(45) 



the curve then each straight line through P has zero points of inter- 

 section /^ with tiie ('ur\e; in otluM' words /' \s ft i>nint of the order zero 

 of' tlic curve, so f' = 0. So \\w I'csult of all our considerations is 

 included in equation (3). 



We formulate this in the following way : 



Theorem II. Let P he a point of tlw order t! of an (i]<i('hnüc curve 

 (inhere t' nuiy al.so he zero) and S an. arhiintrij jtouit of the order t of 

 tJiat carve. Suppo.se the stralt/ht line P S Iniersects the carve in m points 

 coincidimj anth S, then the class of dee curve is equal to t' increased by 

 die sum of w — t over all die jtoints S of the curve. If S is in P 

 }ve have to rec/ard (dl straiijht lines throuj/h P as di.e line cotmectiny 

 P and S. 



When speaking of all points S or, when >S' is in P, of all 

 straight lines divouyh. /^ we mean that we take those points or lines 

 contributing to — {iv.^ — t-^) and as many other points oi- lines as 

 one likes. 



Theorem I is a special case [t' =^ 0) of this theorem II. The 

 theorem always holds good for any singularities the cui've may have. 



Sneek, May 1904. 



Geology. — "Some considerations on. the conclusions arrived at in 

 the communication made hy Prof. Eug. Dubois in the meetinei 

 of June 27, 190o, entitled: So)ne facts leadiny to trace (uit 

 the motion and the oriyin of the underyround ivater of our 

 sea-provinces y By H. E. de Bruyn. 



(Communicated in the meeting of Septemf^er 2G, 1'JÜ3). 



In the meeting of June 27, 19Ü3 Prof. Dubois made a communication 

 dealing with a problem of great general importance, namely the presence 

 of proper <lrinking-water in the province of Holland. Altiiough 

 readily ackiiowledging the many [)oints of merit of this communica- 

 tion and entirely agreeing with many of its conclusions, I differ 

 from the author on a principal point whicii indeed is essential, 

 namely the origin of the fresh wafer in our polderland. So a speedy 

 refutation of the author's opinion on this point seemed to me to be 

 desirable. 



In his communication Prof. Dubois speaks of our sea-provinces ; 

 this ill my opinion ought to be Holland, since the conditions [)revail- 

 ing in Fi-iesland and Zeeland are diirerent, so that considerations 

 which are xalid lor Holland caiiuol be ap|tlied fhei-e. So I will 

 only cojisider the tract of (Miuulry chielly dealt with in the above- 

 mentioned communicadon, w liicli is bounded i»y the dykes of the Y 



