MECHANICS AND USEFUL ARTS. 87 



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perfect metallic continuity, by being secured together by coupling 

 ferrules. 



2. To secure it from rust the rod should be coated with black 

 paint, itself a good conductor. 



3. It should terminate in a single platinum point. 



4. The shorter and more direct the course of the rod to the 

 earth the better ; bendings should be rounded, and not formed in 

 acute angles. 



5. It should be fastened to the building by iron eyes, and may 

 be insulated from these by cylinders of glass (I don't, however, 

 consider the latter of much importance). 



6. The rod should be connected with the earth in the most per- 

 fect manner possible, and nothing is better for this purpose than 

 to place it in metallic contact with the gas-pipes, or, better, the 

 water-pipes of the city. This connection may be made by a 

 ribbon of copper or iron soldered to the end of the rod at one of 

 its extremities, and wrapped around the pipe at the other. If a 

 connection of this kind is impracticable, the rod should be con- 

 tinued horizontally to the nearest well, and then turned vertically 

 downward until the end enters the water as deep as its lowest 

 level. The horizontal part of the rod may be buried in a stratum 

 of pounded charcoal and ashes. The rod should be placed, in 

 preference, on the west side of the building. A rod of this kind 

 may be put up by an ordinary blacksmith. The rod in question 

 is in accordance with our latest knowledge of all the facts of 

 electricity. Attempted improvements on it are worthless, and, 

 as a general thing, are proposed by those who are but slightly 

 acquainted with the subject. 



OCEAN TELEGRAPHY. 



Captain Rowett at the meeting of the British Association read a 

 paper "On Ocean Telegraph} 7 ." He discussed at length the va- 

 rious properties of the hemp telegraph cable, and to the' satisfac- 

 tion of the section cleared away the generally received objections 

 to light cables, by giving several illustrations, which indisputably 

 proved to the audience how perfectly still was the bottom of the 

 ocean, and even waters of moderate depths, in which the light 

 hempen cable would lie in security. He gave also some striking il- 

 lustrations of the disadvantages of mixing iron wire with hemp, and 

 made a polite appeal to the numerous ladies present whether their 

 linen was not seriously damaged by contact with iron. Hemp 

 was only a coarser kind of the same material, and would be de- 

 stroyed by the oxide of iron. He maintained also, and gave ex- 

 cellent specimens of the fact, that hemp can be preserved for any 

 length of time, and even the salt of the sea preserves the fibre, 

 whilst on the other hand it destroys iron. Captain Rowett made a 

 forcible appeal for the adoption of the hemp cable, which would 

 be half the cost of cables now used, and so do great service to the 

 millions who desire to have ocean telegraphy within their reach ; 

 and as there was no possibility of doing justice to the subject at a 

 meeting of a section of the Association where so much business 



