1864. | Mechanical Science. 157 
No iron-master nor engineer can afford to be ignorant of this simple 
and effectual mode of determining the structure and texture of the 
metal he has to do with. 
Two papers were read on Submarine Telegraphy—one by Captain 
Selwyn, R.N., and the other by Mr. Fairbairn, the latter referring to 
the mechanical properties of telegraphic cables. Captain Selwyn 
urged that the ordinary cable defended by a spiral wire was weak in 
principle, as the first strain must be borne by the straight conducting- 
wire which alone requires defence. He also pointed out that a line 
to America might take advantage of a shoal in 38° 50’ W. long. in the 
direct great circle track between England and Bermuda, thus dividing 
the cable into two sections. Lastly, he recommended that in place of 
winding the cable as at present, so as to be packed in a ship’s hold, 
it should be wound on one or more closed cylindrical drums acting as 
floats, and large enough to carry the whole weight. Such cylinders 
need not be larger than an ordinary canal barge, and could be towed 
by a steamer, unwound when convenient, and left floating in case of 
storm. They would be perfectly independent and much cheaper, as 
well as safer, than the method hitherto adopted. Captain Selwyn 
proposed for the Atlantic cable a cylinder 120 feet long by 90 feet 
diameter, which would carry 22,000 tons. The whole weight of the 
present Atlantic cable is about 6,000 tons. 
Mr. Fairbairn’s experiments are more fully described at p. 624 of 
this Journal, than they were before the Association. 
