November 17, 1911] 



SCIENCE 



689 



says, may be profitably employed in much of 

 the agricultural portion of the United States. 

 The distance at which the effect of the trees 

 may be felt averages twenty times their height, 

 although absolute protection of a crop such as 

 corn, in a wind with a velocity of 50 miles per 

 hour, can not be expected beyond a distance of 

 from six to eight times the height of the wind- 

 break. Partial protection is given over a dis- 

 tance of from twelve to fourteen times the 

 height. In extreme cases the efficiency of a 

 windbreak in checking evaporation from the 

 soil may amount to 70 per cent, of the mois- 

 ture ordinarily lost. Protection in this respect 

 is appreciable for a distance equal to five times 

 the height of the trees in the windward direc- 

 tion, and fifteen or twenty times the height 

 leeward. The absorption of soil moisture by 

 the roots of the trees may in the case of an 

 orchard be appreciable, but need not result in 

 real damage. There is little basis for the 

 belief that windbreaks sap the fertility of the 

 soil. The trees' absorption of soil moisture 

 may, however, reduce the activity of the nitri- 

 fying bacteria and cause temporary sterility in 

 the zone of root influence. The effect of a 

 windbreak upon temperature in the region of 

 its influence is much greater than is commonly 

 supposed. The diurnal range in temperature 

 in an area protected by a windbreak is nearly 

 9° P. greater than where the air circulates 

 freely. The effect of the superheating of both 

 air and soil in a protected zone is favorable to 

 crops which must begin growth at a time when 

 the heat is barely sufficient for generation. 

 An abstract of the book prepared by Mr. Pind- 

 ley Burns appears in the Journal of the Wash- 

 ington Academy of Science, Vol. I., No. 3. 



Two recent studies of the rainfall in special 

 regions are noteworthy. With characteristic 

 German thoroughness, Dr. Hellmann and G. v. 

 Eisner have completed an investigation of cer- 

 tain heavy rains in the valley of the Oder 

 during the years 1888-1903, inclusive, and 

 their relation to the summer high water of that 

 river. The research is published in two vol- 

 umes, a descriptive text and an atlas, the lat- 

 ter consisting of 55 large colored plates show- 



ing in detail the distribution of these rains in 

 northern Germany and the meteorological 

 conditions which accompanied them. " The 

 Rains of the Nile Basin " is a report by J. I. 

 Craig, of the Survey Department, Egypt, 

 based upon eleven years' observations. The 

 Nile flood has been of great moment to the 

 residents of that valley from remote antiquity. 

 The author now says " there are hopes that 

 within a few years the prediction of the main 

 features of the flood may be embodied in an 

 algebraic formula such as has already been 

 obtained for the Indian monsoon by Mr. G. T. 

 Walker." It is now well established that " the 

 rainfall in Abyssinia during the flood months 

 is due almost entirely to the precipitation 

 caused by diurnal ascensional movements act- 

 ing on the southwesterly current which again 

 is kept at the point of saturation by its ascent 

 on to the Abyssinian tableland." The latter 

 current has been traced backward across the 

 Sudan plains, and the watershed between the 

 basins of the Nile and Congo, and thence down 

 the basin of the latter to the South Atlantic. 



A COMPLETE summary of the free air data 

 obtained at Mount Weather for the three years 

 ending June 30, 1910, appears in Vol. IV., 

 Part 2, of the Bulletin of the Mount Weather 

 Ohservatory. The aeorological work is in 

 charge of Dr. William E. Blair, who prepared 

 the summary. On 980 of the 1,096 days of 

 the period, 1,013 ascensions were made— 896 

 by means of kites and 117 by means of captive 

 balloons. Air temperature, air pressure and 

 wind direction aloft were observed, in addition 

 to noting weather conditions and keeping the 

 usual continuous meteorological records at the 

 earth's surface. The temperatures have been 

 grouped by months and by seasons, and the 

 means have been computed for levels 250 

 meters apart up to 7,250 meters above sea 

 level. Several other valuable tables summar- 

 izing the data obtained for the various other 

 elements are included, and their relation with 

 reference to the centers of cyclones and anti- 

 cyclones are also shown. Previously derived 

 conclusions are verified by means of the new 

 data. Since the beginning of this period the 



