only do they resemble each other in their physiological action, but that their toxic action increases with their molecular weight, as I have shown to be the case with the inorganic elements, where, in each isomorphous group, the toxic action increases with the atomic weight of the elements.

In conclusion, I would reprint an extract from a paper published forty years ago :-" A moment's reflection on the problems to be solved will suffice to show that experiments conducted with this class (inorganic) of substances are more likely to furnish useful results than those made with bodies derived from the animal or vegetable kingdom, although, owing to the striking effects caused by some of these substances, physiologists have mostly directed their attention to them. By so doing, however, we are employing re-agents with the properties and composition of which we are imperfectly acquainted, to the neglect of those on the nature of which chemistry has already thrown much light, for not only are we better acquainted with the more purely chemical properties of inorganic compounds, but their relation to heat, electricity, and molecular polarity has been to a considerable extent made out." JAMES BLAKE

Disinfection by Heat

IN Dr. Parsons's Report on Disinfection by Heat (NATURE, vol. xxxiv. p. 583) occurs the statement: "It appears that there are no tables or formulæ in existence by which the degree of humidity of the air corresponding to a given difference between the wet and dry bulb thermometers at these high temperatures can be ascertained." There are both tables and formule; but the tables are the numerical values for the formulæ, and such tables are to be found in Balfour Stewart on "Heat," Dixon's "Treatise on Heat," Blanford's "Meteorologist's Vade-mecum," and numerous works on the steam-engine.

Let the degree of humidity be represented by h; vapourtension at dew-point by x; wet-bulb temperature by 1, its vapour-tension by f; dry-bulb temperature by 7, its vapourtension by F; barometric pressure by b. Then, the theory of the dew-point gives

The Beetle in Motion

MUCH has been written on "the horse in motion." Can any readers of NATURE supply me with references to published matter on the subject of hexapod progression?

The few observations I have made may be summed up in a few words. I use the letters and I to signify the right and left legs respectively, and number the limbs from before backwards. When walking rapidly the appearance is as if 11, r2, and 13 moved forward together simultaneously, alternating with I, l 2, and 3. When the pace is slower it is seen that / I and r2 start together and come down at about the same time, some

starts.

times one sometimes the other being a little the first. Then, lifted almost but apparently not quite at the same time, 13 The motion of this leg being somewhat slower, and the limb having further to travel, the foot generally comes to the ground appreciably later than I or r2. The general effect is to produce, at the moments of pause between the strides, the position indicated in the figure, which differs considerably from the conventional position delineated by artists who seek to represent the beetle in motion. C. LLOYD MORGAN

University College, Bristol

The Astronomical Theory of the Great Ice Age

IN Sir Robert Ball's paper on this subject, which appears in your last number (p. 607), that author states that the calculation given "has convinced him that Mr. Croll's theory affords an adequate explanation of the Ice age." It is more in the hope of obtaining from Sir Robert a statement of the grounds of this conviction than for the purpose of controversy that I write this letter.

It will of course be conceded that the frost and snow of a single winter, melted off during the following summer, would not produce an Ice age. But, on Sir Robert Ball's figures, the increase of winter cold at the period in question was accompanied by a corresponding and equal increase of summer heat. Why, then, should the latter prove insufficient to melt the winter accumulation of snow and ice in any locality where it now suffices to melt it?

The question is one of the joint result of two opposing forces. Both, under the supposed conditions, are intensified and equally intensified. How does this affect the result? More srow and ice is doubtless formed in the winter, but then more heat is employed in melting it during the ensuing summer. Why, then, was it not melted in any p'ace where it is now melted? A kind of answer to this question may be extracted from the writings of Mr. Croll, but not, I think, a satisfactory one. I am therefore anxious (in common, I am sure, with many others of your readers) to hear the reply of Sir Robert Ball. W. H. S. MONCK Llandudno, October 25

The Enormous Loss from Ox-Warble

I VENTURE to solicit your co-operation in making some points better known in order that farmers may be better able to protect themselves from the enormous loss from warbles on cattle from the bot-fly, positive proof having been furnished that it largely exceeds 2,000,000/. to 3,000,000%. yearly! To begin: I appeal to those farmers who have somewhat studied the question to make it clear to those who have not done so that each warble lump has a large maggot under it, feeding on the juices of the hide or flesh. These lumps many call "health lumps" or "thriving bumps," and seem to prefer that their cattle should have them. It is readily seen how this serious fallacy has arisen, viz. from the fact that the warble lumps begin to show about Christmas (from the growth of the maggot under them), which also happens to be the time that the cattle receive their most nourishing food, and are then warmly housed or sheltered. But there could be no greater mistake than to think that the swellings

