PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 627 



the small perforated aperture in tlie centre of disc B, immediately over _ 

 which is the glass tube G, into which it rises to the point indicated by the 

 register, 



A is a gum ring or cushion to receive the conical end of the glass tube 

 G, which is firmly pressed upon it by screwing on the top cap of the brass 

 tube F. 



It is desirable that this gauge should never be placed in a position where 

 it can be heated to an extent which would destroy the gum diaphragm. 

 The steam pipe should be sufficiently long and slightly curved or bent to 

 allow the accumulation of water, so as to prevent the steam from super- 

 heating the body of the gauge. With these precautions it will prove 

 always true, and may be said to be almost indesti'uctible. 



Mr. Fisher said that he had a simple and effective plan to propose for 

 ascertaining the pressure of steam within a boiler. It was to raise the 

 lever of the safety valve from time to time with an ordinary spring bal- 

 ance; the weight required to raise the lever as indicated by the Spring 

 weighing machine, deducted from the known weight oh the safety valve, 

 will give the exact pressure within the boiler. 



Guns and Gunboats. 



Mr. Ileaton took the floor by invitation and continued his lecture com- 

 menced at the last meeting.'']^ He exhibited a very complete model of a 

 vessel of war constructed upon his design, and having a propelling power 

 consisting of a spring with the requisite gearing. The model also em- 

 braced a plan for steering the vessel when under very slow motion by the 

 rotation of a wheel whose axis is parallel to the keel. The guns in this 

 model could all be fired on either side of the vessel; they were stationed 

 near the central line, and were protected by zigzag biilwarks. The various 

 kinds of guns in use were all explained by the speaker, and their merits 

 and demerits fully set forth, after which he answered queries from Messrs. 

 Dibben, Rosevelt, Garvey and Bartlett, 



Mr. Justice gave an account of the late improvements made by Captain 

 Parrott upon his guns, which consisted in the substitution of steel rings in 

 the place of the iron bands formerly used. 



Steel. 



Mr. A. L. Fleury, of Philadelphia, exhibited specimens of steel made by 

 a process claimed to be new, which he fully explained. It consists in heat- 

 ing scraps of iron in crucibles or their equivalents to a high degree and 

 then introducing into the crucibles oxyde of iron or other suitable substance 

 containing oxygen, and immediately after pouring a quantity of melted 

 pig iron into the crucibles. The amount of oxyde is so proportioned that 

 any iexcesps of carbon which exists in the cast iron above that necessary to 

 form steel, will combine with the oxygen gas liberated from the oxyde and 

 pass off with the products of combustion. By increasing the proportion of 

 oxyde of iron the steel may be decarbonized to such an extent as to reduce' 

 it to wrought iron. It will of course be understood that the steel may be 

 greatly varied in quality by the introduction of other substances in con- 



