METEOROLOGICAL INSTRUMENTS. 135 



MASON'S HYGROMETER. 



The use of this instrument (Fig. 619, next page) in the 

 sick chamber will be at once evident, as a fire kept up in a 

 closed room naturally dries the air which the patient has to 

 breathe, and it soon becomes either more detrimental or bene- 

 ficial in many diseases of the lungs, skin, or intestinal canal. 

 It is the duty of the medical attendant to point out those 

 conditions of the body which will be benefited or injured by 

 atmospheric influences, and suggest the means by which this 

 can be obviated as far as art will allow ; for in many cases 

 life depends upon the temperature, state of dryness, or hu- 

 midity of the climate or room in which an individual resides, 

 which condition of the air it is the office of the instrument to 

 constantly register, and show, by mere inspection. 



If the apartment is too dry, which is frequently the case 

 in frosty weather, it will be necessary to maintain sufficient 

 evaporation from a tea urn, or other convenient apparatus, 

 while the hygrometer points out when the proper degree of 

 humidity has been attained ; the urn is then removed, and 

 may be brought into the room again when required. On the 

 contrary, if the air be required remarkably dry, it may be ren- 

 dered so, either by raising the temperature of the room, or re- 

 sorting to those substances which absorb vapors most rapidly. 



Thus with the aid of this instrument (as it indicates both 

 the temperature, dryness, and humidity of the air), an arti- 

 ficial locality may be produced by very simple and easy 

 means ; and those, whose circumstances, avocations, or family 

 ties, prevent them from seeking a climate suited to their 

 peculiar constitution, can, to a very great extent, obviate the 

 necessity by the assistance of the instrument now submitted 

 to the public, the desideratum of which has been long felt, 

 and its prospective uses fully appreciated by the reflecting 

 portion of the profession. 



If the air be very dry, the difference between the two 

 thermometers will be great ; if moist, less in proportion ; 

 and when fully saturated, both will be alike. For general 

 purposes, it is only necessary to place the instrument in a 

 retired part of the room away from the fire, and not exposed 

 to the open doors or passages ; but for nice experiments, 

 the observation should be always made in the open air and 

 in the shade, taking especial care that the instrument be not 

 influenced by the radiation of any heated bodies, nor any 

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