APPENDIX. 271 



few boards about four feet loni>-. Upon these dirt was piled to hold the pot 

 of burning tar. The four upright sticks were spiked to the runners, the 

 tops of which, about eighteen inches above the bed of the sled, were con- 

 nected by stri])s of inch boards four to six inches wide. To these strips the 

 ■chicken-wire netting was attached. This rude box or screen supported the 

 wet straw or manure used as smudge material. Four of these sleds, two 

 wagons rigged after the Fleming plan, and about five hundred sacks of 

 manure were found sufficient protection for an orchard of three hundred 

 acres during each night of the severe April frost of 180(5. The orchard was 

 successfully protected during six successive nights of severe frost, at an ex- 

 pense of less than one per cent, of the value of the crop undoubtedly saved 

 by this means. 



This device can be made much more efficient by supporting the center of 

 the screen by an arch of heavy, stiff wire passing diagonally from runner 

 to runner and forcing up the bottom of the screen so as to cause it to present 

 a concave surface to the fire, thus causing more of the heat to pass through 

 the smudge material and less to escape upward about the sides of the screen. 



DIRECTLY HEATING THE AIR HY MEANS OF FIRES. 



Mr. Edward Cophu's phui — Mr. Edward < 'opely. of Riverside, California, 

 in several ai'ticles published in the Riverside I'rcxK, of April, 1890, describes 

 at length experiments which he has made in heating the air directly bj" 

 small fires of coal, placed in wire buckets hung a short distance above the 

 ground. In his discussion, he takes into consideration the fact that on frosty 

 nights the air for some distance above the ground is considerably warmer 

 than the surface, consequently it would be possible to warm the lower air 

 nntil its temperature and resulting density were equal to those of the air 

 above the surface before there would be any tendency of the surface air to 

 rise and escape. Therefore, he believes that it is possible, by means of 

 small fires to warm the lower stratum of air sufficiently to prevent frost, 

 and. at the same time, avoid loss of heat, which would result were there an 

 upward draft of sutficient force to carry the heated air above the tree tops. 



The difficulties experienced in all methods of directly heating the air 

 arise from the unequal distribution of the heat through the lower portion of 

 the air, on account of which the warmer masses of air rise above the region 

 needing protection, and cold, denser air is continually flowing in from the 

 sides to replace them. Of course, this upward draft will be less with small 

 than with large fires. 



During the winter of 1897-98 a number of unusually severe frosts occurred 

 in the citrus region of California. Advantage was taken of these occasions 

 by the Horticultural Club of Riverside to test many devices. Below is given 

 an account of these experiments, which were probably the most extensive 

 and carefully conducted of any ever made in this country. These show 

 very conclusively the value of these small fires in protection in such a dry 

 climate as exists at Riverside. In fact this method proves most satisfactory 

 of all those tested, and a similar result will probably be found to be the case 

 in places where the dew-point is 10° or more below the temperature of the 



