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282 



METEOROLOGY. 



[Sect. IX 



a secure and efEcient protection both from injury and 



xious 



The Self-registering Thermometers should he placed 

 with the same precautions as the external thermometer 

 and in similar exposures, and so fastened as to allow one 

 end to be detached and lifted ; so that the indices within 

 the tubes may slide down to the ends of the fluid columns 

 which they will readily do on gentle tapping. They are 



apt to get out of order by the indices becoming entangled, 



or by the brcctkiug of the column of fluid. When 

 happens to the spirit-thermometer, it is easily rectified 

 by jerking the index down to the junction of the bulb 

 and tube: then, by cautiously heatiug and cooling 



alternately the bulb, tube, and air-vessel at the top, the 

 disunited parts of the spirit m,ay be distilled from place 

 to place till the whole is collected into one column in 

 union with that in the bulb. 



When the steel index of the mercurial thermometer 

 becomes immersed in the mercury, first cool the bulb (by 

 evaporation of ether, if necessary) till the mercury is 

 either fairly drawn below the index, or the column 



leaving the index with mercury above it. 



. m 



Loosen the index by tapping, by a magnet, or by heating 

 the tube, then apply heat to the bulb, and drive the 

 index with its siiperincumbGnt mercury up into the air- 

 vessel When there, hold the instrument bulb down- 

 wards, and, suspending the index by a magnet, effect a 

 union between the globule of mercury and the column 

 below, by continuing to apply the heat till the latter 

 rises into the air-vessel, As the bulb cools the whole 

 merciu-y should descend in an unbroken column, after 



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