Variable focus four-part lens US Patent 3 486 809 granted to Jos. Schneider & Co, Gptische Werke Kreiznach, Bad Kreuznach, Germany.

Five-component objective lens US Patent 3 486 810 granted to Perkin-Elmer Corp, Norwalk, Conn., USA .

Optical lens British Patent 1176 659 granted to Hans-Joachim Gasa, Marechal Candidido Rondom, Parana, Brazil

Lens in which one or both surfaces have an elliptical curvature. The design is aimed at giving perfectly focused images free from spherical abberations, colour errors and distortion.

Spectrophotometer British Patent 1 176 902 granted to Smith Kline & French Labs, 1500 Spring Garden St, Philadelphia, USA Spectrophotometer is suitable for determining the concentration of solutes in liquid solvents.

High-speed photography and shock tubes

Conference at University of Liverpool, 6-8 April 1970

THREE INTRODUCTORY PAPERS by L. Davies, R. J. North and J. W. C. Gates (NPL) outlined the basic principles of shock tubes, shock tunnels, and gun tun- nels, and the current practice in photographic and electro-optical recording, with a look ahead for the prospects of employing lasers and holography. Other papers presented some examples of new principles and techniques. J. M. Dewey (University of Victoria, British Columbia) described some elegant work in collaboration with B. T. Whitten on the fundamental parameters in steady and unsteady flow in shock tubes, based on measurements of the trajectories of particles in ten narrow streams of tobacco smoke drawn across the shock tube.

D. S. Bradley, J. S. Higgins Q M. H. Key (Queen’s Uni- versity, Belfast) described a gated image intensifer with a duration of 2ns, triggered by a laser spark gap. The experimental verification of the duration made ingenious use of picosecond laser pulses in a train with 0. 5ns intervals. B. Fontaine, B. Forestier J. Bouesc (Institute de Mecaniques des Fluides, Mar- seille) have developed and applied a high-power argon laser for streak recording of plasma acceleration. R. Hislop (Field Emission UK Ltd) described novel semiconductor light sources emitting a 3ns light pulse, stimulated by a linear electron accelerator.

Most of the remaining papers were concerned with. specific applications. Barr & Stroud/AWRE rotating mirror cameras had been employed by M. Nettleton & R. Knight (CERL, Leatherhead) on burning fuel particles, by J. Douglas (Rolls-Royce Ltd., Derby) to

OSA spring meeting

Philadelphia, USA, 7-10 April 1970

PAPERS AT OPTICAL SOCIETY meetings come in two grades: invited and contributed. A major advant- age in belonging to the first is that the speaker has only to compete with the bar. In the second, up to four papers may be given simultaneously. However, with about 160 of the latter and 16 of the former there is little else that the organisers can do. Some little difficulty was caused by lecture rooms being 17 floors apart! I heard a chosen 25 or so contri- buted papers relevant to my field and felt well satis- fied. To review only these particular papers here would be misleading and invidious. The invited papers

study spark ignition and detonation waves, and by J. H. L. Ranson (Pilkington Bros Ltd, Lathom) to study the shattering of non-uniformly toughened wind- screens. Other framing-camera records presented included some particle combustion studies by J. M. Webster (CEGB, Marchwood) who also gave examples of holographic recording of metal droplets in a plasma.

In the field of shock-tube measurement, W. Wyborny (DFVLR, Germany) described some drag measure- ments on bodies with spikes and the visualization of flow. Efforts by K. Willeke, H. Klingenberg & R. Zichert (Institute fiir Plasmaphysik, Garching, Germany) in building a large non-magnetic Mach- Zehnder interferometer to resist distortion by large pulsed magnetic fields were rewarded by successful streak interferograms of reflected shocks.

Arranged with the aim of stimulating discussion of common ground (mainly optical) between high-speed photographers and shock-tube fluid dynamicists, this meeting produced 25 papers. It contrasted the long- established optical techniques which have been deve- loped to such a high degree of refinement in high- speed recording and measurement with the newer (and often basically simpler) techniques that new light sources and electro-optical systems make pos- sible. Although run on modest lines, the two groups have strong international connections, and overseas visitors came from Belgium, Canada, France, Germany Italy and USA

J. W. C. Gates

were generally of wider interest, given single billing, and maintained a high standard. About half of these were grouped into two symposia.

In the first, on identification of air pollutants, a federal government speaker explained some of the time-scale and pollutant level legislation for the USA in the 1970s pointing out instances where present levels were four times these values. Singled out for early attack were SO, from fuel burning, CO from motor traffic and particulate matter. Four papers dealt with instrumentation to measure these sub-

162 Optics and Laser Technology August 1970