( "^^i ) 



almost iiniHcdialely, which intlueiice is tar more [)<)uoiïiil Ihaii an}* 

 other. After the heavy rains in the Ibiirth week of April J 903, 

 a Jiumber of deep wells on being sounded (April 27^'') showed a 

 higher level of 0.18 to 0.20 M. A week later it had sunk about 

 0.06 M., and only after the dry latter half of May, towards the 

 end of that month, it was again what it had l)een tow^ards the end 

 of April, before the heav^y rains. The rising of the deep well-water, 

 immediately after much rain, may be in part the result of the 

 greater pressure of the upper-soil. In the same way, a train passing 

 over the railway-dike in the Watergraafsmeer polder, for a moment 

 raised the water 7 m.ni. in a deep well, at a distance of 18 M., 

 which well was 34.5 M. beneath the surface of the polder. Pi-incipally 

 the rain will increase the hydrostatic pression. Li the second place, 

 changes in the pression of the atmosphere iiave a passing influence 

 on the level of the water in deep wells. Those changes make them- 

 selves felt at once, but that natural barometer is an imperfect one; 

 the effect of the changes in the atmospheric pression soon disappears. 

 For some hours hoAvever millimeters rising or falling of the quick- 

 si l\er ha\e their equivalent in centimeters on the watergauge. 



In the third place the low and the high tide of the sea, exercise 

 a negative or a positive pression on the dee]) underground water, i. e. 

 on those spots, which are not too far from the sea (3 or 4 K. M. 

 seems to l)e the utmost limit here). T liaxe always taken those 

 circumstances in te account. For the rest, as far as necessary, the dates 

 of the observations are stated here. With a few exceptions, I myself 

 ascertained the level of the water (with respect to N.A.P., the new 

 A\ ater-mark of Amsterdam, as a standard) or it was done under my 

 control ; some other results I hold from reliable sources. 



In the dunes now, the pression of the deep underground water ascends 

 to about 3 M. above A. P. So on March 30^'' 1903, in a well of the 

 Harlem waterworks sunk dowii to 53 M. ^ A. P., situated in the 

 midst of the dunes, at 3 K. M. west of Sandpoort, and a little further 

 from the polderland, the level of the water was observed to be at 

 2.91 M. -|- A. P. ; in another well in the dunes, deep 45.5 M. -.- A. P., 

 almost 2 K. M. further south, and at a distance of 2\', K. M. from 

 the polderland, the Avater ascended to 2.19 M. -|- A. P. Iji a third 

 well, close to the water-tower near Overveen ajid 1 K. M. from the 

 low-lying lands, as deep as 54 M. -.- A. P., it rose only to 1..20 -f- A. P. 

 Those three wells are at a distance of 2\/^ to 3 K. M. fi'om the sea. 

 In another well, near to the Brouwerskolkje, sunk down to 70 jM. ! A. P., 

 (in 1890), at '/^ K.M. from the one near Overveen and less than ^/j K.M. 

 from the low-lying land, the water had been seen to ascend to 



