METEOROLOGICAL INSTRUMENTS. 



435 



portion of the column. The instrument is again brought back to its 

 horizontal position and the pin restored to its place. 



Thermometers constructed after this plan were first exhibited by 

 Professor Phillips, accompanied by a description, at the Oxford 

 meeting of the British Association for the advancement of science, 

 in 1832. The principle of the instrument is, as we have stated, the 

 employment of a certain portion of the column of mercury detached 

 as a marker. The length of this is capable of a great range of adap- 

 tation to suit the objects of experiment ; the instrument is inde- 

 pendent of change by time or chemical action, and as delicate in 

 operation as the best ordinary thermometer. Mr. Phillips constructed 

 a number twenty-five years ago, some of which remain in an excellent 

 state to the present time. The length of the marker may be varied 

 at pleasure by means of a second hollow ball blown at the extremity 

 opposite the ball containing the mercury. The longer this marker 

 is left the more moveable it becomes. With a certain small length 

 depending on the diameter of the tube it will remain, without moving, 

 in any position, and requires strong shaking to change its place. 

 Among the samples presented to the Association was one planned by 

 Professor Phillips for special researches on limited sources, or areas 

 of heat, with small bulb, fine bore, and short detached marking column. 

 Thus constructed, the thermometer may be used in any position — ver- 

 tical, inclined, or horizontal — and the short detached marking column 

 will retain its place with such firmness that the instrument may be 

 carried to a distance, or even agitated, without disturbing the regis- 

 tration. 



Fig. 3. 



M y y 



Fig. 3 represents an instrument of the same kind with black 

 bulb for solar radiation. 



Fi". 4. 



rf eUa r-^' ^-v--f7^-r-f-\ -j-i p " R 



Fig. 4 represents the ordinary minimum thermometer in which 

 the index is a small piece of enamel. 



Pig. 5. 



