A Short Course in Elementary Meteorology

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1921 edition. Excerpt: ...In Table IV. will be found values facilitating conversion from one system of barometric units to another. The values refer to standard conditions of temperature and latitude. Table IV. The principal advantage of using the millibar as a unit is that a pressure quoted as a number of millibars is completely definite; millibars can be used just for pressure and for nothing else. As the reading of a barometer is not independent of either the temperature of the instrument or of the latitude of the place where it is set up, it follows that the 1,000 millibar graduation can only be correct for one particular temperature at each latitude. The temperature appropriate to latitude 45 is termed the standard temperature of the barometer. The temperature at which the 1,000 millibar graduation reads correctly in any other latitude is termed the fiducial temperature for that latitude. Both the standard and the fiducial temperatures refer to sea level, and it should be noted that the standard temperature in latitude 45 is also the fiducial temperature for sea level in latitude 45. It needs to be recognised, however, that the conditions of temperature and latitude which ensure that the 1,000 millibar graduation is correct are not necessarily such as make graduations in other parts of the scale correct. The standard temperatures applicable to latitude 45 for several readings of the scale are usually supplied with a good barometer graduated in this system, and from these standard temperatures the corresponding fiducial temperatures for the various readings of the scale given can be computed. In any particular case, then, the barometer graduated in the...