supposed strengthening by increasing the thickness of the top plates. QUESTION 292. [73]_How can we find by calculation the elasticity or deflection of a given steel spring?_ [73] The following rules for calculating the proportion and strength of steel springs are from Clark’s Railway Machinery. _Answer._ BY MULTIPLYING THE BREADTH OF THE PLATES IN INCHES BY THE CUBE OF THE THICKNESS IN SIXTEENTHS, AND BY THE NUMBER OF PLATES: DIVIDE THE CUBE OF THE SPAN[74] IN INCHES BY THE PRODUCT SO FOUND, AND MULTIPLY BY 1.66. THE RESULT IS THE ELASTICITY IN SIXTEENTHS OF AN INCH PER TON OF LOAD. [74] The span is the distance between the centres of the spring-hangers when the spring is loaded. QUESTION 293. _How can we find the span due to a given elasticity and number and size of plates?_ _Answer._ BY MULTIPLYING THE ELASTICITY IN SIXTEENTHS PER TON BY THE BREADTH OF PLATE IN INCHES, AND BY THE CUBE OF THE THICKNESS IN SIXTEENTHS, AND BY THE NUMBER OF PLATES: DIVIDE BY 1.66, AND FIND THE CUBE ROOT OF THE QUOTIENT. THE RESULT IS THE SPAN IN INCHES. QUESTION 294. _How can we find the number of plates due to a given elasticity, span, and size of plate?_ _Answer._ BY MULTIPLYING THE CUBE OF THE SPAN IN INCHES BY 1.66; THEN MULTIPLYING THE ELASTICITY IN SIXTEENTHS BY THE BREADTH OF 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. QUESTION 295. _How can we find the working strength, that is the greatest weight it should bear in practice, of a given steel-plate spring?_ _Answer_. BY MULTIPLYING THE BREADTH OF PLATES IN INCHES BY THE SQUARE OF THE THICKNESS IN SIXTEENTHS, AND BY THE NUMBER OF PLATES; MULTIPLY, ALSO, THE WORKING SPAN IN INCHES BY 11.3: DIVIDE THE FORMER PRODUCT BY THE LATTER. THE RESULT IS THE WORKING STRENGTH IN TONS (OF 2,240 POUNDS) BURDEN. QUESTION 296. _How can we find the span due to a given strength, and number and size of plate?_ _Answer_. BY MULTIPLYING 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. THE RESULT IS THE WORKING SPAN IN INCHES. QUESTION 297. _How can we find the number of plates due to a given strength, span and size of plates?_ _Answer_. BY MULTIPLYING THE STRENGTH IN TONS BY THE SPAN IN INCHES, AND BY 11.3; MULTIPLY ALSO, THE BREADTH OF PLATE IN INCHES BY THE SQUARE OF THE THICKNESS IN SIXTEENTHS: DIVIDE THE FORMER PRODUCT BY THE LATTER. THE RESULT IS THE NUMBER OF PLATES. QUESTION 298. _How can we find the required amount of curvature or set of the spring before it is loaded?_ _Answer._ BY MULTIPLYING THE ELASTICITY, PER TON, IN INCHES, BY THE WORKING STRENGTH IN TONS; ADD THE PRODUCT TO THE DESIRED WORKING COMPASS. THE SUM IS THE WHOLE ORIGINAL SET, TO WHICH AN ALLOWANCE OF ¹⁄₈ TO ³⁄₈ IN. SHOULD BE ADDED TO THE PERMANENT SETTING OF THE SPRING.