B. TERRESTRIAL PHYSICS AND METEOROLOGY. 53 



liable, the author has further been able to calculate, as he 

 believes for the first time, the amount of annual contraction 

 of our globe; and to show that, if that be assumed constant 

 for the last 5000 years, it would amount to a little more than 

 a reduction of about 3^ inches on the earth's mean radius. 

 This quantity, mighty as are the effects it produces, is thus 

 shown to be so small as to elude all direct astronomical ob- 

 servation ; and, when viewed in reference to the increase of 

 density due to refrigeration of the material of the shell, to 

 be incapable of producing, during the last 2000 years, any 

 sensible effect upon the length of the day. At the rate of 

 contraction of 3-J inches in 5000 years, as above given, it 

 would require about ninety millions of years to diminish the 

 earth's radius by one mile; and, if there be any approximate 

 truthfulness in these numbers, and in the number given by 

 Mallet in his original memoir, for the entire contraction of 

 the earth since it was a molten mass, the resulting figure ex- 

 pressing the age of the earth will be large enough to satisfy 

 all the demands of the most extreme geological theories. 

 12 A, 1874, IX., 57. 



THE DAILY VARIATION IN TERRESTRIAL MAGNETISM. 



Wolf, on comparing the maxima and minima of solar spots 

 with the magnetic observations made at Prague, concludes 

 that both the range of daily variation of magnetic declina- 

 tion, and also the range of daily variation of horizontal in- 

 tensity of the earth's magnetism, allow themselves to be very 

 approximately represented by means of formula consisting 

 of the sum of two terms, the first a constant and the second 

 a variable, depending on the relative frequency of solar spots. 

 Astron. Nach., LXXXIIL, 290. 



THE TIDES OF THE LAKE OF GENEVA. 



A peculiar tidal phenomenon, known as the seiches, which 

 has long been observed on the Lake of Geneva, forms the 

 substance of an exhaustive investigation by Professor Forel, 

 who adheres to the theory generally accepted in explanation 

 of the phenomenon namely, that it is due to variations of 

 atmospheric pressure, the pressure diminishing at one part of 

 the lake and increasing at another. The surface of the water 

 rises in the former case, and sinks in the latter; thus a swing- 



