498 



SCIENCE. 



[N. S. Vol. XXII. No. 564. 



fifteen or twenty minutes, exert an influence 

 which is great enough to very materially in- 

 fluence the discharge of water into wells, field 

 drains, springs and. river channels. It is well 

 known too, in the case of breathing or blow- 

 ing wells, that there is for days together a 

 continuous flow of air out of and into the 

 ground, the currents being strong enough, in 

 a case which we have personally observed, to 

 rattle loose two-inch planks lying over the 

 well, itself nearly a hundred feet deep and 

 four feet in diameter. In this particular case 

 we Avere called to examine the well because it 

 was impossible to prevent the suction pipe in 

 the well freezing and bursting during the 

 winter, caused by the large volume of cold 

 air sinking into the well at times of high 

 pressure when the thermometer was very low. 

 The owner informed me that in digging the 

 well, after a depth of eighty feet had been 

 reached, work was stopped for the Christmas 

 holidays and that after taking up the work 

 again the gravel was found frozen so that a 

 pick was necessary to loosen it before begin- 

 ning digging. 



We. have observed fluctuations in the dis- 

 charge of water from tile drains, associated 

 with and apparently caused by changes of 

 barometric pressure, amounting to fifteen per 

 cent., and in the case of a deep well, discharg- 

 ing through a six-inch pipe, where the rate of 

 flow was measured in a reservoir on ten con- 

 secutive days, the discharge per minute was 

 found to vary between the wide limits of 

 15.441 and 13.947 cubic feet per minute, — a 

 variation of fully ten per cent. We have also 

 secured autographic records on the Wisconsin 

 and Fox Rivers and from Lake Mendota which 

 seem to indicate that the general seepage over 

 wide areas changes its rate with changes in 

 barometric pressure to such an extent that 

 when the discharge is collected into channels 

 the differences in depth are measurable, and 

 when we have such changes as these it is diffi- 

 cult to believe that the inflow and outflow of 

 air are not greater than is suggested by the 

 conclusions of this Bulletin. 



In regard to the influence of simple dif- 

 fusion, in effecting soil aeration, it appears to 

 the writer that the author has obtained values 



which must be much too large for fleld condi- 

 tions. In carefully rneasuring the rates of 

 diifusion, under the conditions of rigid con- 

 trol, which he did, the author has done ex- 

 actly the right thing; but what is lacking is 

 supporting field checks which are greatly 

 needed in verifying the conclusions reached, 

 particularly when the results are used so pre- 

 cisely as to compute the amount of carbonic 

 acid escaping from a given field surface from 

 the per cent, of carbonic acid found in the soil 

 air at a given distance below the surface, 

 where the porosity of the soil is known. Re- 

 ferring specifically to some of the author's 

 data : If it is true, as indicated on page 39, 

 that carbonic acid was escaping from soil in 

 the flower bed in front of the building of the 

 Bureau of Soils at the time of observation at 

 the rate of .04 of a cubic foot per day and that 

 it was being produced at this rate in the soil 

 below the depth- of six inches throughout the 

 growing season — let us assume of 120 days — 

 this would mean a production of carbonic acid, 

 through the oxidizing of organic matter, at the 

 rate of 209,088 cubic feet per acre; and, taking 

 the weight of a cubic foot of carbonic acid at 

 .12323 pounds, there would have been a loss 

 from the soil of 7,026 pounds of carbon per 

 acre. This amount of carbon represents, us- 

 ing an analysis of Hall's, 13,970 pounds of 

 water-free grass per acre, or eight tons of hay 

 containing the usual 15 per cent, of moisture. 

 If we take Ebermayer's observations on the 

 amount of carbonic acid in soil air, extending 

 over a full year, except that August, Septem- 

 ber and October are not included, as given in 

 the Bulletin, we shall find by the method of 

 the author a still larger loss of carbonic acid. 

 We use for this computation the mean 

 amounts found for the year under the five 

 conditions reported upon. At a depth of 15 

 centimeters (6.9 inches) the mean amount of 

 carbonic acid found in the soil air was 1.09 

 per cent., the smallest amount in any single 

 observation being .02 per cent., the next 

 smaller .13 per cent, and the next .27 per cent., 

 while the highest amount found was 4.61 per 

 cent. Taking 120 days, as in the former case, 

 and calculating from^ the table the amount of 

 carbon carried out of the soil during this 



