85 



for which so little has been done in distant voy- 

 ages*. Without entering into the question, 

 whether inaccurate experiments are more inju- 

 rious to the progress of the sciences than the 

 total ignorance of a certain number of facts, I 

 may affirm, that several hygrometers, constructed 

 by Mr. Paul at Geneva, and reduced from time 

 to time to the point of extreme humidity^, have 



* Mr. Peron thinks, " that it was in the voyage of Captain 

 Ban din, that hygrometers for the first time crossed the ocean." 

 But before this voyage, and even a long time before my own, 

 hygrometrical observations had been made in the voyage of 

 Laperouse, and at Bengal by the son of Mr. Deluc. 



f I made this correction every time that I had any doubt 

 of the indication of the hygrometer. I employed immersion 

 in rain water, as Mr. Deluc recommends for whalebone. It 

 is known, that this method of verification, even with hair, can 

 cause but a slight error of 1° or 1*5° (Essai, § 32, p. 37) ; 

 while the best hygrometers often differ from each other two 

 degrees. I have never been able to reduce the hair or whale- 

 bone to the degree of extreme siccity, for want of a portable 

 apparatus, which I regret not having made before my de- 

 parture. I advise travellers to provide themselves with a nar- 

 row jar, containing caustic potash, quicklime, or muriat of 

 lime, and closed with a screw by a plate on which the hygro- 

 meter may be fixed. This small apparatus would be of easy 

 conveyance, if care were taken to keep it always in a per- 

 pendicular position. As under the tropics Saussure's hygro- 

 meter generally keeps above 85°, a frequent verification of the 

 single point of extreme humidity is most commonly sufficient 

 to give confidence to the observer. Besides, in order to know 

 on which side the error lies, we should recollect, that old hy- 

 grometers, if not corrected, have a tendency to indicate too 

 great dryness. 



