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Harry H. Laughlin, Department of Genetics, Carnegie Institution of Washington, Cold Spring Harbor, Long Island, N. Y. SCALE .7

A. The Mathematical Model for the Specific Formula of Heredity.

W. D Johnston. Jr., and T. B. Nolan, "Isometric Block Diagrams in Mining Geology." Economic Geology. August 1937, SCALE .5

B. Block Diagram of a Large Mine Drawn by the Isometric Method. The Original Drawing Is Eight Feet Long.

1. The mine layout, shown isomctrically in conjunction with contour lines of the surface

areas adjacent, serves the general purpose of a three-dimensional model with huge saving in space and cost.

2. For fully illustrated description of methods, reference should be made to the Johnston-

Nolan paper.

THREE-DIMENSIONAL METHODS

W. D. Johnston, Jr., and T. B. Nolan, "Isometric Block Diagrams in Mining Geology," Economic Geology, August 1937.

A, Isometric Protrac+or.

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B. Isometric Cross Section Paper.

A drawing on isometric paper combines the principles of mechanical and perspective drawing. The principal lines are drawn vertically, horizontally, and 30 or 60 degrees to the horizontal. As a result all parallel lines of an object are drawn parallel and three faces of the object are shown.