XVI. On the influence of the gulf-stream on the winters of the British Islands. In a letter from Professor Hennessy to Major-General Sabine, V. P. and Treas. R. S. Communicated by Major-General Sabine

Abstract

My dear Sir,—In your work on 'Pendulum Experiments,’ and subsequently in a paper printed in the ‘Philosophical Magazine’ for April 1846, you have directed attention to the influence of the Gulf-stream on the winters of the British Islands. You have been led to attribute the remarkably mild winters which we sometimes experience, to an abnormal extension of the warm waters of that stream towards our latitudes. In this view I entirely concur, and beg to submit the following additional proof of its correctness. An abnormal extension of the Gulf-stream in the direction of the British Isles necessarily implies that the waters bathing our coasts acquire a temperature which exceeds their mean temperature for the season of the year at which the extension takes place. The temperature of the air over the sea, and finally of the air over the islands, becomes sensibly increased. The entire temperature at any point will thus depend chiefly on what it gains from sunshine, and from the warm sea-air, and on what it loses by radiation. If the excess of what it gains from sunshine over its losses by radiation be considerable compared to its gain from the influence of the sea, the temperature will depend principally on the latitude. If, on the contrary, the thermal influence of the sea be very considerable, places at different latitudes may possess nearly equal temperatures. It follows that during cold winters we should expect a greater difference between the temperatures of the southern coasts of Great Britain and Ireland, and the remainder of their coasts, than during mild winters. It also follows, that during warm winters the difference of temperature between stations situated on coast and inland stations having nearly the same latitude, should be greater than during cold winters.