^22 PRESIDENT S ADDRESS. 



Ordinary light can only penetrate to a comparatively small 

 depth, for at 200 fathoms practically no action on a photographic 

 plate can be detected. At depths greater than 2,000 fathoms 

 the water is never more than a very few degrees above freezing 

 point and is practically uniform in temperature over the bulk of 

 the ocean floor. It thus comes about that the same forms of life 

 are dredged from great depths everywhere, and there is abso- 

 lutely no barrier at such depths to the uniform migration of 

 animals in all directions. 



Of the superficial characters of the ocean, waves are probably 

 the first feature which would attract the attention of an observer. 

 In ordinary wave-motion there is very little drift or translatory 

 movement of the water ; the water remains practically in the 

 same spot: it is the motion only which travels. A wave is, in 

 fact, the passage of motion from position to position. The water 

 is first heaj)ed up, forming the crest, and then depressed, forming 

 the trough, the mass of water which forms a given crest sinking, 

 and, as it were, forcing up the mass in front to form the next 

 crest. From this it is obvious that the motion exists equally 

 beneath as above the surface, and the consequent friction is the 

 principal cause of the rapid flattening of the water which ensues 

 when the wind ceases. The greatest height attained by ocean 

 waves does not, probably, often exceed 45 feet, but to reach such 

 a height the essential conditions are a sufficient stretch of ocean 

 and a great enough velocity of wind sustained for a long enough 

 period. There is a relationship between the size of waves and 

 the velocity of the wind, which may be expressed in the terms 

 that the velocity of the wind in miles per hour is roughly twice 

 that of the height of the waves in feet. Thus, suppose the wind 

 to be blowing over a stretch of ocean of sufficient breadth at the 

 rate of twentj'-five miles per hour, it is able to raise waves having 

 a height of about 12^ feet. The waves are prevented from 

 attaining a greater height because they have not a sufticient 

 thickness to permit of their withstanding the increased total 

 v?ind pressure which they would then have to bear, and, accord- 

 ingly, the wind would merely tend to depress them. A given 



