476 REPORT—1904, 
2. Eddy-current Losses in Three-phase Cable-sheaths.+ 
By M. B. Frexps. 
In three-phase electric power distributions the use of three-core lead-sheathed 
cables is common practice. 
The alternating currents in the cable-cores induce eddy-currents in the sheath. 
If the cores have circular cross sections, and the current be evenly distributed 
over the section, the calculation of the sheath-loss (with certain reservations) is 
easy. Two effects exist which tend toward uneven current distribution in the 
cores: (1) the skin-effect, (2) the mutual induction effect of the cores on one 
another. Any uneven distribution of current flowing axially is shown to be equi- 
valent to a uniform distribution superposed upon an eddy-current distribution 
(the eddy-currents flowing axially). The complete problem therefore includes the 
eddy-currents induced in the cores as well as in the sheath. The eddy-currents 
in the cores are considered under the headings of self-induced eddy-curreuts 
(skin-effect) and mutually induced eddy-currents. It is shown that owing to the 
manner in which cable-cores are made up in practice (being stranded and twisted) 
the calculation of the mutually induced eddy-currents is indeterminate, but if the 
stranding and twisting be sufficiently carefully executed these eddy-currents are 
negligible. The skin-effect in circular conductors does not materially complicate 
the calculation of sheath loss. The mathematical calculation is then given for 
three-core cables having cores of circular and segmental cross-sections. In this 
calculation the magnetic forces due to the sheath-currents may be, and are, 
neglected. It is shown that for different cables having similar cross-sections, 
working at the same current density in the cores, and at the same frequency, the 
sheath-loss per unit length varies as the sixth power of the diameter, and that 
were it desirable, from general considerations, to build large cables, this fact alone 
would limit the economical size. An example of a low-tension cable is then 
worked out. 
The paper concludes by showing that just as the losses due to skin-effect of a 
given round conductor can be allowed for by assuming a definite increase of the 
specific resistance of the material for a given frequency, so in a three-core cable 
the extra loss due both to the skin-effect of the cores and the sheath-currents can 
be allowed for by assuming a definite increase of specific resistance of the core 
material for a given frequency. The formula for the increase of specific resistance 
is derived, 
3. Magnetic and Electric Properties of Nickel at High Temperatures. 
Ly Professor C. G. Knorr. 
4. On the Viscosity of Colloidal Lron Hydrate. 
By A. D. Dennine, U.Sc., Ph.D. 
Simultaneous measurements of the viscosity of similar solutions were made 
(i) by finding the logarithmic decrement of a glass disc swinging in the solution 
according to the method described by Grotrian and W. Konig (readings obtained 
by mirror, lamp, and scale method), and (ii) by taking time of flow of a fixed 
volume through the capillary tube (Hagen-Poisseuille’s transpiration method) of 
an Ostwald apparatus. 
In order to more conveniently compare the results thus obtained by the two 
methods the logarithmic decrement was generally calculated by means of the 
O, E. Meyer formula from values of viscosity obtained by method (ii). 
The initial values found for the viscosity 7 were, for method (i), yo, = 0'0146; 
for method (ii), ni9:= 00144 ; whilst for water 7,, =0:01105, 
1 See also Journal Inst. Hlect, Eng , vol, xxxiii. pe 936 (19040 
