TRANSACTIONS OF THE SECTIONS. 29 



VIII. This column shows that the difference between the corrected mean time 

 and the calculated time in no case exceeds 



0-01 second. 



IX. The appro-ximate velocities, deduced by drawing tangents to the cm-ve. 



X. The true velocities, calculated from the formula 



^*=0-368(27-7-s). 

 at 



XI. The retarding force, calculated by 



_^f = 0-136(27 -7 -.s)- 



Experiments on Vortex- rinr/s in Liquids. By H. Deacon. 



On Units of Force and Energy. By Professor J. D. Everett, F.B.S.E. 



The object of the paper was to urge the necessity of giving names to absolute 

 units of force and energy, that is, units not varying with locality, like the gravita- 

 tion units vulgarly employed (pound, foot-pound, &c.), but defined by reference to 

 specifi.ed units of length, mass, and time, according to the condition that unit 

 force acting on unit mass produces unit acceleration. 



The author proposed that the iinits of force and of energy (or of work), thus 

 related to the metre, gramme, and second, be called respectively the dyne and the 

 pone {biivafiLs, ttovos), and that the names kilodyne, megadyne, kilopone, viegapo^ie be 

 employed to denote a thousand and a million dynes and pones. The megadyne 

 and megapone will thus be the units of force and energy related to the metre, the 

 tonne, and the second. 



He also proposed that the units of force and energy related to the foot, the 

 poxmd, and the second be called respectively the kinit and the erg *, 



On the Corrosion of Copper Plates hy Nitrate of Silver. 

 By J. H. Gladstone, F.B.S., and Alfred Tribe, F.C.S. 



In some recent experiments in chemical dynamics, the authors had occasion to 

 study the action of nitrate of silver on copper plates in various positions. They 

 observed that when the plate was vertical there was rather more corrosion at the 

 bottom than at the top. This is easily accounted for by the upward current, which 

 flows along the surface of the deposited crystals, and which necessitates a movement 

 of the nitrate-of-silver solution towards the copper plate especially impinging on 

 the lower part. It was also found that when the copper plate was varnished on 

 one side it produced rather more than half the previous decomposition, and was 

 most corroded at the edges of the varnish. Bj' making patterns with the varnish, 

 this edge action became very evident. This was explained by the fact that the 

 long crystals of silver growing out from the copper at the borders can spread their 

 branches into the open space at the side, and so draw their supply from a larger 

 mass of solution than the crystals in the middle can do ; and increased crystalliza- 

 tion of silver means increased solution of copper. This was proved by making the 

 varnish a perpendicular wall instead of a thin layer, when the greater corrosion was 

 not obtained. In a plate completely surrounded with liquid, the greatest growth of 

 crystals is also evidently from the angles. It was likewise observed that if a vertical 

 plate be immersed, the lower part in nitrate of copper, and the upper part in nitrate of 

 silver, there is greater corrosion about the point of jimction. This was attributed 

 to the greater conduction of the stronger liquid. 



Some RemarJcs on Physics. By M. Janssen. 



* Since the reading of the paper, a Committee has been appointed by the Association 

 " to frame a nomenclature of absolute units of force and energy." 



