The best length of bubble depends on the length or curvature of the tube, a short babble being required for a tube with a small radius of curvature, and increasing regularly in proportion with the increase of the radius of curvature.

Springs, Steel. -to find elasticity of a given steel-plate spring: Breadth of plate in inches multiplied by cube of the thickness in 1/16 in., and by number of plates. Divide cube of span in inches by product so found, and multiply by 1.06. Result, equal elasticity in 1/16 in. per ton of load. To find span due to a given elasticity and a number and size of plate: Multiply elasticity in sixteenths per ton by breadth of. plate in inches, and divide by cube of the thickness in inches, and by number of plates; divide by 1.66, and find cube-root of quotient. Result, equal span in inches. To find number of plates due to a given elasticity, span, and size of plates: Multiply the cube of the span in inches by L.66. Multiply the elasticity in sixteenths by the breadth of the plate in inches, and by the cube of the thickness in sixteenths; divide the former product by the latter. The quotient is the number of plates. To find the working strength of a given steel-plate spring; Multiply the breadth of plate in inches by the square of the thickness in sixteenths, and by the number of plates. Multiply also the working span in inches by 11.8; divide the former product by the latter. Result, equal working strength in tons burden. To find span due to a given strength and number and size of plate: Multiply the breadth of plate in inches by the square of the thickness in sixteenths, and by the number of plates: multiply also the strength in tons by 11.3; divide the former product by the latter. Result, equal working span in inches. To find the number of plates due to a given strength, span and size of plate: multiply the strength in tons by span in inches and divide by multiply also the breadth of plate in inches by the square ■ thickness in sixteenths; divide the former product by the latter. Result, equal number of plates. The span is that due to the form of the spring loaded, Extra thick plates must be replaced by an equivalent number of plates of the ruling thickness before applying the rule. To find this, multiply the number of extra plates by the square of their thickness, and divide by the square of the ruling thickness; conversely, the number of plates of the ruling thickness to be removed for a given number of extra plates may be found in the same way