60 STUDIES LN ANIMAL LIFE. 



finely says of the mountain, it is " familiar with for- 

 gotten years." Not only are there obvious traces 

 of age in the crumbling mortar and the battered 

 brick, but there are traces, not obvious except to 

 the inner eye, left by every ray of light, every rain- 

 drop, every gust. Nothing perishes. In the won- 

 drous metamorphosis momently going on every 

 where in the universe, there is change, but no loss. 



Lest you should imagine this to be poetry, and 

 not science, I will touch on the evidence that every 

 beam of light, or every breath of air which falls 

 upon an object, permanently affects it. In photog- 

 raphy we see the effect of light very strikingly ex- 

 hibited ; but perhaps you will object that this proves 

 nothing more than that light acts upon an iodized 

 surface. Yet, in truth, light acts upon, and more or 

 less alters the structure of every object on which it 

 falls. Nor is this all. If a wafer be laid on a sur- 

 face of polished metal, which is then breathed upon, 

 and if, when the moisture of the breath has evapo- 

 rated, the wafer be shaken off, we shall find that the 

 whole polished surface is not as it was before, al- 

 though our senses can detect no difference; for if 

 we breathe again upon it, the surface will be moist 

 every where except on the spot previously shelter- 

 ed by the wafer, which will now appear as a spec- 

 tral image on the surface. Again and again we 

 breathe, and the moisture evaporates, but still the 

 spectral wafer reappears. This experiment suc- 

 ceeds after a lapse of many months if the metal be 



