Part 9

Hales' belief that plants draw part of their food from the air, and again, that air is the breath of life, of vegetables as well as of animals (p. 148), are based upon a series of chemical experiments performed by himself. Not being satisfied with what he knew of the relation between "air" (by which he meant gas) and the solid bodies in which he supposed gases to be fixed, he delayed the publication of _Vegetable Staticks_ for some two years, and carried out the series of observations which are mentioned in his title-page as "An attempt to analyse the air, by a great variety of chymio-statical experiments," occupying 162 pages of his book. {133}

The theme of his inquiry he takes (_Vegetable Staticks_, p. 165) from "the illustrious Sir _Isaac Newton_," who believed that "dense bodies by fermentation rarify into several sorts of Air; and this Air by fermentation, and sometimes without it, returns into dense bodies."

Hales' method consisted in heating a variety of substances, _e.g._ wheat-grains, pease, wood, hog's blood, fallow-deer's horn, oyster-shells, red-lead, gold, etc., and measuring the "air" given off from them. He also tried the effect of acid on iron filings, oyster-shells, etc. In the true spirit of experiment he began by strongly heating his retorts (one of which was a musket barrel) to make sure that no air arose from them. It is not evident to me why he continued at this subject so long. He had no means of distinguishing one gas from another, and almost the only quality noted is a want of permanence, _e.g._ when the CO2 produced was dissolved by the water over which he collected it. Sir E. Thorpe {134a} points out that Hales must have prepared hydrogen, carbonic acid, carbonic oxide, sulphur dioxide, and marsh gas. It may, I think, be said that Hales deserved the title usually given to Priestley, viz. "the father of pneumatic {134b} chemistry."

Perhaps the most interesting experiment made by Hales is the heating of minium (red-lead) with the production of oxygen. It proves that he knew, as Boyle, Hooke and Mayow did before him, that a body gains weight in oxidation. Thus Hales remarks: "That the sulphurous and aereal particles of the fire are lodged in many of those bodies which it acts upon, and thereby considerably augments their weight, is very evident in Minium or Red Lead, which is observed to increase in weight in undergoing the action of the fire. The acquired redness of the Minium indicating the addition of plenty of sulphur in the operation." He also speaks of the gas distilled from minium, and remarks: "It was doubtless this quantity of air in the Minium which burst the hermetically sealed glasses of the excellent _Mr. Boyle_, when he heated the Minium contained in them by a burning glass" (p. 287).

This was the method also used by Priestley in his celebrated experiment of heating red-lead in hydrogen, whereby the metallic lead reappears and the hydrogen disappears by combining with the oxygen set free. This was expressed in the language of the day as the reconstruction of metallic lead by the addition of phlogiston (the hydrogen) to the calx of lead (minium). Thorpe points out the magnitude of the discovery that Priestley missed, and it may be said that Hales too was on the track, and had he known as much as Priestley it would not have been phlogiston that kept him from becoming a Cavendish or Lavoisier. What chiefly concerns us, however, is the bearing of Hales' chemical work on his theories of nutrition. He concludes that "air makes a very considerable part of the substance of Vegetables," and goes on to say (p. 211) that "many of these particles of air" are "in a fixt state, strongly adhering to and wrought into the substance of" plants. {135a} He has some idea of the instability of complex substances, and of the importance of the fact, for he says {135b} that "if all the parts of matter were only endued with a strongly attracting power, [the] whole [of] nature would then become one unactive cohering lump." This may remind us of Herbert Spencer's words: "Thus the essential characteristic of living organic matter, is that it unites this large quantity of contained motion with a degree of cohesion that permits temporary fixity of arrangement" (_First Principles_, section 103). With regard to the way in which plants absorb and fix the "air" which he finds in their tissues, Hales is not clear; he does not in any way distinguish between respiration and assimilation. But as I have already said, he definitely asserts that plants draw "sublimed and exalted food" from the air.

As regards the action of light on plants, he suggests (p. 327) that "by freely entering the expanded surfaces of leaves and flowers" light may "contribute much to the ennobling principles of vegetation." He goes on to quote Newton (_Opticks, query_ 30): "The change of bodies into light, and of light into bodies, is very conformable to the course of nature, which seems delighted with transformations." It is a problem for the antiquary to determine, whether or no Swift took from Newton the idea of bottling and recapturing sunshine as practised by the philosopher of Lagado. He could hardly have got it from Hales, since _Gulliver's Travels_ was published in 1726, before _Vegetable Staticks_.

