iiB HEPOBtS OJf THE StAffi OF SCIENCE. 



meteorological data thus compiled are prepared for publication, princi- 

 pally in the form of monthly averages. Daily values are published fof 

 comparatively few of the whole number of meteorological stations. In 

 those cases in which daily values are required, inquiries should be directed 

 to the meteorological authorities of the countries concerned. 



It is necessary that in preparing vital statistics for comparison with 

 climatic statistics, these facts should be borne in mind at the outset, so 

 that comparisons may be, as far as possible, conducted for months, or 

 combinations of months ; otherwise the investigator may find himself 

 face to face with the practically ioipossible task of recovering the original 

 observations and recompiling them for his own purpose.s. 



In complete form, the organisation of meteorological stations is 

 designed to afford data from which the following meteorological elements 

 can be obtained : — 



1. The mean barometric pressure, la order that observations may be 

 strictly comparable, the means should be determined from twenty-four 

 liourly readings. In most cases the only observations available are those 

 taken at two or more fixed hours during the day, and a correction must 

 be applied to the means determined from these observations, in order to 

 reduce them to the true daily means. The amount of this correction can 

 be determined from the recoi'ds of the stations of the first order, where 

 such exist. Stations of the first order arc those which are provided with 

 self-recording instruments, or at which personal observations are made 

 every hour. 



'2. The mean air temperature. To render observations strictly com- 

 parable, the means should be determ.ined from twenty-four hourly read- 

 ings. Means determined from ob.servations at fixed hours can be reduced 

 to true daily means by the application of a correction which can be 

 determined from the recox'ds of first-order stations, where such exist. 



3. The mean maximum and mean minimum temperature, and the 

 absolute extremes of tempei'ature with the dates of their occurrence. 



4. The mean pressure of aqueous A-apour and the mean relative 

 humidity, determined from readings of dry and wet bulb thermometers. 



•3, The total rainfall, and the maximum fall in one day, with the date 

 of its occurrence. 



C. The mean amount of cloud, expressed as a decimal fraction of the 

 sky covered. 



7. The frequency of days of rain, snow, hail, thunderstorm, clear sky, 

 overcast sky, and, for some stations, fog. 



8. The frequency of winds from each of eight points of the compass, 

 and information concerning wind force. 



9. Information concerning temperature of the soil, grass minimum 

 temperature, and solar radiation temperatures. These elements are not 

 included in the international scheme, but information about them is given 

 in some cases. 



These means, Avith such modiflcations as are imposed by the circum- 

 stances of the several cases, form the basis of the monthly summaries 

 which are so largely represented in meteorological publications. Informa- 

 tion as to the diurnal variation of the various elements beyond what is 

 indicated in the foregoing statement, is not given as a rule in meteoro- 

 logical tables, but for a number of stations it could be supplied on appli- 

 cation to the Meteorological Authorities. 



