From the introduction:
"The original project of producing an Atlas of all the diatoms to be found in the British Isles was the idea of the late Horace G. Barber, one of the foremost diatomists in the country. In addition to being a diatomist of some note Horace Barber was also an accomplished artist. He has brought together both these skills in this present for us to appreciate. Over a period of some forty years, he was assisted in this work by three diatom colleagues, Robert I. Firth, John R. Carter and Bernard Hartley, who corresponded with each other, exchanged material and slides, and discussed problems of taxonomy and allied matters. At the time of his death, the work consisted of some 299 plates containing 6332 detailed illustrations, all drawn to a scale of ×1900. Horace Barber's illustrations were also circulated for comments to many diatomists including Norman Hendey, Elizabeth Haworth, Klaus-D. Kemp, T. Barrie Paddock and Patricia A. Sims.
It is to be emphasised that Horace Barber had actually seen all these forms, and that none were copied from the work of previous illustrators. The manuscript and plates were generously presented to the British Natural History Museum by Mrs Gwen Barber, as Horace Barber had often intimated that he would like his work to be of use to posterity. At a later date the Museum staff invited Bernard Hartley to reorganize this unique collection of drawings and arrange them in generic and specific order – a formidable task which has taken two years to complete. Account has also been taken of the many taxonomic revisions which have taken place in the last ten years.
John Carter assisted in this work of revision and prepared a further 600 detailed line drawings to the same scale to supplement those species which had not been included in the original work. Both Horace Barber and John Carter used microscopes with first-class oil immersion objectives (1.3 apochromatic) and on John Carter’s microscope, an oil immersion condenser. Horace Barber worked to an upper limit of resolution of 30 striae/puncta in 10 μm and John Carter using very high magnification eyepieces could discern up to 50 striae in 10 μm. Both were superb microscopists who could adjust their microscopes to give the optimum resolution. Neither used a camera lucida for drawing, but each made meticulous measurements of the diatom, using an eyepiece graticule which had previously been calibrated against a stage micrometer. After first drawing the outline of the diatom within the measured frame, the further details of striae pattern, raphe features and other particulars were added gradually and meticulously to each drawing.
It will be appreciated that line drawings are often more useful than photographs in the recognition of species. They represent more nearly what the eye sees of an organism, the identification of which depends on the recognition of sculpturing and pattern which owing to the curvature of many valves requires careful focussing of the valve sides and especially of the apices. This is particularly so in the recognition of very small taxa where limitations of photographic reproduction in printed works often prevent the illustration being of any value whatsoever. A further point is that the eye will accommodate different depths of focus whereas the lens performance is limited.
The marine planktonic species have not been included as these were not readily available to the authors. As we go to press a large work on marine planktonic diatoms has just appeared (Hasle & Syvertsen 1996). The work now completed contains 6152 detailed illustrations covering almost all known forms of British freshwater, brackish and littoral marine species. The majority of diatom species have been recorded in the literature as cosmopolitan and therefore this Atlas, although illustrated solely from British collections, is valuable to students world-wide. However, it is now apparent that "cosmopolitan" is an unfortunate designation and workers will find that specimens deviating from the forms illustrated are likely to be new, undescribed diatoms. The fact that experienced workers such as Horace Barber and John Carter also illustrated some species but were unable to name them shows the wealth of forms yet to be described – a fact which should encourage workers relying on light microscopy to expand our knowledge of diatoms – the biogeography and biodiversity of which is hardly known.
The collections and manuscripts of the late Horace Barber and John Carter are housed in The Natural History Museum, London, and slides of individual British species of diatoms mounted by Robert Firth and Bernard Hartley are kept as a separate reference collection in the Diatom Section at the Museum."