1851 Great Exhibition: Official Catalogue: Class X.: Negretti and Zambra
160A. NEGRETTI and ZAMBRA, 11 Hatton Garden — Inventors and Manufacturers.
Standard open cistern barometer, with adjusting scale. Self-registering barometer.
New pocket barometer.
Pocket sympiesometer or air barometer.
Standard thermometer, with comparative scales for atmospheric and chemical purposes.
Rutherford's thermometer.
Sixes' self-registering thermometer.
Set of very sensitive thermometers, for delicate experiments.
Registered thermometer for out-door exposure.
Three of the most approved hygrometers now in use: a Daniel's hygrometer: a dry-bulb and wet-bulb thermometer, and Regnault's condenser hygrometer; the latter instrument is so constructed as to be used like the preceding one, having been altered from Regnault's original form, by substituting black glass for silver caps, to avoid the necessity of cleaning the caps, an operation rendered necessary by the oxidation of metal caps.
Two distinct thermometers in one stem.
Simple and improved pressure gauge, less liable to get out of order than the ordinary mercury gauge.
[The dry and wet bulb thermometers consist of two of these instruments, whose readings, when under the same circumstances, are identical. In use, one of the bulbs is covered with thin muslin, and moistened by means of water passing by capillary action from a vessel containing that fluid, and will take a temperature depending on the amount of moisture in the air. If the air be saturated with moisture, there will be no difference in the readings of the two thermometers; but if the air be not saturated, it will take up additional vapour: this vapour will be combined with heat, and the reduction of temperature will be shown. The different readings of the two thermometers will be according to the quantity of heat which has been required to change the state of water on the bulb to vapour. From the readings of the dry and wet bulb thermometers, nearly all hygrometrical problems can be solved. Ether is more generally used for evaporation with Daniell's hygrometer. —J. G.]