THE METEOROLOGY OF EDINBURGH. 89 



during at least the last 165 years. The seasonal distribution of pressure, temperature, 

 wind and rain is the same now as at the beginning of the eighteenth century, and so far as 

 we can ascertain there has been no change in the annual means of the more prominent 

 elements of climate, while the prevalent weather of special months does not appear to 

 have altered in the slightest. These conclusions are entirely in accordance with what 

 we should expect. As is well known, the climate of a place is largely determined by the 

 prevailing winds ; these in turn are simply the result of the distribution of the weight of 

 the earth's atmosphere over the globe. The latter is determined by the position and 

 extent of the ]and and water surfaces, and as these have not materially altered within 

 the last 200 years it may fairly be assumed that the circulation of the air and the 

 climatic results springing therefrom are practically unchanged. Local influences, more 

 especially drainage and deforesting, produce slight changes in climate ; but so far as 

 Edinburgh is concerned no alteration appears to have taken place during the last 

 century and a half. 



Does the Weather Move in Cycles ? 



Tables of continuous five year averages of the more important climatic elements have 

 been calculated with the primary object of giving an answer to this question. The 

 method adopted was as follows : — The mean temperature of the five Januarys 1764-68 

 was calculated and found to be 1°'7 below the normal temperature of the 

 month ; the difference, 1°"7 was accordingly entered in Table LV. opposite the 

 year 1766 which is the middle year of the series. Then the mean of the five 

 Januarys 1765-69 was similarly ascertained, and entered in the Table opposite 1767, and 

 so on for each of the 129 groups of five year periods embraced in the 133 Januarys, 

 means above the normal being entered in heavy and those below it in italic type. The 

 eleven months and the year were similarly dealt with. The data discussed comprise 

 temperature, pressure, wind direction, and rain (see Tables LV. to LVIIL). With 

 regard to rainfall, the inquiry has been extended back to the year 1766 by differentiating 

 during the missing years from registers kept at Peebles, Dumfries, and Branxholm. For 

 copies of these registers I am indebted to Mr Gr. J. Symons, F.R.S. The hiatus thus 

 completed comprises the years 1766-1769, 1777-79, July 1781 to Dec. 1784. The 

 Peebles register was employed during most of this period, the rainfall of that spot 

 approximating closely to the mean rainfall of Edinburgh during years which are common 

 to both series. The mean monthly rainfalls for the period 1766-1896 were then 

 ascertained, and the percentage of excess or defect calculated for each of the five year 

 groups. Similar values were computed showing the percentage excess or defect of east 

 and west winds. The winds were resolved to these two points by including S., S. W., W., 

 and N. W. winds under west, and N., N.E., E., and S.E. winds under east. During some 

 years calms were entered ; these were, however, eliminated from the discussion. It is not 

 necessary to give the table showing the percentage excess or defect of east winds as they 

 are simply the converse of west winds. 



