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Variation and deviation--factors carefully guarded against in ordinary circumstances--were affecting the boat's liquid compass, but to what extent Sefton knew not.

In the box which I gave to Mr. Whitney were packed one French sextant; one surveying compass, aluminum, with azimuth attachment; one artificial horizon, set in a thin metal frame adjusted by spirit levels and thumbscrews; one aneroid barometer, aluminum; one aluminum case with maximum and minimum spirit thermometer; other thermometers, and also one liquid compass.

The instruments carried on my northern trip, and left with Mr. Whitney, and which he had seen, consisted of one French sextant; one aluminum surveying compass, with azimuth attachment, bought of Keuffer & Essen, New York; one glass artifical horizon, set in a thin metal frame, adjusted by spirit levels and thumbscrews, bought of Hutchinson, Boston; one aneroid barometer, aluminum, bought of Hicks; an aluminum case with maximum and minimum spirit thermometer; other thermometers, and one liquid compass.

It is said that the idea of a liquid compass was suggested to Crow by the experience of the captain of a coasting vessel whose compass card was oscillating wildly until a sea broke on board filling the compass bowl, when the card became steady.

The first liquid compass used in England was invented by Francis Crow, of Faversham, in 1813.