14 



Marine Dynamometery This dynamometer is contained in an iron 

 cylinder, which is fixed to the rock where the experiments are to be 

 made. The instrument consists of a plate or disc attached to a 

 powerful spring, which is lengthened by the action of the waves. In 

 graduating the instrument, the pressure required 'to lengthen the 

 spring, a given quantity is ascertained by loading the disc with 

 weights, so that when the quantity that the spring has yielded by 

 the action of the sea is known, the pressure due to the area exposed 

 is known also. The discs employed varied from 3 to 9 inches in 

 diameter, and the resistance of the springs from about 10 lb. to 

 about 50 lb. for every \ inch of elongation. With a view to check 

 the results, three instruments, of very different powers of springs, 

 were besides placed each other on an exposed i-ock, for a space of about 

 six months, and the results were found to be remarkably concordant 

 As the action of a wave may be supposed to combine the effects of a 

 sudden impact with a subsequent continuous pressure, an objection 

 mio-ht be urged against estimating these effects statically ; and the 

 author has accordingly made some remarks I'elative to this subject, 

 which it is not, however, necessary here to state. 



The results obtained are, up to this date, 260 in number, and 

 these embrace a continuous register of the agitations of the Atlantic 

 (as ascertained at the Skerryvore Rocks, Argyllshire,) for the last 

 22 months ; together with a later train of similar observations, on 

 the German Ocean, made at the Bell Rock Lighthouse. The fol- 

 lowing is a digest of the results obtained : — 

 Atlantic Ocean. 



Average of results for 5 summer months, dui*ing the years 1843 

 and 1844, is 611 lb. per square foot. 



Average of results for 6 winter months during the same years 

 is 2086 lb. per square foot, or thrice as great as in the summer 

 months. 



Greatest result yet obtained at Skerryvore, being on the 20th 

 December 1844, is 4335 lb. per square foot. 

 German Ocean. 



Greatest result yet obtained at the Bell Rock, being on the 9th 

 October 1844, is 3013 lb. per squai-e foot. 



The greatest effect of the sea, which has been observed, is, there- 

 fore, that of the Atlantic, which is equal to about 2 tons per square 

 foot. 



There are also a few observations (made in April and June 1842) 

 upon the Irish Sea, on the coast of Kirkcudbright, but the weather 



