Bournemouth Natural Science Society

Joint meeting with the Quekett Microscopical Club

Saturday 25th July 2020

NOT FINISHED – More words and photos to be added

This meeting was scheduled to be held in Bournemouth in the Lecture Hall of the Victorian building that houses the Bournemouth Natural Science Society, but was instead held online using Zoom, because of the COVID-19 epidemic. Paul Smith and Grenham Ireland managed the technical side, and Grenham managed the participants. Details had been e-mailed to BNSS and Quekett members in advance so that they could prepare their presentations.

Quekett members can watch the video of the meeting.

Jeremy Poole informed and entertained us with videos of diatoms moving, illustrations of the structure of a pennate diatom, valve and girdle views of a centric diatom, SEMs of the diatom frustule, diagrams of vegetative and sexual reproduction, SEMs of frustules, SEMs of marine diatoms, old and new theories on how diatoms move, and diatoms in art. You can see Jeremy’s slides in this PowerPoint:


Click the arrows to move through the slides. Click the symbol at bottom right for a larger version.

Pam Hamer wanted to demonstrate that rock samples can be polished flat on one side with simple equipment and then observed and photographed with a simple stereomicroscope.

Tools for polishing rocksTools for polishing rocks

Unpolished rockUnpolished rock

Pam polishes rocks in 3 stages, with increasingly fine abrasives. For the first stage, she uses Rolson 24252 Diamond Whetsones.

Polishing rock with diamond whetstonePolishing rock with diamond whetstone

For the second stage, Pam uses Wilko wet and dry sandpaper.

Polishing rock with sandpaperPolishing rock with sandpaper

For the final stage, Pam uses T-Cut Rapid Scratch Remover applied with felt.

Polishing rock with scratch removerPolishing rock with scratch remover

Polished rockPolished rock

The following photographs of rock inclusions and polished rocks were taken using a simple digital camera (Brunel Digital Eyecam) and the small stereomicroscope shown in Pam’s first photo.

Inclusion in polished rockInclusion in polished rock

Inclusion in polished rockInclusion in polished rock

Inclusions in polished rockInclusions in polished rock

Inclusions in polished rockInclusions in polished rock

Polished rock

Polished rockPolished rock

Rock sections are normally ground to a standard thickness of 30 µm, a process that needs specialist equipment. Pam had been experimenting with her polishing technique and had managed to produce sections that provided useful information, although they were not even and not very thin. She polishes one surface and then glues that surface to a slide. Then she polishes the other side of the section as thin as she can.

Rock sectionRock section

Pam’s images are all in a new leaflet that will be given away at outreach events to encourage youngsters and families to use microscopes. The leaflet will also be available as a free download.

Chris Thomas told us that his children once had head lice (Pediculus humanus capitis) when they were young, and that his wife kept specimens for him. Under the microscope, he could see their claws that enable them to move easily along hairs.

Head louseHead louse

The muscles in mounted specimens of head lice appear bright under polarised light:

Head louse (crossed polarisers)Head louse (crossed polarisers)

Adding a retarder changes the colours in the specimen and the background, and rotating the retarder changes the colours.

Head louse (crossed polarisers plus retarder)Head louse (crossed polarisers plus retarder)

Chris showed a PowerPoint presentation with several slides to show how polarising filters only allow light waves with a precise orientation to pass through, so that 2 polarising filters at right angles block almost all light, a condition called extinction. When a specimen that exhibits birefringence is placed between the crossed polarisers, it changes the orientation of some light waves so that they pass through the second polariser; birefringent parts of the specimen thus become visible and may also be coloured. Adding a retarder (also known as a wave plate) changes the colour of the background and parts of the specimen. Rotating the specimen and/or one of the polarisers and/or the retarder changes the colours and the affected parts of the specimen. You can see Chris’s slides in this PowerPoint:


Click the arrows to move through the slides. Click the symbol at bottom right for a larger version.

Chris wanted to produce a stacked image for improved depth of field, but he also wanted to capture the different colours. To do this, he took more than the usual one photo at each focus point, rotating the retarder to vary the colours. He then combined all of the photos in his stacking software.

