Science 171 approximation to TT now known to be 3*1415. . .. The Babylonians used 3, as did the writer of I Kings vii. 23. 8. Find the content of a cylinder of diameter 12 and height 8 cubits. The area of the base is found as in No. 7 above. This is then multiplied by the height. The question whether the Egyptians knew that a triangle whose sides are proportional to 3, 4, and 5 is right-angled has been much discussed. It seems inconceivable that they should not have made this discovery. Yet there is no direct evidence that they did so. We find equations of the form 32+4z = 52, but there is no statement of the general relation nor any evidence such as three rods of lengths 3, 4, and 5 cubits bundled together, or a cord knotted at points dividing it in the same ratios. One example indicates that the Egyptian had a clear con- ception of the nature of a geometrical series, of which the first term is unity. The sum of 5 terms is correctly given. It is not clear from the solution that any general formula was known. Problems dealing with pyramids illustrate the Egyptian method of measuring an angle of slope by the horizontal offset per unit vertical height (the seked), a measure of what we now call the co-tangent of the angle. In the practical application to the cutting of casing stones to the required angle, the stone mason would mark off one cubit vertically and then set out the seked horizontally. He then drew the line indicating the direction in which the stone should be cut. Such lines have often been found on stone blocks. The problem most widely discussed in modern times is one dealing with the volume of a truncated pyramid. It is far in advance of anything we know of Egyptian geometry. Many attempts have been made to reconstruct the mentai processes required for the sequence of operations, which follows the use of the modern formula V = %h (a2-\-ab+b2)9 where b is the