100 YEARS AGO

Owing to very ill-health, I have not been able to make observations of Jupiter during the last few weeks, but have been interested in receiving the results of some other observers. It appears that the great red spot is rapidly accelerating its motion, so that its longitude is decreasing, and with a continuation of this behaviour the spot will ultimately correspond with the position of the zero meridian of system ii. of Crommelin's ephemerides... The variations in the velocity of the spot during the past few years have exhibited a curious oscillation, and it will be important to watch the future developments of the object. It would be interesting to see in NATURE during ensuing months some reports from observers as to whether this singularly durable marking maintains its present rapid westerly drift.

W. F. Denning

From Nature 15 September 1904.

50 YEARS AGO

Obituaries: Dr. A. M. Turing, O.B.E., F.R.S.

...During his first years of research he worked on a number of subjects, including the theory of numbers and quantum mechanics, and started to build a machine for computing the Riemann ζ-function, cutting the gears for it himself. His interest in computing led him to consider what sort of processes could be carried out by a machine: he described a ‘universal’ machine, which, when supplied with suitable instructions, would imitate the behaviour of any other; he was thus able to give a precise definition of ‘computable’, and to show that there are mathematical problems the solution of which are not computable in this sense. The paper which contains these results is typical of Turing's methods: starting from first principles, and using concrete illustrations, he builds up a general and abstract argument. Many years later he used an elaboration of the same ideas to prove the unsolvability of the word problem in semi-groups with cancellation... He was awarded the O.B.E. for the work he did during the War, and after it he was invited by the National Physical Laboratory to direct the design of an electronic digital computor (which he christened “The Automatic Computing Engine”)... while the final construction was in progress he turned to long-term problems, considering how machines might be made to learn by trial and error and the ways in which they could be compared with human brains.

R. O. Gandy

From Nature 18 September 1954.