Looking to the article 'Telegraph (Electric)' in the last volume of
the old edition of the 'Encyclopaedia Britannica,' which was
published about the year 1861, we find on record that Jenkin's
measurements in absolute units of the specific resistance of pure
gutta-percha, and of the gutta-percha with Chatterton's compound
constituting the insulation of the Red Sea cable of 1859, are given
as the only results in the way of absolute measurements of the
electric resistance of an insulating material which had then been
made. These remarks are prefaced in the 'Encyclopaedia' article by
the following statement: 'No telegraphic testing ought in future
to be accepted in any department of telegraphic business which has
not this definite character; although it is only within the last
year that convenient instruments for working, in absolute measure,
have been introduced at all, and the whole system of absolute
measure is still almost unknown to practical electricians.'
A particular result of great importance in respect to testing is
referred to as follows in the 'Encyclopaedia' article: 'The
importance of having results thus stated in absolute measure is
illustrated by the circumstance, that the writer has been able at
once to compare them, in the manner stated in a preceding
paragraph, with his own previous deductions from the testings of
the Atlantic cable during its manufacture in 1857, and with Weber's
measurements of the specific resistance of copper.
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