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Sfecti IX.] 



METEOKOLOGY. 



273 



2ndly. When a party leaves the shi{), furnished with a 

 portable barometer or other instruments, for the measure- 

 ment of heights of mountains, or with other objects. Srdly. 

 During threatening weather, and especially during the 

 continuance of gales, and for some time after their sub- 

 sidence as will be more particularly specified under the 

 head of " Storm Observations." 4thly. In certain spe- 

 cified localities mentioned in a subsequent article by Mr. 

 Birt. 5thly. Whenever a continued rise or fall of the 

 barometer has been noticed as at all remarkable, it 

 should be pursued up to and past the turn, so as to 

 secure the maximum elevation or depression, and the 

 precise time of its occurrence ; and a register of such 



maxima or minima should be kept distinct from the 



regular entries. 



Of Meteot ological Instruments ; and first, of the Baro- 



meter and its attached Thermometer. 



Tlie 



girnbal frame, which ought not to swing too freely, but 



rather so as to deaden oscillations by some degree of 

 friction. Before suspending it, it should be carefully 

 examined for air-bubbles in the tube and for air in the 

 upper part above the mercury, by inspection, and by 

 inclining the instrument from the vertical positidn rather 

 suddenly till the mercury rises to the top with a slight 

 jerk, when, if it do not tap sharp, the vacuum is imper- 

 fect ; and if the sound be puffy and dead, or is not heard 

 at all, air exists to an objectionable extent, and must be 

 got rid of by inversion and gently striking with the hand 

 to drive the bubble up into the cistern. The lower end 



N 3 



m. 



