22 



Art. 1.— T. Terada: 



Since a has a very large value for not very high latitude, the term 



a2^tanh-a(a; — a;o)[2a^sech^a(a; — x^f 

 is predominant in the expression of a\; hence the graph of ai, with 

 X as abscissa takes an M-shape with the minimum lying in the sea 

 at a distance 16.9 km. from the coast. Carrying out the calculation 



for some values of x, we obtain Table VI. 



Table VI. 



Here, the unit increase of a{x+Xo) corresponds 

 to 119 km. in the increment of x. 



In applying the above to the actual case, 

 a difficulty is met with in assigning a suitable 

 value of X for each station, since in the actual 

 case the coast line is by no means straight even 

 approximately, or even if portions of the coast 

 line could be regarded as nearly straight, the 

 cases are rare in which we may directly apply 

 the above theory with confidence- However, 

 let us consider the geometrical distribution of 

 land and water expressed by means of infinite series, for example 

 in terms of spherical harmonics and retain only the first few terms, 

 neglecting the remaining terms pertaining to the minor irregulari- 

 ties. The resulting coast lines will be devoid of all irregular zigzags. 

 For such an ideal distribution, the applicability of our theory be- 

 comes more justifiable, since the portions of the coast lines with the 

 length of several hundred km. may be regarded as nearly straight, 

 or at least as portions of a plane curve of second degree with no 

 remarkable curvature. In such a case, it may be in some measure 

 plausible to consider the coast as straight. In applying the above 

 formula, we will take for x, i.e. the distance of the station from the 

 coast, the value proportional to the continentality of the station, 

 instead of taking the distance from the nearest coast, since the 

 latter distance is very uncertain for the most cases. For, it may be 

 easily shown that when the coast is actually straiglit, the conti- 

 nentality as defined in the previous paragraph, is given by 



K = 



n , , sin2(z^ 



— + « + -— — 



2 2 / 



B 



x<:B, 



(22) 



