VOL. LXXXI.] 



PHILOSOPHICAL TRANSACTIONS. 



113 



the unavoidable irregularities of every hygroscopic substance produce frequent 

 anomalies ; from which cause it was very difficult for M. de Saussure, consider- 

 ing the form of his experiments, to discover the hygroscopic law expressed by the 

 2d conclusion ; and with the unknown existence of that law, to suspect the 

 march of his hygrometer. 



When Mr. D. published those results of his experiments and observations, 

 M. de Saussure rejected them ; not from having made new experiments that had 

 confirmed his opinions ; but because he conjectured inversely, that Mr. D.'s 

 theory resulted from a fallacious march of his hygrometer ; and the well-earned 

 reputation of that celebrated philosopher engaged Mr. D. to undertake every ex- 

 periment that could help to detect on which side was the error. Mr. D. has re- 

 lated, in the first part of this paper, some of those experiments ; and now, for 

 their application, as well as for giving an account of some others, he follows more 

 particularly M. de Saussure's process. In this account Mr. D. states many rea- 

 sons and experiments to show that, in his judgment, the method of Saussure is 

 fallacious. He then gives the results of some of his experiments, part of which 

 are retained in the following tables. 



Table of experiments on the comparative changes in the 



v^ei^ht and the length of the same substance by increase of 



moisture, 



BOX. 



We see in this table the slip 

 of box following, in its increases 

 of length, the increase of weight 

 in the shavingsof the same wood, 

 nearly in the same manner as 

 the slips of whalebone, quill, and 

 deal, follow those of their own 

 shavings ; while the thread of 

 box, after having gained some 

 length by decreasing steps, be- 

 gins soon to shorten, at the 

 same time that its substance con- 

 tinues to imbibe water ; being 

 thus the shortest, when it can- 

 not receive any more water in 

 its pores. That excess of the 

 hygroscopic phenomenon of 

 threads cannot but throw a full 

 light on the nature of those hy- 

 groscopes. He next assembles, 

 in 2 tables, the comparative 

 marches of all the threads, and 



