294 M. Quetelet's Memoir of Prof. Moll. 



servatory and those of the cabinet of natural philosophy of 

 the university, which by his care had increased considerably, 

 he had also at his disposal the collections of the society of sci- 

 ences of Utrecht, which were not less rich. A circumstance 

 very honourable for our colleague enabled him to add still more 

 to the treasures that he had at command : by the death of Pro- 

 fessor Ekama, in 1826, the chair of physical sciences in the 

 university of Leyden had become vacant, and the curators of 

 this establishment had made an overture to Moll to induce 

 him to fill it. These honourable offers had not been posi- 

 tively I'ejected ; but the university of Utrecht felt that their 

 honour and interest would be compromised by permitting a 

 philosopher who shed so much lustre upon it to remove. 

 M. Moll yielded to the solicitations addressed to him by the 

 university, and resolved to remain in his situation. The city of 

 Utrecht wished to present him with a testimony of its grati- 

 tude ; but our colleague refused to accept anything for him- 

 self, he only expressed a desire to see something done for the 

 interests of science, and the government of the city placed at 

 his disposal the sum of ten thousand florins for the purchase 

 of instruments. 



One of the most important labours of M. Moll was that 

 which he accomplished in conjunction with M. Van Beek 

 upon the velocity of sound. The experiments of these philo- 

 sophers took place in 1823, a year after those which were 

 made by a commission of the Bureau of Longitude of France, 

 composed of MM. Arago, Gay-Lussac, De Humboldt, &c. 

 The government placed at their disposal all the necessary 

 means of execution ; and the base that the sound had to 

 traverse extended over a length of 17,000 metres, between 

 Kooltjesberg near Naarden and the elevation named the 

 Seven Trees {zeve?i boomen), near Amersfort. Six nights were 

 devoted to these experiments, which were made with a care 

 which seemed to leave nothing to be desired. The results of 

 them were recorded in the Memoirs of the Institute of the 

 Low Countries *. The Royal Society of London, by insert- 

 ing them in its Transactions, also proved the interest it at- 

 tached to them. 



M. Delaplace had also advised them to communicate their 

 labours to the Bureau of Longitude ; and I myself was en- 

 trusted with a letter, in which that illustrious philosopher 

 oblio-ingly invited the professor of Utrecht to make this com- 

 munication. 

 The inquiries of CErsted, in 1819, relative to the action which 



* Memoires dc Flnstitul des Pays Bas, vii. 281; and Philosophical 

 Transactions, I. 823. 2nd part. 



