MAGNETIC ORIENTATION OF AMPHIBOLE FIBRES
Amphibole fibres have been exposed to a unitbrm magnetic field while suspended in a dilute solution of celloidin in amyl acetate. The solvent was allowed to evaporate while the field was maintained so as to obtain a coherent film of magnetically oriented fibres bonded together by celloidin. X-ray-diffraction patterns were then recorded in transmission geometry, and the orientation of the fibrils around their fibre axis was determined. The fibres are oriented in azimuth as well as lengthwise, though those that align normal to the field show a much more restricted range of azimuthal orientations than those that align parallel to the field. Crystallographic control of the principal maguetic axes is discussed; the orientation properties are not fully explained, but their attribution to magretite present in bulk samples is rejected.
Structural imperfection and morphology of crocidolite (blue asbestos)
ELECTRON microscopic studies of fibrous materials, including a range of chain silicates1–6, synthetic polymers7 and carbon fibres8, have almost exclusively involved examination of the structural characteristics visible when the fibre axis is perpendicular to the electron beam. It is extremely difficult to prepare ultra-thin sections of fibrous samples such that this axis is parallel to the beam; and yet it is in this projection that the greatest insights into structural and morphological irregularities are likely to be achieved, a fact well illustrated by the high-resolution studies of Yada9 on chrysotile asbestos which, being less brittle than crocidolite and other amphiboles, was amenable to the normal techniques of ultra-microtomy. We present here preliminary results of a successful axial study of crocidolite (blue asbestos), the fibrous form of the amphibole mineral riebeckite (idealised formula Na2Fe5(Si4O11)2(OH)2, space group C2/m, a = 0.973, b = 1.806, c = 0.533 nm, β = 103.3°). The electron micrographs reveal several novel features.
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.