on the magnetism of iron ships, and asking
whether they ought to be continued; a steamer being offered at _L50_
per week. I applied to Beaufort for a copy of Johnson's Observations,
and on Jan. 7th replied very fully, discouraging such observations;
but recommending a train of observations expressly directed to
theoretical points. On Feb. 17th I reported that I had examined the
Deptford Basin, and found that it would do fairly well for
experiments. On July 14th, 1838, Capt. Beaufort wrote to me that the
Admiralty wished for experiments on the ship, the 'Rainbow,' then in
the river, and enquired whether I would undertake them and what
assistance I desired, as for instance that of Christie or Barlow. I
replied that one person should undertake it, either Christie, Barlow,
or myself, and that a basin was desirable. On July 16th and 17th I
looked at the basins of Woolwich and Deptford, approving the
latter. On July 21st the Admiralty gave me full powers. From July 23rd
I was almost entirely employed on preparations. The course of
operations is described in my printed Paper: the original maps,
curves, and graphical projections, are in the bound MSS.: 'Correction
of Compass in Iron Ships--"Rainbow,"' at the Greenwich
Observatory. The angular disturbances were found on July 26th and
30th, requiring some further work on a raft, so that they were finally
worked out on Aug. 11th. I struggled hard with the numbers, but should
not have succeeded if it had not occurred to me to examine the
horizontal magnetic intensities. This was done on Aug. 14th, and the
explanation of the whole was suggested at once: graphical projections
were made on Aug. 16th and 17th for comparison of my explanation with
observations, and the business was complete. On Aug. 17th and 18th I
measured the intensity of some magnets, to be used in the ship for
correction. It is to be remarked that, besides the effect of polar
magnetism, there was no doubt of the existence of an effect of induced
magnetism requiring correction by other induced magnetism: and
experiments for this were made in the Magnetic Observatory. All was
ready for trial: and on Aug. 20th I carried my magnets and iron
correctors to Deptford, mounted them in the proper places, tried the
ship, and the compass, which had been disturbed 50 degrees to the
right and 50 degrees to the left, was now sensibly correct. On
Aug. 21st I reported this to the Admiralty, and on Aug. 24th I tried
the ship to Grav