IN connection with Prof. O'Reilly's letters in NATURE of October 14 and 28 (pp. 570, 618), and your notice of October 21 (p. 599), I supply a few data, which at first I thought of too little interest for your columns. At 6.12 p.m. local time (17h. 41m. universal time), on October 16, two shocks occurred with a short interval, the direction being approximately that of the meridian. The intensity was such as might be produced by very heavy carts pa-sing. H. DU BOIS

Strasburg, October 31

Meteor

THIS evening, at about 8.25, I saw a magnificent meteor, of a blue colour, falling a little to the left of the Pleiades. Belfast, October 31 JOSEPH JOHN MURPHY

FR

FREDERICK GUTHRIE

REDERICK GUTHRIE was born in Bayswater on October 15, 1833. and was the youngest of six children. His father, Alexander Guthrie, was a tailor, carrying on business in New Bond Street, and is said to have been a man of literary taste and ability; that he was a man of cultivation is shown by the education he provided for his children, one of whom, Francis, early distinguished himself at University College, London, and at the London University, as a mathematician, and is now Principal of the South African College, Cape Town. As a boy, Frederick Guthrie was taught privately until his twelfth year by the late Henry Watts, F.R.S.; afterwards he was sent to University College School, then under the head-mastership of Prof. Key, whence he passed into University College, London. There he remained three years, the last two of which were devoted mainly to the study of chemistry, under Profs. Graham and Williamson, and of mathematics under De Morgan, a teacher with whom it was impossible for a young man of Guthrie's power to come into contact without receiving a life-long impress. There also he again came into contact with Watts, who was then principal assistant in Prof. Williamson's laboratory, and an intimate friendship was cemented with his old tutor that remained unbroken till the death of the latter. In the spring of 1854 Guthrie went to Germany to continue his chemical studies, and worked first at Heidelberg, under Bunsen, and then at Marburg, under Kolbe, where he took the degree of Doctor of Philosophy (“summa cum laude") in 1855, having previously graduated as Bachelor of Arts of the University of London. After returning to England he was appointed, in 1856, assistant to Dr. Frankland, then Professor of Chemistry in Owens College, Manchester. In 1859 he went to Edinburgh as assistant to the late Vice-President of the Council, who had just succeeded Dr. William Gregory as Professor of Chemistry in the Edinburgh University.

Two years later Guthrie accepted the Professorship of Chemistry and Physics in the Royal College, Mauritius. He arrived in the island in May 1861, and for six years he devoted himself to endeavouring to introduce and establish on a durable basis scientific instruction in the colony. Here one of his colleagues was Mr. Walter Besant, the eminent novelist, with whom he formed a friendship that remained intimate and uninterrupted through life. He returned to London on leave in 1867, and in 1869 he was elected Lecturer on Physics in the Royal School of Mines, a post which, with extended duties and modified title, he retained till his death.

In the spring and early summer of this year many of Guthrie's friends remarked upon his looking ill and seeming to be in low spirits. After a while he complained of a difficulty in swallowing, which presently became so

serious that he was unable to take solid food. When at last he was prevailed upon to consult a physician, it was discovered that he was suffering from cancer of the throat. He sank rapidly during the last two or three months, and the inevitable end of his disease came on October 21. He was buried in Kensal Green Cemetery on the 26th.

Such were some of the chief outward and visible stages in Frederick Guthrie's career. Perhaps the first thing to strike any one on making his acquaintance was his strongly marked individuality. His opinions were, much more than most men's, of his own forming, not simply picked up as they floated about in talk or in print. And his conduct followed his opinions he did what he thought right, with very little regard to the consequences to himself, or to what might be thought of him by others. His scientific knowledge, too, was, much more than most men's, of his own getting, the result of his own observation and experiment. In others, also, he valued even a small scrap of self-gotten knowledge more than a large store of secondhand erudition. In this respect he sometimes went to excess, and, though not without mathematical knowledge, he was somewhat apt to underrate the scientific importance of the work of mathematical physicists in comparison with that of pure experimentalists. But even this mistake had root in the thoroughly sound conviction that it is the duty of a man of science to be a strictly faithful interpreter of the observed facts of Nature, and that, the further he ventures in the field of theoretical deduction the more room is there for self-deception. He seemed, however, sometimes to forget that phenomena do not present themselves to the natural philosopher ready clothed in words, and that all that can be expressed in human language is the conception formed in the mind of the observer. The true function of the mathematical physicist is in reality, as Kirchhoff has pointed out, nothing more than to find out the simplest statements that are consistent with observation.

