“On Jan. 4th Mr Wood wrote to me, mentioning that Capt.  Johnson had made some observations 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 Gravesend.  On Aug. 30th I had the loan of her for an expedition with a party of friends to Sheerness, and on Sept. 9th I accompanied her to Gravesend, on her first voyage to Antwerp.—­On Oct. 5th application was made to me by the owner of the ‘Ironsides’ to correct her compasses.  In consequence of this I went to Liverpool on Oct. 25th, and on this occasion made a very important improvement in the practical mode of performing the correction.—­On