casionally it would have put up the signal:—'Data incompatible with each other.' The machine was, however, not completed; it is kept in the Mathematical Department of the South Kensington Museum. Babbage's book and pamphlets, more valuable than the machine would ever have been, are practically unknown to the majority of the scientific world.
George Boole. My husband carried out Babbage's idea by means, not of a machine, but of a self-acting algebraic notation, which automatically produces the symbol for 'insufficient data' (), and that for 'these conditions are incompatible in the sphere of human consciousness' (). He also carried out into other automatic notations Babbage's suggestions about the psychological value of certain traditional opinions on metaphysical subjects. The notations adopted by him have been used in the application of mathematics to the Physical Sciences; the use of them for this purpose would be largely facilitated if mathematical teachers had any clear idea of their meaning and origin. His books are still used in Germany and Austro-Hungary for educational purposes. In England they have been superseded by others in which the same notations are employed, but in a manner which tends to conceal their
