23,708,715
   11,890,625
      945,754
      823,543
   15,308,805
   60,466,176
   30,685,377
   10,077,696
   19,416,381
   43,046,721
  ===========
  740,685,681

[Illustration]

Eight volunteer observers to whom this example has already been submitted showed wide difference in arithmetical skill.  One of them took but a few seconds over two minutes, in the best of six trials, to add by the usual figures, and set down the sum, but one figure in all the six additions being wrong; another added once in ten minutes fifty-seven seconds, and once in eleven minutes seven seconds, with half the figures wrong each time.  The last-mentioned observer had had very little training in arithmetical work, but perhaps that gave a fairer comparison.  In the binary figures she made three additions in between seven and eight minutes, with but one place wrong in the three.  With four of the observers the binary notation required nearly double the time.  These observers were all well practiced in computation.  Their best record, five minutes eighteen seconds, was made by one whose best record was two minutes forty seconds in ordinary figures.  The author’s own best results were two minutes thirty-eight seconds binary, and three minutes twenty-three seconds usual.  He thus proved himself inferior to the last observer, as an adder, by a system in which both were equally well trained; but a greater familiarity (extending over a few weeks instead of a few hours) with methods in binary addition enabled him to work twice as fast with them.  Of the author’s nine additions by the usual figures, four were wrong in one figure each; of his thirty-two additions by different forms of binary notation, five were wrong, one of them in two places.  One observer found that he required one minute thirty-three seconds to add a single column (average of five tried) by the usual figures, and fifteen seconds to count the characters in one (average of six tried) by the binary.  Though these additions were rather slow, the results are interesting.  They show, making allowance for the greater number of columns (three and a third times as many) required by the binary plan, a saving of nearly half; but they also illustrate the necessity of practice.  This observer succeeded with the binary arithmetic by avoiding the sources of delay that particularly embarrass the beginner, by contenting himself with counting only, and not stopping to divide by two, to set down an unfamiliar character, or to recognize the mark by which he must distinguish his next column.  One well-known member of the Washington Philosophical Society and of the American Association for the Advancement of Science, who declined the actual trial as too severe a task, estimated his probable time with ordinary figures at twenty minutes, with strong chances of a wrong result, after all.