NEGBETTI AND ZAMBEA, HOLBOEN VIADUCT, E.G., 



FIG. 173. 



173 Negretti and Zambia's Faimer's Baiometer, for ascer- 

 taining the humidity of the atmosphere, the general character of 

 the weather, and the approach of wind or rain. The Farmer's 

 Barometer combines three distinct instruments the Barometer, 

 the Thermometer, and the Hygrometer, and is equally valuable to 

 the Agriculturist and the Invalid, a difference of 5 to 8 being 

 considered a healthy amount of moisture in the air of dwelling 

 rooms. The action is very simple, and so long as a sufficient 

 supply of water is kept in the cistern, the Hygrometric condition 

 of the atmosphere can be known at any moment. 



It is a well-known fact that the Barometer is as much, or even 

 more affected by a change of wind as it is by rain, and the ob- 

 jection raised against a simple Barometer reading, as leaving the 

 observer in doubt whether to expect rain or wind, is entirely re- 

 moved in the instrument now offered to the Public by the addition 

 of the Hygrometer, an instrument indicating the comparative 

 degree of dryness or dampness of the air ; a most important 

 item in the determination of the coming weather. 



Hitherto the use of scientific instruments of this class has 

 been confined to very few observers. Nevertheless, through 

 the instrumentality of James Glaisher, Esq., F.R.S., as Secretary 

 of the British Meteorological Society, multitudes of observations 

 have been taken with extreme accuracy, and duly registered ; 

 and it is from these carefully collected data that we are enabled 

 in a measure to interpret the various changes that we feel and 

 see going on in our atmosphere, and by the aidj of well-con- 

 structed instruments, are in a position to predict with a great 

 degree of certainty the weather that is likely to prevail from 

 time to time. 



Instructions for using the Wet and Dry Bulb Hygrometer 

 will be found at page 77. And at page 76 will be found a table 

 giving the value of Hygrometric readings in a simple form, 

 sufficient for the use of ordinary observers. 



The Fanner's Barometer as fig. 173 .... 2 10s. 

 Ditto, ditto, in Ornamental Mountings 5 5s. 6 6s. 



174 Negretti and Zambra's Miners' Barometer. It having 

 been observed, that explosions of gas in mines mostly occur when 

 the Barometer is very low (showing diminished atmospheric pres- 

 sure), it is important that a good Barometer should be at hand, 

 for observation by the Managers and others. For this purpose 

 Negretti and Zambra make strong and sufficiently accurate 

 Barometers, as fig. 174, at . . 1 Is. 2 2s. 3 3s. 



175 Aneroid Barometers for Miners' use, exceedingly convenient and sensitive, 



with Extended Scale 2 10s. 3 10s. 4 4s. 



176 Miners' Pocket Aneroids, see also page 143. 



3 3s. 4 4s. 5 5s. 



STANDARD AND MOUNTAIN BAROMETERS (see pages 1 to 13). 



