charge of the installation, but where it will not be interfered with by irresponsible persons. In large installations, where a number of separate buildings receive service-pipes from one long main, each service-pipe should be provided with a governor. GASHOLDER PRESSURE.--In drawing up the specification or scheme of an acetylene installation, it is frequently necessary either to estimate the pressure which a bell gasholder of given diameter and weight will throw, or to determine what should be the weight of the bell of a gasholder of given diameter when the gas is required to be delivered from it at a particular pressure. The gasholder of an acetylene installation serves not only to store the gas, but also to give the necessary pressure for driving it through the posterior apparatus and distributing mains and service-pipes. In coal-gas works this office is generally given over wholly or in part to a special machine, known as the exhauster, but this machine could not be advantageously employed for pumping acetylene unless the installation were of very great magnitude. Since, therefore, acetylene is in practice always forced through mains and service-pipes in virtue of the pressure imparted to it by the gasholder and since, for reasons already given, only the rising-bell type of gasholder can be regarded as satisfactory, it becomes important to know the relations which subsist between the dimensions and weight of a gasholder bell and the pressure which it "throws" or imparts to the contained gas. The bell must obviously be a vessel of considerable weight if it is to withstand reasonable wear and tear, and this weight will give a certain hydrostatic pressure to the contained gas. If the weight of the bell is known, the pressure which it will give can be calculated according to the general law of hydrostatics, that the weight of the water displaced must be equal to the weight of the floating body. Supposing for the moment that there are no other elements which will have to enter into the calculation, then if _d_ is the diameter in inches of the (cylindrical) bell, the surface of the water displaced will have an area of _d^2_ x 0.7854. If the level of the water is depressed _p_ inches, then the water displaced amounts to _p_(_d^2_ x 0.7854) cubic inches, and its weight will be (at 62° F.): (0.7854_pd^2_ x 0.03604) = 0.028302_pd^2_ lb.