680 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



of Mexico and in the Pacific Ocean, reference should be had to the reports 

 of the United States Coast Survey. These annual quartos contain a vast 

 fund of information, which seems to be providentially provided for the use 

 of our navy, when it is charged with the duty of guarding a great extent 

 of coast. The phenomenon of the meeting of the tide waves occurs daily 

 in our own vicinity. The tide, which is nearly simultaneous along the 

 main headlands of our Atlantic coast, enters at Montauk Point and Sandy 

 Hook. In about three and a half hours the waves meet at or near Throgg's 

 Neck, one ^laving traveled through Long Island Sound 120 miles, and the 

 other through the East river about 40 miles. The dividing of the waves 

 from Sandy Hook, at the junction of the North and East rivers, the narrow 

 channel and the natural obstructions at Hell Gate, will account for its 

 tardy movement. 



The range or rise and fall of the spring tide at important points is as 

 follows: At Havre, France, 22 feet; at London, 19^-; at Liverpool, 26; at 

 Bristol (King Road), 44; at St. John, N. B., 23; at Sackville, N. B., 30; at 

 Quebec, 18; at Portland, 9.9; at Boston, 11.3; at New Haven, 6 2; at New 

 York, 6.4; AYest Point, 3.2; Albany, 2.5; Philadelphia, 6.8; Baltimore, 1.5; 

 Washington, 3.4; Charleston, 6. A little less than one-half of each of these 

 sums would respectively expi'ess the range of the neap tide. 



The declination of the moon has an important relation to the periodical 

 decrease in the height of the tide wave. 



It will be readily perceived the waters cannot instantly respond to the 

 power of the moon, and there is consequently a lagging of the great pri- 

 mary wave. 



One of the deductions of Dr. Mayer, in his essay " On Celestial Dyna- 

 mics," is thus aptly presented by Prof Tyndall in his work on "Heat as a 

 Mode of Motion: " "Standing upon one of the London bridges we observe 

 the current of the Thames reversed, and the water poured upward twice a 

 day. The water thus moved rubs against the river bed and sides, and heat 

 is the consequence of friction. The heat thus generated is, in part, radia- 

 ted into space, and there lost as far as the earth is concerned. What is it 

 that supplies this incessant loss ? The earth's rotation. Let us look a 

 little more closely at this matter. Imagine the moon fixed and the earth 

 turning like a wheel from west to east in its diurnal rotation. A moun- 

 tain on the earth's surface, on approaching the moon's meridian, is, as it 

 were, laid hold of by the moon; it forms a kind of handle by which the 

 earth is pulled more quickly round. But when the meridian is passed, the 

 pull of the mountain would be in the opposite direction; it now tends to 

 diminish the velocity of rotation as much as it was previously to augment 

 it, and thus the action of all fixed bodies on the earth's surface is neutralized. 



But suppose the mountain to lie always to the east of the moon's meri- 

 dian, the pull then would always be exerted against the earth's rotation, 

 the velocity of which would be diminished in a degree corresponding to the 

 strength of the pull. TJie tidal wave occupies this position — it l[es always 

 east of the moon's meridian. The waters of the ocean are iu part dragged 

 as a brake along the surface of the earth, and as a brake they must dimin- 

 ish the velocity of the earth's rotation. The diminution, though inevitable, 



