G4 INTRODUCTION TO THE 



" The number of places, at which the rise and 

 times of flowing of tides have been observed, in 

 these voyages, is very great ; and hence an im- 

 portant article of useful knowledge is afforded. In 

 these observations, some very curious and even 

 unexpected circumstances have offered themselves 

 to our consideration. It will be sufficient to in- 

 stance the exceedingly small height to which the tide 

 rises in the middle of the great Pacific Ocean; where 

 it falls short, two-thirds at least, of what might 

 have been expected from theory and calculation. 

 " The direction and force of currents at sea make 

 also an important object. These voyages will be 

 found to contain much useful information on this 

 head ; as well relating to seas nearer home, and 

 which, in consequence, are navigated every day, 

 as to those which are more remote, but where, 

 notwithstanding, the knowledge of these things 

 may be of great service to those who are destined 

 to navigate them hereafter. To this head also we 

 may refer the great number of experiments which 

 have been made for enquiring into the depth of 

 the sea, its temperature, and saltness at different 

 depths, and in a variety of places and climates. 

 " An extensive foundation has also been laid for 

 improvements in magnetism, for discovering the 

 cause and nature of the polarity of the needle, and 

 a theory of its variations, by the number and 

 variety of the observations and experiments which 

 have been made, both on the variation and dip, in 

 almost all parts of the world. Experiments also 

 have been made, in consequence of the late voyages, 

 on the effects of gravity, in different and very dis- 



works, in various departments ; and particularly that afforded to 

 Mr. Herschell, which has enabled him to devote himself entirely 

 to the improvement of astronomy ; these and many other instances 

 which might be enumerated, would have greatly distinguished his 

 Majesty's reign, even if he had not been the patron of those success- 

 ful attempts to perfect geography and navigation by so many 

 voyages of discovery. 



