Fig. 615. 



METEOROLOGICAL INSTRUMENTS. 

 Fig. 616. 



129 



O 



O 



The Oat Beard Hygrometer. (Fig. 616.) 

 This hygrometer is formed of the beard of the 

 wild oat, one end of which is fixed in a small 

 column, and usually placed in the centre of a 

 round brass case, covered with a glass ; the 

 other end has a small index attached, usually 

 made of a slender piece of light wood. Within the case 

 there is a dial, divided into equal parts and numbered from 

 to 30 each way, and on one side the word Dry, and on 

 the other Damp. In the sides of the case there is a num- 

 ber of holes, in order that the atmosphere may have free 

 access to the interior of the instrument. There is a spring 

 in the back of the case, attached to the column, by which 

 the index may be set at on the dial. 



When this instrument is exposed to dryer or moister air, 

 the small index, by turning round, either in one direction or 

 the other, indicates the state of the atmosphere. 



This is a simple and useful instrument for ascertaining 

 the comparative dry ness or dampness of different apart- 

 ments, beds, &c., but it is not suited for meteorological ob- 

 servations. 



Priee, $2.50. 



