Preliminary Exercises. 167 



according to circumstances. The change which tree-planting has ah-eady 

 produced upon our western phiins is an unmixed good, but, by increasing 

 the humidity of the cHmate of certain health resorts, valued mainly for their 

 dryness — as Denver, for example — is not unaccompanied with evil. 



4. Trees modify temperature — wooded countries being warmer in winter 

 and cooler in summer. This they do by radiation, but, owing to their slow 

 conducting power, the times of their daily maximum and minimum do not 

 occur until some hours after the same phases in the temperature of the air, 

 thus distributing the heat of the day more ec^ually over .the twenty-four 

 hours. The special significance of this effect lies in the fact that, as relating 

 to human health, the daily range of the thermometer is of more importance 

 than the mean temperature of whole seasons. 



5. Trees radiate and evaporate through a stratum of air equaling in thick- 

 ness their height, whilst the radiation and evajioration from grasses, plants 

 and shrubs is confined to a stratum limited to the comparatively lesser planes 

 which they occupy. 



6. From the preceding it may be fairly inferred that they modify climate 

 to the extent of influencing the amount and character of the diseases in their 

 vicinity. (In this inquiry' residence in forests is not considered, universal 

 experience having shown those situations which are permanently shaded to 

 be insalubrious.) 



7. Forests and tree belts are of undoubted value in preventing the dissem- 

 ination of malaria. 



8. Trees are of positive sanitary value in affording shelter from the exces- 

 sive heat of the sun, from the violence of winds, and in promoting aesthetic 

 culture. 



9. The importance of devoting to forests all regions unfit for profitable 

 culture, and of jirotecting them by an enlightened public sentiment, as well 

 as by legal enactment, may be fairly assumed as a sanitary as well as an eco- 

 nomical necessity. 



Kourtli Dav — Saturday. 



Forenoon Session. 



At 10 o'clock A. M. President Earle called the Society to order. 



Mr. F. P. Baker, of Kansas, from the Committee on Excursion 

 to Mobile, reported that near one hundred members had expressed 

 a desire to make the excursion, and that Tuesday A. m. had been 

 agreed upon as the time of leaving this city for Mobile. 



On motion by Mr. E. H. AVilliams, of Indiana, a committee, 



