National Geographic : 1951 Dec
designed? The Bureau squeezes them in its giant testing machines as easily as you can break a graham cracker or bend a tin can, and gets the answers engi neers need. These ma chines can crush brick and glass block walls, stretch steel cables, and pull apart ship bulk heads, to find weak spots. Though in the United States we commonly measure lengths in feet and weights in pounds, you will find no stand ard foot or pound at the National Bureau of Standards. Instead, it carefully preserves a standard meter and a standard kilogram, which are precisely cali brated against the in ternational standard meter and kilogram kept in Paris. Our foot is slightly over three-tenths (.3048) of a meter, and a pound is 45.36 percent of a kilogram. The Bureau's stand ard meter and kilogram are guarded in a secure ly locked vault. The kilogram is never touched by human hands, for a spot of per spiration could alter its weight. When the kilogram is taken out, it is carried by two men, so that if one should faint or stumble the other would keep it from falling to 758 National Geographic Photographer John E. Fletcher the floor. When it is "Automatic Redcap" Lifts Luggage until the Handles Snap placed on scales, for To set quality standards for manufacturers, this machine picks up and sets checking other weights down brick-weighted suitcases at the Bureau of Standards. A strong handle, against it, the operator it has been determined, should survive 25,000 pickups (page 774). works by remote control 10 feet away, lest the sample. Unless he can be sure his sampling heat of his body affect the test (page 783). pipette contains a known amount of blood, Though no one ever has seen electricity or the count is meaningless. Accuracy of such even knows just what it is,* the Bureau pipettes is tested by the Bureau. "weighs" it regularly to get the value of an Bending Steel Bridge Girders ampere of current. A small electric coil hung from one end of a delicate balance is placed Is a concrete slab six inches thick strong between two larger coils. When current is enough for a main highway? Will a steel * See "The Fire of Heaven," by Albert W. Atwood, bridge girder carry the load for which it is NATIONAL GEOGRAPHIC MAGAZINE, November, 1948.