XIV INTRODUCTION. 



The results that are embodied in Plate I. alone of this edition 

 would, had the data for it been collected by a force speciall}' 

 employed for the purpose, have demanded constant occupation 

 from a fleet of ten sail for more than one hundred years. The co- 

 ordinating of these observations after they were made, and the 

 bringing of them to the present condensed form, has involved a 

 vast amount of additional labour. Officers here have been 

 engaged upon the work for many years. This patient industry 

 has been rewarded with the discovery of laws and the develop- 

 ment of truths of great value in navigation and very precious to 

 science. 



It would be presumptuous to claim freedom from error for a 

 work like this : true progress consists in the discovery of error 

 as well as of truth. But I may be pardoned for saying that the 

 present edition of this work will be found to contain more of 

 truth and less of error than any of its predecessors, simply 

 because it is founded on wider research, and based on the results 

 of more abundant observations than they. Indeed, it could not, 

 or, rather, it should not be otherwise ; for, as long as we are 

 making progress in any field of physical research, so long must 

 the results continue to increase in value ; and just so long must 

 what at first was conjecture grow and gain as truth, or fade and 

 fall as error. 



The fact seems now to be clearly established that the atmo- 

 sphere is very unequally divided on opposite sides of the equator, 

 and that there is a mild climate in the unknown regions of the 

 antarctic circle. Over the extra-tropical regions of our planet, 

 the atmosphere on the polar side of 40° N. and 40^ S. is so 

 unequally divided as to produce an average pressure, according 

 to the parallel, of from 10 to 50 lbs. less upon the square foot of 

 sea surface in southern than upon the square foot of sea surface 

 in northern latitudes. These, and many other developments not 



Mr. Trembley^ to conclude that there are, "at the bottom of the water, 

 niountaias, plains, valleys, and caverns, just as upon the land." 



But by far the most interesting and valuable book touching the physical 

 geography of the Mediterranean is Admiral Smyth's last work, entitled " The 

 Mediterranean ; a Memoir, Physical, Historical, and Naltical. By 

 Rear-Admirul William Henry Smyth, K.S.F., D.C.L.," &c. London : John 

 W. Parker and Son. 1854. 



1 Philosophical Transactions. 



