of the Earth 's Atmosphere. 285 



local hours of observation change by the difference of longi- 

 tude between the standard meridian and the local meridian, so 

 that 8 a. m., 8 p. m. becomes 7 a. m., 7 p. m. on the 90th 

 meridian, 6 a. m., 6 p. m. on the 105th meridian, 5 a. m., 5 p. m. 

 on the 120th meridian. If the mean of 8 a. m. and 8 p. m. on 

 the 75th meridian gives the same mean as the mean of 21 

 hourly observations, it will not do so on other meridians at 

 some distance from it, because the temperatures change with 

 the local hours. The mean of the maximum and the mini- 

 mum temperatures, taken with the standard thermometers, is 

 the best substitute for 21 hourly readings, considering all the 

 irregularities produced by local conditions, though a correction 

 is required for accuracy. It is obvious that these selected 

 hourly readings having been used to compute the daily, monthly 

 and annual means, from which the normals, departures, and 

 residuals are derived, introduce systematic errors in the varia- 

 tions, which render them unlit for discussion by any graphic 

 method or harmonic analysis. If the published reports in 

 meteorological libraries are used without any reconstruction 

 such as that indicated, it is evident that conclusions derived 

 from them cannot carry much weight in any problem of solar 

 and terrestrial synchronism. 



Grouping of Stations into districts and size of means. 



A preliminary examination of the pressure and temperature 

 departures for the whole earth, 1873-1901, as published in the 

 Monthly Weather Review, November 1903, indicates the fol- 

 lowing conclusions : (1) inversion of pressure variations between 

 the eastern and western hemispheres ; (2) inversion of tempera- 

 ture variations between the tropics and the polar temperate 

 zones ; (3) very small survival of the long, or 11-year, period, 

 for the entire earth ; (1) comparatively large departures for the 

 short, { or 3-year, period ; (5) the inversion of temperature from 

 the tropics to the poles producing a vanishing or irregular 

 variation along the high pressure belt near latitude 35° ; (6) an 

 increase of amplitude in the direct temperature type towards 

 the equator, and an increase in the amplitude of the inverse 

 type towards the pole from latitude 35° ; (7) a tendency to 

 invert between the ocean and continent ; (8) that the 11-year 

 period amplitude does not diminish from the equator to the 

 pole by the function' of the cosine of the latitude ; (9) that it 

 is not proper to combine tropical and temperate zone stations 

 in the same summation without regard to inversion ; (10) that 

 it is not proper to combine several periods of unequal length 

 in one summation without 'reducing the phases for the short 

 period to an assumed standard period, as 11-years. 



