Capt. Rice D. Knight, ca. 1829 – 1885
and his 1871 Quest for Unmounted Diatoms

by Brian Stevenson
last updated May, 2015

One frequently comes across historical items that, at first glance, look very unremarkable. But, as one learns of that item’s origins, it turns out to have a fascinating history. One such artifact is the slide illustrated in Figure 1. It is a plain, home-made looking microscope slide of poorly-arranged diatoms, made by a "Capt. Knight". As I researched the slide’s maker, I discovered some interesting stories about amateur microscopy in the Victorian era. In particular, it was often very difficult for a non-professional mounter to acquire diatoms in order to make his own slides. Details in the following essay are largely culled from letters by and about Captain Knight.

Figure 1. A microscope slide of arranged diatoms, by Captain Rice D. Knight. The slide presumably dates from between 1871 and 1885.


Figure 2. Another microscope slide that was evidently produced by R.D. Knight. The typeset label suggests that it was produced after the slide shown in Figure 1. Adapted from an internet acution site for nonprofit, educational purposes.


The stimulus for Knight’s hunt for unmounted diatoms came from an October, 1870, presentation made to the Reading Microscopical Society by its President, Captain Frederick H. Lang (1816 - 1892). Lang’s paper, On Selecting and Mounting Diatoms, appears to have been widely distributed throughout the popular scientific press. Lang prefaced his article with a suggestion that microscopists should produce slides of only selected diatoms, as opposed to mixed strews, “in the very last year of the late Dr. Arnott's life, I heard him say that were he to commence a fresh collection of diatomaceae he would admit none but perfectly pure and unmixed gatherings into his cabinet... But if pure gatherings of all species cannot be obtained, it is now comparatively easy to pick out those that are required from the general mass; and it is a matter of wonder to me that this has not been more generally attempted, for I am not aware of a single collection of the kind, with the exception of that which Eulenstein is now making for his subscribers. Selected diatoms of the more showy sort are occasionally to be obtained at the opticians, even arranged in patterns as pretty ‘Oh law’ objects for the microscope; but I would fain induce our members, and others also, to isolate and mount on separate slides every diatom, common or rare, that is to be procured in their own locality, or in gatherings from elsewhere; for if every one would set to work to do this, we should soon be in the possession of a complete series of really instructive slides of the diatomaceae. The object of my paper this evening is not only to insist upon the advantages of this plan, but to render the task easier by giving you the benefit of my own experience, reaped through many failures, in selecting and mounting these exquisitely delicate and beautiful forms.

Lang then went on to describe methods he had learned by which one could select and mount individual diatoms. The article ends with “In conclusion, I will only remark that though perhaps none of us can hope to equal Möller's beautiful type-slide, with which we are so well acquainted, I do trust that the time is not far distant when the diatomists of this country will be able, each of them, to make type-slides of the prevailing species of their own localities, arranged according to some acknowledged synopsis; for thus alone can a sound knowledge, of these organisms be obtained, the vast number of synonyms be reduced, order replace the present chaotic confusion, and the pursuit converted into a regular science.

Captain Knight was obviously intrigued by the Lang’s article, and sought out unmounted diatoms, so that he might try his hand at mounting them. He was met with frustration, as raw diatoms from locations outside his immediate neighborhood proved to be impossible for him to acquire. In the April, 1871, issue of The Monthly Microscopical Journal - Transactions of the Royal Microscopical Society, Knight lamented “At present, among amateurs, there exists much difficulty in getting material which shall contain a great variety of species and genera. You may make gathering after gathering in your own neighbourhood, but though you may make a large collection of material, which you could not use up in your lifetime, your gatherings would very likely contain but multitudinous repetitions of the same class of diatoms…Diatomaceous material, either prepared or unprepared, cannot, as far as I am aware, be bought unmounted, whether it be of British or foreign genera; and the present mode of exchanges amongst amateurs, carried out through the exchange columns of different journals, is unsatisfactory in the extreme, as one can never know what kind of rubbish he may have sent him in the way of barter.”

As modern students of Victorian era microscopy well know, professional mounters produced large numbers of slides, containing wide varieties of diatoms from far-off lands. One would assume that amateurs would also have access to those vast supplies of exotic diatoms. However, Knight states “the professional preparers will not sell material in even the smallest quantities. It seems almost incredible, but let the following statement, which I vouch for as fact, speak for itself, and you will see, that though to prepare a mixed slide for the market the preparer has to put a certain sized dip of material on a glass slide and evaporate it, if you ask him to stop the process there, and sell you that slide for a shilling—the same price, mind you, that he will ask for it when it is completely mounted and ready for the market—he will not sell it you. No! He will cover it with Canada balsam and a glass, he will clean off the superfluous material, and perhaps take the trouble of putting on a ring of cement, and when he has thus spoilt it for the purposes for which you want it, he will offer it you for a shilling. This is precisely what happened to me. I offered to a well-known preparer of microscopic objects, whose name I will not mention, a shilling a-piece for a single dip - the ordinary quantity put on a slide - each of certain deposits from which I wanted to select forms myself for my own cabinet, and he refused to let me have them. I thought I should succeed in my object by ordering some of these preparations mounted dry, and by melting the cement and removing the cover I could get what I wanted. But do you think I was allowed to have them? No! It is usual to mount them in balsam, and in balsam I must take them, or go without. There is a certain class of diatoms only, that the mounters put up dry for the market, and from these only are you allowed to select. Foiled in my first attempt, I made application to another equally well-known mounter, and I should like to publish his name, because he did at any rate write me a very civil letter in reply, showing me that it was not his fault that he could not comply with my request, but as I have not his authority to do so, and he might not like it, I refrain from doing so; but I give the text of his letter, as I think it may be interesting. He says: ‘Sir, I beg to assure you that I have not forgotten or neglected to notice your letter of the 14th instant, but have given to it frequent thought. I regret that I cannot comply with your wish, from various causes. Many of those diatoms are not my own mounting, and those who have the material would not listen to your wishes, I am sure, however reasonable they may seem. If I were to try, it would take me immense labour to write a long letter to each of twenty persons, perhaps, which ten out of twenty would not understand, and would not reply to; and the few who might comply would be almost sure to send something not pleasing to you. If you go one inch out of the daily beaten track every obstacle is thrown in the way, and everything that is possible is done wrong. If I could get you twenty dips the time alone would be worth 20s. With thanks, I am, &c’.

