Froceeduii/s of the Royal Societi/ of Victoria. 215 



lUiitter of fact, the hostility of the natives rendered it a diflicult 

 matter to carry on geological exploration and on some occasions 

 exploring parties had narrowly escaped spearing. The magnetic 

 action of the shoal was exactly similar to what would be produced 

 by a ridge of magnetic iron ore. At that place the water was 

 only about 75 feet deep. 



Mr. RosALES said that in going about Ballarat his compass 

 was very often aftected in the way that had been described. In 

 some places the granite had become greatly decomposed, and 

 formed a magnetic iron ore. 



Mr. Ellerv said that there were a good many magnetic 

 centres on basalt formations in the Colonies. 



Mr. White said that in Madagascar and other places it had 

 been found necessary to disregard the compass altogether for the 

 pui-poses of surveying, and indeed, he Avas astonished, not at so 

 many wrecks taking place, but at so few. Flinders, who was 

 not equalled as a careful navigator in his day of wooden ships, 

 had stated that in his opinion, by extreme care a course could be 

 made good to a quarter point, or three degrees, about one mile in 

 nineteen. It was nothing unusual in these days for a ship to 

 run 400 miles in twenty-four hours, and thus, by trusting to the 

 compass, a navigator could not make for any point with greater 

 certainty than that he would arrive at within twenty miles of it. 

 When captains of vessels found themselves out of their course, 

 they generally set it down to the action of some unknown 

 current. His impression was that it was generally due to some 

 abnormal action of the compass. In fact, anyone who would 

 trust the compass for absolute direction would be a madman. 



Mr. Lucas asked if Mr. Ellery could give any reason why the 

 north-seeking pole should be uppermost. He thought the iron 

 ore would attract either pole. 



Mr. Ellery said it was only surmise. Judging from the 

 effect produced, that was the conclusion that seemed most 

 probable. 



Mr. RosALES said that if the deflection of the needle were 

 due simply to a large mass of magnetic iron ore, the deflection 

 would be greater and greater as the ship neared the Island, but 

 there would be no deflection to tlie other side. 



Mr. Ellery said that no doubt the mineral, whatever it was, 

 was polarised. 



Mr. Lucas asked whether it could become polarised by lying in 

 a certain position. 



Mr. Ellery replied that if it were lying anywhere parallel to 

 the magnetic axis, it would become polarised. As the Chairman 



Q 2 



