can never be transformed into a mammal." There is something more therefore than blind chance at work here. But within the limits, it is a matter of experience that every possible variation may occur. If anyone will take the trouble to examine the leaves of the ribbon-grass so commonly cultivated in gardens, he will find it impossible to obtain any pair in which the green and white striping is exactly alike. If it were possible to raise to maturity all the progeny of some prolific organism, the same diversity (in different degree, of course) would manifest itself; but the whole group of variations in respect of any one organ would obey Quetelet's law. When we attempt to give some physical explanation of this fact, we know from the objective facts which have been made out about fertilization that, although the protoplasmic content of the fertilized ovum is, in a general sense, uniform, its actual structure and physiological components must be combined in as endless variety as the green and white stripes of the leaves of the ribbon-grass. If, with Prof. Lankester, we say that the combinations are kaleidoscopic, I do not see that we go beyond the facts. And it appears to me quite permissible to correlate the ascertained variable constitution of the ovum arising from this cause with the equally ascertained varying structure of the organism developed from it. Of the varied progeny, we know that some survive and others do not. And what Darwin has taught us is, that the reason of survival is the possession of favourable variations. The surviving race necessarily differs somewhat from its progenitors, and Dar-, win has further stated that it is probable that by the continued repetition of the process all the diversity of organic nature has, been brought about. The area of fortuity is narrowed down therefore, on this point of view, to the variable constitution of the individual ovum. And it is upon the recognition of this fact, for which there seems to be good scientific evidence, that the Duke of Argyll founds his charge that the neo-Darwinians make fortuity their idol. The reason appears to be that it comes into collision with teleological views. But such collisions are no new event in the history of the biological sciences. And teleology, like a wise damsel, has generally, though temporarily ruffled, managed to gather up her skirts with dignity and make the best of it. For some element of fortuity is inseparable from life as we see it. It is at the bottom one of the most pathetic things about it. Nowhere is this more vividly portrayed perhaps than by Addison in the "Vision of Mirzah." Yet I do not remember that anyone was ever so unwise as to taunt Addison with making fortuity his idol. But, philosophically considered, what is gained by this tenacity about out-works? I reply, exactly as much as was gained by the tenacity of the Church in respect to the geocentric theory of the planetary system. Scientific men cannot be stopped in the application of their best ability to the investigation of Nature. If their conclusions are false, they will detect the falsity; if true, they will not be deterred from accepting them by some a priori conception of the order of the universe. It is not justifiable to say that this is due to any devotion to such an empty abstraction as fortuity. No scientific man is, I hope, so foolish as to suppose that, however completely mechanical may be his conception of Nature, he is in any way competent to account for its existence. The real problem of all is only pushed further back. And the Duke of Argyll's difficulty resolves itself into the old question, whether it is more orthodox to conceive of the universe as an automatically self-regulating machine, or as one which requires tinkering at every moment of its action. It may be replied that this is all very well, but that it is not the way the neo-Darwinians state their case. I may be, therefore, excused for quoting some passages to the contrary from Weismann's "Studies in the Theory of Descent" : "This conception represents very precisely the well-known decision of Kant: 'Since we cannot in any case know a priori to what extent the mechanism of Nature serves as a means to every final purpose in the latter, or how far the mechanical explanation possible to us reaches,' natural science must everywhere press the attempt at mechanical explanation as far as possible" (p. 638). Further, he quotes from Karl Ernst von Baer : "The naturalist must always commence with details, and may then afterwards ask whether the totality of details leads him to a general and final basis of intentional design" (p. 639). Again, he says :— "We now believe that organic nature must be conceived as mechanical. But does it thereby follow that we must totally deny a final universal cause? Certainly not; it would be a | great delusion if anyone were to believe that he had arrived at a comprehension of the universe by tracing the phenomena of Nature to mechanical principles " (p. 710). In truth, this revolt of teleology against Darwinism is a little ungrateful. For, if Darwinism has done anything, it has carried on and indefinitely extended its work. In the last century, teleology was, it seems to me, a valuable motive power in logical research. Such a book as Derham's "Physico-Theology" (1711) may be read with interest even now, I well remen ber that my first ideas of adaptive structures were obtained from the pages of Paley. Thirty years ago I do not know, except from them and the notes to Darwin's "Botanic Garden," where such information was to be otained. The basis of research was however, too narrow to continue; it did not look beyond the welfare of the individual. The more subtle and recondite springof adaptation opened up by the researches of Darwin, which lak to the welfare of the race, were not within its purview. Const quently it dried up, and virtually expired with the Bridgewater Treatises. To return, however, to the Duke of Argyll. ** Neithe mechanical aggregation, nor mechanical segregation, can possibly account for the building up of organic tissues." Who has sari they did? The Duke has entirely misunderstood the matter Prof. Lankester never suggested that it was possible to put 16 much protoplasm into a vessel, and shake out a cockatoo or guinea-pig at choice. His image of the kaleidoscope ha nothing to do with the building up of organisms, only with th varied combination of the elements known to take part in tformation of the fertilized ova from which organisms originate " I am not sure that I perfectly comprehend what tollows Perhaps some further emendation than that already published needed in one of the sentences. But it seems evident that the Duke is re-stating his old doctrine of "prophetic germs." He has already defined what he means by these (NATURE, vo! xxxviii. p. 564). "All organs,' he says, "do actually