scholarly journals X. On the electro-chemical equivalent of silver, and on the absolute electromotive force of clark cells

1884 ◽  
Vol 37 (232-234) ◽  
pp. 142-146 ◽  
Keyword(s):  
Electric Current ◽  
Electromotive Force ◽  
Large Diameter ◽  
British Association ◽  
Electric Currents ◽  
Terrestrial Magnetism ◽  
Accurate Knowledge ◽  
Series Of Experiments ◽  
The Absolute

The paper contains a record of a long series of experiments, extending over nearly two years. The measurement of the electric currents is direct, not depending upon a knowledge of the force of terrestrial magnetism. Three horizontal coils are traversed in succession by the electric current. Of these two of large diameter are fixed, and at a distance apart equal to the radius of either. Symmetrically between them a smaller coil is suspended in the balance. When the current passes, the suspended coil is pressed down, or lifted up, according to the connexions, and the observations relate to the double force called into operation when the direction of the current in the fixed coils is reversed . In a paper read before the British Association at Southampton it was shown that this construction presents special advantages, and in particular that the calculation of the result does not require an accurate knowledge of the radii of the coils, but only of the ratio of the radii of the small and large coils. In this way one of the principal difficulties, the measurement of the small coil, is evaded.

scholarly journals II. On the electro-chemical equivalent of silver, and on the absolute electromotive force of clark cells

1883 ◽  
Vol 36 (228-231) ◽  
pp. 448-450
Keyword(s):  
Electromotive Force ◽  
British Association ◽  
General Character ◽  
Daily Work ◽  
The Absolute ◽  
The Difference

The investigations upon this subject which have been carried on by Mrs. Sidgwick and myself during the last year and a half, though not yet quite finished, are so far advanced that no doubt remains as to the general character of the results; and as these results have application in the daily work of practical electricians, it is thought desirable to communicate them without further delay. The currents are measured by balancing the attraction and repulsion of coaxal coils against known weights, as described before the British Association in 1882, a method which has fully answered the favourable expectations then expressed. To what was said on that occasion it will be sufficient for the present to add that the readings are taken by reversal of the current in the fixed coils, and the difference of weights thus found (about 1 gram) represents the double force of attraction, free from errors depending upon the connections of the suspended coil, and other sources of disturbance.

scholarly journals An absolute determination of the acceleration due to gravity

1939 ◽  
Vol 238 (787) ◽  
pp. 65-123 ◽  
Keyword(s):  
Electric Current ◽  
Absolute Value ◽  
Absolute Determination ◽  
Accurate Knowledge ◽  
Recent Advances ◽  
Gravity Measurements ◽  
Relative Gravity ◽  
The Absolute ◽  
Made In

Recent advances in the precision obtainable in length and time measurements have made it possible to determine the absolute value of the acceleration due to gravity with greater accuracy than has hitherto been possible. An accurate knowledge of the actual value of the acceleration due to gravity is essential, for example, in connexion with the determination of the absolute unit of electric current by means of the current balance. It has been usual to refer relative gravity measurements made in this country to the absolute value determined at Potsdam by Kühnen and Furtwängler (1906) over 30 years ago, and although relative determinations can now be carried out with an accuracy approaching one part in a million, it appears that the basic Potsdam value may be in error by something between one and two parts in 100,000. Very few absolute determinations have been made within the last 50 years, but those which have been carried out at various stations show discrepancies of this order when related to the Potsdam value by relative determinations.

scholarly journals I. Measurement of the electrostatic force produced by a Daniell’s battery

1860 ◽  
Vol 10 ◽  
pp. 319-326 ◽  
Keyword(s):  
Electric Potential ◽  
Electrostatic Force ◽  
Atmospheric Electricity ◽  
British Association ◽  
Electric Currents ◽  
Philosophical Magazine ◽  
Absolute Measure ◽  
The Absolute

In a paper “ On Transient Electric Currents,” published in the Philosophical Magazine for June 1853, I described a method for measuring differences of electric potential in absolute electrostatic units, which seemed to me the best adapted for obtaining accurate results. The ‘‘absolute electrometer” which I exhibited to the British Association on the occasion of its meeting at Glasgow in 1855, was constructed for the purpose of putting this method into practice, and, as I then explained, was adapted to reduce the indications of an electroscopic or of a torsion electrometer to absolute measure. The want of sufficiently constant and accurate instruments of the latter class has long delayed my carrying out of the plans then set forth. Efforts which I have made to produce electrometers to fulfil certain conditions of sensibility, convenience, and constancy, for various objects, especially the electrostatic measurement of gal­vanic forces, and of the differences of potential required to produce sparks in air, under definite conditions, and the observation of natural atmospheric electricity, have enabled me now to make a beginning of absolute determinations, which I hope to be able to carry out soon in a much more accurate manner. In the meantime I shall give a slight description of the chief instruments and processes followed, and state the approximate results already obtained, as these may be made the foundation of various important estimates in several departments of electrical science.

