152 Recent Advances in Mechanical Science. 



This is no doubt very good. But I may point out that it is 

 not by any means usual or economical to carry coal at so high 

 a speed as 15 miles an hour at sea. To illustrate this, a penny- 

 worth of coal will carry a ton at i '^\ miles an hour no less than 

 365 miles, or at 12^- miles an hour about 390 miles. In the 

 " Gaekwar," which we built about a year and three-quarters ago, 

 and which is, I imagine, about aseconomicalash'pas canbefound 

 afloat, a peimyworth of coal has absolutely carried a ton 448 

 miles at a speed of 12 miles an hour — i.e.^ she has carried 6,575 

 tons of dead weight of coal at a speed of io| knots (=12 miles 

 an hour) on a consumption of 27 tons of coal per day of 24 

 hours, and this steamer has been regularly doing this between 

 Liverpool and Calcutta. 



Well, to return to my story, I joined in the conversation 

 with these railway gentlemen, and got them to guess what 

 distance a ton could be carried afloat at 15 miles an 

 hour for onepenny worth of coal. One, after some con- 

 sideration, thought, all things considered, that it might be 

 a longer distance than the train could carry it, probably 40 

 miles ; the others made various guesses up to 80 miles. They 

 would hardly believe me when I told them the fact. You will 

 agree with me that it is an astonishing way of looking at it. 



These few remarks on the subject of coal naturally lead to the 

 consideration of the appliances in which the coal is burnt and 

 steam is raised. Probably no subject in connection with 

 engineering has given more scope or variety in design than 

 boilers. I remember seeing many years ago vessels fitted and 

 worked with copper boilers, simply arranged with a furnace and 

 a return flue to the chimney, worked at a maximum pressure of 

 61bs. on the square inch ; while now there are two vessels of our 

 own build at sea (the " Philadelphian " and the " Lancastrian ") 

 working across the Atlantic with 200 lbs. boiler pressure upon 

 the square inch, giving most satisfactory results. Probably no 

 type of boiler gives a belter result than that at present in use 

 in the mercantile marine. Designers seem to have had to 

 settle down to this type after having pursued others through 



