tl£ IMPROVED HYGROMETER. 



The axis ef is made of silver wire, very smooth and 

 straight, arid of the size of a large knitting needle; on the 

 axis a screw is formed, bv twisting a smaller silver wire 

 tightly around it from left to right: this screw should he 

 fourteen or fifteen threads in length; the end of the axis,/, 

 is divided, and is to be closed by a small sliding ring. As 

 this is the most important part of the hygrometer, fig. 6, re- 

 presents it on an enlarged scale. 



A loop and drop (fig. 7) is made of fine gold wire, of such 

 a size as that when suspended on the screw it may slide 

 along it with perfect freedom by means of the revolution of 

 the axis, but not escape from one interval to another by any 

 other motion; should the loop, on trial, be found too large 

 (as indeed it ought to be) it may be easily closed a little, by 

 placing it on the screw, and pulling it gently by the drop, 

 it will then assume an elliptical form, as in the figure. This 

 Joop is intended to register the number of revolutions made 

 by the index, as it hangs freely from the axis, and advances 

 one interval between the threads pf the, screw, for each re- 

 volution. 



The index, g h, is made of fine wire, accurately balanced, 

 and as light as possible ; it fits on the end of the axis e, and 

 is to be placed at right angles with the commencement of the 

 screw. (See fig. 6.) 



The beard of the oobeena hooloo is represented between 

 f and d, (fig. 5.) The top of it, which is crooked, being 

 cut off, it is first secured between the cheeks of the axis, 

 at/, by means of the small sliding ring; the axis is then 

 turned round till the gold loop is brought to the fifth or 

 sixth interval of the screw, counting from the dial plate; 

 the. screw at c is then advanced, so as to receive the lower 

 or thick extremity of the beard of the oobeena hooloo in the 

 notch, where it is also confined by the sliding ring d. 

 Adjustment of The extremes of dryness and moisture are determined in 

 this hygroma the following manner. The hygrometer is placed in a new 

 earthen pot, which has never been wetted, 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 hy- 

 grometer is to be taken out of the vessel, and the screw at 

 t turned round with a pair of pincers, so as to bring the 



gold 



