OF THE ATMOSPHERIC TEMPERATURE. 311 



thus from Maine to Georgia these waves are of a broad and well-defined shape, as 

 at New Haven, but they become somewhat changed in their appearance over the 

 vast area watered by the Mississippi and its tributaries; here the undulations 

 become more narrow and numerous, as at Fort Snelling. The change from one 

 form into the other is very gradual, and with an increase of the geographical 

 distances some of the old features become obliterated and new ones make their 

 appearance. The curve for Cincinnati, for instance, partakes of an intermediate 

 character between the eastern or Atlantic type and that of the Mississippi basin. 

 On our western coast, as might have been expected, a new feature is developed, 

 subject perhaps to less irregularities than in any other part of the country, and for 

 this reason well suited for the study of the proximate causes whicli determine its 

 laws. The curve for San Francisco is presented as a type for the Pacific coast. 



The remarkably cold epoch about 1837 with cold years preceding and following 

 is common to all stations represented between the Atlantic coast and the eastern 

 flank of the Kocky Moimtains, and the exceptionally warm period about 1827 

 perhaps extended likewise over a very large area. 



There is nothing in these curves to countenance the idea of any permanent 

 change in the climate having taken place, or being about to take place ; in the last 

 90 years of thermometric records, the mean temperatures showing no indication 

 whatever of a sustained rise o-r fall. The same conclusion Avas reached in the dis- 

 cussion of the secular change in the Eain-Fall, which appears also to have remained 

 permanent in amount as well as in annual distribution. 



The degree of parallelism of the curves is sufficiently close to warrant an addi- 

 tional consolidation of results for a few characteristic stations, for further study; 

 one typical curve will be given for the Atlantic coast and another for the Missis- 

 sippi valley. 



The first is composed of the long series of mean annual temperatures at Bruns- 

 wick, Me., Salem, Mass., New Haven, Conn., and Philadelphia, Penn., to represent 

 during 91 years the type of the secular change for those eastern States Avhich are 

 situated between the Atlantic and the Alleghany Mountains. These four series 

 are unbroken between 1807 and 1865, and for these 59 years the individual means 

 are set down, as in the table below; to reduce those values which lie outside of these 

 limits to uniformity, the 59 differences for each series from the mean series were 

 formed, and the respective mean difference applied as reductions ; they are, for 

 Brunswick +4°.5, for Salem +0°.6, for New Haven — 0°.4, and for Philadelphia 

 — 4°. 7. After this the means were taken for each of these years, except for the 

 years 1780, 1783, 1784, and 1785, which are covered by one series only. 



