and Descriplion of a Seff-reghlering Hygrometer. 2 15 



cumstance necessary to be taken into the account, in estimating 

 the absolute quantity of water lield in ^;olution by the atmosphere 

 at the moment. I hope it will not be supposed that these re- 

 marks are intended to throw anv obstacles in the way of a more 

 extended and general use of an instrument which is likely to be 

 of such essential service to science, and which has already done 

 bO nuich honour to the ingenious inventor. My object is to 

 press upon those who may not have, had an opportunity of making 

 a!iy observations with the hvi^rometer, but who are f;\mi!iar with 

 the use of the thermometer, not to neglect the means which they 

 possess of collecting- facts on a branch of science which is still 

 in its infancy, and which nevt r can make anv advancement, but 

 by the patient a])plication of the inductive philosophy. 



1 reinain, sir, yours respectfully, 

 K s, July 2, ISl/". ■ ■ G. 



l.ETTl'R II. 



Deseriptum of a Self-regislering Hygrometer. 



Mr. Editor, — I have already endeavoured, more than once, to 

 direct the attention of yonr readers to the subject of hygrometry, 

 as a branch of science naturallv interesting, and which has of 

 late become still more so, from the ingenious discoveries of Leslie 

 and Anderson. To the former of these gentlemen we are in- 

 debted for the best, and indeed the only, ])hilosoi)hical instrument 

 hitherto employed for ascertaining the state of the atmosphere 

 with regard to moisture ; and to the research.es of the latter we 

 owe some beautiful theorems for its practical application to the 

 science of meteorologv*. Simple, however, and philosoi)hic:iI 

 as that instrument is, it appears to me to be still capable of im- 

 provement. In its ))resent form it can be employed only in find- 

 ing the hvgroinetric state of the atmosphere at the moment of 

 observation; nor have anv attempts been made, as far as I know, 

 ro construct it so as to mark the extremes of dryness and mois- 

 ture, in the absence of the observer, i formerly thought that 

 the instrument might easily be made to register the greatest dry- 

 ness, but that it would be diificnlt to construct it so as to mark 

 the greatest degree of moisture. It has since occurred to me, 

 however, that the latter object may be as easily accomplished as 

 the former, and both on the same princijjle with the self-regis- 

 tering thermometer commonly in use. For a description of the 

 instrument, as originally constructed by Professor Leslie, I refer 

 your readers to that author's treatise on heat and moisture, and 

 to the article Hygrometry in the Edinburgh Encyclopicdia. In 



* The researches of Mr. Anderson were published, for the first time, in 

 the EdinLuigh Eiicyclopa-'dia, conducted by Dr. Browstcr, 



Q 3 the 



