1917] KUKAL ENGINEERING. 785 



monas, to which the name Trichomonas puUm-um is given, is the cause. The dis- 

 ease appears the second week after hatching, commonly about the tenth day, 

 young chicliS only being affected. Stoclc that is a month old proves resistant, 

 and chronic cases that reach this age usually recover. Diarrhea is absent in 

 the early stages but is present in the chronic stage. In the acute stage the 

 chick may succumb in a day or two, and only the more vigorous birds enter 

 the chronic stage. On the ranch where the investigation was first made 800 of 

 900 chicks hatched at one time from a thrifty stock of White Leghorns died 

 within 10 days after hatching. 



" Examination showed that a single species was present, frequently in over- 

 whelming numbers ; that it was not present in healthy stock, or in newly 

 hatched chicks; that healthy chicks kept in cages with sick chicks developed 

 the disease and showed the protozoan in the ceca ; and finally that control chicks 

 did not develop the disease when kept under identical conditions. We con- 

 cluded, therefore, that this protozoan is the cause of the disease." 



RURAL ENGINEERING. 



Evaporation from the surfaces of water and river-bed materials, R. B. 

 Sleight {U. S. Dept. Agr., Jour. Agr. Research, 10 (1917), No. 5, pp. 209-262, pis. 

 6, figs. IS). — Part 1 of this report deals with evaporation from water surfaces. 



Experiments on the evaporation from circular land tanks of different diam- 

 eters showed that " over the range of areas 0.785 sq. ft. to 113.1 sq. ft., or 

 diameters 1 to 12 ft., the range in evaporation for the year is 76.18 to 49.16 in., 

 and in percentage 154.9 to 100 per cent." 



In experiments on the relation between evaporation from circular tanks and 

 square tanks set 3 ft. in the ground, of equal exposed water surface, circular 

 tanks with diameters of 3.39 ft. and 2 ft, and square tanks of dimensions 3 by 3 

 ft. and 1.77 by 1.77 ft. were used. " Based upon the totals, the evaporation from 

 the larger square tank is 102.7 per cent of that from the circular one of the 

 same area. That from the other square one is 103.5 per cent of that from the 

 circular one of the same exposed area. Based upon mean weekly averages, 

 these figures are 104.7 and 104.9. In the case of the 9 sq. ft. area the ratio, 

 perimeter divided by area, is 0.15 greater in the case of the square tank than 

 for the circular one. This has apparently caused an incr3ase in evaporation 

 of 2.7 per cent. For the tanks of 8.14 sq. ft. area there is a corresponding in- 

 crease of 0.26 in the ratio snd an increase of 3.5 per cent in evapoi'ation." 



Experiments on the variation of evaporation with the depth of the tank set 

 in the ground showed that " during the months wiien the cooling effects of the 

 night were not so great, the shallow tanks show the greater evaporation, but 

 later, when the day temperatures and the heat storage of the shallow tanks 

 are more than offset by the low night temperatures, the shallow tanks indicate 

 a lesser evaporation. This difference in evaporation is not great, but for gen- 

 eral use a tank not less than 2 ft. deep is recommended, since its contents will 

 not become heated or cooled as quickly as those of the shallower tank. The 

 difference between the results from the 6 ft. tank and the 3 ft. one is so slight 

 that under all ordinary conditions there is no necessity for using a tank deeper 

 than 3 ft." 



Experiments on evaporation from flowing water showed that " for the first 

 set of tanks evaporation from the flowing water was 107 per cent of that from 

 the still water under exactly the same conditions. For the other set, a tank 

 25 ft. long, the evaporation from the flowing water was 108 per cent of that 

 from still water. . , . There seems to be no definite relation between evaporation 

 and velocity within the limits of the experiment." 



