62 



PROCEEDINGS OF THE CANADIAN INSTITUTE, 



At 8 p.m. of this day Medicine Hat reported 52 degrees below zero. On the 

 24th and 25th the cold wave, though greatly diminished by lake influence, had 

 reached Toronto, giving a minimum temperature of 8 degrees below zero. 



After carefully measuring and tabulating the duration of the larger wave inter- 

 vals taken from a great number of these lake records, it was surprising to find a 



FIG. 6. 



marked 20-minute interval. There appears to be a correspondence between these 

 time intervals and those marked upon the barograph records for the same period. 



Professor Forel suggests that the smaller, and more rapid oscillations observed 

 upon the foregoing traces, may be due to the lake surface becoming divided into 

 many nodal points of rest, similar to the nodes upon a violin string, when set 

 vibrating. Although these researches cover too short a time to make any definite 

 assertion, there seems to be a wonderful correspondence between the lake waves, as 

 recorded at the Humber, and those found upon the Observatory photographic 

 barograph traces. To illustrate this, let us look at the Humber record, plotted with 

 the photographic barograph trace, during a thunderstorm on the 29th of July last. 

 Here you will observe a marked coincidence between the two ; that is, as the 

 atmospheric pressure varied, so did the water rise and fall. The smaller and more 

 rapid movements are not recorded upon the barograph, as it is not sufficiently 

 sensitive. The sudden fluctuations and great range of water level preceding and 

 during thunderstorms, are almost beyond conception until graphically shown, as be- 

 fore us. Here you will note, shortly after 4 p.m., a rise of water of five and a half 

 inches in six minutes, followed by a fall of six inches in five minutes ; the rise 

 almost exactly corresponding to 'the crest of a decided barometric wave. This cer- 

 tainly points to local action, which would not be of sufficient extent to set the whole 

 surface of the lake into multi-nodal vibrations. 



These peculiar oscillations appear to be probably due to the action of atmos- 

 pheric waves or billows, in passing over the surface of the lake, which tend to 

 form minute undulations upon the surface, corresponding in length to these billows, 

 ■ and as they move farther into the bay, become magnified as they reach narrower 

 and shallower portions, until, finally, they assume the proportions recorded upon the 

 instrument. If not thus, how are we to account for the secondary undulations 

 foimd upon the ocean tide gauges situated at the end of bays, where the shores 

 cannot encircle the disturbed body of water, save at three sides at most ? (i) 



(i) "A Probable Solution of the Secondary Undulations Found Upon Tide Gauges." Read i6th 

 January, 1897. Supra, p. 28. 



