324 FISHES OF THE FIRTH OF FORTH. 



ing a ripple on the surface with their fins, while they be- 

 come the principal food of many marine birds, which assail 

 them in the water or prey on them from above. As the 

 cold weather advances, these little fish are no longer seen in 

 the lower part of the estuary, but are found to ascend the 

 Firth to a considerable distance, and to select that part of 

 the river where the fresh and salt waters mingle together : 

 " for it is a well-known law in chemistry, that when two 

 fluids of different densities come in contact, the temperature 

 of the mixture is elevated for a time in proportion to the 

 difference in density of the two fluids ; owing to mutual pe- 

 netration and condensation ; such a mixture is constantly 

 taking place in the rivers that run into the sea, and the 

 temperature of the mixed water is accordingly elevated."" 

 In the year 1830, Sprats were remarkably abundant all 

 over the British coasts, but more particularly on the coast of 

 Kent and Essex, where they were taken in immense quanti- 

 ties, so that they were sold at sixpence a bushel as manure for 

 the land. The Sprat is generally considered as a delicious, 

 well-flavoured, and wholesome fish, and is eaten in consider- 

 able quantity in this country, both fresh and salted. Prior 

 to the year 1836, it was of rare occurrence to see Sprats 

 brought to the Edinburgh market, and when they did 

 appear they were sold at the rate of twelve a-penny ; but 

 now, owing to the immense numbers that are taken in 

 the Firth of Forth, they are enabled to be sold in the 

 Edinburgh markets at a low price, and consequently form 

 a cheap and agreeable food to many of the inhabitants. 

 The most common size of a Sprat is from four to five in- 

 ches in length ; yet it is observed occasionally to exceed six 

 inches and a half, when it is named in the neighbourhood 

 of Alloa the King of Gar vies. Sprats spawn early in the 

 month of March, and feed on small crustaceous animals. 



