694. REPORT—1863. 
These results go to prove that external pressure exercises a decided influence 
upon the electrical condition of gutta percha and india-rubber, and probably 
upon every other substance in nature. They go to prove, moreover, that this 
change of electrical condition cannot be attributed to general physical laws,— 
as, for instance, to the supposition that the nearer approach of the particles 
under the influence of external pressure interferes with their transmission of 
electrical motion,—but must be referred to the specific atomic arrangement of 
the material in question. 
It appears to me desirable that these researches should be extended to other 
materials, including both good and bad conductors, in order to arrive at more 
satisfactory general conclusions ; but such experiments are of a difficult and 
expensive nature, and I thought that even the few results I have put together 
in this paper would be acceptable to the Association. 
On the Construction of Iron Ships and the Progress of Iron Shipbuild- 
ing on the Tyne, Wear, and Tees. By Cuaries M. Paumer. 
Tue art of constructing ships dates from remote antiquity, and we find in 
history, sacred and profane, many particulars of the ships in use in ancient 
times. As civilization advanced, and the science of navigation became better 
understood, ships increased in size, strength, capacity, and speed. Year after 
year brought its improvements, century after century its changes, until the 
art of shipbuilding in wood approached perfection, and the rude coracles 
and row galleys of our forefathers had given place to the clipper-ship, with 
its fine lines, tapering masts, and flowing canvas, the merchantman driven 
by steam at a high speed across the ocean, and the three-decked, steam- 
propelled man-of-war. Then a demand arose for vessels of a still higher 
character—merchantmen possessing still greater speed, men-of-war suffi- 
ciently powerful to resist the destructive shot and shell which the genius of 
men like our friend and townsman, the President of the Association, was 
inventing. With wood as the material to be employed, this demand could 
not be met; but human skill was equal to the emergency. The important 
discovery was made that ‘ships built of iron float lighter, strength for 
strength, than ships built of wood;” and although for many years the pre- 
judices of some men and the interests of others prevented the general adop- 
tion of the principle, it eventually triumphed, and now iron is rapidly super- 
seding wood as material of which ships are constructed. 
The principal advantages that are claimed for ships of iron, as compared 
with vessels of timber, are briefly these :— 
In vessels of 1000 tons the iron ship will weigh 35 per cent. less than 
the timber vessel, the displacement of water being the same. The iron 
ship will therefore carry more weight, and as the sides are only about one- 
half the thickness, there will consequently be more space for cargo. The 
additional strength obtainable, too, allows iron ships to be built much longer 
and with finer lines, thus ensuring higher sailing or steaming qualities, with 
greater carrying power, and therefore greater commercial results. In 
wooden vessels, repairs of ruinous extent are frequently required, while the 
repairs in iron ships are generally of a lighter character, and are only needed 
at long intervals. An iron ship is not liable to strain in a heavy sea, 
whereas the straining of a timber vessel often damages a valuable cargo. The 
bilges of an iron ship ean be kept clean and free from the disease-engendering 
