40 lbs., or 32.14 lbs. to the cubic foot, in case of oats; 60 lbs. to the bushel, or 48.21 lbs. to the cubic foot, in case of wheat; hay pressed in bundles, weighs 11 lbs. per cubic foot. 21. What weight does an infantry soldier carry when in marching order? About 45 lbs. in all. His knapsack when packed weighs 24 lbs.; canteen when filled, and one day’s provisions in haversack, 5 lbs.; rifle, musket, sling, and bayonet, 10½ lbs.; belts, complete, including 20 rounds of ammunition, 6 lbs. 22. How is the area of a circle found; Square the diameter, and multiply by .7854 for the area; or square the circumference, and multiply by .07958 for the same result. 23. How is the content of a conical frustum found? Add into one sum, the areas of the two ends and the mean proportional between them; take one-third of that sum for the mean area, and multiply it by the perpendicular height of the frustum, for its content. [Sidenote: 155]] 24. How is the mean proportional found for the above? By multiplying the areas of the two ends together and extracting the square root of their product. A more simple rule is the following: As the diameter of the large end is to that of the small end, so is area of base to mean proportional required. 25. How is the content of a spherical segment found? From three times the diameter of the sphere, take double the height of the segment, then multiply the remainder by the square of the height, and this product by .5236; or, to three times the square of the radius of the segment’s base, add the square of its height, then multiply the sum by the height, and this product by .5236, for the content. 26. How is the capacity or content of a Gomer chamber computed? This chamber being the frustum of a cone with a hemispherical bottom, its capacity will be found by applying the foregoing rules, viz: first find the content of the frustum, then that of the spherical segment or bottom, and add their contents into one sum for the capacity. 27. How is the content of a rectangular box ascertained? Multiply the length by the breadth, and this product by the depth. 28. How is the capacity of a cylinder calculated? Multiply the area of the base by the height. 29. How is the content of a barrel found? Multiply half the sum of the areas of the two interior circles, taken at the head and bung, by the interior length; or, to the area of the head, add twice the area at the bung, multiply that sum by the length, and take one-third of the product for the content. [Sidenote: 156]] 30. What is meant by the term, enfilade? Sweeping the whole extent of a work, line of troops, deck of a ship, &c., with shot or shells. 31. What does defilade mean? The art of disposing guns, troops, or works in such a manner, that they shall be protected from a plunging-fire from adjoining heights. 32. What are the dimensions required for an earthen parapet to resist the fire of field or siege guns?