224 Royal Geological Society of Corriwall. 



noway accords with the experiments made. Whatever quanturrf 

 of fluid any tube will suspend, will also be the measure of the 

 mechanical resistance of the fluid with respect to the tube. If 

 the columnar pressure and the resistance were the same, there 

 would be no difference in the levels. As the ratio of the co- 

 lumnar pressure exceeds the resistance in the same degree as 

 the squares of the diameters exceed the proportion of the dia- 

 meters, so the fluid will rise to a height above the level of the fluid 

 exterior to tiie tube in the same proportion. Supposing a tube 

 immersed one inch in a vessel of water, and the resistance equal 

 to half an inch — in tliis state the fluid will rise half an inch within 

 the tube ; and it might then be supposed that a balance would 

 take place, and that a depression instead of an elevation of the 

 fluid would be the consequence. In this position the columnar 

 pressure of the fluid becomes as nothing, for it is supported by 

 the mechanical resistance of the sides of the tube : hence the 

 pressure of the external fluid determines more towards the tube; 

 and the operation may be considered as continuing until the • 

 fluid within the tube is of the same height as the fluid on the 

 outside, plus that portion which is in the measure of the resist- 

 ance of the fluid against the sides of the tube. 



The resistance of fluids against the sides of tubes Dr. W. re- 

 ferred to the same mechanical cause which occasions two leaden 

 hemispheres with polished surfaces to cohere most powerfully 

 when brought into contact. This cohesion, the Doctor ob- 

 served, does not take place, unless a rotatory motion is induced 

 on the hemispheres when in contact; nor can they be easily se- 

 parated unless by a similar motion. When the surfaces are ex- 

 amined, particles of lead appear raised up from the surface of 

 each hemisphere, and closely locked together ; the resistance to 

 separation is in proportion to the number of particles thus en- 

 tangled ; but unless the metal is soft, no such effect takes place* 

 Experiments were made with hemispheres of lead and tin, and 

 tin and brass. It has been stated that polished brass hemi- 

 spheres will strongly adhere, if their surfaces be smeared with oil. 

 Dr. W. maintained that the interposition of any substance be- 

 tween metallic plates must tend to keep the metallic surfaces at 

 a greater distance, contrary to the admitted laws of attraction 

 ' being in the inverse duplicate ratio of the distances ; the cohesion 

 in this instance he conceived to be merely referable to the te- 

 nacity of the oil. 



ROYAL GEOLOGICAL SOCIETY OF CORNWALL. 



At a meeting of this Society on the 24th of February last, at 

 Penzance, a paper was communicated by J, H, Vivian, Esq. 



Vice- 



