OP ARTS AND SCIENCES : SEPTEMBER 13, 1864. 355 



" For this purpose two delicate tide-gauges were established on that 

 lake in October, 1861, and were observed on both day and night until 

 late in December, 1863, — a period of more than two years, — without 

 any other interruption than that which unavoidably arose from the 

 ice in the severe winter months in that climate. 



" The observations, as in the case of the previous ones on Lake 

 Michigan, were made with great regularity, at intervals of half an 

 hour of time, except that at certain phases of the moon the intervals 

 were reduced to fifteen minutes of time apart. 



" The positions selected for the two observing stations were the 

 wharf at Tawas City, on Tawas Bay, and Thunder Bay Island ; the 

 former situated in latitude 44° 15' 12" N., and the latter in latitiide 

 45° 2' 17" N. 



" These observations have not yet been reduced, but a general ex- 

 amination of them shows that they develop the existence, in Lake 

 Huron, of a semi-diurnal lunar tide, and al^o a semi-diurnal solar tide, 

 which is separable from that produced by the combined action of the 

 sun and moon, as has been shown in regard to the tide in Lake 

 Michigan. 



" It is worthy of notice that no observations have, as far as we 

 know, ever been instituted by the philosophers of the Old World to 

 ascertain the existence and extent of any similar phenomenon in the 

 waters of the Caspian Sea. This sea is a 2)erfect lake ; that is to say, 

 it is not connected with any other body of water. It is the largest and 

 deepest lake known on our globe. Its area is greater than the areas 

 of all our Northern and Northwestern lakes added together, and its 

 greatest depth is more than twice that of Lake Superior, the largest 

 and deepest of our North American lakes. The Caspian, therefore, 

 offers peculiar advantages for investigations concerning the theory of 

 the tides, and it might perhaps be not inappropriate for the Academy 

 to invite the attention of foreign scientific societies to the imjjortance 

 of a series of tidal observations there." 



On the motion of Mr. F. H. Storer, it was voted that our 

 Secretary be directed to correspond with the Secretary of the 

 Academy of St. Petersburg, for information respecting the 

 tides of the Caspian and other seas of the Eastern continent. 



