and their Distance from the Windward Shore. 359 



do in such circumstances is to select an existing work which 

 is as nearly as possible similarly exposed. Perhaps the most 

 important element in such a comparison is what may be 

 termed the line of maximum exposure, or in other words, 

 the line of greatest " fetch" or reach of open sea. This line 

 can be measured from a chart, and in this manner the differ- 

 ence of exposure at the existing harbour and at the place where 

 the new one is to be built, may be ascertained, but the en- 

 gineer still does not know in what ratio the height of the 

 waves increases in relation to any given increase in the 

 line of maximum exposure. 



As this inquiry is one of great importance in the practice 

 of marine engineering, and has not, so far as I know, been 

 in any way investigated, I have, during the last two years, 

 been making occasional observations on the subject when 

 favourable circumstances occurred, and when my professional 

 avocations would permit me. The localities selected were a 

 small fresh-water loch, the Frith of Forth, and the Moray 

 Frith. 



These observations have been but limited in extent, and I 

 have thought it proper therefore to avail myself of your far- 

 spread Journal, in directing the attention of others to the 

 prosecution of this inquiry, which can be perfected only by 

 multiplied trials. So far as my own observations have as 

 yet gone, the waves seem to increase in height most nearly 

 in the ratio of the square root of their distances from the 

 windward shore. — I remain, yours faithfully, 



Thomas Stevenson. 



Professor Jameson. 



