304 



Mr. R. H. Scott. The Variability of the [Mar. 27, 



naturally conic out higher than when means for the whole day are 

 taken. 



The only British stations among the ninety were Makerstoun for 

 five years, 1842-46, and Oxford for ten years, 1860-70 (the year 1869 

 being omitted). The Makerstoun means were obtained from different 

 combinations of hours in different years, and the Oxford figures from 

 twelve bi-hourly readings of the thermograph curves. 



Inasmuch as daily mean temperatures derived from twenty-four 

 hourly measurements of the thermograms exist at the Meteorological 

 Office for the seven observatories during the period of their continu- 

 ance, the fifteen years 1869-83 inclusive, it seemed desirable to dis- 

 cuss this amount of material so as to exhibit the results for these 

 islands as an instance of a typically insular climate. 



The method followed has been to extract the differences between 

 the successive daily means, irrespective of sign, and then to take the 

 average of the figures so obtained for each month. 



The mean of these fifteen monthly values gives the mean monthly 

 variability from the station, and this is shown in Table I. 



I have appended to the tables the values given by Hann for Oxford 

 and Makerstoun, as well as for three Continental stations, as speci- 

 mens of excessive variability, and finally those for Georgetown, 

 Demerara, as exhibiting the great constancy of temperature in that 

 tropical locality. The last-named figures are the result of six years' 

 observations, probably by P. Sandeman, though that is not expressly 

 stated. 



It will be seen at once that the figures for our seven observatories 

 are much lower than those for either Oxford or Makerstoun. This 

 may possibly be due to the fact that the periods for those two records 

 are both of them less than fifteen years, and they are not equal to each 

 other or synchronous. 



The contrast between the British stations and the three stations of 

 Vienna, St. Petersburg, and Barnaul is very remarkable, as is also, 

 in the other direction, that with Georgetown, where the average on 

 the whole year is only 1°*1 F. 



Dealing with our own returns, it will be seen that the mean annual 

 difference is greatest (2°"7) at Kew : then follow Armagh, Glasgow, 

 and Stonyhurst with 2° "5, Aberdeen with 2°*4, and the list is closed 

 by Falmouth and Valencia with 1°"9. 



The annual range of these differences is very similar at all the 

 seven stations, reaching a maximum in December and a minimum in 

 August. The chief exceptions to this assertion are that at Kew the 

 maximum of 3°*3 occurs in January and November, not in December, 

 and that at the two south-western observatories, Falmouth and 

 Valencia, the minimum is in July. 



The highest absolute figure in any month is 5°'4, for Glasgow 



