31 4- Mr. R. Brown's Remarks on the Stniciuie 



lectively, must have a prevailing tendency ; and it follows from 

 the direction of the needle, that this tendency, as it respects 

 the positive currents, must be fiom the east, more or less 

 towards the west. 



It appears that the ores themselves, in some instances, 

 possess opposite thermo-electric properties. The sulphurets 

 of lead and of copper, for example, when partially heated in a 

 very moderate degree, yielded positive electricity to the less 

 heated part; whereas in the case of sulphuret of iron, it was 

 yielded from the latter to the former. When two of these 

 ores were respectively placed in contact with each other at 

 different temperatures, the sulphuret of lead was always po- 

 sitive with respect to the other two, whether it was at a higher 

 or lower temperature than they were ; and the sulphuret of 

 copper was, when heated, positive with regard to iron pyrites, 

 but negative when the temperature of the latter was the 

 greater. In some instances the nature of the electricity be- 

 came reversed before the heated ore had entirely cooled ; this 

 occurred when lead or copper ore was placed in contact with 

 iron pyrites at an inferior temperature. 



These different thermo-electric properties of metallic sub- 

 stances seem to throw some light on the cause of opposite 

 currents in mineral veins, and are, perhaps, connected with 

 the periodical variation of the needle. 



Several observations have been made in the mines of Coi'n- 

 wall on the intensity of the earth's magnetism, from which it 

 is to be inferred, that if at the greatest accessible depths it 

 differ at all from the intensity at the surface, the difference is 

 very inconsiderable, and that therefore the principal source, 

 or cause of the terrestrial magnetism, must be far removed 

 from us, so far indeed as to require powerful electrical cur- 

 rents to produce the effects observable at the surface. 



I^YlII.Remarks on the Structure and Affinities of Cephalotus . 

 By Robert Brown, Esq. F.R.S. <^r. * 



TN the Botanical Appendix of Captain Flinders's Voyage to 

 Terra Australis, a figure and description of Cephalotus fol- 

 liailaris are given, in some respects more complete than those 

 of M. Labillardiere, by whom this remarkable plant, a native of 

 the south-west coast of New Holland, was first published. 

 Both accounts, however, are equally imperfect with regai'd to 

 the fruit; and my principal object in the present communica- 

 tion is to supply that deficiency. 



My earliest knowledge of the ripe fruit of Cephalotus was 



* Comniunicatecl by the Author. 



