18S9.] 1*^^ [Haupt. 



vessels, or from any local, incidental causes, were eliminated by means of 

 the perforated boxes surrounding the float. 



"A fair representation of the record is shown in the illustration by 

 Kudolpli Hering in his paper to the Engineers' Club of Philadelphia ; 

 although there is a distinctive curve for each locality of observation, and 

 the curve for Chicago would be distinguishable from that of Milwaukee 

 or from that of any other locality. 



"The curve at Milwaukee showed that for more than half the season of 

 observation there were series of waves coming in at intervals of approxi- 

 mately two hours, whose height were from one-third of a foot to one and 

 a half feet. Generally the waves are subdivided, sometimes very deeply, 

 into two or more parts. At Milwaukee, on Lake Michigan, there were 

 more nearly eleven of these waves in twenty-four hours, and at Marquette, 

 on Lake Superior, eight in the same length of time. The two-hour inter- 

 val at Milwaukee was supposed to be due to the time required for a wave 

 to travel across the lake and return, where the width of the lake was 

 nearly eighty miles and depth 400 feet. 



"Greater disturbances, known as 'seiches,' occurring generally several 

 times in a season and lasting several hours, bring waves upon the shore 

 at intervals of twenty or thirty minutes, the crests of which waves exceed 

 two feet in height above the troughs. The cause of this phenomenon is 

 probably a difference in atmospheric pressure on different parts of the 

 lake, and the more decided 'seiches' probably result from severe cyclones. 

 The same cause may for the most part account for the generation of the 

 two-hour waves above noted. 



"There is also a change in the relative water level of the two ends of a 

 lake due to the direction of the wind, but the wave thus produced has 

 generally a day or more in length of duration." 



Mr. G. Y. Wisner, a colleague of Mr. Wheeler's, also an experienced 

 Lake Survey Assistant, writes, under date of March, 1888, that "the laws 

 of the natural forces, which you have so ably set forth in your article, as 

 applied to tidal harbors, hold equally true with a large number of the 

 harbors on our lake coasts. It is true the tides on the lakes are impercep- 

 tible, yet other natural causes combine to produce the same effect." 



" Owing to unequal barometric pressures on different portions of such 

 vast bodies of water, series of waves are generated which are usually 

 about an hour in passing from crest to crest at any given point, and vary 

 all the way from six to eighteen inches in amplitude. These waves fol- 

 low each other along the shores similarly to those of flood tides ; their 

 effect in generating littoral currents depending, of course, on the general 

 direction in which the waves approach the shore and the conformation of 

 the coast line. I have noticed the rise and fall of the lakes due to this 

 wave action, for days at a time, in perfectly calm weather, with almost 

 the regularity of clock-work, and have observed currents generated in the 

 open lake of over three miles per hour. * * * Most of the lake har- 



