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TRANSACTIONS OF THE SECTIONS. 



1. MATHEMATICS AND PHYSICS. 



On the CotnpressihiUty of Water. By Professor CErstf.d. 

 {From a Letter to the iiet;. WilliamWhewell, dated Copen- 

 hagen, June 18, 1833.) 



[_With an Engraving.] 



" Were I not withheld by official duties, I should certainly not 

 omit so excellent an opportunity of renewing the very interest- 

 ing and useful acquaintance 1 made during my last visit to 

 England and Scotland, and of forming new ones with those 

 distinguished scientific characters that I was not fortunate 

 enough to meet with at that time, or such as have risen to emi- 

 nence of late years. But though I must now forgo this ad- 

 vantage, I will not let this opportunity pass without giving the 

 illusti'ious assembly some mark of my high esteem, and of my 

 desire to keep up the friendly intercourse which I have main- 

 tained with the British philosophers since my acquaintance with 

 your happy country. 



" You are, perhaps, aware that I have pubHshed several no- 

 tices upon the compressibility of water, the first as early as 

 1818, and the first description of the improved method in 1822. 

 Since that time I have still gone on improving my methods, and 

 am now preparing a paper on the subject for the Transactions 

 oj the Royal Society of Sciences at Copenhagen. I will endea- 

 vour to give you a succinct account of my method and its re- 

 sults. It has been found that the apparatus for compressing 

 water, a description of which I pubhshed in 1822, can give very 

 accurate results ; so that the results it has given in the hands of 

 philosophers in different countries, have agreed more than 

 might have been expected. Next to the accuracy of the mea- 

 surements, however, one of the most important requisites oi 

 such an apparatus is, that the experiments be performed with 

 the greatest celerity possible. When the experiment is pro- 

 tracted, the change of temperature produces great variations in 

 the volume of the water, -rlw of the thermical measure (1° cenr 



1833. 2 a 



