The power of a steam engine does not lie in its cylinders, beam, shatt, and levers ; no, these only apply the power usefully. The force that moves the engine is steam, and that which produces steam is a, chemical action the combustion of fuel. Combustion appears to be-a very simple operation, but we do not know a chemical phenomenon more difficult of a clear explanation. It consists of decomposition and recomposition. In the first place coal is solid carbon, a heavy substance, but if this be united chemically with oxygen, in parts (CO2) it becomes carboni* acid gas. This gas can only be formed of carbon and oxygen, by the chemical action which we eall combustion, as exhibited in a fire (we do not speak of fermentationslow combustion). The question may well be asked, what is the cause of combustion ' It is an important one, and like a great many others, it is easier asked than answered. We only know that when II certain amounirloof heat is generated in fuel, by the particles of it changing their condition and arrangement, the oxygen of the atmosphere separates from the nitrogen with which it is chemically united, and combines with these carbon particles forming carbonic acid gas. This action is called combustionfire great heat is developed, the coal is said to be decomposed by it, and the union of the carbon 'particles with the oxygena new composition forming a gM, which, strange to tell, extinguishes flame and fire, although it is itself the direct product of fire. The heat generated by combustion imparts a like action to water, through bars of brass and plates of iron, and changes its condition from water to steam, which occupies 1,700 times the space of water. It is this expansive forcethe' combination of water and heat, which i. the vital power of the steam engine. There is just lis much philosophy to be learned in investigating the causes of making a tea kettle boil, ail thoBe of volcanic eruption, and the ' infoima- (tion to be derived is'more practical and useful. As carbonic acid gas is formed of (CO') it requires two pounds of oxygen to saturate every pound of coal to form this gas. If, when burning coal, it is not completely saturated with oxygen, a gas called carbonic oxide (CO) is formed With one pound of oxygen to one of carbon, which is not so ejpansive, consequently a great loss of heat is experienced. We1 then see the necessity of supplying fuel in a state of combustion, especially when' fresh coal is put on the fire with a plentiful supply of oxygen. As the atmosphere is composed of 21 volumes of oxygen to 79 of nitrogen, it follows that a great quantity of air must pass through a fire to suppl y a few pounds of coal with sufficient oxygen to form perfect combustion. For every two pounds of oxygen extracted from the atmosphere, exactly 7 pounds of nitrogen must also pass through a fire (nitrogen is the heaviest gas,) consequently nine pounds of air must pass through a fire for the perfect combustion of every pound of pure carbon coal. Now, as 100 cubic inches of the sir weigh 31'0117 grains, and as 5,760 - grains is one pound, and 1,728 cubic . inches form 1 cubic foot, it follows, 5760X10(J-:-31' 0117= (leaving out the decimals) that we have 18,583 cubic inches, or more than 10 cubic feet of air to weigh 1 lb., which makes more than 90 cubic feet of air which pass through a fire for the perfect combustion of one pound of coal. In furnaces, it is calculated that nearly, 200 cubic feet of air pass through the fuel for the combustion of one pound of coal. We see by this what an amount of air is necessary to be admitted into rooms during the winter season for the complete combustion of the fuel in stoves and grates. This must be supplied through crannies, cracks, or open seams, for it is chemically impossible that the fire will burn unless supplied with its due proportion of oxygen. This is the reason why, in a close w m rom, it we lay our hand upon any seam near a window, we feel a rapi!l. current coming in. This fact teaches us how necessary it is to have rooms well ventilated, and why large rooms are more healthy than small ones. How won- d erful an atmosphere is that of ours, which acts as the generator, regenerator, and conductor of both, heat and cold; its own purifyer and renovator. Well Sln ArteBlan Wells. (Continued from page 98 ) TOOLS.In the annexed cut, figures 1, 2, and 3 show an elevation, plan and section of an auger. The tapped socket is for the purpose of allowing the rods to be screwed into it. The leading nose, a, is for cutting, and the valve, b, is to prevent the material that is cut from falling out of the auger while it is being raised to the mouth of the bore. Figures 4, 5, and 6 represent a similar auger of larger size; it has not a screw tapped into a socket as the former one, but is bolted, instead, to an intermediate rod. Figs. 7 and 8 are two views of a small auger with a longitudinal slit and no valve; ' it is used chiefly for boring through clay and loam. In very stiff clay the slit may be a very wide one, in solt clay narrower ; w\lile in very moist ground, it's inadmissible altogether. Figs. 9, 10, and 11 show an S chis el for cutting through rocks, flints, &V; this tool is worked. with a vertical and circular motion. -a Thomas Prosser, C. E ... of No. 28 Platt street, this' city, who furnishes tubes answer, able for Artesian borings, has issued a small pamphlet on this subject. It is merely, as it states, a fevir loose remarks thrown together with reference to works where other information may be found. It quotes an extract from the " London Mechanics' Magazine," which recommends Dr. Pott's method of sinking iron tubes for wells of large diameter, when the substances to be bored consist of loose sand or the like. This process of sinking tubes is by atmospheric pressure, extracting all the air from the interior of the tube by an air-pump, when it - descends with great rapidity. It is secured by a patent in the United States, of which C. Pontez, C. E., is the assignee. The process is illustrated on - the first page of this volume of the Scientific American. The boring tool must always excavate or bore, an opening somewhat wider than the tube, in order that it may descend into its proper place as the sinking proceeds. If the boring for water was through a rolid rock, no cylinders would perhaps require to . be sunknone if there were no veins of water met wit!? above the main supply. When the lower water supply is depended upon entirely, no intermediate seam of water should be allowed to have any communion with that which rises from the lowest depth; it is therefore necessary that the sunken pipes should be well fitted, to prevent any communication between the lower water stratum, and any one that may be above it. The surface water must also be perfectly stopped out, and Pott's iron cylinders appear to us to be a good plan for this. The common way is to stone or brick up the first 30 or 50 feet o f excavation, puddling between the outer courses of brick with good clay, and making good joints with hydraulic cemeht. (To be continued.)