CORRESPONDENTS who expect to receive answers to their letters must, tn all cases, sign their names We have a right to know those who seek information from us; beside, as sometimes happens, we may prefer to address correspondents by mail SPECIAL NOTEThis column is designed for the general interest and instruction of our readers,notf or gratuitous replies to questions of a purely business or personal nature We will publish such inquiries, howeverwhen paid for as advertisemets at $1*00 a line, under the head of "Business and Personal" KWAH reference to back numbers should be by volume and page H A, of N JIf an upright cylindrical vessel be filled with water, the pressure against each point of the walls varies from nothing at the top to a quantity proportional to its depth at the bottom It will be upon each square inch of area equal to a column of water of a hight found by measuring from the center of the area to the surface of the water, and having for its base one square inch If now the top be closed and pressure be applied through a tube or other means, this pressure will be transmitted equally in all directions That is, suppose the pressure at the top to be nothing previous to applying pressure, and at the bottom to be ten pounds per square inch, then if ten pounds additional pressure to the square inch were applied, the pressure on the top would become ten pounds to each square inch and at the bottom twenty pounds And if the pressure were sufficiently increased*the cylinder being of uniform thickness and strength throughout would burst first at the bottom In a vertical boiler 17 feet high the difference in pressure against the walls at the top and at the bottom would be equal t about seven and one half pounds per square inch B D M, of N TAll kinds of bricks are more or less conductors of heat, and though you should cover your boiler with a mountain of masonry you cannot avoid some loss Nevertheless there is great economy in such a covering The man who will flrst discover a means whereby the heat of boilers, steam pipes, and cylinders, can be wholly confined, will immortalize his name, and secure the means of obtaining the largest fortune ever yet made, but we don't think he is born yet ST, of MassIt has been claimed by some engineers that the heat expanded in producing a proper draft by means of a chimney will produce a still better draft by means of a blower A practical test of this statement would be of value R H, of N HThe oscillations of the common pendulum only take place in equal times within a certain amplitude of arc This amplitude ought not to exceed live degrees The varying density of the atmosphere making unequal resistances to the oscillations of the pendulum, is a constant source of irregularity, as well as the variation in the length of the pendulum rod C P, of AlaNo more heat can be theoretically obtained by the conversion of mass motion into heat, than the heat required to produce the mass motion Practically not so much Could more be obtained the problem of a perpetual motion would be solved S W Gr, ofThe length of a telescope is adjusted to the focal distance of the lenses The magnifying power depends entirely up on the latter, and the relation between the power of telescope and its length is only an indirect one The power of a telescope depends upon tlie focal distances of the lenses and the illuminating power of the object glass The latter increases with thesize of the object glass H R, S, of VtA great many machines for cutting stono for architectural work have been tried "We do not think any of them have been found adapted to general use, or have attained much success We do not know that the carbon tool point has been specially applied to this purpose N 0, of KyAll springs lose their power by oycrtaxing them The load should always be less than that required to produce a permanent set You will also find that brass wire will vary very much in elasticity throughout a coil The only safe way is to keep within the iaferior limit R C, of La'The action of an airpump will cease to extract airfroma receiver as soon as the expansive force of the residual air or gas becomes too weak to raise the valves, The best pumps leave about one thousandth of the air unexhausted L M V, of N YYou can fasten rubber hose to a coupling1 so as to be watertight by winding it with annealed brass wire You will find no trouble in accomplishing it L C, of KansasThe substance of which you make inquiry is mostly gum dextrine You will find a process of making this gum in Dr Ure's "Dictionary of Arts and Manufactures," or you can purchase it ready made, of dealers It dissolves readily in water, and is very adhesive, G O,, ofIn your case capillary attraction is as you suppose, overccme by centrifugal force The oiler you employ is in our opinion not adapted to a fast running pulley