MECHANICS AXD USEFUL AKTS. 4:3 



above referred to. which has so long paralysed the efforts of shipbuilders, 

 must now give place to the more hopeful one, namely, that the resistance to 

 the motion of boats may be made the same for ah 1 velocities, by suiting the 

 form of the boat to the velocity required of it. A similar proposition, in 

 regard to railway?, was early made by Mr. Maclaren, with the happiest 

 results, at a time when eight or ten miles an hour was the greatest speed 

 they were thought capable of achieving. The author stated, that it was to 

 be hoped that enterprising shipbuilders would not be slow in realizing the 

 same speed in steamboats which the railway engineers have done in the rail, 

 and that by the elaboration of the self-same proposition, namely, that the 

 resistance to motion may be made the same for all velocities. A considerable 

 advance in speed has been attained of late years by fining the lines of steam- 

 boats, by cutting them in two, and inserting an addition to their length 

 amidships, or by increasing their original length, though this last is often 

 marred by a proportionately increased breadth of beam. These were all steps 

 in the right direction, and tend to support the principle just stated ; but 

 nothing short of an attempt to reach thirty or forty miles an hour will satisfy 

 the occasion. Various members discussed the subject of the paper at some 

 length ; and while they admitted, as mathematicians, ftie correctness of the 

 principle advanced by Mr. Aytoun, they considered that that gentleman had 

 not given sufficient weight to other sources of resistance to the motion of 

 boats, such as friction, which would become very formidable when boats 

 of the great length which he advocated, were urged to great speed. 



IXTEEESTIXG EXPERIMENTS WITH STEA3I BOILERS. 



Mr. William Radway, of England, published in the London Mining Journal 

 the following detail of experiments recently made by him on the explosion of 

 steam boilers : 



He had a cylinder 4^- feet long, 12^ inches diameter, of an inch thick, of 

 good iron, and capable of standing a pressure of 480 pounds to the square 

 inch. This he sometimes used as a steam boiler, and had a furnace under 

 it of 2J square feet. A short time since it was worked till it was empty, 

 while a powerful fire was under it, and as a consequence, one-third of the 

 lower surface became red hot. In this state 4 gallons of hot feed water were 

 let into it slowly, which produced a roaring sound, but not sufficient steam to 

 raise a safety valve of 10 Ibs. weight to the inch. As the steam rose, the gas 

 in the boiler was collected and tested, and was found to be only atmospheric 

 air not an inch of hydrogen. Shortly after this he evaporated nearly all the 

 water in the boiler, and then left it to cool, with the safety valve. open, to 

 allow the free entrance of air. Xext day he replaced the safety valve, loaded 

 it with 30 Ibs. to the square inch, and forced in a cubic foot of impure hydrogen 

 gas. 



He then, by a contrivance, ignited and exploded this hydrogen gas and 

 air mixture in the boiler ; a puff came through the safety valve, and a small 

 . steam engine was worked for 42 strokes by it, but the boiler was neither 

 burst nor strained. 



