and few early travellers were philosophers, at any rate so far as migration was concerned. In Germany, however, the Emperor Frederic II. realised in the thirteenth century many truths concerning migration (27), but in Britain uncertainty or myth held sway until the end of the eighteenth century. Herr Herman, reviewing the variation in thought, says—" But as in other fields, this period is followed by a time of decadence, a natural consequence of departing from immediate experience."
British, and many Continental observers too, saw when birds had come and in autumn that they had gone. Early swallows and martins were always met with near water, and were watched dropping to roost in the reed beds, as they always do in autumn before departure. Next morning none was visible. Certainly then they had vanished to hibernate in the water. The discovery of masses of torpid swallows, dead or dying, by no means an unknown thing when birds are overtaken by sudden falls in temperature in autumn or by a severe setback in the spring, was to these puzzled men confirmation of their theory of hibernation. Other details of the many stories of swallow hibernation are due to exaggeration or to misconception. In the second half of the eighteenth century a fierce discussion waged for and against hibernation, and many, including Geoffrey St Hilaire and Montagu,
