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I 



In diversified farming by irrigation lies the salvation of agriculture 



HOW TO PREVENT INJURY FROM 

 FROST. 



BY F. C. BABKER, NEW MEXICO. 



IN studying methods of preventing injury 

 from frost it is necessary to have a clear 

 knowledge of how and why the tempera- 

 ture falls and frost is produced. 



The surface of the earth is continually 

 losing heat by radiation into space, but 

 during the day it usually receives heat 

 from the sun more rapidly than it loses it 

 by radiation, and therefore it grows warmer. 

 Radiation, and consequent loss of heat, 

 takes place most rapidly when there is 

 nothing to obscure the sky. Clouds or any 

 other obstruction act as a screen in retard- 

 ing it. The escaping rays of heat strike 

 the obstruction and are driven back to the 

 earth. This is why frost is more likely to 

 occur on a clear night than when the sky 

 is cloudy. It also explains why smudge 

 fires, by forming a screen of smoke over the 

 orchards, are a protection against frosts. 



Cold air is heavier than warm air, and 

 this principle causes the air on slopes, as 

 it becomes chilled by radiation, to flow 

 down into the valleys, where it accumu- 

 lates and becomes injurious. We thus 

 understand why trees on the foot hills 

 often escape injury from frost, while 

 those in the adjoining valleys are damaged. 

 Smudge fires are only effective on broad, 

 flat expanses of land. In narrow valleys 

 the cold air comes down from the hillsides 

 and gets underneath the smoke. On windy 

 nights the danger from frost is lessened 

 by the warmer air above getting mixed 

 with the colder air below. 



The above theories of the radiation of 

 heat and the falling of the colder air are 

 tolerably well recognized by all orchardists, 

 but there is another and perhaps more 

 important law of nature, which is but little 

 understood, and this is the " dew-point " 

 theory. 



Every one knows that the atmosphere 

 holds a very considerable amount of water 



in the form of vapor, and that this invisi- 

 ble vapor, which is invariably present in 

 greater or less quantities, can always be 

 condensed into water if the temperature 

 of the atmosphere be sufficiently lowered. 

 If the condensation takes place at temper- 

 atures above the freezing point of water, 

 the moisture is deposited as dew; if below 

 the freezing point, the condensation is in 

 the form of frost. To fully comprehend 

 what follows, it must be understood that the 

 temperature at which condensation begins 

 is called the dew-point, and this varies 

 with the amount of moisture or vapor in 

 the air. The greater the proportion of 

 moisture the less the fall of temperature 

 required to condense it into dew or frost. 

 When the air is saturated with moisture 

 the dew-point will be reached at a 

 higher temperature than when the air is 

 dry. For instance, in a dry atmosphere 

 the dew-point may not be reached un- 

 til the thermometer falls to 28 degrees 

 Fahrenheit, when frost forms. At this 

 point peach buds are seriously injured. 



If, however, you can artificially add to 

 the amount of vapor in the air by keeping 

 the land moist by means of recent irriga- 

 tions, then you raise the dew-point and 

 frost may be formed at a higher degree of 

 temperature, or say at over 30 degrees 

 Fahrenheit, which is the amount of cold 

 necessary to injure peach blossoms. If, 

 therefore, you can prevent the tempera- 

 ture of the atmosphere from falling to 

 30 degrees, you are safe. At first sight it 

 may appear that if the vapor in the air 

 freezes at 30 degrees and the indication of 

 heat still continues, the temperature will 

 continue to fall until injury results. But 

 here a very wonderful natural law comes 

 into play. 



Of course it is well understood that an 

 enormous amount of heat has been re- 

 quired to convert water into atmospheric 

 vapor. This heat is latent in the vapor, 

 and when the latter is condensed into frost 



