A/A' WILLIAM SI I-.M 1-..\S, l-.R..^. 339 



satisfactorily for those irregular deposits which they found, 

 particularly in the Barrow district. The somewhat analogous 

 deposits of pipe-clay in Devonshire had been caused, he thought. 

 through similar agencies in the decomposition of granite. 



Dr. SIEMENS said, with regard to the observations that had 

 just been made as to the dip of the needle over a field of magnetic 

 oiv, he thought it was quite natural and evident that the needle 

 must dip more or less as they approached the one end or the other 

 of the magnetic deposit. He should look upon a deposit of 

 magnetic ore, between faults and its natural limits, as a magnetic 

 needle polarised by the earth's magnetism ; one end of the deposit 

 would, therefore, be positive, and the opposite end negative 

 magnetic ; the one would, towards the south, be the north pole, 

 and the other, towards the north, would be the south pole of the 

 magnetic needle ; therefore, if they travelled over that deposit 

 with a dipping needle, they would find its north pole dip down to 

 one end, and the south pole to the other end, whereas, about the 

 middle of the deposit, no dip would take place. This would ex- 

 plain Mr. Maynard's observation regarding the Lake Champlain 

 deposits, and also the reference in Mr. Smith's paper to the 

 Swedish lodes of magnetic iron ore, without adopting the con- 

 clusion that ore, over which the needle did not dip, was necessarily 

 of a different constitution from other portions of the same over 

 which the needle did dip, either with the south or north pole. 



In the, (lisrtf.ssion of the Paper 



"OX THE HELICAL PUMP," 

 By Mr. JOHN bin AY, 



Mil. C. AY. SIKMKXS * said, he was much struck with the novel 

 mechanical idea involved in the helical pump of propelling the 

 water by putting it as it were into a sling, and slinging it forwards. 

 That, this pump would compare favourably with the ordinary 



* Excerjit Minutes f Proceedings of the Institution of Mechanical En^' 

 , ].. 2UO. 