Graham Matthews has recently been investigating the invertebrates that can be found in leaf litter at Warnham Local Nature Reserve. He explained the equipment that he uses to collect, prepare and observe the specimens, and showed us examples of the springtails, beetles, mites, spiders and pseudoscorpions that he has collected.


Click the arrows to move through the slides. Click the symbol at bottom right for a larger version.

Alan Wood gave an introduction to polarised light microscopy, explaining the minimum equipment that is needed (2 polarisers) and showing some of the colourful results that can be obtained. You can see Alan’s photographs and notes in this PowerPoint:


Click the arrows to move through the slides. Click the symbol at bottom right for a larger version.

Alan then switched to a live view through his Olympus BH-2 microscope (using a Canon EOS digital SLR controlled by EOS Utility) and showed how to rotate one polariser to achieve extinction (the darkest image) on a clear part of the slide. Then he moved the specimen (a thin rock section) into view to show the colours produced by crossed polarisers, and showed how they change when the slide is rotated. Then he added a retarder on top of the polariser to show how it changes the background and foreground colours, and showed the effect of rotating the specimen, the polariser and the retarder.

Thin section of sillimanite with crossed polarisers and a retarderThin section of sillimanite (crossed polarisers plus retarder)

He repeated the process with a slide of a mosquito larva and showed how polarised light produces colours in the muscles.

Muscles in mosquito larva (crossed polarisers plus retarder)Muscles in mosquito larva (crossed polarisers plus retarder)

Steve Limburn, 17th century Wilson microscope

Gordon Brown recommended a mica window (available on eBay) as a retarder; he had obtained better results than with plastic films. He had obtained interesting results by holding the mica window at an angle instead of horizontal, supporting it with Soldering Helping Hands (available on eBay).

Soldering Helping HandSoldering Helping Hands

Gordon also showed an annular mount for holding plastic film retarder, similar to the one that Alan showed in his PowerPoint presentation. They are easy to make from thin card (Gordon uses 300 gsm paper, Alan uses Kellog’s Corn Flakes packets) using a compass cutter (available on eBay or from craft shops). The clear central area is large enough to cover the light outlet on the base of the microscope, and the annulus is about 10 mm wide to make the mount easy to handle and reasonably stiff.

Compass cutter and annular card mounts for retardersCompass cutter and annular card mounts for retarders

Tony Pattinson showed some photomicrographs of copepods with eggs, using dark ground illumination provided by an LED ring light instead of a condenser. He simultaneously used crossed polarisers plus coloured filters or a wave plate (also known as a retarder) on top of the polariser. The crossed polarisers make all of the muscles appear brighter.

Copepod with eggs (dark ground plus crossed polarisers)Copepod with eggs (dark ground plus crossed polarisers)

By using coloured filters on top of the polariser, and rotating the polariser, Tony found that he could brighten up all of the muscles with coloured light.

Copepod with eggs (dark ground plus crossed polarisers and green filter)Copepod with eggs (dark ground plus crossed polarisers and green filter)

Copepod with eggs (dark ground plus crossed polarisers and magenta filter)Copepod with eggs (dark ground plus crossed polarisers and magenta filter)

Copepod with eggs (dark ground plus crossed polarisers and green filter)Copepod with eggs (dark ground plus crossed polarisers and green filter)

Copepod with eggs (dark ground plus crossed polarisers and red filter)Copepod with eggs (dark ground plus crossed polarisers and red filter)

Copepods with eggs (dark ground plus crossed polarisers and red filter)Copepods with eggs (dark ground plus crossed polarisers and red filter)

Using a wave plate (with no coloured filters) produces colours in the muscles that depend on the direction of the muscles. The colours can be changed by rotating the wave plate.

Copepods with eggs (dark ground plus crossed polarisers and retarder)Copepods with eggs (dark ground plus crossed polarisers and wave plate)

Robert Ratford, in response to a question about lowering coverslips onto mountant without trapping air bubbles, recommended a vacuum pen (available on eBay) for picking up and releasing coverslips.

Handi-Vac with suction headsHandi-Vac with suction heads

Lecture by Prof. Pippa Hawes, Head of Imaging, Pirbright Institute entitled:

“Studying the cell biology of virus-host interactions with light and electron microscopy”

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