BAIRD &TATLOCK (LOM)ON) LTD. 



6139 



6139 s Negretti & Zambra's Horticultural Hygrometer (Registered Design No. 507313). 



An instrument for ascertaining in a simple manner the likelihood of a frost during the night. 



The Hygrometer is an instrument for determining, with the aid of special tables, the relative humidity of the 

 atmosphere and the dew point. The late Dr. Buchan, in his text-book, remarks that in the evening " the dew 

 point determines the minimum temperature of the night," and if this dew point be below freezing point, it is only 

 fair to presume that there will be a frost during the night. In the majority of cases there are no signs to indicate 

 that the dew point is below 32 F.. as, for example, with an air temperature of 60, the dew point will be below 

 freezing point if the wet bulb temperature be 44 or less. 



The object of the Horticultural Hygrometer is therefore to show in a simple manner, without the use of tables, 

 whether the dew point is below freezing, and consequently whether frost may be expected. 



We need hardly point out to horticulturists and agriculturists the importance of detecting the arrival of frost, 

 whether it be an Early Winter Frost, or a Late Spring Frost. One should have some means of knowing whether 

 to take the necessary steps for the protection of valuable plants, crops, fruit trees, etc. 



The Instrument is a wet and dry bulb Hygrometer, with a special cylindrical scale revolving between the 

 thermometers. The cylinder is figured in three sections, which are intended to apply as follows : 



White Section : Frost highly improbable. 

 Shaded 

 Black 



It will be seen that the cylinder has ten lines, numbered i, 2 

 degrees between the readings of the wet and dry thermometers. 



The Method of Observing is as follows : 



The instrument must be placed in the open air, but in such a position that the sun's rays do not fall upon it. 



The observation should be taken as late in the evening as possible. 



Upon arriving at the instrument, note at once the dry bulb reading note the wet bulb reading, and the 

 difference between the two. Turn the cylinder (by means of the handle) until the line and figure representing 

 this difference is at the right-hand side of the opening. Look down the scale on the right-hand side of the opening, 

 and the wet bulb reading (just observed) will fall opposite one of the three sections. From this the observer knows 

 whether frost is likely to occur during the night. 



AN EXAMPLE. 

 The dry bulb reads . . . . . . . . 41 deg. 



The wet bulb reads . . . . . . . . 36 deg. 



1 1 



Frost doubtful. 



Frost very probable. 



3, 4, up to 10 ; these represent the difference of 





Difference . . . . . . 5 deg. 



The 5 line along the right edge of the opening and 36 deg. (wet bulb) reading comes opposite the black section : 

 hence a probable frost. 



CROSS STREET HATTO>T GARDEN, E-C 



