100 YEARS AGO

An automatic telephone exchange system, which does away with the necessity for the staff of skilled operators at present exquired at exchanges, is being introduced into this country from the United States by the Direct Telephone Exchange Syndicate. Instead of ringing up the central station, requesting the attendant to put him in communication with the person to whom he wishes to speak, and waiting while the required alterations are made on the switch-board, the subscriber to an exchange worked on the automatic plan is himself able to connect his telephone with that of any other subscriber without the intervention of a third person. Each subscriber has upon the front of his instrument a circular disc pivoted at the centre, and having one-half of its circumference inscribed with figures from to 0 to 9. If he wishes to communicate with another, he sets the disc so that the number of the other subscriber appears upon the dial, and he then finds his telephone in circuit with that of the person whose number he has indicated by his disc. When he has finished his conversation he simply hangs his receiver on its hook. Immediately, the switch which represents him at the exchange returns to its normal position, and communication is cut off.

From Nature 12 May 1898.

50 YEARS AGO

It is known that the spherical aberration of electron lenses sets a limit to the resolving power of electron microscopes at about 5 A. ⃛ The new microscopic principle described below offers a way around this difficulty, as it allows one to dispense altogether with electron objectives. Micrographs are obtained in a two-step process, by electronic analysis, followed by optical synthesis, as in Sir Lawrence Bragg's ‘X-ray microscope’. But while the ‘X-ray microscope’ is applicable only in very special cases, where the phases are known beforehand, the new principle provides a complete record of amplitudes and phases in one diagram ⃛ It is a striking property of these diagrams that they constitute records of three-dimensional as well as of plane objects. One plane after another of extended objects can be observed in the microscope, just as if the object were really in position. — D. Gabor.

From Nature 15 May 1948.