and evident of these causes are variations of atmospheric pressure and local storms. With regard to earthquake shocks as a cause of such fluctuations of level, it is a singular and significant fact that since Forel has established the delicate self-registering apparatus on the shores of the Lake of Geneva, no less than twelve earthquake shocks have been experienced in this portion of Switzerland, and they have had no sensible influence on these sensitive instruments. In fact, a little consideration in relation to the character of such shocks renders it highly improbable that such brief tremors of the earth’s crust could have been any agency in the generation of rhythmical oscillations of the whole mass of water in the lake. Indeed, it is very questionable whether any earthquake waves are ever produced in the ocean, except when the sea-bottom undergoes a permanent vertical displacement.
Lake Tahoe. From inquiries made of the inhabitants of the shores of Lake Tahoe, I was not able to discover that any rhythmical oscillations of the level of its waters have ever been noticed. Some residents declared that they had observed sudden fluctuations of level, which, from their suddenness, they were disposed to ascribe to disturbances of the bottom of the Lake due to volcanic agencies, although they were unable to coordinate such oscillations with any earthquake manifestations on the adjacent shores.
It is evident, however, that until arrangements are consummated for recording systematic observations on the variations of the level of this Lake, we cannot expect that its Seiches will be detected. Of course, self-registering gauges would give the most satisfactory results; but any graduated gauge, systematically observed, would soon furnish evidence of the phenomenon. For the longitudinal Seiches, “Hot Springs,” at the northern extremity of the Lake, or “Lake House,” at the southern end, would be eligible stations for gauges; and for the transverse Seiches, Glenbrook, on the eastern shore, or Capt. McKinney’s on the western margin, would afford good stations. As far as I am aware, true Seiches have never been observed in any of the American lakes. This fact is the more remarkable from the circumstance that long-continued and careful observations have been made on the fluctuations of level of several of the large Canadian lakes, with the view of testing the possible existence of lunar tides. Perhaps these lakes may be too large to manifest the uninodal rhythmical oscillations which have been so successfully studied by Forel in the smaller lakes of Switzerland.
Be this as it may, there can be no doubt that Lake Tahoe is a body of water in all respects adapted for the manifestation of this species of oscillation; and that, like the Swiss lakes, it is subject to Seiches. Indeed, the far greater simplicity in the configuration of the basin of Lake Tahoe than that of the Lake of Geneva must render the phenomena much less complicated in the former than in the latter.
Professor LeConte then gives his computations as to the probable duration of the oscillations on Lake Tahoe, should they occur there.