‘908 REPORT—1885. 
chemical industries filled the air with gases destructive to iron wires; but the Post 
‘Office Telegraph Department has recently erected a No. 14 copper wire, ‘080 in. in : 
diameter, weighing 100Ib. per mile, all the way from London to Newcastle, 278°08 
miles in length, and it became desirable to measure very accurately its electrical 
elements, so as to see if it possessed, as was anticipated, any marked advantage as 
a telegraph line over the galvanised iron wires hitherto used. 
There were two series of experiments made. In the first series the relative 
electrical condition of the two kinds of wires was determined, and in the second 
series their relative rates of working. 
The first series was divided into two parts, the one consisting of tests made 
from Bishop Auckland to Teams, near Newcastle, a distance of 30°235 miles on 
the north side, and to Pierce Bridge, a distance of 9:172 miles on the south side, 
and the other consisting of tests of a section of line between Pierce Bridge and 
Baldersby Cross Roads, 26-7 miles in length. The poles carried ten wires. The 
tests were made in dry and favourable weather by Messrs. Kempe and Eden. 
The electrostatic capacity of an aérial line is known to vary as 
4h 
d 
where / is the height of the wire above the ground, and d its diameter. Now, the 
vaverage height of the copper wire on the sections between Bishop Auckland and 
Teams and between Pierce Bridge and Baldersby Cross Roads is 28 feet, and that 
of the iron wire (on a lower arm of the pole) 22 feet, their diameters being ‘V80 in. 
and ‘171 in. respectively. We have, therefore, for copper wire 
4h 4 x 23 x 12 x 1000 
log 
log d log. 30 = 41398791, | 
for iron wire i 
log =” = log £* 23 12 x 1000 _ 3.7908678, 
d 171 
-and 
3°7906678 _ 
Tis05791 916 nearly, 
which makes the capacity of the copper wire to be 100—91°6, or 8:4 per cent. less 
than that of the iron wire. This result agrees pretty closely with the mean value 
-of the differences of capacity obtained by actual measurements on these sections— 
viz., 9°] per cent. 
For the Bishop Auckland-Pierce Bridge section we have :— 
For copper wire 
Nee logs 2 RIO cr g0ngney 
d 80 
For iron wire 
4h 4x20x12x1000 4. ? 
log 4 = log 4420 x10 x 1000 _ 3.749975 
and 
3°7492751 _, 
#1003705 ~ °!4 
making the capacity of the copper wire to be 100~91°4, or 8°6 per cent. less than 
that of the iron, whilst the actual value was found to be 9°7 per cent. The 
differences between the calculated and the experimental values are probably due 
to the influence of trees, buildings, &c., which cannot be allowed for theoretically. 
These measurements were made when the other wires on the poles were left 
insulated. The effect of having all the other wires to earth when the capacity of 
any one wire was measured was very marked. Thus, on one wire the capacity was 
increased from ‘362 to ‘451 microfarad, or 22 per cent. 
_ As regards the induction between wire and wire the effects obtained were very 
slight, though their actual value was determined with comparative accuracy. 
The second series of experiments were conducted between London and New- 
