Box 17, Folder 4: Lake Michigan, 1859-1872

[1859]

[List of Books & Papers on the Fluctuations of Level of the Great Lakes, or Tide-]

1859

Lake Michigan by I.A. Lapham—

The changes of level, and the currents oberv= able especially about the amounts of the rivers and in narrow channels, in the waters of lake Michigan have been noticed since the earliest times. The French explorers , who first gave the world a knowledge of this great inland sea, also told of its remarkable currents. Some of them are apparent to the most careless observer and from their frequent occurrence are often noticed; others are casual and are seen only by a few; others require long continued and careful observations and are consequently less known.

These changes are now known to be of five different kinds;

1st—A regular lunar tide like those of the ocean, but of very small amount.

2d Sudden elevations of the water caused by a diminished atmospheric pressure, giving rise to tide waves like those produced on the ocean by earthquakes.

3d annual changes caused by the changes of the season, like those of all rivers; Lake Michigan being a part—of the great river St Lawrence, or rather a branch of it.

4th Currents and changes of level occasioned by wind, especially [illegible] winds, causing

the water to accumulate on the windowed shore.

5th Periodical changes running through a series of years, occasioned by the difference of different years in regard to the amount of rain and evaporation.

(1) The long disputed question as to whether there is a regular lunar tide on the lakes, as on the ocean, remained unsettled until august 1849 when by a series of careful observations made five times daily, the writer was able to determine and to announce in the public prints "that there is a slight lunar tide on Lake Michigan".*

Tide Table. 1849

From a slight-examination of this table it might be supposed that the fluctuations of the water level were so irregular that there could be us laws by which they are governed; and if we constrict a table with these figures for ordinates, so tide will appear. But if we select all those observations that were made at near the lines when according to the theory of tides, they should be high. and again all [illegible] made at or near the times when the tide should be low, we shall find

*Notice of this discovery was immediately sent to the scrutiny of the Smithsonian Institution, Professor Joseph Henry..

*Milwaukee Sentinel and Gazette Sept. 3d 1849 and wildly copied the Press.

3 1859

the mean of the former a little more than the mean of the latter; thus showing conclusively the existence of the tide. The mean height of the water by this table when the moon was on the meridianhigh tide 0.30 ftWhen on the horizon-low water 0.21 ft.- Thus showing a difference in favor of a lunar tide of 0.09 or an inch and a quarter.

This conclusion was fully confirmed by the results of a series of hourly observations made day and night-for two months in 1852 under my direction by Louis Henes and Carl Doerflinger. These show a mean level at time of high tide of 2.048 ft. at time of low water 1.946" Difference on tide 0.097 " or about one and one quarter inches. That this result is not an accidental difference is shown by dividing the two months into periods of ten days each when it will be found that the same law holds good.

Tide Table Being observatious on the water level of Lake Michigan made five times daily during the month of August 1849. The figures

4 1859

show the highest in feet and hundreths of a foot above or below the zero of grades of streets in the city of Milwaukee.

[Data Table].