

TRANSACTIONS OF THE SECTIONS. 27 
time an application was made to the Board of Trinity College, and to the Heads of 
the Queen’s Colleges of Belfast, Cork and Galway, requesting their cooperation in 
the meteorological observations ; and a similar application was addressed to Dr. Robin- 
son and Mr. Cooper, and to several private individuals who were known to be in- 
terested in meteorologieal inquiries. These applications were, for the most part, 
cheerfully acceded to, and the observations, upon the plan laid down by the Academy, 
were commenced everywhere before the elose of the year, 
Dr. Lloyd having been requested by the Council of the Academy to superintend 
the reduction of the meteorological observations, some of the principal results to 
which he has been conducted are given in the present communication. 
The first point to which he invited the attention of the Section was the distribution 
of mean temperature in Ireland at the different seasons of the year. On an exami- 
nation of the mean monthly temperatures at the several stations, it was found that 
those of the inland stations (Armagh, Markree, Portarlington and Athy) were in defect, 
as compared with the corresponding coast stations; the defect being (as might be 
expected) least in summer and greatest in winter. The daily and yearly ranges of 
temperature are, of course, greater at the inland than at the coast stations. 
Upon examination of the results at the coagt stations, it is found that there is a 
decrease of mean yearly temperature, in proceeding northward, amounting to 3°°5; 
the mean temperature at Castletownsend being 52°-2, and that of Buncrana 48°*7. 
The rate of decrease is about 1° in 80 geographical miles. 
Again, there is a decrease of mean yearly temperature, although not so rapid, in 
proceeding eastward. Thus from Westport to Dublin, places nearly in the same 
parallel of latitude, the decrease of temperature is 1°°3; the mean rate of decrease 
in proceeding eastward being about 1° in 130 geographical miles. In consequence 
of this variation, the mean temperature of the western coast of the island exceeds 
that of the eastern by about 2°. 
The following are the angles which the isothermal lines form with the meridian 
at the several seasons of the year :— : 
Spring...e..... S. 63° 
Summer ......... N. 77° 
Autumn we... S. 27° 
Winter ........ Be Fe 
It thus appears that the direction of the isothermals makes a wide oscillation in the 
course of the year, viz. through an angle of about 80°, their mean direction for the 
entire year being S. 57° E. It appears, further, that their two extreme positions are 
in the consecutive seasons of summer and autumn. 
The latter conclusion, startling as it is at first sight, is completely explained by the 
form and annual movement of the isothermal lines, as shown in Dove’s maps. In 
fact, there is a rapid flexure of these lines in the neighbourhood of the British 
islands in the autumn and winter months, the lines (as we follow them eastward) 
first tending to the N.E., and then, after a sudden bend, taking a S.E. course. Now 
this flexure, which is due to the influence of the Gulf-stream, begins to manifest itself 
in the month of September, and the maximum advances westward with the advance 
of the season; so that the ascending and descending branches of the curve pass 
through Ireland at a short interval. It is to this flexure that we owe, in this country, 
the mildness of our winter climate. : 
The next point connected with the meteorology of Ireland referred to by Dr. Lloyd, 
was the mean elusticity of vapour and the mean humidity, The maximum elastic 
force of vapour occurs, as might have been expected, at the southern stations, 
Cahirciveen and Castletownsend; and the minimum at the northern, Buncrana and 
Armagh. The mean elastic force of vapour in Ireland, during the year 1851, was 
*314 of an inch of mercury; and the extreme variation depending on position was 
046. 
If we divide the actual elasticity of vapour by the maximum elastic force corre- 
sponding to the temperature, we obtain the measure of the humidity, The humidity 
is, as we know, very great in Ireland; its mean yearly value for the whole of Ireland 
being ‘86. The driest stations are, as might be expected, on the eastern coast, and 
the most humid on the western. 
