as a theory with the most important consequences, at once fruitful and terrible, and looking into the world with that Janus-face which all great knowledge possesses. 38. HOW FAR USEFUL.--It must remain for ever undecided whether psychological observation is advantageous or disadvantageous to man; but it is certain that it is necessary, because science cannot do without it. Science, however, has no consideration for ultimate purposes, any more than Nature has, but just as the latter occasionally achieves things of the greatest suitableness without intending to do so, so also true science, as the _imitator of nature in ideas,_ will occasionally and in many ways further the usefulness and welfare of man,--_but also without intending to do so._ But whoever feels too chilled by the breath of such a reflection has perhaps too little fire in himself; let him look around him meanwhile and he will become aware of illnesses which have need of ice-poultices, and of men who are so "kneaded together" of heat and spirit that they can hardly find an atmosphere that is cold and biting enough. Moreover, as individuals and nations that are too serious have need of frivolities, as others too mobile and excitable have need occasionally of heavily oppressing burdens for the sake of their health, should not we, the more _intellectual_ people of this age, that grows visibly more and more inflamed, seize all quenching and cooling means that exist, in order that we may at least remain as constant, harmless, and moderate as we still are, and thus, perhaps, serve some time or other as mirror and self-contemplation for this age? 39.