Guthrie's devotion to science was complete and singleminded. He had a deep conviction of the value and dignity of any kind of genuine, self-forgetful, scientific work, and he knew how, if necessity arose, to claim the dignity due to a sharer in such work. But from affecta

dissertation on taking his Ph.D. degree; it was entitled "Ueber die chemische Constitution der ätherschwefelsauren Salze und über Amyloxydphosphorsaure." In the six years between taking his degree and going to Mauritius, he published eight or ten papers, mostly on points of organic chemistry-one of them, on the amyl group, contains the discovery of the therapeutic action of nitrite of amyl, and suggestions for its introduction into the pharmacopœia. His first physical investigations were published while he was in Mauritius, and included two researches into the formation of drops and one into the properties of bubbles. It is striking evidence of the reality of Guthrie's love of science and of his force of character that, under circumstances in almost all respects adverse to scientific work beyond what was required by his official position, he should have persevered steadily with his experiments and produced papers of great value. While in Mauritius he also published a paper on the iodide of iodammonium, and a pamphlet on "The Sugar-Cane and CaneSugar," and made complete analyses of the waters of the principal rivers of the island. After his return to England his scientific work was almost wholly confined to physics, but it is perhaps significant of the side from which he approached the study that the subjects that occupied him principally had relation to what is usually called in the text-books "molecular physics." Among many other researches the following may be specially mentioned: on the thermal conductivity of liquids; on approach caused by vibration; on stationary vibrations of liquids in rectangular and circular troughs; on salt-solutions and attached water (the results of this investigation were contained in a series of eight papers, and included the discovery of the substances named by Guthrie "cryohydrates," a class of solid hydrated salts which melt without change of composition, in most cases below oo C.); on Eutexia," an investigation into the properties, especially the melting-points, of metallic alloys and mixtures of salts.

"

As a teacher, it has been well said of Guthrie by one who knew him well, that "he did not desire merely to fill his pupils' heads, but to make them use them"-a far more valuable but more difficult result to attain. A large proportion of his pupils consisted of "certificated science teachers," and for these he introduced a system of instruction, consisting largely in making them construct with their own hands the apparatus required for their experiments, which was probably more fruitful (especially in the case of this particular class of pupils) than any other that he could have adopted.

not astonish those who knew his ability in this direction to learn that as a young man he published (under the nom-de-plume of Frederick Cerny) a poem called "The Jew," and a metrical drama called "Logroño."

With regard to Guthrie's scientific position and achievements it may be remarked, in the first place, that he belonged to a class that was probably commoner in his generation, and in that which preceded it, than it is likely to be in the future-that, namely, of physicists who served their time as chemists. Until within the last twenty years or so the only accessible school of experimental science was a chemical laboratory, and consequently, for the last two generations, a large proportion of the most prominent physicists have been men who began their scientific career as chemists. Among many others, it may suffice to mention Faraday and Regnault. Guthrie's first published investigation seems to have been his

In 1873 Guthrie issued to his scientific friends a characteristically worded little circular, which resulted in the formation, early in the following year, of the Physical Society of London, a Society which now includes, with very few exceptions, all the leading physicists of the United obtained from the Lords of the Committee of Council on the Physical Laboratory of the Science Schools at South Kensington. He chose for himself the somewhat onerous post of "Demonstrator" to the Society, and in this capacity placed his time and the resources of his laboratory freely at the disposal of those who wished to exhibit experiments or apparatus at the Society's meetings. It not till 1884 that he consented to become

was

President.

In the early part of the present year he gave a course of three lectures before the Society of Arts on "Science Teaching," in which he advocated with equal vigour and humour the advantages of a training in experimental science.

Besides the poetical works already mentioned, and his numerous papers on scientific subjects, Guthrie was the author of the following books :-" Elements of Heat and Non-Metallic Chemistry," " Electricity and Magnetism,"

THE LONGEVITY OF GREAT MEN

THE conclusion that the intellectual giants of the race are favoured by an abundance of years on the scene of their heroic activity, and are thus further differentiated from their more common fellow-men, seems natural, and has been accepted upon evidence which, in a less pleasing conclusion, would be considered ridiculously insufficient, and even false. The usual method of attempting to answer the question whether great men are longer-lived than others, is to prepare a list of the ages, at death, of a number of eminent men, take the average age, and compare it with a similar average of a number of ordinary men, or even with the average lifetime of the race, and in this way to make the results speak decidedly in favour of the superior longevity of great men. All that such a method can prove (and this it does prove) is that it takes long to become great. It neglects to consider that a select class of men is dealt with, and that, to be even potentially included in this class, one must have lived a certain number of years.

