We sometimes classify sciences as exact and inexact, in accordance with our ability exactly to weigh forces and results. The exact sciences deal with simple data accessible and capable of measurement. The results of their interactions can be reduced to mathematics. Because of their essential simplicity, the mathematical sciences have been carried to great comparative perfection. It is easier to weigh an invisible planet than to measure the force of heredity in a grain of corn. The sciences of life are inexact, because the human mind can never grasp all their data. Nor has the combined effort of all men, the flower of the altruism of the ages, that we call science been able to make more than a beginning in this study. But however incomplete our realization of the laws of life, we may be sure that they are never broken. Each law is the expression of the best possible way in which causes and results can be linked. It is the necessary sequence of events, therefore the _best_ sequence, if we may imagine for a moment that the human words "good" and "bad" are applicable to world-processes. The laws of nature are not executors of human justice. Each one has its own operation, and no other. Each represents its own tendency towards cosmic order. A law in this sense cannot be "broken." A broken law would be a discarded universe. "If God should wink at a single act of injustice," says the Arab proverb, "the whole universe would shrivel up like a cast-off snake-skin." If God should wink at any violated law the universe would vanish. Not long ago, in an examination in a theological seminary, the question was asked of the candidates for the ministry, "Is it right to pray for a change of season?" The candidates thought that it was not, for the relations which produce winter and summer are fixed in the structure of the solar system and cannot be altered for man's pleasure or man's need. "Is it right to pray for rain?" The candidates generally thought that it was, because the conditions of rain are so unstable that a little change in one way or another would bring rain or fair weather, and that it was proper to ask for such change, as it did not concern the economy of the universe. The third question was: "When the signal service of the United States is well established, so that weather conditions are perfectly known, will it then be right to pray for rain?" And the candidates for the ministry could not tell, for they began to see that even simple changes of weather may have the strength of the whole universe behind them. It has never yet rained when by any possibility it could do otherwise. It has never failed to rain when rain was possible. The Spanish padres in California, wise in their generation, allowed prayers for rain only in winter, when the wind was in the south. The wind is only in the south when the air is affected by a cyclonic movement, and this in the California winter means rain.