Nevertheless, Hales is not quite consistent about the action of light; thus (p. 351) he speaks of the dull light in a closely planted wood as checking the perspiration of the lower branches, so that "drawing little nourishment, they perish." This is doubtless one effect of bad illumination under the above-named conditions, but the check to photosynthesis is a more serious result. In his final remarks on vegetation (p. 375) Hales says in relation to green-houses, "It is certainly of as great importance to the life of the plants to discharge that infected rancid air by the admission of fresh, as it is to defend them from the extream cold of the outward air." This idea of ventilating greenhouses he carried out in a plant-house designed by him for the Dowager Princess of Wales, in which warm fresh air was admitted. The house in question was built in 1761 in the Princess's garden at Kew, which afterwards became what we now know as Kew Gardens. The site of Hales' greenhouse, which was only pulled down in 1861, is marked by a big wistaria which formerly grew on the greenhouse wall. It should be recorded that Sir W. Thiselton-Dyer {137a} planned a similar arrangement independently of Hales, and found it produced a marked improvement of the well-being of the plants.

It is worthy of note, that though Hales must have known Malpighi's theory of the function of leaves (which was broadly speaking the same as his own), he does not as far as I know refer to it. In his preface (p. ii.) he regrets that Malpighi and Grew, whose anatomical knowledge he appreciated, had not "fortuned to have fallen into this statical {137b} way of inquiry." I believe he means an inquiry of an experimental nature, and I think it was because Malpighi's theory was dependent on analogy rather than on ascertained facts that it influenced Hales so little.

There is another part of physiology on which Hales threw light. He was the first, I believe, to investigate the distribution of growth in developing shoots and growing leaves, by marking them and measuring the distance between the marks after an interval of time. He describes (p. 330) and figures (p. 344) with his usual thoroughness the apparatus employed; this was a comb-like object made by fixing into a handle five pins .25 inch apart from one another; the points being dipped in red-lead and oil, a young vine-shoot was marked with ten dots .25 inch apart. In the autumn he examined his specimen, and finds that the youngest internode or "joynt" had grown most, and the basal part having been "almost hardened" when he marked it, had "extended very little." In this--a tentative experiment--he made the mistake of not re-measuring his plants at short intervals of time, but it was an admirable beginning, and the direct ancestor of Sachs' {138a} great research on the subject. In his discussion on growth it is interesting to find the idea of turgescence supplying the motive force for extension. This conception he takes from Borelli. {138b}

Hales sees in the nodes of plants "plinths or abutments for the dilating pith to exert its force on" (p. 335); but he acutely foresees a modern objection {138c} to the explanation of growth as regulated solely by the hydrostatic pressure in the cell. Hales says (p. 335): "But a dilating spongy substance, by equally expanding itself every way, would not produce an oblong shoot but rather a globose one."

It is not my place to speak of Hales' work in animal physiology, nor of those researches bearing on the welfare of the human race which occupied his later years. Thus he wrote against the habit of drinking spirits, and made experiments on ventilation by which he benefited English and French prisons, and even the House of Commons; then too he was occupied in attempts to improve the method of distilling potable water at sea, and of preserving meat and biscuit on long voyages. {139a}

We are concerned with him simply as a vegetable physiologist, and in that character his fame is imperishable. Of the book which I have been using as my text, namely, _Vegetable Staticks_, Sachs says: "It was the first comprehensive work the world had seen which was devoted to the nutrition of plants and the movement of their sap. . . . Hales had the art of making plants reveal themselves. By experiments carefully planned and cunningly carried out he forced them to betray the energies hidden in their apparently inactive bodies." {139b} These words, spoken by a great physiologist of our day, form a fitting tribute to one who is justly described as the father of physiology.

IX NULLIUS IN VERBA {140}

There is a well-known story of Charles Darwin which I shall venture to repeat, because nothing can better emphasise the contrast between Shrewsbury School as it is and as it was.

Charles Darwin used, as a boy, to work at chemistry in a rough laboratory fitted up in the tool-house at his home in Shrewsbury. The fact that he did so became known to his school-fellows, and he was nicknamed "Gas." I have an old Delphine Virgil of my father's in which this word is scrawled, together with the name Miss Case, no doubt a sneer at his having come from Case's preparatory school. Dr. Butler, the Head Master, heard of the chemical work, and Charles Darwin was once publicly rebuked by that alarming person for wasting his time on such useless subjects. My father adds, "He called me very unjustly a _poco curante_, and as I did not understand what he meant it seemed to me a fearful reproach." A _poco curante_ means of course "a don't-care person" or one who takes no interest in things, and might perhaps be translated by "slacker." I do not suppose that Dr. Butler is likely ever to be forgotten, but as it is, he is sure of a reasonable share of immortality as the author of a description so magnificently inappropriate. {141a}

