100 YEARS AGO

Suppose I toss a penny, and let it fall on the table. You will agree that the face of the penny which looks upwards is determined by chance, and that with a symmetrical penny it is an even chance whether the “head” face or the “tail” face lies uppermost. For the moment, that is all one can say about the result. Now compare this with the statements we can make about other moving bodies. You will find it stated, in any almanac, that there will be a total eclipse of the moon on December 27, and that the eclipse will become total at Greenwich at 10.57 p.m.; and I imagine you will all feel sure on reading that statement, that when December 27 comes the eclipse will occur; and it will become total at 10.57 p.m. It will not become total at 10.50 p.m., and it will not wait until 11.0 p.m.You will say, therefore, that eclipses of the moon do not occur by chance. What is the difference between these two events, of which we say that one happens by chance, and the other does not? The difference is simply a difference of degree in our knowledge of the conditions. The laws of motion are as true of moving pence as they are of moving planets⃛

From Nature 22 September 1898.

50 YEARS AGO

That Newton had a just appreciation of the work of Huygens and fully understood it is significant, because Huygens signally failed to comprehend Newton's full achievement, although he realized Newton's greatness as a mathematician and as an experimenter. He criticized Newton's fundamental work on colour because it did not explain the ultimate nature of colour — “Besides, if it should be true that the rays of light, in their original state, were some red, others blue, etc., there would still remain the great difficulty of explaining, by mechanical principles, in what consists this diversity of colours”. He did not understand Newton's “But to examine how Colors may be explained hypothetically is beyond my purpose”. Huygens himself wrote little about colour, since the problem as he conceived it, to find a mechanical explanation, seemed to him intractable. ⃛ To say this is not to disparage Huygens, whose fundamental achievements make a formidable list.

From Nature 25 September 1948.