A knowledge of the general principles which direct the flow of our prevailing winds is, however, only of general assistance in enabling us to forecast the weather which we experience in these islands. This is governed and produced to a great extent by the development of subsidiary centres of depression in and between the great cyclonic systems. These generally approach our shores from the west, travelling in a north-easterly direction; and they are responsible for most of the variable weather with which we are so familiar. They generally carry with them a certain well-defined course of weather. The readings of the barometer taken simultaneously at many places over a wide area on a system such as that now controlled by the Meteorological Office, enables us to determine the approach and development of these small cyclonic systems, and so to forecast with a certain degree of confidence the weather likely to be experienced in a certain district from twelve to twenty-four hours in advance. Most of the disturbing influences reach us from the west; and as the west coast of Ireland is the extreme limit to which our stations reach in that direction, we can receive only very short notice of their approach. This is one of the principal reasons why, with the means at present at our disposal, we cannot expect to make our weather science as perfect as in a country such as America, where the central office receives warnings from stations dispersed over the face of a vast continent. Nevertheless, we have made great advances since 1861, when the first weather forecasts were prepared and issued in this country by the Board of Trade, under the superintendence of the late Admiral Fitzroy. The forecasts at that time, although admitted to be of considerable utility to the country, were thought to be scarcely accurate enough to justify their continuance upon the system then in operation, and they were discontinued in 1866.