Description of an improved Hygrcnctei-. 325 



convenient, as it lacilitales the comparison of observations 

 made with diflfcrcnt Iiygroniett^rs. An example may not be 

 thought superfluous. Suppose the scale of the hygrometer 

 to be 1113, or eleven intervals and forty five parts; and 

 that at the time of observation there are fmir intervals be- 

 tween the dial plate and gold loop, and fifty ^*cf//) shown 

 by the index; this would be written 430. Then as 1143 : 

 1000 : : 450 : 393 nearly, the number of degrees to be re- 

 gistered. 



If two of these hygrometers, in whieh the extremes of 

 dryness and moisture are well determined, be compared to- 

 gether, they will seldom difi'cr ten divisions from each other*; 

 whieh is as near a coincidence as can be exjiected. 



In the above description I have confined myself to the 

 name by which the grass is known in I he Canarese lan- 

 guage, viz. Oof'eciia koalno ; but it may be proper to re- 

 mark that it h ihe yl)uIrop''>gnn coniorlwn o? lj\r\r\tPA\s. It 

 is found in every part of the M'/soor country in the month 

 of January ; w hen it should be gathered, and thoroughly 

 dried in the sun before it is used. 



This grass appeats to be far superior to any other hygro- 

 scopic substance hitherto discovered. In the Encyclopcsdiu 

 Brifannica the scale of Saussure's hygrometer is said to con- 

 sist of 400 degrees, or rather more than one revolution of 

 the index. The hygrometer here described makes eleven or 

 twelre rcroli/tions. It possesses also the advanta^.e of bcino 

 very portable, cinmot easily i)e deranged, and mav be much 

 reduced in size, if thought nece^sar)', without affeciing the 

 extent of the scale, 



S;. Helena, May 15, l!!Of>. 



I'.S. It is evident i!iat, tliriugh the princ!{)!e and scale 

 remain the same, the form of this instrument may b'; varied 

 so as to render it far mr)rc portable anrl sale; and this has 

 been done by Mr. .Jones, who has uiado several in a very 

 superior manner of a cjlhidricul form, three incl.Hs only in 

 length and one inch and an eighth in diameter. 



* As the obr.pivei". diflercncc l>ctvfeii tlie roiiiparcJ h .j^roniprer" v.-ps al- 

 ways nearly the .aine, and on the same iUle, I have ny.m to tliiiik the dif- 

 TiTcnrt incrilioiicd .ihove arnse, in a great mp:!.>iirc, li/un ll^e exin;.uc» not 

 haviinj been Jc-ierniiucU with suffu-iei^ arcuraty. 



X>1 LIV. S((ond 



