assumptions of constancy of drop-density and independence of drag of the medium on the charge on the drop. The values of and obtained graphically from the -intercept and the slope in Fig. 5 are and , being measured, for the purposes of Fig. 5 and of this computation in centimeters of Hg at 23° C. and being measured in centimeters. The value of in equations 15 and 16 (p. 101) corresponding to this value of is .874. Instead, however, of taking the result of this graphical evaluation of , it is more accurate to reduce each of the observations on to by means of the foregoing value of and the equation The results of this reduction are contained in the last column of Table X. These results illustrate very clearly the sort of consistency obtained in these observations. The largest departure from the mean value found anywhere in the table amounts to 0.5 per cent and “the probable error” of the final mean value computed in the usual way is 16 in 61,000. Instead, however, of using this final mean value as the most reliable evaluation of , it was thought preferable to make a considerable number of observations at atmospheric pressure on drops small enough to make determinable with great accuracy and yet large enough so that the whole correction term to Stokes’s Law amounted to but a [Pg 116] small percentage, since in this case, even though there might be a considerable error in the correction-term constant , such error would influence the final value of by an inappreciable amount. The first 23 drops of Table X represent such observations. It will be seen that they show slightly greater consistency than do the remaining drops in the table and that the correction-term reductions for these drops all lie between 1.3 per cent (drop No. 1) and 5.6 per cent (drop No. 23), so that even though were in error by as much as 3 per cent (its error is actually not more than 1.5 per cent), would be influenced by that fact to the extent of but 0.1 per cent. The mean value of obtained from the first 23 drops is , a number which differs by 1 part in 3,400 from the mean obtained from all the drops. When correction is made for the fact that the numbers in Table X were obtained on the basis of the assumption , instead of (see Section II), which was the value of chosen in 1913 when this work was first published, the final mean value of obtained from the first 23 drops is . This corresponds to