This is the contrast I referred to; on one hand a Head Master in 1822 doing his best to discourage a boy from acquiring knowledge of a great subject in the best possible way, _i.e._ by experiment. And on the other, a Head Master of the same school in 1911 encouraging, with a wise zeal, the rational study of science as a regular part of the school course. It may not be possible to trace out the complete evolution of these Darwin Buildings, but I like to fancy that the germ from which they have sprung is that tool house at the Mount. {141b}

It is some comfort to us to know that Shrewsbury was not the only place which failed to educate my father in the regulation lines. When he left school he went to Edinburgh University to study medicine. But he found anatomy and _materia medica_ intolerable, and the operating theatre was a horror. So he began to work at science in his own way. He learned to stuff birds from an old negro who had known Waterton. Of this instructor he says, "I used often to sit with him, for he was a very pleasant and intelligent man." He also caught sea beasts in the pools on the shore, and made one or two small observations, which were communicated to the Plinian Society.

Then he was sent to Cambridge with a view to taking Orders. He enjoyed himself riding and shooting, and especially in catching beetles in the fens. But also in more intellectual ways, as in listening to the anthem in King's Chapel, and looking at the pictures in the Fitzwilliam Museum. Henslow, the Professor of Botany treated him as a friend rather than as a pupil, and finally settled his career by sending him round the world in H.M.S. _Beagle_. He entered the ship an undergraduate, and left it after five years a man of science. I give these well known details to show how little he profited by any regular course of study either at Shrewsbury, Edinburgh, or Cambridge. His start in life depended on the recognition of his capacity by Henslow, and was nearly wrecked by FitzRoy, the Captain of the _Beagle_, suspecting that no one with a nose like my father's could be an energetic person.

Are we therefore to conclude that the best method of scientific education is to force a boy to work at uncongenial subjects? In the case of a genius it may not much matter what he is taught; he will succeed, in spite of his education. But for us lesser mortals it does matter. I am not going to talk about the way in which science should be taught in schools, a matter about which I am not competent to speak. What I shall speak of is the learning rather than teaching of the subject.

I once heard Lord Rayleigh refer to the necessity of putting one's subject-matter clearly before an audience, and he illustrated his point by the following story. Somebody, possibly a lady, came from listening to a lecture by Mr. So-and-So, and when asked what it was about, replied, "He didn't say." I shall follow Lord Rayleigh's advice and tell you that my subject is "Why science should be learned." Why it is worth while for a boy to give up some of his time to this particular form of knowledge, and what advantage he may expect to gain from so doing.

There are many possible reasons for a boy's learning science.

I Because he is told to. This is an excellent reason, but not inspiriting. II To get marks in an Entrance Scholarship examination. This is a virtuous reason but not intellectual. III To gain knowledge which will be of use when he comes to follow a profession, and wants to know physics in view of becoming an engineer, or physiology as a part of medical training. This is a worthy reason, but not a common one. IV Lastly, a boy may learn science because he wants to; because he finds it entertaining; because it satisfies an unreasoning desire to know how things in general work.

This is the best possible reason and the most efficient, and what I propose, is to inquire whether this wish to know something of science can be justified.

The word 'science' simply means knowledge, but it is usually applied to knowledge that can be verified. Thus we learn by heart that Queen Anne died in 1714. I believe this to be a fact, but I have no means of verifying it. But if I am told that putting chalk into acid will produce a heavy gas having the quality of extinguishing a lighted match, I can verify it. I can do the thing and see the results. I am now the equal of my teacher; I know it in the same way that he does. It has become my very own fact, and it seems to have the satisfactory quality that possession gives. This characteristic of scientific knowledge is not always recognised. I mean the profound difference between what we know and what we are told. When science began to flourish at Cambridge in the 'seventies, and the University was asked to supply money for buildings, an eminent person objected and said, "What do they want with their laboratories?--why can't they believe their teachers, who are in most cases clergymen of the Church of England?" This person had no conception of what the word 'knowledge' means as understood in science.

Another characteristic of science is that it makes us able to predict. I have already referred to the fact that Queen Anne is dead, and we know, or are told, that she died, as I said before, in 1714; we also know that George I. died in 1727, and George II. in 1760, but that would not enable us to predict that George III. would die in 1820. They are isolated facts not connected by the causal bond that knits together a series of scientific truths. And this is after all a fortunate thing for the peace of mind of reigning sovereigns.

It is said that you should never prophesy unless you know. But science is made up of prophecies. Some are famous, like the prediction of Adams and Leverrier that a new planet would be found in a stated position. Some are on a humbler scale, such as my father's prediction that a big moth would be found to carry the pollen of Hedychium by brushing it off with the tips of its hovering wings, a method of fertilisation unheard of at the time, which however proved to be the fact.

