90 MR ROBERT COCKBURN MOSSMAN ON 



The annual values of the non-instrumental phenomena during the last 127 years, 

 1770-1896, have also been discussed (Table LIX.). The results are graphically shown 

 along with other data on Plate III., the monthly departures of pressure, temperature, 

 wind, and rain being shown on Plates I. to III. 



It may be here mentioned that we do not at present intend to discuss at any length 

 or with any degree of elaboration the peculiarities, resemblances, and contrasts shown 

 by an inspection of the diagrams, but merely to point out some of the more prominent 

 features. 



Dr Buchan, in the results of an investigation into the mean temperature of the N.E. 

 of Scotland,* says :- — "The tendency of types of high and low temperature to be pro- 

 longed through terms of years, very unequal as regards duration, is shown, both as 

 regards the months and the year, in a manner so decidedly as to suggest no appearance 

 of a temperature cycle." I have only to add in this connection that the above remark 

 is equally applicable to pressure, wind, and rain, as well as to the non-instrumental 

 phenomena. The most casual glance at the diagrams will establish the truth of this 

 assertion. There is, apparently, no periodicity in the recurrence of weather. If such a 

 period could be found weather-forecasting would be a very simple matter, as it would 

 only be necessary to have observations over one of the periods. Our weather, as is well 

 known, is the result of the distribution of cyclonic and anti-cyclonic areas over western 

 Europe and the adjacent parts of the Atlantic. The average path pursued by, and rate 

 of motion of these areas, are known, but they are subject to many irregularities. In 

 winter, for example, the normal condition of pressure in our immediate vicinity is low 

 to the N. and W. , and high to the S. and E. The result of this pressure distribution is a 

 predominance of warm equatorial winds, the atmospheric flow being from the Atlantic 

 Ocean towards the interior of the Eurasian continent. In some winters, however, as in 

 that of 1895, the normal distribution of pressure is reversed, with the result that the 

 whole wind system of Europe passes from N.E. to S.W., the prevailing winds being there- 

 fore from the N. and E. Little or nothing is at present known regarding the causes 

 concurring in the production of these weather anomalies. All that can be done in the 

 meantime is to steadily accumulate and reduce observations. 



The following is a condensed abstract of the prominent weather conditions prevailing 

 during the past 133 years, the time under discussion being divided when possible into 

 periods of twenty years. 



1766 to 1780. — This period was characterised by low pressure, there being also a 

 great depression of temperature till 1776. The cold was pretty evenly partitioned 

 throughout the months and the seasons, a noticeable feature, however, being the mild- 

 ness of the Decembers. From 1777 to the end of this period very warm weather 

 prevailed which culminated in 1779. Rainfall was above the average during the time, 

 the excess being largely brought about by the wetness of the autumns and winters. 

 After 1770, equatorial winds predominated. Snowfall was about normal, but hail, 



* Jour. Scot. Met. Soc, vol. ix. p. 227. 



