VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 425 



XXXIX. On the Sections of a Solid, hitherto not considered by Geometers. By 

 Wm. Brakenridge, D.D., F.R.S. p. 446. 

 On an imaginary solid that never can occur, or be of any real use. 



XL. A Letter to the Hon. J. Th. Klein, Secretary to the City of Dantzic,from 



Mr. Peter CoUinson, F.R.S. , concerning the Migration of Swallows, p. 459. 



Mr. C. dissents from Mr. K. in an article he takes great pains to establish; 

 which is, that swallows are not birds of passage; but at the time of their disap- 

 pearing retire under water, and live therein all the winter. This Mr. C. cannot 

 comprehend, being so contrary to nature and reason ; for as they cannot live in 

 that state without some degree of breathing, this requires the circulation of the 

 blood, however weak and languid. Now as respiration is absolutely necessary for 

 circulation, how is it possible to be carried on for so many months under water 

 without the risk of suffocation ? Besides, if so remarkable a change was in- 

 tended, the great wisdom of the Almighty Creator would undoubtedly be seen in 

 some particular contrivance, in the structure of the organs of the heart of this 

 bird, to enable it to undergo so very remarkable a change of elements. 



An easy experiment may throw some light on this doubtful affair. At the 

 time of their going away, take a swallow, and confine it in a tub under water : 

 if it remains there for a week or two alive, without any remarkable inconveni- 

 ence, then there may be some probability of its continuing so many months in 

 that state. The conclusions that are drawn from some of the tribe of insects 

 subsisting under water, are far from being conclusive to found an analogy on ; 

 as insects differ from other animals in so many particulars, that very little or 

 nothing can be concluded or inferred of the one from what we observe in the 

 other. 



Towards the end of September, the swallows assemble on the reeds in the 

 islands in our river Thames, and have no doubt so done for ages past; and yet 

 Mr. C. never heard or read of any fisherman or other person that has ever found 

 in the winter months a swallow under water in a torpid living state; for if such 

 a marvellous thing had ever happened, it would have been soon communicated 

 to the public. Besides, as these islands of reeds and willows are annually cut 

 down for several uses, and yet not a swallow has been discovered in his aquatic 

 abode; and considering the multitudes seen on these reeds and willows in the 

 autumn ; if they took their winter's residence under water, it is most reasonable 

 to think, in a river so frequented, and in so long a course of years, some would 

 have been found in that situation. Another circumstance is, that in great towns 

 remote from water, where rivers and reeds are not near, it is frequently observed 

 that a little before the swallows depart, they every morning early gather together 



VOL. XT. 3 I 



