Scientific Intelligence — Hi/drography. 173 



times the water-level varied rapidly in the harbour, while no such 

 vai-iations occurred 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 eleva- 

 tions and depressions, recurring, as they often do, at intervals of ten 

 or twelve minutes; and the result of observations at such time may, 

 in some degree, be regarded as negative. Besides, it may not un- 

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

 observation, the cause which produced them may be so far removed 

 as not to influence 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 at- 

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

 conforming to the laws which govern two fluids thus relatively situ- 

 ated, would accumulate where the pressure was the least, and be dis- 

 placed 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 perpendi- 

 cular 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. — 

 American Annual of Scientific Discovery, p. 245. 



4. Water Thermometer. — Lieut. Maury states that he has been 

 very much assisted in developing his theory of winds and currents by 

 means of the thermometer used by some vessels for determining the 

 temperature of the water. It was by means of these observations 

 on the temperature of the water that he was enabled to prove that, 

 ofl'the shores of South America, between the parallels of 35° and 

 40° south, there is a region of the ocean in which the temperature 

 is as high as that of our own Gulf stream, while in the middle of 

 the ocean, and between the same parallels, the temperature of the 

 water is not so great by 22°. Now, this very region is noted for 

 its gales, being the most stormy that the as yet incomplete charts of 

 the South Atlantic indicate. Lieut. Maury says, however, that 

 very ^evf navigators make use of the water thermometer, so that he 

 has experienced some inconvenience in his undertaking. He is the 

 more surprised at this, from the fact that New York owes much of 

 her commercial importance to a discovery that was made by this 

 thermometer. At the time when Dr Franklin discovered the Gulf 

 Stream, Charleston had more foreign trade than New York and all 

 the New England States together. Charleston was then the half- 

 way house between New and Old England. When a vessel, in at- 

 tempting to enter the Delaware or Sandy Hook, met a north-west 

 gale or snow storm, as at certain seasons she is apt to do, instead of 



