28 



VARIATIONS IN THE LEVEL OF THE LAKES. 



[1853 



and in the Autumn, they are, however, more "considerable" (rise 

 higher) in the summer, and in particular towards the close of that 

 season. The highest that have been observed happened in the 

 month of September. 



bthly, The minimum of the Seiches has no precise term, their 

 maximum seems to be 5 feet. 



Qthly, That although the duration of the Seiches is very 

 variable, its greatest extent seems not to exceed 20 or 25 minutes, 

 but usually lasts a much shorter time. 



Ithly, That the Seiches are not peculiar to the Lake of Geneva, 

 Mr. Vaucher having observed them on the Lakes of Zurich, of 

 Annecy and of Constance. 



It appears unquestionable that the phenomenon of the Seiches 

 is due to an unequal pressure of the atmosphere on different parts 

 of the Lake at the same time, that is, to the simultaneous effect of 

 columns of air of different weight or different elasticity, arising 

 from temporary variations of temperature or from mechanical 

 causes ; and if such be in fact the case, all lakes of a certain extent, 

 and even inland seas, must be subject to the same influence, and 

 therefore present the same phenomenon ; and I have little doubt 

 but that correct observations will verify this presumption. 



Moreover, the effect of unequal atmospheric pressure, in pro- 

 ducing inequality in the level of the surface of large masses of 

 water, once established as a positive fact, will throw much light 

 upon several subjects interesting to physical geography, particularly 

 upon that of currents, as affected by sea and land breezes, irregular 

 winds, sudden changes of temperature, the configuration and 

 aspect of coasts as regards the Sun, and the consequent periodical 

 influence of reverberated heat on the density of the circumjacent 

 air. It is, therefore, upon these considerations that I am desirous 

 of calling to the subject the attention of such persons, as from the 

 habitual nature of their occupations, or their studies, or their love 

 of science, are best enabled to add to our knowledge regarding it ; 

 and in the hopes that some of the members of our Society, or 

 that, at their instigation, others who may be in the vicinity of 

 lakes in any part of the world, will take up the subject, I shall 

 venture to offer what I conceive to be the best method of 

 operating. 



1st, Several points must be chosen on the lake, some in its 

 narrower and some in its wider parts, as well as at the mouth of 

 its most considerable affluent, and at the immediate egress of its 

 main outlet. If the surface of the lake be observed to incline 

 towards the outlet from any distance, a station should be estab- 

 lished at 'the commencement of this slope, as well as at the 

 immediate egress. 



Indly, These points once chosen, a squared pole must be 

 driven, having marked upon it, in white upon a black, or in black 

 upon a white ground, feet, inches, and lines, for at least five feet 

 above and as many below, the general water level. To this pole 

 must he added a float, surrounded by a rod to act as an indicator, 

 which rod must slide easily in brackets fastened to the pole. 

 Round the pole and rising above the water, an inclosure of about 

 2 or 3 feet diameter must be established of hurdles or planks, in 

 such wise, that while the water within has free communication 

 with that which is without the enclosures, so as to rise and fall 

 with it, the former may be kept calm and secured from all 

 influence of winds and waves. 



3rdly, These stations being established, two observers at least, 

 •and more if possible, must commence their observations at an 

 hour agreed upon, having first compared their watches. If each 

 observer could at the same time be furnished with a barometer, 

 thermometer, and hygrometer, the general results of their obser- 

 vations would be so much the more satisfactory; but one 



instrument of each kind is indispensable. In the former case, 

 each observer will note the indications of his own instrument. 



ithly, Care must therefore be taken to note down at the 

 beginning, during, and at the close of the observations, the 

 indications of the several instruments, together with the general 

 state of the weather and the direction of the wind, if there be any, 

 though it is most advisable to observe before and after wind. 



5thly, The change of level of the water must be noted some- 

 times every minute; at others every ten minutes — every half hour 

 ■ — or every hour. The observations should be sometimes made 

 at sunrise, three hours after his ascension, at noon, at 3 in the 

 afternoon and at sunset, as also after, if convenient, in order to 

 see how far the hour exercises an influence on the phenomenon. 

 It would likewise be well to observe if the moon has any 

 influence, and, for this purpose, observations should be made at 

 the new and full moons and at the quadratures. 



ethly, On an outline sketch plan of the lake must be marked 

 the different stations, numbered or lettered, indicating the 

 distance of each station from each other. This is necessary in 

 order that the observer may be assured whether the rise or fall 

 observed simultaneously at two or more stations are distinct and 

 independent, though simultaneous effects, or dependent and 

 corresponding oscillations. 



*lthly, For each series of observation, a table, in the following 

 form, should be arranged: 



Observations on the Seiches of Lake 

 made by Dat 



e. 















Time op day. 



Station A. 



Station B. 



&e 



Remarks. 





Hour. 



MlN. 



9 





 10 

 20 



rorf.*ftinli. 



v. or f. ft. in li. 







Moreover, in order that nothing may be omitted which can be 

 supposed to exercise any influence, the topographical structure of 

 the basin, and particularly the aspect, height, condition, and 

 nature of the hills in the immediate vicinity of the lake, if there 

 be any ; or, otherwise, their absence must be carefully noted. 



It were needless to add, that the more numerous the observa- 

 tions, the better; and the more that may be made simultaneously, 

 the more satisfactory will be the result. 



I will not presume so far to question the sagacity of the 

 Societ}-, as to enumerate all the advantages that are likely to 

 accrue from observations of the kind just stated, they will be, I 

 doubt not, as evident to all, as they are to myself, and it is from 

 this conviction, that I venture to call the attention of my colleagues 

 to the subject. 



Schutter, as may be seen in the "Memoirs de TAcademie des 

 Sciences de Stockholm" for 1804, explains the irregular rise and 

 fall of the Baltic on the same principle as de Saussure and 

 Vaucher explain the Seiches of the lake of Geneva. I hope to 

 be one day enabled to add further observations in support of the 

 general prevalence of the phenomenon. 



I have lately written to a most eminent philosopher, the 



* R. or F. for rise or fall, as it may be. All that is required is relative rise ami 

 fall, the height nt which the water may be found on commencing the operation will 

 always be 0. In the column of remarks will be consigned the indications -of the 

 barometer, &c. 



