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of the contest which, as a living being, it has to maintain against 

 the surrounding influences which are ever tending to dissolve the 

 vital bond and subjugate the organised matter to the ordinary che- 

 mical and physical forces. Any changes, therefore, in the external 

 circumstances in which a species may have been created to exist, 

 will militate against that existence in probably a geometrical ratio 

 to the bulk of such species. If a dry season be gradually prolonged, 

 the large mammal wiil suffer from the drought sooner than the 

 small one ; if such alteration of climate affect the quantity of 

 vegetable food, the bulky Herbivore will first feel the effects of the 

 stinted nourishment ; if new enemies are introduced, the large and 

 conspicuous quadruped or bird will fall a prey, whilst the smaller 

 species might conceal themselves and escape. Smaller quadrupeds 

 are usually, also, more prolific than larger ones. The actual presence 

 therefore of small species of animals in countries where the larger 

 species of the same natural families formerly existed, is not to be 

 ascribed to any gradual diminution of the size of such larger animals, 

 but is the result of circumstances which may be illustrated by the 

 fable of 'the oak and the reed'; the small animals have bent and 

 accommodated themselves to changes under which the larger species 

 have succumbed. 



May 15, 1851. 

 The EARL OF ROSSE, President, in the Chair. 

 The following papers were read : — 



1. " Note relating to M.'Foucault's new mechanical proof of the 

 Rotation of the Earth." By C. Wheatstone, Esq., F.R.S., Corre- 

 sponding Member of the Academies of Science of Paris, Berlin, 

 Brussels, Turin, Rome, Dublin, &c. Received May 15, 1851. 



The experiment which led M. Foucault to his ingenious and in- 

 teresting researches relating to the rotation of the earth, is stated 

 by him thus : — " Having fixed on the arbor of a lathe and in the 

 direction of the axis, a round and flexible steel rod, it was put 

 in vibration by deflecting it from its position of equilibrium and 

 leaving it to itself. A plane of oscillation is thus determined, which, 

 from the persistence of the visual impressions, is clearly delineated 

 in space ; now it was remarked that, on turning by the hand the arbor 

 which serves as a support to this vibrating rod, the plane of oscil- 

 lation is not carried with it." 



This persistence of the plane of oscillation of a vibrating rod, 

 notwithstanding the rotation of the point to which its end is fixed, 

 does not appear to have hitherto been made the subject of philoso- 

 phical observation. Ordinary notions even seem to have been 

 opposed to this now recognised fact. Chladni in his treatise on 

 Acoustics, in the chapter " On the co-existence of vibrations with 

 other kinds of motion," states as follows : — 



" Vibratory motions may co-exist with all other kinds of motions 

 Proceedings of the Royal Society. Vol. VI. No. 80. 5 



