( 436 ) 



will in every case remain Scandinavian, or rather Northern. At the 

 same time I would recommend a closer study of the Diluvium in 

 Texel and Wieringen, in order to ascertain, whether it contains 

 erratics, the origin of which may be traced to other parts than 

 of those which are found in the eastern parts of our country. 



What I consider to be very "doubtful" indeed, is the right to 

 trace the direction which the Northern glacial flow is supposed to 

 have taken, solely from the examination of erratics, found at such a 

 large distance from the rocks of their origin. In reference to this 

 matter, I would strongly recommend "revision" and would especially 

 suggest a wider field of investigation than the Flondsrug in Groningen. 



Mathematics. -- "Huygens' sympathie clocks and related phenomena 

 in connection with the principal and the compound oscillations 

 presenting themselves lohen two pendulums are suspended to 

 a mechanism ivith one degree of freedom." By Prof. D. J. 

 Korte WEG. 



(Communicated in the meeting of October 28, 1905). 



Introduction. 



1. When in February 1665 Christiaan Huygens was obliged to 

 keep his room for some days on account of a slight indisposition he 

 remarked that two clocks made recently by him, and placed at a 

 distance of one or two feet, had so exactly the same rate that QWQry 

 time when one pendulum moved farthest to the left the other deviated 

 at that very moment farthest to the right ^). Yet when the clocks 

 were removed from each other one of them proved to gain daily 

 five seconds upon the other. 



At first Huygens ascribed this "sympathy" to the influence of the 

 motion of the air called forth by their pendulums; but he soon 

 discovered the real cause — the slight movability of the two chairs 



1) ,Ge qu ayant fort admire quelque temps" ; he writes : „j'ay enfin trouvé 

 »que cela arrivoit par une espèce de sympathie : en sorte que faisant batlre les 

 , pendules par des coups entremeslez; j'ay trouvé que dans une demieheure de 

 , temps, elles se remettoient tousiours a la consonance, et la gardoient par apres 

 „constamment, aussi longtemps que je les laissois aller. Je les ay ensuite eloignées 

 „Tune de I'autre, en pendant Tune a un bout de la chambre et I'autre a quinze 

 flpieds de la: et alors j'ay vu qu'en un jour il y avoit 5 secondes de difference 

 „et que par consequent leur accord n'estoit venu auparavant, que de quelque 

 „sympathie". Journal des Sgaraus du Lundy 16 Mars 1665. Oe^^rres cZe Christiaan 

 Huygens, Tome V. p. 244. 



