Plan of a Journal of, Meteorological Observations, #c. 99 



The cistern, which is turned in mahogany, is lined with iron. 

 The tube dips 1.1 inch below the surface of the mercury, and 

 a thermometer is inserted in it to mark it's temperature. 

 There is also a float, which corresponds with a fixed mark 

 when the column stands at the neutral point. The observa- 

 tions are made by means of a vernier, carrying an index both 

 before and behind the tube, the coincidence of which with 

 the highest part of the surface of the mercury, which is always 

 more or less convex, is easily ascertained. The proper cor- 

 rection is always applied for the varying temperature of 

 the mercurial column, and the entry in the register is the 

 actual pressure of the atmosphere at the station, as it would 

 be measured by a column of mercury of the temperature of 

 32° of Fahrenheit. 



The barometer is firmly fixed against the wall of an 

 apartment, at the back of the small Green-house, in the Ex- 

 perimental Garden, which is otherwise used as a seed-room ; 

 the window and door of the room open to the north, and 

 there is no fire-place in it. Its position is nearly 14 feet above 

 the mean level of high water in the Thames, at Chiswick. 



The observations with the barometer are made at three 

 periods of the day , viz. morning, noon, and night. 



A Daniell's Hygrometer is used for ascertaining the 

 state of the vapour in the atmosphere. The naked ball 

 upon which the dew is deposited, is formed of black glass, 

 and the observations are made three times in the day, at the 

 same periods as those with the barometer, with every precau- 

 tion recommended by Mr. Daniell in his Meteorological 

 Essays. The tension of the vapour, and the moisture of the 

 atmosphere, are calculated from the dew-point, from the tables 

 in that work. 



