RECOLLECTIONS AND REFLECTIONS
light valuable results ". My personal relations with him when I was a student are a very pleasant recollection ; he was always very kind to me, had a winning way with him and a charming smile.
My first introduction to physics was when I attended in my second year at Owens the lectures on Elementary-Physics given by Professor Balfour Stewart; these I found very attractive and so clear that, young as I was, I had' no difficulty in understanding them. He looked a very old man ; his hair was quite white, and I was very much surprised when I was told he was only forty-three. Quite at the beginning of his work at Owens he had been badly injured in a terrible railway accident, one of the worst on record, at Abergele, North Wales. After about a year he was able to resume work, and though he looked so much older his mind was as clear and vigorous as before. When a young man, he had been assistant to Professor David Forbes at Edinburgh, and it was while at Edinburgh that he made his most important contribution to physics—the relation between the radiation and the absorption of radiation. In a paper published in the Edinburgh Transactions vol. xxii. p. i, March 1858, he enunciated the important principle that in any enclosure bounded by opaque walls, the radiation from any body of any kind of light must, when the temperature throughout the enclosure is uniform, be equal to the absorption of the same kind of light by the body. Thus, if the body gives out light of a particular wave-length it will absorb light of that wave-length, or if a body like a plate of tourmaline absorbs light polarised in one plane, it will, when radiating, give out light polarised in one plane. The same principle was published about a year and a half later by KirchhofT, to whom it is gener-
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