Z 6z THE POPULAR SCIENCE MONTHLY. 



disinfection more than any others. The whole soil of the earth is a 

 great disinfectant, kept in constant activity, being constantly required, 

 holding; in itself the most nauseous and unwholesome things, and still 

 having healthy people living over it. However, the soil may be too 

 full, and at times it becomes so, and therefore we run to places which 

 cannot contain much impurity, such as bare rocks ; and in such places 

 we obtain pure air. If in houses we have too much organic matter for 

 the porous substances to oxidize, we must resort to non-porous sur- 

 faces ; but then they must, like the rocks, be often washed, or exces- 

 sively exposed to the air or the warm sun. 



To purify rooms the air must blow long into them, or every part 

 must have the organic matter rubbed off by the hand. This is a suffi- 

 cient rule for both hospitals and private houses. Good rubbing will 

 purify furniture, and this our housewives know ; long-continued cur- 

 rents of air are also known to be good, but better as a supplement to 

 rubbing. The rules are very easy chemically, but mechanically they 

 are difficult. This is merely a repetition of that which has been said 

 elsewhere, and long ago, although it is here stated in other words. 

 The world must be told every thing in ten thousand different ways 

 before it learns, and it is wearisome to repeat the lesson. I am only 

 saying, also, what every clean house-keeper carries out ; and yet there 

 is an apparent novelty in it when we compare it with the sayings and 

 doings of many persons, intelligent and observing although they be. 

 Air and Rain. 



-*~-+- 



PROF. JAMES D. DANA. 



MODERN science, in giving rise to a new order of knowledge, 

 fundamentally contrasted with the older eruditions, among its 

 numerous influences cannot fail to give us a more satisfactory basis for 

 the estimation of mental character and attainment. In proportion as 

 the later knowledge is definite, positive, and universally accepted, does 

 it become a better standard by which the intellectual greatness of men 

 may be judged. In no sphere of mental performance can a man's work 

 be brought to such decisive tests as in science. Each department has 

 its special and authoritative cultivators who subject all new ideas to 

 an inexorable ordeal of verification. While, in the various fields of lit- 

 erature and art, reputations may be made with little regard to substan- 

 tive merit, because their appeal is to taste and feeling, and the canons 

 of criticism are uncertain, in science, on the other hand, the rules of 

 judgment are unmistakable, and men are measured by the quality and 

 extent of what they have really accomplished. Human nature is, of 

 course, imperfect, and in science, as elsewhere, its imperfections may 



