4- 



TRANSACTIONS OF THE 



D 



[OCT. 5, 



The hygrometer which was tested is shown in the accompany- 

 ing cut, Figs. I. and II. ; the essential parts of the instrument 

 are designated by letters, and the parts so indicated are ex- 

 plained in the following paragraphs : 



A and A' are two thin brass supports, respectively 23.7 centi- 

 meters and 22 centimeters long and 2 centimeters broad. 



B, small rivets which connect the supports A and A', but leave 

 an air space which separates the latter by .7 of a centimeter. 



C, six fine hairs about 18 centimeters long, placed parallel, 

 and laid close together, so as to hang like one large hair in the 

 air space between A and A'. 



D, an adjusting screw, from which the six hairs, C, are sus- 

 pended. 



E, a short lever, to which the lower ends of the hairs, C, are 

 fastened (a small weight is attached to this lever in such a way 

 that the hairs are kept at a slight tension). 



F, an indicator, 4.7 centimeters long, fastened to the lever, E, 

 which shows changes in the length of the hairs, C ; by the use 

 of this indicator the actual change in the length of the hairs is 

 multiplied a convenient number of times. 



G, a scale of percentages of relative humidities, from to 100 

 per cent. 



