24 Dr. Masons Description 



all these objections, and is so simple and easily constructed, 

 that by mere inspection the results can be ascertained with 

 as little diflSculty as attends the common thermometer. 



The form of the instrument is portable ; it may be readily 

 used in every climate and under all circumstances ; and its 

 graduation depends upon no arbitrary or disputed determi- 

 nations of wet and dry ; it is liable to no deterioration from 

 use, age, or accidental circumstances ; it acts with an un- 

 erring fluid ; and above all things, if the thermometers be 

 carefully selected, so as to indicate the same degree under 

 similar circumstances, it is impossible with moderate care 

 to obtain erroneous results ; so that the comparative varia- 

 tions of humidity, from the point of saturation, being exhi- 

 bited in degrees of the thermometric scale, are at once re- 

 ferred to a known standard of comparison which every 

 person can understand and appreciate. 



The only trouble which attends the use of this instru- 

 ment is the renewal of the silk on the moistened bulb once 

 a month ; and the addition of a fresh supply of well boiled 

 or distilled water from time to time as it may be necessary. 



Description of the Instrument. 



Upon the outer margin of a stand M is fixed an upright 

 rod of brass/ supporting by a semi-circular clyp the scale J J, 

 (the clyp is seen in shadow at o, and is f of an inch in dia- 

 meter, thus removing the scale JJ \ of an inch from the 

 brass support/.) In the middle of the scale J J a space is 

 left to receive a glass tube A on the principle of the bird 

 fountain, having on each side of it two thermometers hh oi 

 equal range from 0° to 120° Fahrenheit, firmly attached to 

 the scale already described. The bulbs c?Jof both ther- 

 mometers are of equal size, and covered with white persian 

 silk ; round the stem of one, a thread of floss silk e is at- 

 tached, which terminates in the cup of the fountain c. 



This fountain is easily removed and re-fixed at pleasure 

 by turning the screw h which allows the support g to move 

 with ease in the groove i bringing the support g to the con- 

 tracted part of the fountain. 



The upper part of the fountain is kept in its place by a 

 double clyp kk. The fountain is hermetically sealed atp ; 



