OCEAN METEOROLOGY. 39 



at one place and slight at another, the air will as naturally flow from 

 the former toward the latter as water will down an inclined plane ; 

 and as the velocity of the water will depend on the inclination of the 

 plane, so will the violence of the wind be chiefly due to the difference 

 of pressure : hence the direction and force of the wind are predicted. 

 Again, whether the day will be warm or cold depends mostly on the 

 temperature of this wind ; and, furthermore, if it contains much vaj)or 

 and blows toward a point where the temperature is lower than that 

 from which it started, clouds, or rain, or snow will follow, according 

 to the difference of temperature and the supply of vapor ; but if a 

 saturated wind blows toward a place where the temperature is high, 

 and air dry, its moisture will be licked up by the thirsty air, and a 

 mere haze will ensue, or clear weather continue. 



This problem in its ever-varying conditions is the one daily solved 

 by the Weather Bureaus of several Governments, in the interest of 

 agriculture, comfort, and commerce ; and perhaps nowhere more suc- 

 cessfully than by our own. With its large corps of trained observers, 

 its military discipline, variety of standard instruments, extensive field 

 of operations covered by telegraphic lines, liberal Government support, 

 and educated intelligence to guide the whole, there is every reason for 

 the confidence so generally felt in the weather prognostics of the Sig- 

 nal Office of the United States Army. 



With this preliminary glance at meteorology on the land, I shall 

 now pass to a consideration of it as regards the ocean — the subject 

 proper of this article ; and as I have already divided the problem 

 into three phases, it will be convenient to maintain this distinction — 

 only, that for the ocean, the cases reduce to tAVO : first, to seek out 

 the hidden cause of the winds, whether as the gentle trades that 

 scarcely ruffle the waters over which they glide, or as the violent hur- 

 ricane that lashes the waves into a tempest of confusion ; and, sec- 

 ondly, to determine the many items that, together, make up the cli- 

 mate of small areas of every sea. 



The third phase of the problem on land is entirely excluded from 

 the ocean. There we can not establish fixed stations and spread a 

 web of electric wu'e over them, with some guiding genius ensconced 

 in the midst. We can not (as is done every morning in the United 

 States, England, France, and Germany, for the limits of each country) 

 say what the weather will be, and how the winds will blow, for the 

 ensuing twenty-four hours, in the Indian Ocean, the South Seas, or the 

 North Atlantic. But we can give information yielding in no degree 

 in importance to this purely ephemeral benefit ; and the manner in 

 which this is obtained and published is what I shall fully describe 

 hereafter. 



To the late Commander M. F. Maury, of the United States Navy, 

 is due the credit of having given to ocean meteorology that vigorous 

 impulse that placed it in the foremost rank of pursuits, and justly 



