CHAPTER XLI. RULES AND TABLES. Rules for Calculating Speeds of Shafts and Diameters of Pulleys. The speed of the driver and the diameter and speed of the driven being given, to find the diameter of the driver. PROBLEM 1. Rule. Multiply the diameter of the driven by its speed, and divide the product by the speed of the driver; the quotient will be the diameter of the driver. PROBLEM 2. The speed of the driven and the diameter and speed of the driver being given, to find the diameter of the driver. Rule.-Multiply the diameter of the driver by its speed, and divide the product by the speed of the driven; the quotient will be the diameter of the driven. PROBLEM 3. The diameter of the driven being given, to find its number of revolutions. Rule.-Multiply the diameter of the driven by its revolutions, and divide the product by the diameter of the driven; the quotient will be the number of revolutions of the driven. We give herewith tables of the specific cohesion and strength and the resistance of wood to pressure as calculated by Professor Wallace. (In this table the experiments are with cubes of 1 inch on the edge.) Table of Specific Gravities of Seasoned Timber, by W. Templeton. In measuring standing timber the length is taken as high as the tree will measure 24 inches in circumference. At half this height the measurement for the mean girth of the timber in the stem of the tree is taken. One-fourth this girth is assumed to be the side of the equivalent square area. The buyer has generally the option of choosing any spot between the butt end and the half-height of the stem as the girding place. All branches, as far as they measure 24 inches in girth, are measured in with the tree as timber. Proportions of Metals for the Production of Useful Alloys (W. Templeton). |