For example: in an article translated in the Popular Science Monthly for May 1884, it is argued that astronomers are a long-lived race because the average lifeperiod of 1741 astronomers is 64 years and 3 months. An average human life is only 33 years; but as one cannot be an astronomer before adult life, the author takes the expectation of life at 18 years, which is 61 years, and thus makes an excess of over 3 years in favour of astronomers. He also divides his astronomers into four degrees of eminence, and finds that those of the first rank live longer than those of the second, and they in turn longer than those of the third, and so on, thus implying that the best astronomers are most favoured with years. The true conclusion is, that it takes longer to become a firstrank astronomer than it does to become a less eminent one.2

If great men were great from their infancy, and we had the means of ascertaining this fact, the method would be correct. But, as it is, we must define in some way or other what we mean by greatness, and then fix the average age at which it becomes possible to distinguish an amount of talent sufficient to enable its possessor to be enrolled in the ranks of the great as already defined. What is known as the "expectation of life" at any number of years tells the most probable age at death of one who has attained the years under consideration: a comparison of this age with the age at death of great men will decide whether they are longer lived or not.

The attempt was made to select about 280 to 300 of the greatest men that ever lived. Throwing out about 30 of the doubtful names, there remain 250 men, about whom

the statement is hazarded that a list of the 250 greatest men, prepared by another set of persons, will not mate

rially differ from our list, as far as all the purposes for which it is to be used are concerned. From this list I have selected at random a set of men of whom it was probably easy to fix the age at which they had done work which would entitle them to a place on this list, or work which almost inevitably led to such distinction: it is a date about midway between the first important work and the greatest work. The average of over 60 such ages is 37 years; which means, that, on the average, a man must be 37 years old in order to be a candidate for a place on this list. The real question, then, is, How does the longevity of this select class of 37-year-old men compare with that of more ordinary individuals? The answer is given by the expectation of life at 37 years, which is 29 years, making the average age at death 66 years. And this is precisely the age at death of these 60 great men; showing, that, as a class (for these 60 may be considered a fair sample), great men are not distinguished by their longevity from other men.

Further interesting conclusions can be drawn if we divide the men into classes, according to real psychological and physiological differences in the ways of manifestation of the several kinds of genius. It is almost surprising how well the ordinary trinity of facultiesintellect, emotions, and will accomplishes this purpose. Greatness seems to appear either in a brilliant thought, a deep feeling, or a powerful will. Under men of thought would be included philosophers, scientists, historians, &c.; under men of feeling, poets, musicians, religionists, &c. ; under men of action, rulers, commanders, statesmen, &c. Before comparing the relative longevity of these three classes of men, I assure myself that the period at which greatness begins to be possible does not materially differ1 in the three classes, and, as was done in the former case, I exclude all cases of unnatural death. I find that men of thought live 69.5 years, or 3.5 years longer than ordinary men; while the lives of men of feeling are 3 years, those of men of action 5 years, shorter than those of average men, -a conclusion that agrees with the commonly accepted view on the subject. If we subdivide these three classes, we find, that, while all classes of men of thought live longer than ordinary men, the moralists live longest, scientists coming next; that among the men of feeling the religionists alone live the full period of life, while poets' lives are 5 years, and musicians' lives 8 years, too short; that, of men of action, rulers and commanders both fail to complete the full term of life by 4 years. One sees from these statements (which, however, in their detail at least, must be accepted with hesitation, owing to the fewness of examples) that the kind of psychical and physical activity pursued influences the life-period; that certain types of genius are apt to die young, while others are particularly favoured with a full allowance of years.

The question of longevity becomes important when we consider that through it the leaders of civilisation are allowed to exercise their important function a few years longer, thus enabling more great men to be alive at the same time; and that, by its tendency to be inherited by the offspring, the children of great men will begin life with a better chance of reaching maturity, and, in turn, of becoming important to the world, if, as we have reason to believe it would, the genius of their ancestors has left its traces in them. JOSEPH JASTROW