THE COMMON LOG 135

Example.—Kequired the length of the knot on the log line for a
14 second glass.

Knot the glass x 14

— -or

Mile an hour 6080 3600
6080X14 n ^ „.
A x knots— —-—— = 23 ft. 7 ins.
ooUU
About 15 fathoms from the end of the line a piece of white rag was
bucked to indicate the beginning of the marked line, and to know in
heaving when the glass was to be turned. The line was then divided
off into equal lengths of 23 ft. 7 ins. and marked as follows.
To indicate a speed of 1 knot 1 small strip of leather.
„ „ 2 knots 2 small strips of leather.
„ >, 3 „ 3 small strips of leather.
»> „ 4 „ a piece of cord with 2 knots in it.
„ „ 5 „ a piece of cord with a single knot.
„ „ 6 „ a piece of cord with 3 knots in it.
„ „ 7 „ a piece of cord with a single knot.
„ „ 8 „ a piece of cord with 4 knots in it.
and so on.
A short method of finding the approximate length of a knot was to
add a cypher to the number of seconds run by the glass, and divide by 6.
This gave the number of feet, the remainder multiplied by 2 gave the
inches.
6)140
23 ft, 4 ins,
The common log is no longer used at sea and we have referred to it
in the past tense, but reference to it is still of historical interest owing
to the fact that the word "knot/' which is a "unit of speed" and not of
distance, is derived from the marks on the hand log line. When, say,
3 knots on the line had run out the seaman knew that the ship's
speed through the water was 6 nautical miles per hour, and if 4 knots
ran out that she was going 8 nautical ni.p.k, hence the query ''how
many knots is she going?"
THE PATENT LOO.
There are many different kinds of patent logs now in use, and all
candidates should have some practical knowledge of the use and care
of them.