TRANSACTIONS OF THE SECTIONS. 35 



slight difierence in the size and number of the cells in different specimens of the 

 same metal, but the^ general resemblance is remarkably constant. 



In silver the form of the cell is somewhat oblong ; but the cell is larger than that 

 of copper or ii-on, and the system is more perfectly developed, that is, the internal 

 commimication from cell to cell appears to be more regular. The form of the cell 

 in copper is spherical ; but in some instances the cells seem to have pressed into the 

 domains of each other^ and their forms are therefore to some extent modified 

 thereby. 



Copper fi'om different -worts may differ a little in the diameter of the cells, and 

 consequently in the number contained, but the general range seems to be from 500 

 to 1000 in the linear inch. It shoidd be remarked that a specimen of the " best 

 select " copper is not any more dense and solid than a less pure metal, but, on the 

 couti-aiy, the partitions between the cells are exceedingly thin — so thin that there 

 appear to be minute openings from each one to its siuTOimding cells ; so that, as in 

 tlie silver, there is an internal communication through the entu-e mass. 



The cells in malleable iron are less regular in fomi and size, their inner surfaces 

 being jagged and uneven, and less biilliant than those of silver and copper ; but 

 the best fibrous iron seems to be equally free from angular crystals, and, like them, 

 shows a high degree of porosity. 



This cell-system is only developed internally in the metals ; the outer surfaces, 

 whether they have been in contact with the mould, or exposed to the atmosphere, 

 seem to be entirely destitute of them. 



In conclusion, the author regards it as highly probable that the malleability, as 

 well as the superiority of the above-named metals for conducting heat and electri- 

 city, may be owing to the perfection of their cellular aiTangement. 



Observations on an Iris seen in Water, near Sunset. By J. J. Walkeb, M.A. 



In this commimication, which might be considered a sequel to and illusti-ation of 

 a paper read by the author at the Meeting of the British Association at Aberdeen 

 in 1859, a description was given of the obseiwation of this Iris — both of the jjmuan/ 

 and, more partially, of the secondary hyperbolic bow — in the calm sheet of water 

 presented by a widening of the Royal Canal near Dublin, about 5.30 p.m., on the 

 29th of September. The sun being then near the horizon, the fonn approximated to 

 that of the rectangiilar hj-perhola. 



There was an Exhibition of Photogi-aphs in connexion with the meeting at 

 Manchester, imder the direction of a Local Committee. 



Electricity, Magnetism. 



On Sjpontanedus Terrestrial Galvanic Currents. 

 By G. B. AiKT, M.A., D.C.L., F.B.S., Astronomer Royal. 



It being now a well-ascertained fact that spontaneous galvanic currents have in 

 several instances prevented the working of the telegraphic wires, the matter had 

 become one of so much importance that he had felt the necessity of steps being 

 taken to ascertain the exact cause of these disturbing influences. With this view 

 he had placed himself in communication with the telegraph companies, but had not 

 been able to obtain much accurate irifonnation from them, probably in consequence 

 of their ofiicers not ha^ang the leisure to note down obsei-vations on the effects pro- 

 duced on the telegTaphic wires. His wish was to have a constant registration of 

 the effect of these galvanic currents, at the Royal Observatory-, and he believed that 

 aU that was requu-ed to ascertain the causes of these spontaneous disturbances 

 was the laying down of an insidated wire. The Government had acceded to his 

 proposal, and he thought it his duty to state that on the part of the Board of Visi- 

 tors there was the most anxious wish expressed that the object he had in view 

 should be canied out. In aU. these instances the Government had acted towards 

 him with the greatest liberality. He (the President) had been in communication 



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