With professional mounters refusing to provide raw diatoms, and exchanges with other amateurs through the post frequently resulting in junk, Knight made some proposals. Chief among these was a suggestion that “in London, or in such a town as Liverpool, where ships are daily coming in from all parts of the world, I am sure it would pay an optician, as a business speculation, to order a quantity of diatomaceous deposits and foraminiferous sands, &c., &c. The localities where they are to be obtained are perfectly well known; the price of the raw material in those places is little more than the cost of labour in collecting them. The freight of a few hundredweights would be trifling, and they could be sold, either prepared or unprepared, at two or three hundred per cent, profit, and if properly advertised, and if notification of the fact of their being on sale were sent to all the Secretaries of Microscopical Societies in England, I venture to say the deposits would not remain long on hand…Can you or any of your readers suggest a better mode of obtaining material, by which so many more of us might be able to profit by Captain Lang's happy discovery? If not, can you assist in carrying this out?” Knight ended his letter with a complaint that he had written to the Secretary of the Liverpool Microscopical Society about obtaining some Californian shell-washings thought to be available in that city, but the gentleman had never written back, and had even kept the stamped reply envelope Knight had posted to him. I do not know whether or not Knight’s scheme ever took off, but judging from the tone of his letter, he was unlikely to have led a venture to import raw diatoms en masse.

More likely, he finally acquired his diatoms by using tips that were provided by Capt. Lang in a subsequent paper. In the October, 1871 issue of The Monthly Microscopical Journal-Transactions of the Royal Microscopical Society, Lang presented “Another Hint on Selecting and Mounting Diatoms.” In a nutshell, Lang described methods by which he removes diatoms from balsam-mounted slides, by melting the balsam on a hot plate, then suspending the diatoms by addition of turpentine. “By this simple and easy method we can not only select from balsam-mounted gatherings any particular valves we may require, but we can reset any spoilt or unsatisfactory mounts of our own.

As the slide shown in Figs. 1 and 2 demonstrates, Captain Knight managed to acquire many varieties of diatom species, probably by breaking up some professionally-made slides he had purchased. The current state of the diatoms is shown in Fig. 3. Quite a few tests are out of place, either from drifting over the past 140 years, or from being originally misaligned. There is also an air bubble in the mountant, visible to the lower right of the picture. Knight’s slide was probably never anywhere the quality of a Möller, but I am certain he had fun making this slide. Knight was a true amateur microscopist, his life history suggests that he never tried to prepare slides professionally. This and any other slides with his name were probably made for his own enjoyment, then either kept or exchanged with colleagues.

Captain Rice Davies Knight was born in approximately 1829 in Bareilly, India (now in the state of Uttar Pradesh), the son of a British surgeon of the same name. Both the father’s and the son’s first names are spelled “Rice” on all records, presumably a corruption of the Welsh name Rhys. The earliest historical record I found on the son was from 18 December, 1858, when “Rice D. Knight, Gent., late Captain in the 98th Regiment of Foot” was commissioned Adjutant of the 2nd Regiment, Warwickshire Militia. In 1861, the unmarried Captain lived as a lodger. Sometime around 1864, Knight married a woman named Mary, 16 years his junior, who had also been born in India. The couple then settled into what appear to have been nice Warwickshire houses and proceeded to make a large family. By 1871, they had 6 children, aged evenly 1 through 6. By 1881, Knight had retired at the rank of Lieutenant Colonel, Mary was an “Artist” and the “Principal of a Ladies School”, and they had 8 children at home. Fate took a bad turn for the family, when Rice Knight died in 1885, at the age of 56. The next census, in 1891, recorded Mary and four of the children as living on Townsend Road, Tottenham, Middlesex, with Mary being a “Music Artiste”.

Figure 3. Magnified detail of the Knight diatom slide shown in Fig. 1. Photographed using an Olympus BX51 microscope, 4x objective lens, dark field illumination and a Retiga 2000R Fast 1394 with QCapture Pro software.



Bulletins and Other State Intelligence (1858) Commission signed by the Queen, page 106

Colburn’s United Service Magazine & Naval and Military Journal (1859) part II, page 149

East India Register & Directory, corrected to the 8th September (1814) Bengal marriages, May, 1813, Rice D. Knight, Esq. (Asst. Surgeon) to Miss C. L. Overbeck

England vital statistics, accessed through

Lang, Frederick H. (1870) “On Selecting and Mounting Diatoms”, reprinted in English Mechanic and World of Science, vol. 12, pages 270-271

Lang, Frederick H. (1871) “Another Hint on Selecting and Mounting Diatoms”, The Monthly Microscopical Journal - Transactions of the Royal Microscopical Society, vol. 6, pages 215-216

Knight, Rice D. (1871) “A Proposal As To Diatoms”, The Monthly Microscopical Journal - Transactions of the Royal Microscopical Society, vol. 5, pages 190-193