PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION/ 533 



mon upright boiler, which has come into use since Maceroni's experiments; 

 but when the flame is driven horizon tall}'- among- upright tubes, as in the 

 water-tube boilers of Montgomery, Martin and others, it is fully as effective 

 as in flue-tube boilers. This direction of the flame may be give in Mace- 

 roni's boiler; and with this modification it would probably make steam as 

 rapidly as any boiler of equal surface, when the best proportions have 

 been found by trial. 



Either this boiler, or that of Ogle & Summers — which differs from it 

 chiefly in having a flue through each tube — is the orig'nal of the water-tube 

 boilers now in general use in our navy. Earl Dundonald adopted Ogle's 

 boiler, deeming it the best for marine service; but probably on account of 

 the difficulty of keeping it clean, he changed the plan and produced what 

 is called the Dundonald boiler; in ships the tubes open into chambers large 

 enough to admit men to clean them. This was an abandonment of the 

 principle of safety, which consists in avoiding large chambers; an aban- 

 donment to which Earl Dundonald was probably constrained by the want 

 of a surface condenser, a want now so well supplied that many vessels 

 have used them for years without repair and with advantage. The Dun- 

 donald boiler sent its smoke downward among the tubes; but its movement 

 was slow and mainly parallel with the tubes. 



The next step toward the present favorite boiler was made by Mr. James 

 Montgomery. He sent the smoke swiftly across the upper half of the 

 tubes, and returned it, under a diaphragm, swiftly across the lower half of 

 the tubes. The swift motion of the hot gases heated the tubes effectively, 

 as the swift motion of cool air cools a body more efficiently than air of the 

 same temperature that moves slowly. 



The boner as modified by Mr. D. B. Martin is free from the engineering 

 objections that obviously hold against the original of Macercjni or Ogle. Its 

 tubes are so short that they can be taken out for repair, and can be cleaned. 

 But this is because there is room for men to work in; and this room, when 

 the boiler is at work, holds power enough to rend a ship in pieces. Thus 

 we have another objection on the score of humanity, which is the greater 

 objection we are called upon to determine with a view to practical improve- 

 ment, if we determine that the inferiority^ in an engineering sense, of the 

 small-chambered boiler is not so great as to outweigh the consideration of 

 safety. 



On this all-important point the committee can at this time only give an 

 opinion, or rather impression, that arises from a general view of the pro- 

 gress of steam engineering. All the engines and boilers now successfully 

 in use have become what they are by a long course of practice and im- 

 provement. They have had break-downs, partial failures and small 

 economy in their beginning. So, it may be expected, will it be with new 

 plans — plans old in point of time, but new in respect to practice. They 

 may be troublesome for many years, yet, after as muclf exercise upon them 

 of talent and capital as have been lavished on the plans now in the ascend- 

 ant, they may be as cheap and convenient. It is the opinion of many of 

 the most celebrated engineers in the world that these boilers, when their 

 proportions and details are worked out, will be lighter, less bulky and 

 cheaper than the present boilers; and your committee have a faith, which 



