108 Baron N. Schilling on the Constant Currents 



the coast detains the current which follows the sun and the 

 moon must the water more or less swell, and thereupon, in an 

 undulatory motion, push the swelling further, in accordance with 

 the law of the wave-theory, and in this manner carry the tide 

 into high latitudes, whither, according to the theory of the 

 moon's attraction, it should not come. 



We are confirmed in this view of the tides by the circumstance 

 that the tide- wave in the atmosphere has not yet been observed, 

 although according to the theory it must show itself there more 

 considerable than in the sea. The question of the atmospheric 

 tide-wave has occupied many scientific men. Laplace, after a 

 long series of observations, expressed a decided opinion that 

 there is no atmospheric tide. More recently Bouvard, Eisenlohr, 

 and Sabine have thought they could perceive a very small tide, 

 expressing itself only in hundredth parts of a line on the baro- 

 meter-scale. 



By the way we must remark that the mercury of the barome- 

 ter, just like all other bodies on the earth's surface, loses a por- 

 tion of its weight by the attraction of the moon and sun ; so 

 that it cannot show the variation of the atmospheric pressure 

 produced by the attraction of the moon, so long as the mass of 

 air above it remains the same ; every current, however, must 

 alter the height of the mercury column. It is just the same 

 with respect to the diminution of weight effected by the centri- 

 fugal force. An aneroid, as such, is not exposed to these influ- 

 ences, and therefore always gives the absolute pressure of the 

 atmosphere; so that in principle it is preferable to the barome- 

 ter. In practice, however, it still needs considerable improve- 

 ments, because errors arise from the metal not possessing per- 

 fect elasticity. It is to be wished that observations of the two 

 instruments were more frequently compared. 



It was not until the present memoir had already appeared in 

 Russian that I got a sight of the extremely interesting and in- 

 structive treatise on Tidal Phenomena by Dr. Schmick. This 

 writing (which, while throwing much light on the phenomena 

 of the tides, contends for many views to which we canuot assent) 

 well deserves a closer consideration than would be in place here. 

 Yet we cannot omit to say a few words on his notion of the dis-. 

 placement of the earth's centre of gravity. Since the height of 

 the tide-wave is greater in the hemisphere turned towards the 

 moon or sun than in the opposite one, Dr. Schmick thinks that 

 the centre of gravity of the earth is displaced somewhat towards 

 the side of the greater gathering of waters, and that the earth 

 cannot by its own force recover its original centre of gravity 

 after it has suffered displacement from without. A constantly 

 repeated displacement, in this way, of the centre of gravity 