You may say that it does not matter whether the moth does this particular thing or not. This is no doubt true from a strictly commercial point of view. But in science all facts have some value. We should cultivate a point of view about facts the very reverse of that of the unknown person who said that all books are rather dull.

I once heard a celebrated physicist describe how he explained to an American business man an elaborate spectroscope for examining the sun. The American asked what good it was. The physicist explained that with it you can discover whether or no sodium exists in the sun. The American was silent for some time, and then said, "But who the 'nation cares whether there is sodium in the sun or not?" He had not the scientific spirit which does care about sodium in the sun.

Scientific discovery is, as I said, made up of a series of prophecies. You observe fact No. 1, and you say if this be so No. 2 ought to be true, and on examination you find this is true, and No. 2 suggests No. 3. Or else you find 2 not to be true; this makes you suspect your original fact, and on carefully going over your observation you find No. 1 was a mistaken observation. The successful man of science is one to whom familiar objects suggest those prophecies generally known as theories. My father was remarkable for not letting what seem to be trifling facts pass without suggesting to him a theory. The flies that are caught on the sundew must have been seen by innumerable people--but it remained for him to prove the truth of his guess that some plants possess digestive ferments like our own, and live on the insects they catch and digest.

The art of being guided by slight indications is sometimes called the method of Zadig, which I learn from Mr. Huxley's essay and not from Voltaire. Mr. Huxley points out that it is not only possible thus to prophesy what will happen, but also to determine what has happened; and he suggests that there should be a word 'backtell' as well as foretell. Zadig, who was an oriental philosopher, met one day the King's servants in great trouble about the loss of their master's favourite horse. When asked whether he had seen it he said, "A fine galloper, is it not? small hoofed, five feet high, tail 3.5 feet long. Cheek-pieces of the bit 23-carat gold, shoes silver." They of course begged to know where it was, and he said he had not seen it.

This will be recognised as the method of Sherlock Holmes, but it is also the method of science. Surely you would like to become scientific under the guidance of that great man. Of course you are not to be Watsons, but actual detectives, with Watsons of your own to admire you. And lest you should fear that the scientific method is alarmingly difficult, I may add that the method of Zadig or Sherlock Holmes, or of science in general, is nothing more than glorified common-sense.

It is difficult to talk about a subject which interests one without seeming to claim that it is superior to all others. I have not meant to imply this. I have only tried to explain in what way science differs from some other sort of knowledge. Nor do I wish to imply that the mind that excels in science is better or worse than that which one finds in a great literary man. An eminent oar is worthy of as much respect as a great cricketer, but he is eminent in a different way.

I am glad to think that there are points in which science, literature, and art are equally excellent--namely, in giving to mankind some of the deepest pleasures of which he is capable, in making him realise the wonder, the beauty and the romance of the world. I spoke of the power of science in knitting together isolated facts into a theory. And such a theory may become so all embracing that it is called a law of nature. Those great generalisations, the laws of gravity and the laws of evolution, or the laws of chemical combination, have a beauty and dignity which appeal to everyone.

And on the practical rather than on the theoretical, side there is wonder, and to my mind beauty, in the bigness and in the smallness of the spaces that man can deal with. The astronomer measures out his work, not by miles, but by the inconceivable distance that light can travel in a year. The man who studies bacteria measures by the micron, 25,000 of which go to the inch. To me there is more fascination in the very small than in the other extreme. It is wonderful to think that a plant--a big tree for instance--is made up of countless millions of cells, each of which was built by a minute protoplasmic body, which Huxley has compared to a delicate Ariel imprisoned like Shakespeare's sprite in an oak-tree.

There is a dramatic effect in even the simplest of experiments. I, for one, am never weary of the time-honoured demonstration of a water-plant giving off oxygen as it assimilates. A twig of Elodea in a large beaker of water gives off no bubbles in the dull light at the back of the room, but when close to the window it does so. And with proper precautions the rate of bubbling becomes an accurate measure of the intensity of assimilation. To complete the demonstration the experiment should be repeated with water which has been boiled, and therefore roughly freed from CO2, when the rate of bubbling is very greatly diminished. Finally, by blowing vigorously into the water it may be charged once more with CO2, and the normal rate of bubbling may be established.

There are of course innumerable experiments in pure chemistry and physics which have this romantic quality in the manner in which they reveal the secrets of the invisible structure of matter--but of these I have not much personal experience.

I think, too, that the human interest of science should always be encouraged. I mean that those classical experiments, by which great men have advanced human knowledge, should be shown: and performed moreover by the original methods, _e.g._ the discoveries of Black, Priestley and Cavendish.