114 PHILOSOPHICAL TRANSACTIONS. [aNN0 1791. 



of all the slips, which he had submitted to that regular course of experiments; 

 laying aside many more of each class, the marches of which he only knew from 

 common observations. 



Table of the correspondent marches, by the same increases of moisture, of different threads or vegetable 



and animal substances taken lensthwise. 



Here the porcupine quill shows no retrogradation ; however, consistent with 

 its tribe, it had some in other experiments. Its last steps have the unsteadiness 

 of the stationary state, and thereby are subject to anomalies. From the same 

 cause, none of the other theads have exactly the same steps in any 2 experiments, 

 though on the whole their march remains essentially the same. The march here 

 given of the hair hygrometer comparatively with his own, is the mean result of 3 

 experiments, with 3 different sets of instruments ; one of the hair hygrometers 

 employed was sent by Mr. Paul, of Geneva, and its point of extreme moisture 

 was determined in a fog. The small and changeable retrogradation of the thread 

 of whalebone and of hair might have been overlooked, were it not for other 

 threads in which the retrogradation begins before that period where the state of 

 moisture is difficult to ascertain ; but from these threads, that phenomenon is 

 placed in a clear light, which is reflected on the others. Mr. D. has marked 

 with an * the greatest elongation of each of them, and with a -f- a point near 

 which their elongation begins, and to which they return at last. These signs 

 will guide the eye in the above table, which shows clearly, he says, that no thread 

 can be trusted to for the hygrometer. 



