700 SEC. 14. METEOROLOGY. 



2863a. Chameleon Hygrometer, based on the property of 

 cobalt of changing colour with the dampness or dry ness of the air. 



Walter B. Woodbury. 



287 Ig. Slide Rule for hygrometrical calculations by John 

 Welsh, F.R.S. Surgeon-Major F* de Chaumont. 



297 Ih. Mason's Hygrometer. E. Cetti $ Co. 



2853. Saussure's Hygrometer ; an old specimen by V. F. 



Hnusman. G. J. Symons. 



2854. Whalebone Hygrometer, by Thos. Jones, of Oxeudon 

 Street. G. J. Symons. 



2855. Darnell's Hygrometer. No maker's name, but 

 formerly belonging to Sir James South. G. J. Symons. 



2856. Balance Hygrometer (drawing and essential part of 

 the instrument). Prof* Buys-Ballot, Utrecht. 



At one arin of a balance is hung a wide glass tube filled with chloride of 

 calcium or any other hygroscopic substance. This tube is closed at its 



upper part by a cork stop, bearing two M I bent glass tubes plunging in oil 



baths, but care is taken not to submerge their open ends.' Two glass 

 bells, ending in tubes at their upper parts and plunging for nearly half an 

 inch in the same oil, render it possible to aspirate air through the chloride of 

 calcium tube without affecting its movability. One of the bells is joined by 

 an india-rubber tube with the spot the air of which is to be examined ; the 

 other with a gas meter and aspirator. In a given time the water contained 

 in a quantity of air indicated by the gas meter can in this manner be 

 weighed, and its humidity ascertained. It is obvious that the instrument 

 can easily be made self-registering. 



2857. Collection of Hygrometers and Psychrometers. 



Dr. H. Geissler, Bonn. 



2857a. Standard Hygrometer, with divisions and figures, 

 protected by an outer glass tube, as in Negretti and Zambra's 

 terrestrial radiation thermometer. Negretti and Zambra. 



2857b. Negretti and Zambra' s Standard Dry and Wet 

 Bulb Hygrometer or Psychrometer. Negretti and Zambra. 



Two thermometers as nearly identical as possible are placed side by side, 

 one marked DRY and the other WET. The bulb of the wet thermometer is 

 covered with thin muslin, and has twisted round the neck conducting threads 

 of cotton, passing into a vessel containing water placed on one side so that the 

 water may not affect the reading of the dry bulb thermometer. The tempera- 

 ture of the air and of evaporations is given by the reading of the two thermo- 

 meters, from which can be calculated the dew point. 



