568 REPORT— 1897. 



instrument w&s placed at the west end of the lake at the Burlington Canal. The 

 records from these two instruments, when studied in conjunction with the Obser- 

 vatory synoptic weather charts and barograph traces, have revealed many interest- 

 ing points. Last January, to obtain a better knowledge of the smaller barometric 

 movements, a simple form of self-recording air barometer was constructed, seven- 

 teen times more sensitive than the mercurial. This again has recently been super- 

 seded by a combined self-recordingwater-level instrument and air barometer — that 

 is, both pens record upon the same time-sheet where an hour equals one inch and 

 one complete revolution of the cylinder equals twenty-four hours. 

 The following are some of the results deduced from the records : — 



1. That the longitudinal and transverse 'Seiche ' movements are very mai'ked 

 preceding and during storms primarily due to differences of atmospheric pressure 

 over the extremities of the lake, but greatly augmented when the gale strikes the 

 water Euri'ace. The mean time interval of longitudinal ' Seiche ' is four hours and 

 forty-nine minutes ; the transverse, forty-five minutes. 



2. There is a marked agreement between the time intervals of the smaller lake 

 undulations and those found upon the corresponding sensitive barograph traces, 

 both showing a predominance of twenty-minute intervals. 



3. These smaller lake undulations are due to atmospheric waves which are set 

 up along the boundary surfaces of different air strata when travelling in opposite 

 directions, the existence of which have been so clearly demonstrated by the late 

 Professor von Helmholtz in his mathematical papers read before the floyal 

 Prussian Academy of Sciences at Berlin in 1889 and 1890. 



4. The action of these atmospheric waves upon the surface of the water tends 

 to form minute undulations, which increase in amplitude as they move into bays, 

 &c., where the water becomes shallower, until finally they assume the proportions 

 as recorded upon the instrument. 



5. It appears, from a careful study of the Canadian ocean tidal records, placed 

 at the writer's disposal through the kindness of Mr. W. Bell Dawson, Director of 

 the Tidal Survey, in conjunction with the synoptic weather charts, that the 

 secondary undulations found upon them may also be due to similar atmospheric 

 action. 



6. Marked rapid and large undulations often occur during the autumn and 

 winter months upon both instruments when the barometer is actually rising and 

 fine weather prevails throughout Ontario. At such times an area of low pressure, 

 or cyclone, is situated over the south or south-western States, which usually moves 

 over or near to the lake region. In such cases the recorded atmospheric waves are 

 due to the lower, denser air of the anticyclone, moving towards the south-western 

 cyclone, along whose upper boundary surface huge waves, extending to the earth, 

 are set up by the rapidly opposing upper poleward current. The mean velocity of 

 this upper current in summer is sixty miles per hour, and in winter one hundred 

 and ten miles per hour. On the other hand, during the approach of an anticyclone, 

 attended by fine weather and westerly winds, these lake undulations become 

 extremely small, because the lower air moves in approximately the same direction 

 as the upper poleward current. 



7. The direct action of these air waves upon the surface of the lake is clearly 

 shown during the passage of a thunder shower. As an instance, on March. 8 last, 

 during the passage of several successive huge atmospheric ' billows,' the water rose 

 8A inches in ten minutes, then fell 10^ inches in filteen minutes, followed by the 

 phenomenal rise of IH inches in fifteen minutes. 



8. These records graphically explain the cause of those erroneously termed 

 ' tidal waves ' which occur upon the lakes, and also tend to solve the problem 

 respecting the larger waves encountered at apparently regular intervals. From 

 information obtained from fishermen on Lakes Eiie, Ontario, and Huron a twenty- 

 minute interval appears to have been frequently observed between these waves. 



As these peculiar undulations occur upon all waters it is hoped the study of 

 them will become more universal, and the time not far distant when instruments 

 similar to those described will be adopted throughout the scientific world. 



