15 18. J Scientific Intelligence. 391 



cut the magnetic meridian nearly at right angles. By a lens of 

 a sufficient size, the whole of the violet ray was collected into a 

 focus, which was carried slowly along the needle, proceeding 

 from the centre towards one of the extremities, and always the 

 same extremity, taking care, as is the case in the common 

 operation of magnetizing, never to go back in the opposite direc- 

 tion. After operating in this manner for half an hour, the needle 

 was examined ; but it was not found either to have acquired 

 polarity or a sensible attraction for iron filings. The process was 

 then continued for 25 minutes more, 55 in the whole, when the 

 needle was found to be strongly magnetic ; it acted powerfully 

 on the compass, the end of the needle which had received the 

 influence of the violet ray repelling the north pole, and the 

 whole of it attracting and keeping suspended a fringe of iron 

 filings. 



It is stated that a clear and bright atmosphere is essential to 

 the success of the experiment, but that the temperature is indif- 

 ferent. At the time when the above experiment was made, 

 about the end of April, the temperature was rather cool than 

 warm. 



VII. Blue Iron Earth. 



The blue iron earth, or native Prussian blue, as it was for- 

 merly called, has been found in many parts of the continent of 

 Europe ; as also in Iceland and in Shetland ; but it had never 

 been discovered in the island of Great Britain, until it was ob- 

 served by Dr. Bostock, at Knotshole, near Liverpool. On the 

 north-east bank of the Mersey, about a mile and a half above 

 the town, a small glen, or dingle, is formed, apparently by a 

 fissure in the brown sandstone, which, in this place, rises up to 

 the edge of the water ; the sides of the dingle are covered with 

 brush-wood, and at the bottom is a flat swampy pasture. The 

 upper stratum of the soil of the pasture is chiefly sand, mixed 

 with a little vegetable mould ; but at the depth of four or five 

 feet, there is a body of stiff white clay, mixed with a consider- 

 able quantity of vegetable matter, consisting principally of the 

 roots and stems of different species of rushes, and other aquatic 

 plants. A portion of this clay was procured for examination, 

 principally in order to ascertain how far it was likely to prove 

 useful as a manure, when, after being exposed for some time to 

 the air, the vegetable fibres which it contained were found to be 

 encrusted with a dusky blue substance, the shade of which 

 became gradually more intense, until at length it acquired a deep 

 indigo colour. It exhibited a pulverulent, or feathery appear- 

 ance, and seemed to be attached to the vegetable matter alone. 

 Its chemical composition was found to agree with that indicated 

 by Klaproth and Laugier, or to consist essentially of oxide of 

 iron and phosphoric acid. With respect to its production, it 

 may be observed, that many circumstances lead to the idea, that 

 the valley formerly occupied a small bay in the river, which was 



