14 THE METEOROLOGY OF JAMAICA 



som of the maximum and minimum temperatures of the day ; 

 or by taking half the sum of the temperatures at 7 a.m. and 

 3 p.m. And by combining these two precepts we get the fol- 

 lowing rule for mean temperature in Jamaica : add together 

 the 7 a.m., 3 p.m., maximum, and minimum temperatures, 

 subtract 2 from their sum, and divide the remainder by 4. 



By employing monthly means we similarly get the mean 

 temperature of the month. 



Table V. gives the results for Kingston, about 50 feet 

 above the sea-level, as deduced from careful observations 

 made by the Weather Service between the years 1881 and 

 1898 inclusive ; and it will be seen that the mean temperature 

 of Kingston is 78-8. 



Now from similar observations made at the Cinchona 

 Plantation (or Hill Gardens), elevation 4907 feet, by the 

 Department of Public Gardens and Plantations, it appears 

 that the mean temperature there is 62*2 ; and from some- 

 what different observations made on the ]>lue Mountain Peak 

 by the same Department, it appears that the mean tempera- 

 ture of the Peak is 56'0 at an elevation of 7423 feet. The 

 mean temperature therefore falls about 1 for every 300 feet 

 of elevation ; more accurately, the mean temperature falls 

 3*4 for the fall of an inch of barometric pressure. 



But the fall of mean maximum and minimum temperatures 

 is more complicated, and Table YI. has been drawn up in a 

 form convenient for general use. 



With regard to extreme temperatures, at Kingston the 

 highest maximum was 96'7, recorded on August 20, 1891, 

 and the lowest minimum was 56' '7, recorded December 4, 

 1887 ; at the Peak the highest maximum was 80'^'9, recorded 

 in February, 1889, and the lowest minimum was 33"3, 

 recorded in February, 1893. 



From observations in Kingston extending over two years, 

 it appears that the minimum temperature on the grass is 6 

 below the minimum temperature inside the Stevenson screen 

 4J feet above the lawn. Now the temperature in the screen 

 at the Peak fell to 38, or below 38, twelve times during the 

 sixteen years of observation ; consequently frost occurred on 

 the Peak twelve times during those sixteen years. 



The diurnal variation of the temperature is, of course, well 



