SAMWORTH'S SNIPPETS

Observation skills of the Victorians

by Mike Samworth

One thing that always amazes me when looking through my favourite old microscopy books is the quality of the hand-drawn plates. There is no better example of this than the plates in 'Micrographic Dictionary' by Griffiths and Henfrey. My copy is the fourth edition, dating from 1883. Not only is this such skilled draughtmanship but also a testament to their powers of observation. It also illustrates the quality of the microscopes they used all those years ago.

In the case of the plate shown, sperms from different species, we only have to think of the size of these cells to appreciate that we are talking about observations carried out at high magnifications. It is interesting to speculate on how accurate these diagrams are when compared with images taken on more modern, sophisticated instruments today, and especially since the advent of the electron microscope of course which has contributed much to the study of sperm. The similarities and differences between sperm of different species is something worth contemplating. It is a sort of variation on a general theme and the fact that the organisms can be so disimilar in other ways is an example perhaps of both convergent and divergent evolution of different parts within the same organism.

Snowflakes are dancing

The Snowflake is almost recognised by everyone and epitomises the beauty that is revealed when small objects are looked at more closely. Indeed the Royal Microscopical Society has a snowflake as it's emblem. Every snowflake has a unique history, and though they all share the six-pointed symmetry, no two are alike.

It is the beauty and quality of the individual snowflake that seems to attract our fascination. Knowledge of the hexagonal character of snowflake crystals has a long history. Indeed there in a book written by Han Ying in about 135 BC there is a clear statement that 'flowers of snow are always six-pointed'. One of the earliest European students was the 13th Century scholar Albertus Magnus who commented on their star-like nature. Two centuries later woodcuts were published that showed 23 varieties of snowflake.

A well-known Scientist, Johannes Kepler wrote a lengthy study in 1611 that not only perceived the hexagonal nature but also tried to explain it on an atomistic basis. He was not wholly successful, but his intuition was later proved true. Other famous Scientists led their weight to further study, including Descartes and the 17th century microscopist Robert Hooke.

Towards the end of the 19th century, the development of photography opened up new possibilities for observation. A farmer from Vermont, W A Bently, obtained some 5,000 pictures over 40 successive winters. Many of these were published in his 1931 book 'Snow Crystals'.

Ice crystals are formed from water droplets at certain temperatures when they come into contact with 'nucleating agents' such as tiny dust particles which trigger the crystallisation process. So how can we explain their similarities and their differences? Well, all water molecules form six-sided structures as they freeze, and snow crystals are symmetrical because all six sides are affected simultaneously by conditions in the cloud. Growing outwards from the central dust particle, the unique shape of each flake is determined by the shape of that particle and the conditions under which the flake forms.

I was inspired to write this article by attending a lecture on photomicrography of snowflakes recently and by the large amount of snow we had just before and during Christmas this year. Why not give it a go for yourself? For details of techniques contact me Mike Samworth.

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