the various...

Topic: measurements and use of instruments/ B0500 Materials science for electrical and electronic...

The author finds a new formula for the mutual inductance between a circle and a coaxial helix. J. V. Jones gives two formulae in terms of complete and incomplete elliptic integrals, but making numerical calculations by them is extremely tedious and laborious. The new formula is first deduced from considerations in connection with the potential of a uniformly magnetised circular disc. It is also deduced from a very general formula given by A. Gray [/b Absolute Measurements/, Vol. II., Part I.,...

Topics: electromagnetic induction, measurements and use of instruments, Electrical instruments and...

In a previous paper the authors deterined the melting-and freezing-points of a number of metals on the temperature scale defined by the Pt-resistace thermometer calibrated in ice, steam, and sulphur vapour (444.70 degrees on the constant-volume notrogen thermometer). In order to throw further light on the probable accuaracy of the temperature scale so defined, in the interval 100 degrees to 500 degrees C, the authors have made some further measurements by the same method on the boiling-points...

Topics: temperature, thermometry, pyrometry and calorimetry, Heat flow, thermal and thermodynamic processes

Theoretical photometry assumes two general laws of radiation. (1) The inverse square law, which on the assumption of the rectilinear propagation of light is merely a statement of a geometrical property, and (2) Lambert's cosine law. The latter is an empirical law, based primarily on the observation that a uniformly bright sphere, when viewed at a distance, appears as a uniformly bright disc. No satisfactory experiments have yet been made to test the law in its application to glowing surfaces....

Topic: photometry

The present paper gives data relating principally to the determination of the mathematical form of the isothermal spectral curve of a black body, and to the computation of the numerical value of the constants relating thereto, for the temperature-range between 450 degrees and 1525 degrees C. The paper also contains data on various subsidiary problems such as (i) the variations of the reflecting power of silver with angle of incidence and with wave-length, (ii) the variation of the reflecting...

Topics: measurements and use of instruments, rays and radiation, Heat flow, thermal and thermodynamic...

Describes convenient methods for adjusting the Thomson bridge when very low resistances are measured. The adjustments are made without the repeated opening and closing of the low-resistance connection between the two low-resistance arms.

Topics: measurements and use of instruments, Condensed matter, electronic structure, electrical, magnetic,...

The formulae of Rowland, Rayleigh, and Lyle for the mutual inductance of two coaxial coils of rectangular cross-section take second differentials only into account. The formulae of Weinstein and Stefan, however, take into account differential coefficients higher than the second. Weinstein deduces his formula by starting with Maxwell's expression in elliptic integrals for the mutual inductance of two coaxial circles, differentiating it and carrying the operation to the fourth order of...

Topics: electromagnetic induction, Electrical instruments and techniques

A survey of previous researches on the refraction of air shows that many investigators have worked either with white light or with one monochromatic radiation, and dispersion measurements have been limited to a small interval of the spectrum. No index measurements exist for waves longer than those corresponding to orange light, and in the ultra-violet the dispersion formulae disagree by more than 10% of the refractivity. Accordingly it was deemed advisable to measure the absolute indices of...

Topic: light refraction

In this paper is treated the measurement of the "effective inductance" of non-inductive resistance coils for use in alternating-current bridges and in potentiometer circuits where it is desired to know the phase-angle. The latter depends on the inductance and the capacities between the windings and between the various parts of the coil and the earth. The "effective inductance" is that value of inductance which would produce the observed phase-angle. The measurements with...

Topics: inductance, measurements and use of instruments, Condensed matter, electronic structure,...

Maxwell's bridge method was employed, a rotating commutator of special design being used to charge and discharge the condenser. The first portion of the paper is devoted to a consideration of the formula for the capacity, the object being to make the correction factor as small as possible. The usual stroboscopic device for maintaining a constant speed was abandoned; in its stead the observer at the galvanometer telescope controlled the speed of the driving motor by observations of the...

Topics: measurements and use of instruments, Electrical instruments and techniques

The wave-lengths of 55 lines in the neon spectrum have been measured by means of the interferometer. These lines lie in the region lambda 3369 to lambda 8495. The strong lines in the visible region have been observed with great accuracy, the probable error being one part in several millions, or less than one-tenth the width of the line. These strong lines were observed by means of three different pairs of interferometer plates which were each used on several interferometers. The ultra-violet...

Topic: spectra

The investigations carried out up to the present time on the equilibrium diagram of the iron-carbon system cannot b6 regarded as exhaustive, because in no case have the investigators worked with pure materials. On this account the authors have prepared a series of alloys containing 0.08 to 3.27% of carbon to serve as the basis for an accurate study of the thermal equilibrium of the Fe-C system. Pure iron has been made by the electrolysis of American ingot iron, and a detailed study has been...

Topics: metallography and properties and treatment of metals and alloys, Electrochemistry and...

The melting-points in pure hydrogen of the metals of the iron group, viz., Ni, Co, Fe, Mn, Cr, also Va and Ti are determined chiefly by means of the micropyrometer which is shown to be an instrument of precision for the determination of the melting-points of refractory metals and salts. In the cases of the metals examined the effect of the alloying of microscopical particles with the Pt or Ir heating strip is found to be inconsequential until after melting, the melting-points determined for Ni,...

Topics: freezing, melting and boiling points, Heat flow, thermal and thermodynamic processes

Describes an investigation of the energy distribution in the radiation from the inside and outside of the turn of a helically wound tungsten filament in an atmosphere of nitrogen. The intensity of the radiation from within the turn of the helix is from 90 to 100% greater than from a similar area on the outside of the turn. This is accounted for on the basis of multiple reflection within the helix. This modifies the quality of the light so that it is redder than the light from the outside of the...

Topics: rays and radiation, lamps and lighting, Heat flow, thermal and thermodynamic processes

This paper discusses the relations between (1) the operation constants, namely, the external critical resistance, the deflection and ballistic periods, and the sensitivity in the particular conditions for use in which the galvanometer is intended, and (2) the intrinsic constants, namely, the inertia, damping, restoring, and displacing constants and the resistance, for critically damped galvanometers. The best relations for these quantities for attaining the desired sensitivity whether to...

Topics: measurements and use of instruments, Condensed matter, electronic structure, electrical, magnetic,...

Tissot has already pointed out the advantages of high spark-frequency when thermal detectors are employed. The author demonstrates that a high spark-frequency is also advantageous from the point of view of the telephone receiver. Rayleigh's and Wien's results are quoted as showing the rapid increase of sensitiveness with the frequency, and a curve of volt-sensitiveness is given for a pair of 800-ohm Schmidt-Wilckes head telephones of the type used for radio-telegraphic work. The change in...

Topics: radiotelegraphy, acoustics, Telephony B6210F Telegraphy