34 HORTICULTURAL SOCIETY OF NEW YORK. 



and instruments of all kinds, and I am quite astonished to have this con- 

 clusion of Mr. Munson's quite contrarj' to our observations, and I think 

 his statement is due to the fact that he is confusing wind action with the 

 actual settling of cold air. 



The President — I think that the difference in the two opinions comes 

 from these facts : "Sir. Munson comes from Texas. The cold weather 

 they have there comes from the north. They do not have any fall, so 

 far as I have found out, in Texas, although I have not been there the 

 year around. Our temperature here falls the most when there is no wind, 

 and that is where you have the air drainage. Buds of our fruit trees are 

 killed on still nights, not on windy nights. They are killed when it is 

 a perfectly still night, when there is no movement of atmosphere. I 

 think here you have the explanation of the difference. I have had ex- 

 perience in the Gulf and in Mexico, myself. 



Mr. Munson — Just a question to Dr. [NlacDougal : In driving across 

 the plains in Nebraska and the West, hundreds of times I have ex- 

 perienced this, that we would come to a ravine that would be several 

 miles in length, having a very little down flow, and bej'ond as we began 

 driving down into that ravine, we felt a body of cold air, and felt quite 

 chill}', while it was quite comfortable on top. On very still evenings 

 when we drive through it, we feel those conditions. How do you ex- 

 plain that? 



Dr. MacDongal — I think it is a splendid explanation of my theory, 

 and I am glad to get it. Just imagine j'ou had a fine mist of rain which 

 is heavier than air, poured on the ground. It naturally seeks the lowest 

 places, doesn't it? 



Mr. Munson — I would like to know where cold air comes from? 



Dr. MacDougal — It is cooled all over the surface of the ground and 

 flows to the lowest places. 



The President — We do not think of cold air coming from high 

 elevations and coming down somewhere. The effect of cold air comes 

 from radiation all over, and it runs like water, and as that water that 

 falls upon the ground runs down into the ground, so this little stream of 

 cold air runs down the valley. 



Dr. MacDougal — It is more accentuated, of course. 



Mr. Munson — Our thermometer all along the surface of the ground 

 and up on the hill does not show that temperature which you should get 

 on the bottom. 



Dr. MacDougal — There is not enough of it there. Just as soon as 

 it is cooled, it begins to move. The moment you have a particle of air 

 that is colder than any particle next to it, it begins to move, so you have 

 on this hill slope particles of cool air that begin to move down into the 

 hollow. You do not have a lake on the side of a hill ; you have a lake 

 falling and running down in a thin sheet. 



The President — If your thermometer was on a slope a foot above 

 the ground, it would not be in the stream of cold air at all. If your 



