402 REPORT—1 890. 
2. Suggestions towards a Determination of the Ohm.) 
By Professor J. Viriamo Jonzs, M.A. 
The main suggestions offered for consideration are— 
1. That the time is ripe for a new determination of the ohm that shall be final 
for the practical purposes of the electrical engineer. 
2. That such a determination may be made by the method of Lorenz, the spe- 
cific resistance of mercury being obtained directly in absolute measure by the 
differential method described. 
3. That the standard coil used in the determination should consist of a single 
layer of wire, the coefficient of mutual induction of the coil and dise circumference 
being calculated by a new formula (communicated by the author to the Physical 
Society in November 1888, ‘ Phil. Mag.’ January 1889). 
Measurements have been made on the lines indicated in the Physical Laboratory 
of the University College at Cardiff. Five complete sets of observations were taken 
in the spring of this year, with the following results for the specific resistance of 
mercury at O° C. :— 
(1) 94,108 absolute units 
(2) 94074, yy 
(3) 94098, 
(ay "ado 
(5) 94,021 ss " 
Mean 94,067 +10 (probable error). 
The result may be otherwise expressed by saying that the ohm is equal to the 
resistance of a column of mercury of one square millimetre sectional area, and 
106307 centimetres long, the probable error being + 0:012. 
[These Papers were followed by a Discussion on Electrical Units. ] 
3. On Alternate Currents in Parallel Conductors of Homogeneous or. 
Heterogeneous Substance. By Sir Witu1am THomsoy, D.C.L., LL.D., 
FE.R.S. 
This Paper consists of a description of some of the results of a full mathema- 
tical investigation of the subject, which the author hopes to communicate to the 
‘ Philosophical Magazine ’ for an early number :— 
1. Two or more straight parallel conductors, supposed for simplicity to be 
infinitely long, have alternating currents maintained in them by an alternate- 
current dynamo or other electro-motive agent applied to one set of their ends at so 
great a distance from the portion investigated that in it the currents are not 
sensibly deviated from parallel straight lines. The other sets of ends may, 
indifferently in respect to our present problem, be either all connected together 
without resistance, or through resistances, or through electro-motive agents. All 
that we are concerned with at present is, that the conductors we consider form 
closed circuits, or one closed circuit, and that therefore the total quantities of — 
electricity per unit of time at any instant traversing the normal sections in opposite — 
directions are equal. 
2. We suppose the period of the alternation to be very great in comparison 
with the time taken by light to traverse a distance equal to the greatest diameter 
of cross-section of our whole group of conductors. This supposition is implied in — 
the previous assumption of parallel rectilinearity of the electric stream lines, and — 
of equality of the quantities of electricity traversing, in opposite directions, the — 
several areas of a normal section. 
3. We further suppose that the length of our conductors and their effective 
1 Published in eatenso in the Electrician, vol. xxv. No. 644. 
