128 VICK-SECKETARY ON SIMMONS'S PATENT HYGROMETEK. 



connected with a vertical arm resembling the hand of a clock. 

 This hand was made to traverse a dial-plate marked off into de- 

 grees, expressing the amount of moisture in the air between what 

 is observed wlien the instrument is plunged in water on the one 

 hand and exposed to excessive atmospheric dryness on the other. 

 The accompanying figure, and the description following, taken 

 from Mr. Simmons's Registration in the Patent Office, will further 

 explain the nature of tiie instrument. 



From trials made with this Hygrometer in the garden of the 

 Society, it has been ascertained that it is much better adapted to 

 Horticultural Purposes than any hygrometer yet in use. For 

 strictly scientific purposes it is not indeed equal to Daniell's, 

 because it is impossible to make two instruments which will work 

 exactly alike ; but it has the great advantage of being as easy to 

 use as a thermometer, and the instruments will be quite as com- 

 parable as common thermometers themselves. In fact, difl^erences 

 between such conti-ivances, to the extent of two or three degrees, 

 are of no practical moment. 



In a trial made between Simmons's and Daniell's Hygrometer 

 in the Orchideous House in the Garden, an unexpected result was 

 obtained. Placed in the same situation the following were the 

 observations : — 



Jan. 22. 



In the course of the night the evaporating tanks lost their 

 water in consequence of the bursting- of a pipe, and the obser- 

 vations that followed the accident were remarkable : 



Simmons's. Daniell's. 



Jan. 23. 8 a.m. . 1 . Saturation. 



„ Noon. . 6 . do. 



„ 4 P.M. . 10 . do. 



Jan. 24. 8 a.m. . 50 . do. 



In this instance the air must necessarily have become drier 

 every hour, because the usual supply of vapour was cut off' by 

 the removal of the evaporating tanks ; and yet Daniell's Hydro- 

 meter remained invariably at what is called " Saturation ;" but 

 Simmons's was faithful to the duty expected of it, and continued 

 to indicate increasing dryness as the vapour suspended in the air 

 diminished. Without pretending to explain this puzzling cir- 

 cumstance, it must be taken as valuable testimony to the efficiency 

 of Mr. Simmons's Hygrometer. 



Two of the instruments are in use in the Society's Garden, and 

 continue to give satisfactory indications. 



