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Sect. IX.] 



METEOROLOGY 



07Q 



It is not only desirable that the zero point of the baro- 

 raeter should be well determined in the first instance ; 

 it should also be carefully verified on every opportunity 

 .hich presents itself And in the first instance, previous to 



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sailing, after suspending the barometer on shipboard 

 should be re-compared with the standard on shore by 

 intervention of a portable barometer, and no opportunity 

 should be lost of comparing it on the voyage by means of 

 such an intermediate instrument with the standard baro- 

 meters at St. Helena, the Cape of Good Hope, Bombay, 

 Madras, Paramatta, Van Diemen's Island, and with any 

 other instruments likely to be referred to as standards, or 



A.ny vessel having a 



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comparative readings 



employed in research elsewhere. 



portable barometer on board, the zero of which has bcai 

 well determined, would do well on touching at any of 

 the ports above-named to tak 

 with the standards at those ports, and record the differ- 

 ences between the standard, the portable, and the ship- 

 barometers. By such means the zero of one standard 

 may be transported over the whole world, and those of 

 others compared with it ascertained. To do so, however, 

 with perfect effect, will require that the utmost care 

 should be taken of the portable barometer ; it should be 

 guarded as much as possible from all accident, and should 

 be kept safely in the "portable" state when not im- 

 mediately used for comparison. To transport a well- 

 authenticated zero from place to place is by no means 



Neither should it be 



a point of trifling importance. 



executed hurriedly nor negligently. Some of the greatest 

 questions in meteorology depend on its due execution, 

 and the objects for which these instructions have been 



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