260 PHYSICAL GEOGIIAI'HY OF THE Si:A, AND ITS METEOROLOGY. 



instruments, when they liave put the different parts of their 

 machinery together, and set it to work, find, as in the chrono- 

 meter, for instance, that it is subject in its performance to many 

 irregularities and imperfections ; that in one state of things there 

 is expansion, and in another state contraction among cogs, springs, 

 and wheels, with an increase or diminution of rate. This defect 

 the makers have sought to overcome ; and with a beantiful dis- 

 play of ingenuity, they have attached to the works of the instru- 

 ment a contrivance which has had the effect of correcting these 

 irregularities by counteracting the tendency of the instmment to 

 change its performance with the changing influences of tempera- 

 ture. This contrivance is called a compensation ; and a chrono- 

 meter or clock that is well regulated and properly compensated 

 will perform its office with certainty, and preserve its rate under 

 all the vicissitudes of heat and cold to which it may be exposed. 

 In the clock-work of the ocean and the machinery of the univeise, 

 order and regularity are maintained by a system of compensa- 

 tions. A celestial body, as it revolves around its sim, flies off 

 under the influence of centrifugal force; but immediately the 

 forces of compensation begin to act, the planet is brought back 

 to its elliptical j)ath, and held in the orbit for which its mass, its 

 motions, and its distances were adjusted. Its compensation is 

 perfect. So, too, with the salts and shells of the sea in the 

 machinery of the ocean ; from them are derived principles of 

 compensation the most perfect ; through their agency the undue 

 effects of heat and cold, of storm and rain, in disturbing the 

 equilibrium and producing thereby currents in the sea, are com- 

 pensated, regulated, and controlled. The dews, the rains, and the 

 rivers are continually dissolving certain minerals of the earth, 

 and carrying them off to the sea. This is an accumulative pro- 

 cess ; and if it were not compensated, the sea would finally become, 

 as the Dead Sea is, saturated with salt, and therefore unsuitable 

 for the habitation of many fish of the sea. The sea-shells and 

 marine insects afibrd the required compensation. They are the 

 conservators of the ocean. As the salts are emptied into the sea, 

 these creatures secrete them again and pile them up in solid 

 masses, to serve as the bases of islands and continents, to be in 

 the process of ages npheaved into dry land, and then again dis- 

 solved by the dews and rains, and washed by the rivers away 

 into the sea again. 



490. Tilience does the sea derive its salts ? — The question as to 



