Editorial
Aragonite - CaCO3 - Orthorhombic crystal which exhibits strong double refraction. Pseudohexagonal twins often found in Aragon, Spain. So says the Field Guide to Rocks and Minerals but what has this to do with the AGM lectures presented at Leeds University on 29th October?
It was this material which Humphrey Lloyd used in 1833 to demonstrate conical refraction which had been so surprisingly predicted by William Rowan Hamilton. As Lloyd himself said:
'here then are two singular and unexpected consequences of the undulatory theory, not only unsupported by any phenomena hitherto noticed, but even opposed to all the analogies derived from experience'.
By a curious piece of editorial serendipity it was also the material whose structure was defined nearly 100 years later by William Lawrence Bragg which according to Hunter* 'broke the sound barrier of x-ray analysis' since up to 1923 as Bragg pointed out:
'it was considered practically impossible to analyse crystals of lower symmetry than cubic, tetragonal or hexagonal'.
But such analytical techniques were essential to the continuing development of x-ray crystallography and it was again at Leeds where great progress was made in the emergent field of molecular biology, specifically with regard to the relationship of molecular structure with gross physical properties of natural polymers, by William Astbury. Although the term 'molecular biology' was not coined until 1938 it is interesting to note that 10 years earlier he had been appointed as Lecturer in Textile Physics which concerned itself very much with these questions.
And many answers were forthcoming from our three speakers as well as yet more questions posed - a thoroughly enjoyable afternoon which was introduced by our host, John Lydon, with a bonus 'armchair science heritage tour of Leeds'.
Malcolm Cooper
* Light is a Messenger by Graeme K Hunter - See Issue 18 for a review