3-24 Dcscripliun of an improved Hijgromcler. 



volutions made by the index, as it hanrs freely from the 

 axis, and advances one interval between the threads of the 

 screw for each revoJution; 



The index g, h, (fig. 1 and 2.) is made of fine wire, ac- 

 curately balanced, and as light as possible. It fits on the 

 end of the axis e, and is to he placed at right uiigles with 

 the commencement of the screw. 



The beard of the Ooleena Itooloo is represented at f, d, 

 (fig. 1.) The top of it, which is crooked, being cut oif, it 

 is first secured between the cheeks of the axis, at /", bv 

 means of the small sliding ring; the axis is then turned 

 round till the gold loop is brought to the fifth or sixth in- 

 terval of the screw, countino- from the dial })late : the screw 

 at c is then advanced so as to receive the lower or thickest 

 extremity of the beard of the Ooleena hootoo in the notch, 

 where it is also confined bv the sliding- rinsi' ^• 



.' DO 



The extremes of dryness and moisture are determined in 

 the following manner : — The hygrometer is placed in a con- 

 venient veisel, and exposed for a considerable time to as 

 great a heat as the grass can bear without injury; when the 

 index is perfectly steady, the hygrometer is to be taken out 

 of the vessel, and the screw at c turned round with a pair 

 of pincers so as to bring the gold loop to the^r^^ interval 

 of the screw on the axis, counting as before, from the dial 

 plate {which is to he placed to the left hand), and the index 

 to lOOj or zero. The hygrometer must now be suffered to 

 cool gradnully, during which, if the atmosphere be in a mean 

 state of moisture, the index will make four or five revolu- 

 tions. The Ooleena hooloo is then to be continually wetted 

 with a hair pencil and water nntil the index is again per- 

 fectly steady ; this will reoiure some time, as it moves very 

 slowly when within a few degrees of extreme moisture. The 

 degree at which the index stands is now to be noted, and 

 the number of intervals counted between the dial plate and 

 gold loop, and this number prefixed to the observed degrees 

 will give the extent of the scale. 



jill olservutions made with this hydrometer are to be re- 

 duced to uhat they would have been had the scale coiisisted 

 of iOUO parts, or ten revolutions of the index. This is most 



convenient. 



