Consequently a bell which is _d_ inches in diameter, and gives a pressure of _p_ inches of water, will weigh 0.028302_pd^2_ lb. Or, if W = the weight of the bell in lb., the pressure thrown by it will be W/0.028302_d^2_ or 35.333W/_d^2_. This is the fundamental formula, which is sometimes given as _p_ = 550W/_d^2_, in which W = the weight of the bell in tons, and _d_ the diameter in feet. This value of _p_, however, is actually higher than the holder would give in practice. Reductions have to be made for two influences, viz., the lifting power of the contained gas, which is lighter than air, and the diminution in the effective weight of so much of the bell as is immersed in water. The effect of these influences was studied by Pole, who in 1839 drew up some rules for calculating the pressure thrown by a gasholder of given dimensions and weight. These rules form the basis of the formula which is commonly used in the coal-gas industry, and they may be applied, _mutatis mutandis_, to acetylene holders. The corrections for both the influences mentioned vary with the height at which the top of the gasholder bell stands above the level of the water in the tank. Dealing first with the correction for the lifting power of the gas, this, according to Pole, is a deduction of _h_(1 - _d_)/828 where _d_ is the specific gravity of the gas and _h_ the height (in inches) of the top of the gasholder above the water level. This strictly applies only to a flat-topped bell, and hence if the bell has a crown with a rise equal to about 1/20 of the diameter of the bell, the value of _h_ here must be taken as equal to the height of the top of the sides above the water-level (= _h'_), plus the height of a cylinder having the same capacity as the crown, and the same diameter as the bell, that is to say, _h_=_h'_ + _d_/40 where _d_ = the diameter of the bell. The specific gravity of commercially made acetylene being constantly very nearly 0.91, the deduction for the lifting power of the gas becomes, for acetylene gasholders, 0.0001086_h_ + 0.0000027_d_, where _h_ is the height in inches of the top of the sides of the bell above the water- level, and _d_ is the diameter of the bell. Obviously this is a negligible quantity, and hence this correction may be disregarded for all acetylene gasholders, whereas it is of some importance with coal-gas and other gases of lower specific gravity. It is therefore wrong to apply to acetylene gasholders formulæ in which a correction for the lifting power of the gas has been included when such correction is based on the average specific gravity of coal-gas, as is the case with many abbreviated gasholder pressure formulæ.