A patent was granted to Henry Waterman of the city of Williamsburgh, N. Y., on the 28th of last December, for an improvement in steam boile.rs, so as to render them safe from dangerous explosions. The claim for this pe-tent will be found on page 134, this volume of the Scientific American. On Wednesday, last week, the 2nd inst., we witnessed an experi ment with a large cylinder boiler, to test the merits of this invention. The experiment was made at Messrs. Waterman's Block Fac tory, near Peck Slip Ferry, Williamsburgh. Mr. Curtis, Inspector of Boilers, in this city, and several other scientific gentlemen, were present. The improvement consists in having a top plate of the boiler perforated with a number of holes opening into a small cham ber inside of a dome. The top plate of the small chamber, is called the safety plate," and is made of thin brass capable of standing a certain defined pressure according to its thick ness and area, of at least six or seven times less than the iron boiler plate. This safety plate is grooved and screwed down by a ring on the perforated top plate of the boiler, leav ing a small chamber between the two. The steam from the boiler passes through the holes spoken of, and presses against the brass or safe ty plate, which, when the steam rises to the defined pressure, said plate, is torn, open, (brass and copper do not fly to pieces like iron plate), the steam escapes up the dome, and thus the boiler is relieved of its excess of pressure, and all danger of its flying to pieces obviated. The object in having the boiler plate perforated, is to prevent the water from being thrown out of the boiler with the steam, when the safety-plate is torn by the pressure ; also to offer a considerable resistance to the escaping steam, so that a too large volume may not jump at once from rest, and by its great and suddenly applied dynamic force tear away the top plate of the boiler. When the safety plate, there fore, is torn open, the boiler is at once relieved of its excess of pressure, hut in such a manner that the water is retained inside, and the con fined steam allowed to escape without danger to the boiler, or any person who may be around it. The experimental brass plate on the boil er, which we saw, was in thickness 0'25 wire gauge, and 19 inches in diameter. We were told that it would be torn open at 60 lbs. pres sure ; and at that exact point, while looking on the steam gauge, the plate was suddenly torn open, but not off, and the indicated pres sure suddenly fell from 60 to 40 lbs.; and gra dually to 10 lbs. A boiler should never be allowed to carry over one-third of the pres sure it is capable of standing, therefore if a boiler is capable of standing 300 lbs. pressure it should only be loaded with 100 lbs., which will be the strength of its safety plate; others are made for boilers, varying from 20 lbs., and upwards, thus insuring a certain and safe relief when the defined pressure point is reached. When the water in a boiler falls below the water line, and covers the flues in a very thin sheet, steam is generated with great rapidity, and we have often seen a very sudden rise in the gauges, from 60 to 80 lbs., a safety valve in such cases presents an inefficient opening for such a sudden generation of steam; this safety plate appears to answer a better pur pose, by being torn open before the flues are uncovered. There can be no doubt but it is more econo mical to generate steam under a high pres sure, and then expand it for working an en gine, than to generate it under a low pressure. A means to insure safety and work high pres sure steam, will enable our ocean steamships to save much fuel. This object appears to us to be obtained by Mr. Waterman's improve ment, which has been tested a number of times with uniform success.