378 Metals and Diffusion of Salt and Fresh Water. [June 18, 



metal thus exposed to the simultaneous action of top and bottom 

 waters) considerably more destructive in its nature and character 

 than the action of sea water alone. 



Moreover, the author has found it (in other experiments extending 

 over long periods) to considerably exceed (in some instances varying 

 from about 55 to 120 per cent) the loss caused by galvanic action 

 between dissimilar metals of the iron and steel group, in circuit in 

 sea water. 



The arrangement of the waters in tidal streams and various effects 

 consequent thereon form an intricate study ; the author trusts, how- 

 ever, that the limited observations recorded in the present and the 

 former paper may have afforded some information on the metallurgical 

 aspect of the subject. 



Appendix. 



The gradual rise and consequent inward flow of salt water and 

 the outward flow of fresh water, has a general tendency to arrange 

 the waters of a tidal stream into long, overlapping, wedge-like, 

 layers or formations, the lower containing denser salt water and the 

 upper more fresh water. This disposition of the waters is modified 

 very considerably by currents, inter- diffusion, and numerous other 

 conditions. The arrangement and diffusion of the salt and fresh 

 water may not necessarily, at all places in the stream, be of an even 

 character, almost isolated bodies of salt and fresh water not impro- 

 bably accumulating in the numerous creeks, basins, or other indenta- 

 tions along the shores. The general contour of a stream, the in- 

 fluence of rainy or dry seasons (affecting the proportion of fresh 

 water), the fact of its estuary being either long, deep, and narrow, 

 affording little fall, or, on the contrary, of a wide shallow character, 

 the states and times of tide, &c, and many other circumstances, also 

 variously modify the diffusion results. 



To illustrate further the basis and nature of this investigation, 

 the author gives on Table D some typical analyses, selected from in- 

 formation relating to the disposition of the waters of tidal streams, 

 kindly furnished by Dr. H. Clifton Sorby, F.R.S. ; reference may also 

 be made to the recent very interesting research " On the Salinity of 

 the Firth of Forth," by Mr. Hugh Robt. Mill, B.Sc, F.C.S. (read 

 before the Royal Society, Edinburgh, January 5th, 1885). 



