Sometimes they even lose all their magnetic properties.
These changes in the compass often lead to disastrous consequences. Many cases are known of ships being steered to destruction through the deviation of the compass. Arago tells of a Genoese ship which, about the year 1808, sailing for Marseilles, was struck a little way off Algiers. The needles of the compasses all made half a revolution, although the instruments did not appear to be injured, and the vessel was wrecked on the coast when the pilot believed he could round the cape to the north. This may account for the total disappearance of certain ships.
Some ships, like certain individuals and certain trees, appear in particular to attract the electric fluid. We have many records of vessels struck several times in the course of a single electric storm. Here are a few:—
On August 1, 1750, the Malacca was struck repeatedly.
In 1848, the Competitor was struck twice within an hour.
At the beginning of December, 1770, between Mahon and Malta, the ship of a Russian admiral was struck three times in a single night.
On January 5, 1830, in the Straits of Corfu, the Madagascar received five destructive discharges in two hours.
We could add many others to this list. But enough. And yet we have not said the last word on the subject. We have to discuss the interchange of sympathetic currents, and those which are the reverse, taking place between the electricity of the skies and that of the telegraph.
Lightning often comes incognito to visit the earth's surface, or even the depths of the ocean. These little excursions to our terrestrial dominions usually pass unperceived; however, in certain cases the telegraph wires commit the indiscretion of revealing them.
On the other hand, we know that the wires entrusted with carrying our thoughts round the world, are almost inconceivably sensitive. Without being conscious of the fact, they are in correspondence with the sun, 149 millions of kilometres away, and any agitation on the surface of this luminary may cause them indescribable agitation, as we witnessed at the close of the year 1903.