IX TIIK XOUTII AMERICAN LAKES. 



1!) 



water. The oi)iiii()n has been so often iulvanccd that tliesc oscilhitory move- 

 ments are (hie to rapid vai-iutions of tlie barometrieal pressnre, tliat the" term of 

 I' barometrieal waves" has eomt; to be llieir reeeived name. It is donbtful wlietlier, 

 if this be the case, a merenrial barometer wouhl sliow them. Tlie movements of the 

 cohimn are too shigjrish, and the apparatus for reading too imperfect to indicate a 

 change of pressure tiiat sometimes occurs in the space of one minute. INIy tables 

 show that an oscillation may be completed in that time. Some more sensitive 

 instrument is needed to indicate atmospherical changes that occupy at intervals of 

 so short a period. 



Professor Mather's observations were taken under circumstances that should be 

 well considered in comparing them with others, made in calm weatlier and on the 

 open Lake. (See Plate II, No. o.) 



Copper Harbor is a long narrow inlet, within which the movements are 

 augmented, and may also be broken up, by counter waves reflected from the 

 sides. During the time of Prof. M.'s observations, violent storms and winds were 

 raging at the liarbor, or were visible in the distance. Such agitations of the 

 atmosphere, although they do not prevent the regular oscillations, would materially 

 interfere with them. His observations were carefully made, and are the earliest 

 exact data of a scientific kind relative to this subject within my reach. 



There is to be found, moreover, in the geological reports upon the Upper 

 Peninsula, a comprehensive historical notice of these phenomena. 



Whether such movements have been observed upon the ocean, I am not aware. 

 But it would seem probable, that, whatever the cause may be, it should be 

 universal, and produce its effects on all bodies of water. 



It IS plain, after the barometer recovered from the effects of the tornado in tlie 

 forenoon, it declined regularly till night, as might have been expected from the 

 stormy condition of the weather. 



The pulsations within the harbor continued all day, although there is a break in 

 the readings from 11 A. M. till 2 P. M., with the exception of one at twelve hours 

 eight minutes. So far, therefore, as these observations indicate, there is no apparent 

 connection between the oscillations and the barometrical ]n-essure; at least the 

 movements for twelve hours were very marked, while the barometer was regularly 

 falling, except during the tornado. The day commenced with the barometer at 

 29.288, and closed with it at 29.150. 



In the autumn of 1856 I had the first opportunity of comparing the state of the 

 barometer with the movements of the water. It was done with an aneroid recently 

 compared with a good cistern barometer. I had not assistants to enable me at the 

 same time to note the actual range of tlie wave in a vertical direction; but in this 

 respect it was apparently the same as is shown in the preceding tables. 



On the 19th of October the Lake was calm, a light breeze blowing off shore from 

 the southeast. The weather was calm and foggy on the 20th, with a gentle breeze 

 from the south, and a liazy, warm atmosphere, like the Indian summer. It rained 

 during a greater part of the night between the 20th and 21st, and on the morning of 

 the last named day the wind was northeast by east, or about parallel with the coast 

 line. During the day rain continued to fixll, and the wind, continuing in the same 



