404 



METEOROLOGY. 



who resides in one of the more central parts of the city, in a somewhat 

 high and dry locality ; while my own station is about two miles further 

 west. The latter is situated on one of the gentle slopes of Rock Spring 

 Creek valley, which forms a shallow depression of the ground, stretch- 

 ing west and east. The station itsetf may be considered on or near 

 the same level with that of Dr. Engelmann's, as Rock Spring creek 

 has in its course a pretty rapid descent towards the east. To the west 

 and north I have an open prairie before me ; and to the south, some 

 scattered houses. It is only towards the east that the view is obstructed 

 by rows of buildings not far off. The thermometers used on both sta- 

 tions are standard instruments. 



From a comparison of the tables of temperature of the two different 

 places, the following facts present themselves in strongly marked fea- 

 tures : 



1. Of the 1,029 observations, made at the usual hours of 7 a. m., 

 2 p. m.j and 9 p. m., 331, or about one third of the whole, agree 

 near enough with those of the city. 



2. The monthly means of the differences of temperature of the two 

 stations show that in the central part of the city the temperature is 

 considerably higher than that of the city limits, as exhibited by the 

 following numbers. 



Month. 



9 p. M. 



Mean. 



February .. 



March 



April 



May 



June 



July 



August.... 

 September 

 October.... 

 November 

 December 



Mean 



1.3 

 1.1 

 0.4 

 1.7 

 2.1 

 2.9 

 2.5 

 2.2 

 3.3 

 1.3 

 1.5 



0.0 



0.8 



0.7 



0.4 



0.9 



0.4 



0.1 



0.3 



0.2* 



0.1 



0.2 



1.5 

 1.2 

 1.7 

 1.7 

 2.1 

 3.7 

 3.3 

 2.1 

 3.4 

 1.5 

 1.3 



0.9 

 1.0 

 0.9 

 1.3 

 1.7 

 2.3 

 2.0 

 1.5 

 2.2 

 0.9 

 1.0 



1.8 



0.3 



2.1 



1.4 



* Cooler. 



3. The greatest, as well as the most numerous differences of temper- 

 ature, are found in the morning and evening; while at 2 p. m., these 

 differences, if any, are, generally speaking, but very small. 



4. During the warmer half of the year, from May to October inclu- 

 sive, the mean difference, viz: 1°.8, is exactly double that of the colder 

 half of the year, which is 0°.9. 



5. The mean difference of the evenings for the five months, from 

 June to October inclusive, amounts to 2°. 9, or nearly 3°; and that of 

 the mornings to 2°. 6; so that the city limits have, during the warmer 

 months, the benefit of cooler nights and mornings; while at 2 p.m., 

 during the same period of the year, the difference is but 0°.03. 



6. Near the city limits the latest frost in the spring occurred seven- 

 teen days later, and the earliest frost in the fall nineteen days earlier, 

 than in town, hereby shortening the season of no frosts by thirty-six 

 days in the former place. The vegetation in the more central part of 



