1896.] NEW YORK ACADEMY OF SCIENCES. 3 



and that the work of measuring these plates is well under way. 

 The Potsdam measurements are practically ready for publica- 

 tion. The Paris and Greenwich reports will be ready in from 

 five to seven years. The limit of accuracy in all of this work is 

 about 0. 2 sec. of arc. The catalogue is expected to contain 

 about 2,000,000 stars. The subject of the reproduction of the 

 chart was left unsettled. 



Prof. Wm. Hallock reported some observations made by Prof. 

 Woodward and himself upon the singing sands on the shore of 

 Cape Cod. 



Mr. G. F. Kunz called attention to a very important paper b^^ 

 Aristides Brezina upon the collection of meteorites in the Vienna 

 Museum. 



Fourteen members and guests were present. 



J. F. Kemp, 



Recording Secretary. 

 Wm. Hallock, 



Secretary of Section. 



THE USE OF THE HAIR HYGROMETER*. 

 By C. C. Trowbridge. 



For some time past there has been an increasing demand for 

 a direct reading hygrometer, so constructed that it would indi- 

 cate the relative humidity of the air with reasonable accuracy. 



Among those hygrometers which have been considered as pos- 

 sibly suitable for this purpose is the Saussure's or hair hy- 

 grometer. Although formerly this hygrometer was looked upon 

 merely as a hygroscope, and was supposed to give only the ap- 

 proximate hygrometric state of the air, now it has reached a 

 higher place among hygrometrioal apparatus by virtue of certain 

 improvements in its construction. 



I have recently tested a form of hj^grometer based on the 

 Saussure principle, with a view of observing its action when 

 subjected to different changes in the degree of saturation of the 

 air. 



* Read by title, May 1, 1896. Revised from issue in " Science " July 17, 1896. 



