22 Proceedings of the Royal Irish Academy. 



having searched in vain for a Loch Monann, mentioned in the Annals, 

 A. D. 1544, I discovered a townland of that name on the Escheatment 

 map, 1609. The lake no longer exists, but the ravine knovs^n as Stra- 

 bane glen, which extends from the townland (whose ancient name is 

 now obsolete), appears to furnish the channel by which it, also, 

 " mio-rated." 



.y III. — On a Cause of the Buotancy of Bodies of a Greater Den- 

 sity THAN Water. By George Sigerson, M. D., Ch. M., F. L. S. 



[Read June 23, 1873.] 



In considering the phenomena attendant on the buoyancj'' of bodies of 

 a greater density than water, observers appear to have confined their 

 attention exclusively to the relations of tliose bodies and the fluid on 

 which they were placed. In other words, they limit iheir observation 

 to the visible substances. Prom certain facts which have come under 

 my notice, the results of some experiments, it seems to me that a dis- 

 tinct and important part is played, in the causal ion of such phenomena, 

 by an agent hitherto unsuspected, because invisible to the eye, namely, 

 the atmospheric air. 



It is known that when small bodies, such as needles, grains of 

 sand, seeds, and so forth, are placed gently on the surface of water, 

 thejr will float, although their density is greater than water. 



On examination, it is found that they rest partly in the water, 

 partly in a depression of the surface, which surrounds them with a 

 convex ridge. To explain their buoyancy in such circumstances, refe- 

 rence has been made to the viscosity of the fluid, or tenacity of molecular 

 cohesion, to a repulsive force supposed to be exerted in some way by 

 the floating bodj^ which repels the water, and to capillarit3^ When we 

 admit the viscosity, for whatever it is worth, it is found insufficient to 

 account for the buoyancy; as for the others, they are explanations which 

 require themselves to be explained. 



What is the actual physical condition of the floating object? 



Firstly: It is partially immersed in water. It loses thus part of its 

 weight, equal to the weight of liquid which it displaces. Two forces 

 are recognised in action: its weight acting vertically downwards, and 

 the resultant of fluid pressures acting vertically upwards. There is, I 

 allege, another force. Secondly: The body is also, be it remarked, not 

 only partially immersed in water — it is also partially immersed in air. 

 Now, to the forces which come into action through this medium, in co- 

 operation with those described, I attribute the buoyancy of such bodies. 



The adhesion of the air to a body surrounds it, as it were, with an 

 atmosphere of its own. This film of air remains in intimate contact 

 with it until replaced, as it may be, by some other medium of greater 

 adhesive power. To describe this air- wetting a word is required, if aera- 

 tion will not serve : it seems, however, a condition perfectlj^ analogous 

 to hydration or water-wetting. To a body wetted in water a layer 



