1979 08 15 Applied Optics - Vol 18 No 16 - R W Mankin

Magazine Overview

Title: APPLIED OPTICS
Issue: Vol. 18, No. 16
Date: 15 August 1979
Publisher: Optical Society of America
Country: USA
ISSN: 0003-6935
Price: $2.50

This issue of Applied Optics delves into two primary areas: the potential explanation of unidentified flying objects (UFOs) as natural phenomena, specifically insect swarms, and technical advancements in optical instrumentation, particularly a novel field-widened Michelson spectrometer.

Insects as Unidentified Flying Objects

The lead article, "Insects as unidentified flying objects: author's reply to comments," by R. W. Mankin, addresses the hypothesis that many UFO sightings could be attributed to insect swarms. Mankin builds upon previous discussions, particularly with Kyaw Tha Paw U, to argue that phenomena like St. Elmo's glow or corona discharges from insects can create luminous effects visible under natural conditions. He notes that while these conditions might be unusual, St. Elmo's fire has been reported from various sources. The article explains that a corona discharge from an insect swarm can be visible, and while a DC corona discharge attenuates rapidly, causing a blinking effect, the intensity estimates of such discharges are difficult to obtain from single insect measurements. The author agrees that the insect-swarm hypothesis is plausible, though not yet completely validated.

Mankin references research indicating that insects, particularly in swarms, can be found at high altitudes, forming part of the "aerial plankton" up to 4267 meters (14,000 ft). He cites data suggesting that over one square mile in Louisiana, the air space can contain up to 93 million insects. Radar researchers at NASA Wallops Island Flight Center and USDA engineers are studying these swarms as they appear on radar scopes, noting their tendency to cluster in atmospheric layers. Personal research by Mankin in Pelham, Georgia, involving insect traps on a TV tower, found more insects at higher altitudes during migration seasons. This observation, combined with later UFO sightings in the same area, led to the speculation that the "blobs of light" observed could be lit-up insects.

The article also touches upon the electrical properties of insect scales, suggesting that if sand can light up via triboelectric effects, then insect scales, which are also dielectrics, could do the same when driven by fast jet streams or air currents. The author expresses his personal conviction, aligning with Wesson, that UFOs are likely natural phenomena rather than extraterrestrial craft, citing arguments about the unlikelihood of advanced extraterrestrial civilizations and the unique combination of circumstances required for scientific advancement.

Field-Widened Michelson Spectrometer

Another significant contribution is the article "Field-widened Michelson spectrometer with no moving parts. Part 2" by J. G. Hirschberg and D. F. Cornwell from the University of Miami. This paper details advancements in interferometer design, focusing on a new method for sweeping a two-beam interferometer without any moving parts. This approach aims to overcome the traditional difficulties of implementing such devices, which often require complex and expensive elements for precise motion control and compensation for optical shift.

The proposed concept involves introducing gases of differing refractive indices into the two legs of the interferometer, with pressure equalization maintained by a servo system and flexible membranes. This, combined with additional field-widening of the corrected system, is claimed to yield attractive results with enhanced resolution-luminosity product and simpler operation.

The authors address a critique regarding the original configuration not being fully field-widened, acknowledging that a meridional ray trace verifies significant field curvature in the optical path difference computation. They reference previous work (Steel) that shows how to correct this condition, resulting in a fully field-widened Michelson interferometer with no moving parts. This current letter presents the culmination of these developments, illustrating a scheme (Fig. 1) that replaces a figured beam-splitter cube with a plane beam splitter and a flat mirror. This modification allows for two reflections from a single concave mirror in each leg of the device.

The beam splitter described is a parallel-plate sandwich with antireflection coatings and a 50% reflection/transmission coating at the interface. The analysis, based on tracing a single meridional ray, computes the vacuum optical path length in each interferometer leg to its quadratic dependence upon field angle. The design is intended for applications where collecting optics are off-axis parabolas.

References

The issue includes extensive reference lists for both articles, citing works on ball lightning, insect migration, UFO reports, and optical instrumentation.

Recurring Themes and Editorial Stance

The recurring themes in this issue revolve around the scientific investigation of anomalous phenomena, specifically UFOs, and the advancement of optical measurement techniques. The editorial stance, as expressed by Mankin, leans towards naturalistic explanations for UFO sightings, emphasizing empirical evidence and scientific reasoning over speculative extraterrestrial hypotheses. The inclusion of a detailed technical paper on interferometry highlights the journal's commitment to publishing cutting-edge research in optics and related fields.