Nature is the source of all energy. Plants, the lowest form of life, have a definite rôle to perform in the economy of nature. Their function is the forming of albuminoids and other substances for higher purposes. All of their nitrates are high-explosives, or low explosives, but explosives anyway. They are powerful sources of some new energy. Animal life uses these “explosives” as food and is correspondingly more dynamic, but in animal life time does not play the rôle it plays in human life. Animals are limited by death permanently. If animals make any progress from generation to generation, it is so small as to be negligible. A beaver, for example, is a remarkable builder of dams, but he does not progress in the way of inventions or further development. A beaver dam is always a beaver dam. Finally humanity, the highest known class of life, has time-binding capacity as its characteristic, its discriminant, its peculiar and definitive mark. It is an unrealized fact that in this higher class of life, _the law of organic growth develops into the law of energy-growth—the mind—the time-binding energy—an increasing exponential function of time._ That fact is of basic importance for the science and art of Human Engineering. In mechanics we have the well-known formula (1) Work ÷ Time = Power. We have seen that, in accordance with the law of geometric progression, _PR__T_ represents the progress made—the work done—in the _Tth_ generation (_T_ being counted from some generation taken as starting point of reckoning); this progress, achievement, or _work_, being done in _one_ generation, we have by (1) (2) ( Work = PRT ) / ( Time = 1) = Power, that is, _PR__T_ = Power; this means that the number _PR__T_, which measures the work done in a given generation, is also the measure of the power that does the work. Now, the total work, _W_, done in the _T_ generations is (3) _W = PR__1__ + PR__2__ + PR__3__ + ... + PR__T_; that is, (4) _W_ = _R_ ÷ (_R_-1) × (_PR_T - _P_) It should be noticed that by (2) this expression for _W_ may also be regarded as the sum of _T_ different powers _PR_, _PR__2_, etc., each working during one and only one generation; if we divided this sum by _T_, the quotient would be a power that would have to act through _T_ generations to produce _W_. The reader should not fail to notice very carefully that the expression (4) for _W_ is an expression for the total progress made—the total work done—the total wealth produced—in the course of _T_ generations and he should especially note how the expression involves the exponential function of time (_T_), namely _PR__T_.