As an example of the operation of the Barbour calculator, let us assume that 7894 is to be multiplied by 348. The first drum to the right would be moved by its setting-racks until the series of multiplying racks for adding the multiples of four are presented, the next higher drum to the left would be set until the series of multiplying racks for adding the multiples of nine were presented, the next higher drum would be set for the multiples of eight, and the next higher drum, or the fourth to the left, would be set for the multiples of seven. Then the hand-knob G, first turned to register zero, may be shoved to the right, engaging the pinions f with the gears D, and by turning the knob to register (8), the first figure in the multiplier, the racks are then set ready to move the numeral wheels to register as follows: The drum to the right or the units drum has presented the multiplying rack for adding the multiple of 8 × 4, thus it will present three teeth for the tens wheel and two teeth for the units wheel. The tens drum presenting the rack for adding the multiple of 8 × 9 will present seven teeth for the hundreds wheel and two for the tens wheel. The hundreds drum presenting the rack for adding the multiple of 8 × 8 will present six teeth for the thousands wheel and four for the hundreds wheel. [Illustration] [Illustration: From Drawings of Bollee Patent No. 556,720] The rack of the thousands drum representing the multiple of 8 × 7 will present five teeth for the tens of thousands wheel and six for the thousands wheel. Thus by sliding the carriage to the right one space, the numeral wheel pinions will engage first the units teeth on one drum, then the tens teeth on the next lower drum and cause the wheels to register 63152. The operator, by turning the knob G to register (4), the next figure of the multiplier, turns the drum so that a series of multiplying racks representing multiples of 4 times each figure in the multiplicand are presented, so that by sliding the carriage another space to the right, the multiple of 4 × 7894 will be added to the numeral wheels. The operator then turns the knob to register three and moves the carriage one more space to the right, adding the multiple of 3 × 7894 to the wheels in the next higher ordinal series, resulting in the answer of 2747112. There are, of course, many questionable features about the construction shown in the machine of the Barbour patent, but as a feature of historic interest it is worthy of consideration, like many other attempts in the early Art. THE BOLLEE MULTIPLIER Probably the first successful direct multiplying machine was made by Leon Bollee, a Frenchman, who patented his invention in France in 1889. A patent on the Bollee machine was applied for in this country and was issued March 17, 1896, some of the drawings of which are reproduced on the opposite page. [Sidenote: _Description of Bollee Machine_]