INTRODUCTION. 



TABLES of meteorological observations afford but little information 

 and give a very indefinite idea of the changes that have taken place 

 in the natural phenomena to which they relate, even to those who are 

 familiar with them ; they require some elucidation to bring the results 

 at once under the eye, and to the mind : in order to effect this object, 

 a series of illustrations have been constructed, which exhibit all the 

 results of the observations of the Exploring Expedition, at sea as well 

 as in port. 



I have also deemed it expedient to add a few remarks under each 

 head of observations, pointing out some of the results deducible there- 

 from, as well as giving other information, derived from authentic 

 sources, likely to throw some light upon the climates and their 

 vicissitudes, in those parts of the globe visited by us. 



On the diagrams, the barometrical observations have been reduced to 

 a uniform temperature (32 Fahr.), and to the level of the sea, and 

 corrected for instrumental errors, as well as brought to the standard 

 of the Royal Society, London, with which they were originally com- 

 pared ; in this respect only they differ from the tables. To each series 

 of observations a diagram is annexed. 



It was my desire to give all the observations made by the Expedi- 

 tion during the period of our four years' absence from the United 

 States ; but I found it impossible to condense them in such a manner 

 as to exhibit the results without confusion. The Meteorological 

 Journal of the Vincennes has, therefore, been adopted throughout in the 

 body of this work, and the Journals kept on board the other vessels 

 of the squadron, on their separate cruises, have been added in the 

 Appendix. The results are thus made to extend over a large area. 

 To have given them separately, would have been but publishing 



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