Peter Collinson, the friend and correspondent of Linnæus, communicated to the Royal Society the following statement by M. Achard:--"In the latter end of March I took my passage down the Rhine to Rotterdam. A little below Basel, the south bank of the river was very high and steep, of a sandy soil, sixty or eighty feet above the water. "I was surprised at seeing, near the top of the cliff, some boys tied to ropes, hanging down doing something. The singularity of these adventurous boys, and the business they so daringly attempted, made us stop our navigation, to inquire into the meaning of it. The waterman told us they were reaching the holes in the cliffs for Swallows or Martins, which took refuge in them, and remained there all the winter, until warm weather, and then they came abroad. "The boys being let down by their comrades to the holes, put in a long rammer, with a screw at the end, such as is used to unload guns, and, twisting it about, drew out the birds. For a trifle I procured some of them. When I first had them, they seemed stiff and lifeless; I put one of them in my bosom, between my skin and shirt, and laid another on a board, the sun shining full and warm upon it; and one or two of my companions did the like. That in my bosom revived in about a quarter of an hour; feeling it move, I took it out to look at it; but perceiving it not sufficiently come to itself, I put it in again; in about another quarter, feeling it flutter pretty briskly, I took it out, and admired it. Being now perfectly recovered, before I was aware, it took its flight; the covering of the boat prevented me from seeing where it went. The bird on the board, though exposed to a full sun, yet, I presume from a chilliness of the air, did not revive so as to be able to fly."[115] On this account I may observe that Collinson would hardly have been the medium of this communication, unless he had been satisfied of the probity of his correspondent. The time was "the latter end of March," a fortnight at least before the arrival of the Sand Martin--the earliest of our migrants; and the whole enterprise of the boys, and the familiarity of the waterman with the circumstance, as well as their assertions, shew that they, at least, had no doubt about this being a case of hybernation. Yet the repeated exploration of the Sand Martin's burrows in this country, in winter, has produced no birds. White of Selborne, who was very much interested in the solution of this question, mentions two instances--both, however, on hearsay evidence. A clergyman assured him that, when he was a boy, some workmen, in pulling down the battlements of a tower, early in spring, found two or three Swifts _among the rubbish_, which appeared dead, but revived in the warmth. The other account was that of the fall of a portion of the cliff near Brighton in winter, when many persons found Swallows among the rubbish; but here even White's informant did not see the birds, but was merely told of them.[116]