VOL. LXXXI.] PHILOSOPHICAL TRANSACTIONS. 3 



extreme, long before it is really so. As for the slips ; since moisture has only 

 one effect on their length, that of widening more or less the meshes of the cross 

 fibres, it is concluded that all iheir hygroscopic indications, in every part of their 

 scale, were true in respect of increase and decrease of moisture ; and that con- 

 sequently, that class of hygroscopes might be depended on in that important 

 point. As for the exact ratio between the indications of those last hygroscopes, 

 and the changes of moisture, that was to be the object of a particular inquiry, 

 to which he now comes, viz. concerning the scale of the hygrometer between 

 the two fixed points. In treating this subject, various experiments are made on 

 the comparative changes of weight and dimensions of some hygroscopic sub- 

 stances. The following table contains the results of the experiments, namely, 

 the correspondent marches of all the hygroscopes ; the shavings increasing in 

 weight, and the slips and threads in length. The last 3 comparative terms do 

 not result from that particular experiment ; for the shavings, they are concluded 

 from the former comparative steps : for the other instruments, they have been 

 obtained by observations in the open damp air. 



From the first 18 terms of this table, which are the immediate results of the 

 experiment, we are now to examine the opinion, that the lengthening of the 

 slips of whalebone, quill, and deal, beyond these terms, is a sure sign that, till 

 they have attained their point 100, moisture continues to increase in the medium 

 where they are placed. In respect of the slips the theory is, that as moisture 

 cannot act on their length but by widening the meshes of their transversal fibres 

 they cannot go on lengthening but by imbibing more and more moisture, from 



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