XI. On the change produced by magnetization in the electrical resistance of iron and steel.—Preliminary notice

1875 ◽  
Vol 23 (156-163) ◽  
pp. 533-535 ◽  
Keyword(s):  
Electrical Resistance ◽  
British Association ◽  
Iron And Steel ◽  
King's College ◽  
Physical Laboratory ◽  
Series Of Experiments

For some time past Mr. Herbert Tomlinson, Demonstrator in the Physical Laboratory of King’s College, has been engaged in carrying out a series of experiments on this subject, and also on the effect of change of tension on the electrical resistance of steel and iron wires. In measuring the resistances of the short lengths of the wires or rods which were employed, a unit was chosen which was a small fraction of the British-Association unit.

scholarly journals IV. The diurnal variation of terrestrial magnetism

1908 ◽  
Vol 208 (427-440) ◽  
pp. 163-204 ◽  
Keyword(s):  
Diurnal Variation ◽  
Barometric Pressure ◽  
Diurnal Changes ◽  
Electric Currents ◽  
Terrestrial Magnetism ◽  
Previous Communication ◽  
Unknown Amplitude ◽  
Order Of Magnitude ◽  
Probable Origin ◽  
Magnetic Oscillations

1. In a previous communication I proved that the Diurnal Variation of Terrestrial Magnetism has its origin outside the earth’s surface and drew the natural conclusion that it was caused by electric currents circulating in the upper regions of the atmosphere. If we endeavour to carry the investigation a step further and enquire into the probable origin of these currents, we have at present no alternative to the theory first proposed by Balfour Stewart that the necessary electromotive forces are supplied by the permanent forces of terrestrial magnetism acting on the bodily motion of masses of conducting air which cut through its lines of force. In the language of modern electrodynamics the periodic magnetic disturbance is due to Foucault currents induced in an oscillating atmosphere by the vertical magnetic force. The problem to he solved in the first instance is the specification of the internal motion of a conducting shell of air, which shall, under the action of given magnetic forces, determine the electric currents producing known electromagnetic effects. Treating the diurnal and semidiurnal variations separately, the calculation leads to the interesting results that each of them is caused by an oscillation of the atmosphere which is of the same nature as that which causes the diurnal changes of barometric pressure. The phases of the barometric and magnetic oscillations agree to about 1¾ hours, and it is doubtful whether this difference may not be due to uncertainties in the experimental data. In the previous communication referred to I already tentatively suggested a connexion between the barometric and magnetic changes, but it is only recently that I have examined the matter more closely. In the investigation which follows I begin by considering the possibility that both variations are due to one and the same general oscillation of the atmosphere. The problem is then absolutely determined if the barometric change is known, and we may calculate within certain limits the conducting power of the air which is sufficient and necessary to produce the observed magnetic effects ; this conducting power is found to be considerable. It is to be observed, however, that the electric currents producing the magnetic variations circulate only in the upper layers of the atmosphere, where the pressure is too small to affect the barometer; the two variations have their origin therefore in different layers, which may to some extent oscillate independently. Though we shall find that the facts may be reconciled with the simpler supposition of one united oscillation of the whole shell of air, there are certain difficulties which are most easily explained by assuming possible differences in phase and amplitude between the upper and lower layers. If the two oscillations are quite independent, the conducting power depending on the now unknown amplitude of the periodic motion cannot be calculated, but must still be large, unless the amplitude reaches a higher order of magnitude than we have any reason to assume.

XXX.—Thermal and Electric Conductivity

1878 ◽  
Vol 28 (3) ◽  
pp. 717-740 ◽  
Author(s):  
Tait
Keyword(s):  
Thermal Conductivity ◽  
Electric Conductivity ◽  
Marked Effect ◽  
Original Method ◽  
The State ◽  
British Association ◽  
Pure Metals ◽  
The Absolute

The following paper contains the results of an inquiry which has occupied me at intervals for somewhere about ten years. It was carried out in part at the expense of the British Association, and I have already reported results to that body in 1869 and 1871. But these provisional reports referred to very short ranges of temperature only, and the experiments were made with faulty thermometers, for which I had not the corrections which had been carefully determined by Welsh at Kew.The inquiry arose from my desire to extend to other metals the very beautiful and original method which Principal Forbes devised, and which the state of his health prevented him from applying to any substance but iron. Forbes' experiments gave a result so very remarkable, and (as it seemed to me) so theoretically suggestive, that I wished to extend them to other pure metals, and also, in one or two cases at least, to alloys.I believe that Principal Forbes had at least two reasons for undertaking his investigations:—(1.) When he commenced his inquiry, there was no really accurate or trustworthy determination of the absolute conductivity of any body whatever for heat. (2.) FORBES had himself, in 1833 and subsequent years, pointed out a very remarkable analogy between the conducting powers of metals for electricity and for heat, and had shown that these were almost precisely proportional to one another—that is to say, that the list of the average relative conductivities of different metals for electricity differed, from that of their relative conductivities with regard to heat, certainly not more than did the several electric lists furnished by different experimenters, and certainly less than the corresponding thermal lists. Hence it was natural to suppose that temperature might have a marked effect on thermal conductivity, as it was known to have such an effect on electric conductivity.

scholarly journals I. Experiments, by the method of Lorentz, for the further determination of the absolute value of the British association unit of resistance, with an appendix on the determination of the pitch of a standard tuning-fork

1883 ◽  
Vol 34 (220-223) ◽  
pp. 438-439
Keyword(s):  
Tuning Fork ◽  
British Association ◽  
Cavendish Laboratory ◽  
Absolute Value ◽  
The Absolute ◽  
The Difference

The experiments described in the present paper were carried out during the spring and summer months of the present year, at the Cavendish Laboratory, and are divided into three distinct series. In the first and second series, the induction coils were situated nearly in the plane of the revolving disk, as in Lorentz’s original use of the method; the difference between the two series relating only to the speed of rotation, which was varied in the proportion of 10:16.

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