"When chemists have brought their knowledge out of their special laboratories into the laboratory of the world, where chemical combinations are and have been through all time going on in such vast proportions,-when physicists study the laws of moisture, of clouds and storms, in past periods as well as in the present,-when, in short, geologists and zoologists are chemists and physicists, and vice versa,-then we shall learn more of the changes the world has undergone than is possible now that they are separately studied."