72 



NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, E.G. 



FIG. 78. 



FIG. 79. 



by the thermometer in the aether at that instant will be the temperature of the 

 dew-point ; the second thermometer showing the temperature of the air at the 

 time of observation. 



Price, in case .... 5 5 



Aspirator for ditto (fig. 78*) 1 15 to 2 15 



88. Regnault's Condenser Hygrometer (fig. 56), of simpler form, 

 only one cylinder or chamber being nsed. The air in this arrangement is blown 

 through the aether by the mouth. A small thermometer is attached to the stand 

 to show the temperature of the external air. 



Price, in Case, with ^Ether Bottle (fig. 79) 3 10 



For practical utility and convenience in use the Wet and Dry Bulb Hygro- 

 meter is vastly superior to all others. The engravings, N"os. 80 to 86, will show the 

 various forms of Negretti and Zambra's Hygrometers from the simplest to the 

 Standard instruments as manufactured by Negretti and Zambra for the various 

 Scientific Observatories and Societies, the Government Meteorological Stations, 

 the Metropolitan and County Hospitals, &c., &c. Most of these Hygrometers 

 ' have Negretti and Zambra's Patent Porcelain Scales and Enamelled Tubes. 



89. Wet and Dry Bulb Hygrometer, simple form, on a stand (fig. 80) 

 for table or shelf. Price, 12s. 6d., 16s., and 110 



90. Ditto Ditto Ditto plain, portable, brass stand 

 and metal cover (fig. 81). Price, 1 10 



