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Geophysics. — “On Lockyxr’s 35-year period in the solar activity.” 
By C. Easton. (Communicated by Dr. J. P. vAN DER STOK). 
(Communicated in the meeting of March 27, 1909). 
In These Proceedings Vol. XI p. 674 the results were communi- 
cated of an investigation by Prof. Eve. Dusors on the oscillations in 
the subsoil water of the dunes of Holland. 
From his well known investigations on the flora of the dunes 
Dr. Vurek had concluded that almost the whole region of the dunes 
on our coast is considerably more arid than it was formerly. He 
supposed that this fact must not be attributed to modifications in the 
climate, but to several other influences’); Prof. Dusots, on the contrary, 
thinks that we are justified in assuming a periodic rise and fall of 
the subsoil water. The period of these oscillations would agree in a 
remarkable way with that which was found by Prof. E. BRÜCKNER 
in many of the meteorological phenomena and which seems to extend 
over 35 years. 
Dr. W..J. S. Lockyer tried to show, in 1901,*) that a similar 
period exists in the fluctuations of the solar activity and in terrestrial 
magnetism. He derived the period mainly from the form and ampli- 
tude of the sunspot-curve since 1854: 1. from the modifications in 
the interval between minimum and maximum in consecutive 11 year 
periods; 2. from the changing frequency: of spots as expressed by 
the “total spotted area’. As the curves for the elements of the 
terrestrial magnetism are fairly parallel to the sunspot-curve, we 
have to see in Lockygr’s period merely the oscillation in the solar 
activity. The data, used by Lockyer, are the following: before 1870 
those of R. Wor; then, up to the sunspot-maximum of 1894, those 
of Enis and finally the observations of the Solar Physics Observatory 
near London. From the epochs of the minima and maxima of the 
1) L. Vuyex, The flora of the dunes, Leyden, Adriani, 1898, p. 186 and p. 301 sq. 
In this discussion [ think that too little weight is attached (even by Dr. Vuycx 
himself) to the difference, fully established by V., between the dune-region of our 
coast (on the mainland) and that of the North-Sea islands. The former is much 
the more arid. It seems likely that the choking up with sand of the pools in the 
dunes, which is considered by V. as the main cause of the desiccation of the dunes 
(not as the only one, as Prof. D. thinks), as well as the climatic changes, must 
have nearly the same influence on the two regions. — Does not, therefore, this 
difference rather lead us to consider such technical works as canals, aqueducts 
etc. as being the main cause of the greater desiccation of the ‘coast region, as: 
compared with the islands ? 
2) W. J. S. Lockyer, The Solar Activity 1833—1900. Proc. Roy. Society LXV HIF 
1901, p. 285. 
