210 'Wisconsin Academy of Sciences, Avis and Letters. 



on the ehb, reaches low water in a little over three hours; theo at 

 the rate of twelve miles an hoar on the flood, reaches high water 

 in SI" hours more 40 miles above New York, which point (New 

 York) it makes in 2^ hours more and is then withia 20 miles of 

 the next low water. Oq the upstream trip the conditions would 

 be different. Here it would only be a question of speed between 

 the boat and the wave, and if the boat left at low water on the 

 first of the Jl-jocl current, it would meet the contrary current 

 about 20 miles below Alban)^ The fact is that the trip upstream 

 is made in less time than that downstream. 



The tide of Long Island Sound and the East river, is remarka- 

 ble in several respects. That portion of the tide which enters at 

 Sandy Hook moves slowly up the narrow channel of the East 

 river and a few miles above New York encounters another por- 

 tion of the same ocean tide which entered the Sound at Montauk 

 Point and flowed back through the Sound over 100 miles in the 

 meantime. 



With a reasonably fair idea of the tides, the most remarkable 

 feature may appear to be their regularity, but by the time the 

 novelty has worn off there may also arise some doubts upon that 

 point in the mind of the observer. 



If the observations should begin at a particular time, there will 

 be two precisely similar waves, in something less than 25 hours. 

 In the course of a few days, during which the tides will appear 

 later each day, the two tides will become unequal in range, at the 

 same time both may be higher or lower than when first observed, 

 the evening tide may be the greater yet it is just as possible that 

 the morning tide will be the greater of the two, depending entirely 

 upon the time when the observations commenced. 



Before progressing any further we will be obliged to assume 

 some means of comparison to enable us to pursue the subject in- 

 telligently. Now, if we find that the phases of anj^ two or more 

 distinct phenomena run parallel, or in other words coincide, we 

 may conclude that one is either the cause or companion of the 

 other. 



The phases of the tide compare in point of time exactly with 

 those of the moon so that the moon is either the cause of the 

 tides or their companion subject to the same laws. 



