45, CORNHILL, E.G., AND 122, REGENT STREET, W., LONDON. 



75 



FIG. 81. FIG. 86. 



97. Dines* Hygrometer. We notice this apparatus chiefly as a matter 

 of record. It is fully described along with an account of some remarkable 

 results obtained from its use by its inventor, George Dines, Esq., in the Journal 

 of the Meteorological Society ; but, like Daniell's, Regnault's, and Jones's 

 Hygrometers, it is not self-acting, and not so simple in its use as the Wet and 

 Dry Bulb Instrument. Therefore, this Apparatus will only be supplied to 

 special order. Price, 2 12 6 to 3 3 



98. Registering Hygrometer, constructed with Negretti and Zambra's 

 Patent Maximum and Minimum Registering Thermometers, each fitted up as a 

 wet-bulb thermometer, to record the highest and lowest temperature of 

 evaporation during any interval of time. Price, 330 



99. Hygrometer Screen. The engraving (fig. 89), page 79, shows one 

 of the best methods of fixing up and protecting the Hygrometer, the louvre 

 boarded case affording free passage to the air and at the same time protection 

 from rain, suow, the sun's rays, or radiated heat from surrounding bodies. 

 This Screen should be fixed at about four feet from the ground, the door 

 facing due North. If fixed against a wall, there should be left a space between 

 the back of the Screen and the wall, at least three or four inches, to insure a 

 free circulation of air. It need hardly be pointed out that the Screen must 

 be securely fastened to its support, wherever used, to prevent vibration or 

 injury from wind. This arrangement is specially recommended by the Board 

 of Trade for Marine Service both for Hygrometers and Thermometers. 



Price, 1 1 0, or made to Order. 



100. From the readings of the two thermometers, the dew-point can be 

 deduced by formulae (that known as Apjohn's is considered the most theoretically 

 true), or from the valuable Hygrometric Tables by J. Glaisher, Esq., F.R.S. 



