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THE POPULAR SCIENCE MONTHLY. 



great extent counterbalanced by the value of the steamship, which 

 bears to that of the sailing-vessel per net carrying ton the proportion 

 of 3 : 1, thus reducing the ratio in favor of steam-shipping as 13"29 to 

 10"38, or in round numbers as as 4 : 3. In testing this result by the 

 charges of premium for insurance, the variable circumstances of dis- 

 tance, nature of cargo, season, and voyage have to be taken into ac- 

 count ; but, judging from information received from shijD-owners and 

 underwriters of undoubted authority, I find that the relative insurance 

 paid for the two classes of vessel represents an advantage of 30 per 

 cent in favor of steam-shipping, agreeing very closely with the above 

 deductions derived from statistical information. 



In considering the question how the advantages thus established in 

 favor of steam-shipping could be further improved, attention should 

 be called in the first place to the material enrployed in their construc- 

 tion. A new material was introduced for this purpose by the Admi- 

 ralty in 1876-'78, when they constructed at Pembroke dock-yard the 

 two steam corvettes, the Iris and Mercury, of mild steel. The pe- 

 culiar qualities of this material are such as have enabled ship-builders 

 to save 20 per cent in the weight of the ship's hull, and to increase 

 to that extent its carrying capacity. It combines, with a strength of 

 thirty per cent superior to that of iron, such extreme toughness, that 

 in the case of collision the side of the vessel has been found to yield 

 or bulge several feet without showing any signs of rupture, a quality 

 affecting the question of sea-risk very favorably. When to the use of 

 this material there are added the advantages derived from a double 

 bottom, and from the division of the ship's hold by means of bulk-heads 

 of solid construction, it is difficult to conceive how such a vessel could 

 perish by collision either with another vessel or with a sunken rock. 

 The spaces between the two bottoms are not lost, because they form 

 convenient chambers for water-ballast, but powerful pumps should in 

 all cases be added to meet emergencies. 



The following statement of the number and tonnage of vessels 

 building and preparing to be built in the United Kingdom on the 30th 

 of June last, which has been kindly furnished me by Lloyd's, is of 

 interest as showing that wooden ships are fast becoming obsolete, and 

 that even iron is beginning to yield its place, both as regards steam- 

 ers and sailing-ships, to the new material mild steel ; it also shows 

 that by far the greater number of vessels now building are ships of 

 large dimensions propelled by engine-power : 



