128 TRANS. OF THE ACAD. OF SCIENCE. 



feet accuracy of the result, the connected observations of Dr. 

 Parry leave no doubt, that, during the summer season at least, 

 the changes of atmospherical pressure in the region of the 

 Rocky Mountains, or, to speak more precisely, of the eastern 

 slope of the main chain of the mountains in Colorado, corre- 

 spond in time very nearly with the changes observed here ; 

 sometimes I find them a day earlier here, and more rarely a 

 day later,* and also that these changes are there much more 

 moderate than they are here. 



From a careful analysis of Dr. Parry's observations, I 

 have further come to the conclusion, that the horary changes 

 of the barometer are not very different from those noticed 

 here, and for which I have from my long continued observa- 

 tions computed tables for the different months of the year, 

 differing somewhat from the table of the Philadelphia correc- 

 tions published by the Smithsonian Institution, (Table D, p. 

 93,) especially in the more decided rise of the mercury in the 

 forenoon and its greater fall in the afternoon, the average 

 difference for the whole year being here 0.076 and in Phila- 

 delphia 0.061 inches. With the assistance of these tables I 

 have reduced Dr. Parry's observations to daily means, and 

 have compared these with the means of the ten days, next 

 preceding and following, at St. Louis, eliminating extraordi- 

 nary and more local changes, which was done by the aid of 

 diagrams, on which the daily means for both stations were 

 laid down. The greatest element of error, no doubt, lies in 

 the influence of the atmospheric temperature. Following the 

 plan ot some computers, I have been induced to adopt, as an 

 element in the calculation, the mean temperature of the day 

 or days of observation instead of the actual temperature of 

 the time of observation; but I am fearful that even thus I 

 may have obtained a result a little too high, especially as 

 I may have estimated the mean temperature too high, not 

 being able to take sufficiently into account the excessive dif- 

 erence of the day and night temperature in those high moun- 

 tains. 



The altitudes of the stations where Dr. Parry was able to 

 take observations for a number of days (Mt. Vernon, 9 days; 

 Tarryall, 4 days ; Soda Springs, 8 days ; Colorado, 5 days; 

 Empire City, 13 days, and Lindstorm's mills, 12 days) are, 

 of course, the most reliable, and to them I have referred as 

 much :is possible other observations made in the neighbor- 

 hood ; thus, especially, those of Tike's Peak to the Soda 

 Springs— Mt. Guy ot to Tarryall — Mt. Flora, Gray's Peak, and 

 Parry's Teak, to Empire City. The direct comparison of the 



• In winter these ehanges sppiii to occur from one to three cUvs earlier 

 there than here, as appears from the Hon. F. M. Case's observations, de- 

 tailed at another place. 



