144 BOARD OF AGRICULTURE. 



Mr. Gilbert. Will you ploaso to carry the illustration far 

 enough to show why the northwest and southwest winds are al- 

 most' always dry? 



Prof. Fernali). They are not dry winds in certain parts of the 

 globe. On the western coast of Europe, thej'^ are the moist winds. 

 Here, the southwest wind is the wind which has passed over 

 mountains and has lost its moisture. When the southwest return 

 trade wind comes in contact with tlie Sierra Nevadas, it pours 

 down its principal burden of rain on the western slopes of those 

 mountains. Then, when it comes to the Rocky Mountain region, 

 where the mountains are higher than those on the western coast, 

 another fall of I'ain is produced, and by the time it passes over 

 these mountains, if not before, its character is entirely changed, 

 so that it is a dry wind, and it retains this character across the 

 continent. If we come down a little further south, into the Gulf 

 States, we find the southwest wind a moist wind from the Gulf. 

 But in the northern part of the United States and in Canada, the 

 character of this wind is necessarily dry. The same is true of the 

 northwest wind, because it blows over a large extent of land. 



Mr. Geo. E. Bracket? of Will do. Last fall there was a rain 

 storm of six hours' duration, with the wind fresh from the west- 

 ward. 1 have lieard it spoken of by several persons. I kept a 

 meteorological register for ten years in succession until the pres- 

 ent year, and I never know such an occurrence before; and judg- 

 ing from the facts stated bj' the Professor, it would hardly be 

 supposed that there could be such a thing. It is an exception to 

 all general rules, and perhaps indicates that some great changes 

 are occurring in our climatic condition. 



Prof. Ferxald. The storm referred to probably resulted from 

 the action of two winds which uniting and propelling clouds gave 

 them a dir(!ction which was the resultant of the two motions, not 

 corresponding with either. While speaking, I wish to give a 

 single illustration of the point, that where there is an expenditure 

 of power, it is at the expense of heat. If you had an air-|)ump and 

 a receiver from which you wished to exhaust the air, and should 

 make a single stroke of the lev(>r, y(ui would see, if the receiver 

 were between yourselves and the light, a slight deposition of mist 

 within it. ANHiy '( You have removed a portion of air I'rom the 

 receiver, and the remaining portifui expaiuls. It exerts power; it 

 performs work ; and this, as has been stated, is attended with a re- 

 duction of temperature. It is actually, by the thermometer, colder 



