This invention consists in combining tight chambered mercury gages for indicating steam pressure or vacuum, with self-adjusting or floating magnets, magnetic needles and index dials, in such a manner as to give true magnetic indications of varying degrees of pressure occurring within steam boilers, or of vacuum in eondeners, the mercury, floating magnet, and body of air through which this result is accomplished being enclosed in a chamber, without the necessity of employing any communicating means with the exterior dial plate likely to affect the accuracy of their movements, the whole being of such a character as to be adapted to the knowledge of the engineer, and completely under his COlltrol, and susceptible of being tested at any time, and adjusted if incorrect while in position for work. In our engraving, Fig. 1 represents a front deration of the improvAd magnetic pregg,,;-e gage, with the needle indicating thirty pounds pressure. Fig. 2 is a front view. of the gage, with the dial plate removed, to expose the contents of the same ; and Fig. 3 is a vertical section of the same. Similar letters in the figures refer to corresponding parts. The magnet, D, having a north and south pole, may be about four inches in length, and is provided with pivots, A, at the center, upon which it is hung within a small pressure or vacuum gage chamber, C, formed by a brass index or dial plate, B, and a dish-shaped iron casting. The length of the ma_gnet should not be increased, for the reason that when the magnet and needle are placed at right angles their points are so remote that certain action cannot be relied upon. The exact form of the magnet is not mnterial, except that one arm is required to be larger than the other, so as to ensure its floating in relation to the surface of the mercury represented, and rising and falling with it. The magnetic needle is made and suspended outside the dial plate in the ordinary way, and corresponds in length with the magnet, D. E is a stop, forprevent-ing the poles of the magnet f"om changing sides in the chamber, and thus insuring the true position of the magnet and index point of the needle. F is a bent tube, which acts as a receiving chamber (in place of which a secondary chamber may be constructed within the body of the instrument) for the mercury, while charging the gage with the same, previous to the application of pressure, and from which tube or chamber the mercury is forced by the pressure of the steam into the chamber of the gage in the exact ratio of the f pressure applied. At the top of the chamber, i C, is an opening, G, for the purpose of charg-! ( ing it with mercury to adjust the point of the needle to the scale on the index. To deter- mine this, mercury should be poured in until the point of the needle points to zero, or to the 0 on the indax, when the opening is closed by a plug, or other means, and the instrument is in working order. The index on the dial plate is correctly graduated under a column of mercury. The index for vactfum may be made on the opposite side of the same dial plate, and the same instrument may be used either as a pressure or vacuum gage by changing the conuections from a boiler to a condenser, or from a condenser to a boiler, and charging the gage, as before stated, for a pressure gage, or by filling the entire chamber with mercnry beforo closing the opening, G, tor a vacuum gage. The pipe, F, is provided with a cock, H, for passing off any superabundunt mercury that may be contain- ed in the chamber, C, to admit of the ready adjustment of the instrument. From the foregoing description it wiII be observed th"t the working parts of this simpIe and effective steam gage are not encumbered by any stuffing box or other device likely to create friction, and in any manner retard their action, "nd that the magnetic attraction between the magnet, D, and needle through the brass dial plats will at all times keep the two parallel, and that moreover the engineer can at all times properly adjust the needle to the dial plate by simply shutting off the pressure of the steam from the boiler by closing a cock, removing the plug from the opening, G, and after setting the instrument again inserting the plug and closing the cock. This important feature places the instrument under the Mle control of the engineer, and enables him to test its accuracy at all times a desideratum not possessed by the ordinary steam gages in use. It was patented by Joshua Lowe and Daniel Barnum, on the 8th of July, 1858. Any further information can be had by addressing Daniel Barnum, No. 2 Sussex Place, Jersey City, N. J.