The great cataracts and the great tides will submit to the genius of man. They are to be for use. Niagara will not be allowed to remain a barren roar. It must become the servant of man. It will weave robes for men and women. It will fashion implements for the farmer and the mechanic. It will propel coaches for rich and poor. It will fill streets and homes with light, and the old barren roar will be changed to songs of success, to the voices of love and content and joy. Science at last has found that all forces are convertible into each other, and that all are only different aspects of one fact. So the flood is still a terror, but, in my judgment, the time will come when the floods will be controlled by the genius of man, when the tributaries of the great rivers and their tributaries will be dammed in such a way as to collect the waters of every flood and give them out gradually through all the year, maintaining an equal current at all times in the great rivers. We have at last found that force occupies a circle, that Niagara is a child of the Sun--that the sun shines, the mist rises, clouds form, the rain falls, the rivers flow to the lakes, and Niagara fills the heavens with its song. Man will arrest the falling flood; he will change its force to electricity; that is to say, to light, and then force will have made the circuit from light to light. ***** ARE Men's characters fully determined at the age of thirty? It depends, first, on what their opportunities have been--that is to say, on their surroundings, their education, their advantages; second, on the shape, quality and quantity of brain they happen to possess; third, on their mental and moral courage; and, fourth, on the character of the people among whom they live. The natural man continues to grow. The longer he lives, the more he ought to know, and the more he knows, the more he changes the views and opinions held by him in his youth. Every new fact results in a change of views more or less radical. This growth of the mind may be hindered by the "tyrannous north wind" of public opinion; by the bigotry of his associates; by the fear that he cannot make a living if he becomes unpopular; and it is to some extent affected by the ambition of the person; that is to say, if he wishes to hold office the tendency is to agree with his neighbor, or at least to round off and smooth the corners and angles of difference. If a man wishes to ascertain the truth, regardless of the opinions of his fellow-citizens, the probability is that he will change from day to day and from year to year--that is, his intellectual horizon will widen--and that what he once deemed of great importance will be regarded as an exceedingly small segment of a greater circle.