246 ANNUAL OF SCIENTIFIC DISCOVERY. 



down like an immense surge, and so sudden was it, that those engaged 

 in catching fish had barely time to escape being overwhelmed. In the 

 summer of 1847, on one occasion, the water rose and fell, at intervals 

 of about fifteen minutes, during an entire afternoon. The variation 

 was from twelve to twenty inches, the day being calm and clear ; but 

 the barometer was tailing. Before the expiration of forty-eight hours, 

 a violent gale set in. At Copper Harbour, the ebb and flow of the 

 water through narrow inlets and estuaries has been repeatedly noticed 

 when there was not a breath of wind on the lake. Similar phenomena 

 occur on several of the Swiss lakes. Professor Mather, who ob- 

 served the barometer at Copper Harbour during one of these fluctu- 

 ations, remarks : " As a general thing, fluctuations in the barometer 

 accompanied fluctuations in the level of the water ; but sometimes the 

 water-level varied rapidly in the harbour while no such variations oc- 

 curred in the barometer at the place of observation." 



As a general rule, these variations in the water-level indicate the 

 approach of a storm, or a disturbed state of the atmosphere. The 

 barometer is not sufficiently sensitive to indicate the sudden elevations 

 and depressions, recurring, as they often do, at intervals o ten or twelve 

 minutes ; and the result of observations at such times may, in some 

 degree, be regarded as negative. Besides, it may not unfrequently 

 happen, that, while effects are witnessed at the place of observation, 

 the cause which produced them may be so far removed as not to in- 

 fluence the barometer. We are, therefore, led to infer that these 

 phenomena result, not from the prevalence of the winds acting on the 

 water, accumulating it at one point and depressing it at others, but 

 from sudden and local changes in the pressure of the atmosphere, 

 giving rise to a series of barometric waves. The water, conforming 

 to the laws which govern two fluids thus relatively situated, would 

 accumulate where the pressure was the least, and be displaced where 

 it was the greatest. It has been remarked by De la Beche, that a 

 sudden impulse given to the particles of water, either by a suddenly 

 increased or diminished pressure, would cause a perpendicular rise or 

 fall, in the manner of a wave, beyond the height or depth strictly due 

 to the mere weight itself. The difference in the specific gravity of 

 the water of the lakes and the ocean may cause these changes to be 

 more marked in the former than in the latter. 



ON THE FALL OF RIVERS. 



MR. AUGUSTUS PE TERM ANN, in a paper read to the Geographical 

 Society of London, communicates some interesting facts, which, he 

 says, are " the result of laborious researches." " The fall of a river 

 influences in part the velocity or force of its current, but not to such 

 an extent that the rate of fall can be taken as a scale for the rate of 

 the velocity and force of the current. We call the Danube, the Rhine, 

 and the Elbe very rapid rivers, and they only exhibit a fall of 1 and 

 2 feet per mile ; but we should not place the Tweed in the same rank 

 of velocity, but in the lower part of its course it has an average fall 

 of 8 feet, and yet it is freely navigated by small boats, while the 



