LET us now turn to some of the material of science in order to study the methods which have been evolved for its examination. The piece of the universe I propose to ask you to examine is something which has never been seen but ~hich everyone has feIt-the air. We have feIt it strike our faces, it has chilIed us to the bone, we have heard it howl and shriek, we have smeIt it-but we have never seen it. And yet, unseen as it has been, "blowing where it listeth," we have mastered it and tumed it to our own use. How has this been done?