324 



The deepei- warm current is shown bj the observations of Sir J. Ross, who 

 found that while the surface water was 28° or 30°, at 400 to 600 fathoms the 

 water was nearly 40°. 



This deep and warmer current impinging on the barrier ice, undermines it, 

 and by dissolving the ice, becomes fresher and lighter, and, rising to the 

 surface, forms a superficial current which recedes from the pole, carrying with 

 it the icebergs formed by fragments of the great barrier. Some of these are 

 stated to be 600 feet high, in which case there must have been 4000 or 5000 feet 

 below the water. Such enormous bergs might be formed by the fall of portions 

 of the barrier, half a mile or three quarters of a mile long, which would float 

 with the heaviest end down. These bergs are stated by Wilkes to advance 70 or 

 80 miles northward in one season. The cold and fresher current as it recedes 

 from the pole must extend over a wider circle, and therefore diminish in 

 depth. Icebergs floating partly in the upper current and partly in the lower, 

 will be carried to such a distance, that the pressure of the two currents shall 

 balance each other ; then, their further progress being arrested, they will form 

 that close pack of icebergs and floe ice, through which Sir J. Ross had to bore 

 his way, while south of this pack he found a clear open sea, free of ice. 



Art. LXV. — Fotes on the Conduction of Electricity, By James Duigan. 



(abstract.) 

 [Read before the Wellington Philosophical Society, July 16, 1870.] 

 The object of this paper is to controvert a view stated in a paper entitled 

 " The earth of New Zealand a bad Conductor of Electricity, as compared with 

 that of other countries, by F. E. Wright," in Transactions of the Neio Zealand. 

 Institute, Yol. ii., pp. 226-227. The transmission of electrical currents along 

 the telegraph wires, in some cases after they have become detached from the 

 insulators, and lie on the ground, attributed by Mr. Wright to a peculiarity in 

 the New Zealand soil or rock formation, is explained by the fact of the 

 New Zealand telegraphs being worked on what is technically known as the 

 "open circuit" system, one of the conditions of such system being, that it 

 never occurs to have more than one battery sending its current of electricity 

 along the line at the same time, whereas in Australia the lines are, or at least 

 were, until very recently, worked on the converse of the "open circuit," viz., 

 the "closed circuit," one of the conditions of this latter system being that 

 there are a plurality of batteries always sending their currents along the whole 

 length of the line, in their respective circuits, and which by so doing prevent 

 a current passing beyond an earth-fault, thus closing the communication 

 between all stations situated on opposite sides of the fault. 



After explaining at length the nature of the two methods of working the 

 telegrapji, the author concluties by expressing his opinion that the term 



