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74
This appeared to me sufficient to account for the mischief, and I
notified the Chief Engineer of the St. James, &c.. Company, of the
results of my test, and requested him to give me notice when the
culvert was opened, in order that I might be present.
Accordingly I was informed that this would be done on the
morning of the 5th instant.
On account of some very important experiments with the new
Standard Ampere Balance, I was unable to inspect the culvert until the
afternoon, by which time it had been partially opened.
There was a good deal of water in it, and in some places this had
evidently touched the positive main.
There were also three lead covered wires, which had been used as " pilot
wires," lying loosely at the bottom of the culvert. Two of these wires
had been fused evidently by a considerable current, and a g'ood deal of
the insulation burnt as was evidenced by a sooty deposit on the main
conductors, and the culvert at the spot.
This had occurred at two separate places, one being near Mr. Barker's
shop, and the other opposite Mr. Peat's.
I have little doubt that a connection between the negative conductor,
and the iron of the culvert was effected by the fused and stripped ends
of these pilot wires.
This is confirmed by the following facts:— At the time of my inquiry
last November into the explosions which occurred on this Company's
system of mains, I found that the insulation of the negative side of
their system of mains from earth was very defective.
This fault was very persistent, I but until the culvert was opened on
the 5th instant it had not been localised and removed.
Immediately, however, that this section of the main was disconnected
to enable the culvert to be opened, the fault on the system disappeared,
and the potential of the positive main from earth which had been
persistently about 190 volts fell to about 110 volts.
The explanation of the action is, I consider, this —
The negative main has been, for some months, in metallic connection
with the culvert in one, or, perhaps, two places in this part of Piccadilly.
If the insulation of the positive side had been perfect, no electric
action would have resulted. But this was not, and, in fact, practically
could not be the case.