pa through rudimentary stages in which actual use is imposible Here, again, as in the case of the transmission of acqurej characters, what one wants is not a reiteration of the assertion but some definite observed evidence. For the production this, if only in a single instance, Prof. Lankester pressed the Duke more than a year ago (NATURE, Ar. p. 5881. Nens. however, has as yet been forthcoming; and it appears to n that it is not permissible to persist in statements for which be does not attempt to offer a shadow of proof. The Duke exults in a very amazing fashion over what ne strangely calls Prof. Lankester's admission that "natural seir tion cannot account for the pre-existence of the structures which are prescribed for its choice." I am afraid I have already tres passed on your space too much with quotations; but I hav done so in order to show, in some measure at any rate, what s the consensus of opinions amongst students of Darwinism; an I must answer the Duke with one more from Prof. Huxley admirable biography. It is true that the Royal Society public these things in the least attractive way possible; but this pa ticular paper could hardly have escaped attention, as it won the notice and admiration of even a journal so little occupied with scientific discussion as Truth, "There is another sense, however, in which it is equally tre that selection originates nothing. Unless profitable varutions occur, natural selection can do nothing' (*Origin,' ed. I. p. 82). Nothing can be effected unless favourable variatio occur (.c., p. 108). What applies to one animal will apuis throughout time to all animals-that is, if they vary-for otherwis natural selection can do nothing. So it will be with plants p. 113. Strictly speaking, therefore, the origin of species if general lies in variation; while the origin of any particul species lies, firstly, in the occurrence, and, secondly, in th selection and preservation of a particular variation. Cleanes on this head will relieve one from the necessity of attending t. the fallacious assertion that natural selection is a deaser marina, or occult agency." And the Duke says he has been waiting for this for thi years. One can only wonder what Darwinian literature has been the subject of his studies during that time. W. T. THISELTON DYEL Royal Gardens, Kew, January 6. The Microseismic Vibration of the Earth's Crust. IN Mr. White's article on British earthquakes (NATURE, Jan. 3 p. 202) he refers to me as having discovered the microseism Ox Sunday, 12th inst., about 8.10 p.m., a bright meteor was seen here, coming into view near & Auriga. It was of a redish colour, moved slowly, leaving a short tail, and burst alowe Leonis, then with diminished light continued its course T. W. MORTON. to the horizon. Beaumont College, Old Windsor, January 13. MAGNETISM♪ of those salient properties of magnetism as exhibited by iron, nickel, and cobalt-properties most of them very familiar, but properties which any theory of magnetism must reckon with and explain. We shall not touch on the great subject of the earth as a magnet-though much has been recently done, particularly by Rücker and Thorpe-but deal simply with magnetism as a property of these three bodies, and consider its natural history, and how it varies with the varying condition of the material. To fix our ideas, let us consider, then, a ring of uniform section of any convenient area and diameter. Let us suppose this ring to be wound with copper wire, the convolutions being insulated. Over the copper wire let us suppose that a second wire is wound, also insulated, the coils of each wire being arranged as are the coils of any ordinary modern transformer. Let us suppose that the ends of the inner coil, which we will call the secondary coil, are connected to a ballistic galvanometer; and that the ends of the outer coil, called the primary, are connected, through Sold as any part of electrical science is the knowledge a key for reversing the current, with a battery. If the that a needle or bar of steel which has been touched current in the primary coil is reversed, the galvanometer with a loadstone will point to the north. Long before the needle is observed to receive a sudden or impulsive deflecErst experiments of Galvani and Volta the general pro- tion, indicating that for a short time an electromotive perties of steel magnets had been observed-how like force has been acting on the secondary coil. If the repoles repelled each other, and unlike attracted each other; sistance of the secondary circuit is varied, the sudden how the parts of a broken magnet were each complete deflection of the galvanometer needle varies inversely as agnets with a pair of poles. The general character of the resistance. With constant resistance of the secondary the earth's magnetism has long been known that the circuit the deflection varies as the number of convolutions earth behaves with regard to magnets as though it had in the secondary circuit. If the ring upon which the magnetic poles respectively near the rotative poles, coils of copper wire are wound is made of wood or glass and that these poles have a slow secular motion. For-or, indeed, of 99 out of every 100 substances which hany years the earth's magnetism has been the subject could be proposed-we should find that for a given of careful study by the most powerful minds. Gauss current in the primary coil the deflection of the galvanoorganized a staff of voluntary observers, and applied his meter in the secondary circuit is substantially the same. unsurpassed powers of mathematical analysis to obtaining The ring may be of copper, of gold, of wood, or glassfrom their results all that could be learned. it may be solid or it may be hollow-it makes no difference in the deflection of the galvanometer. We find, further, that with the vast majority of substances the deflection of the galvanometer in the secondary circuit is proportional to the current in the primary circuit. If, however, the ring be of soft iron, we find that the conditions are enormously different. In the first place, the deflections of the galvanometer are very many times as great as if the ring were made of glass, or copper, or wood. In the second place, the deflections on the galvanometer in the secondary circuit are not proportional to the current in the primary circuit; but as the current in the primary circuit is step by step increased we find that the galvanometer deflections increase somewhat, as is illustrated in the accompanying curve (Fig. 1), in which the abscissæ are proportional to the primary current, and the ordinates are proportional to the galvanometer deflections. serve that as the primary current is increased the galvanometer deflection increases at first at a certain rate; as the primary current attains a certain value the rate at which the deflection increases therewith is rapidly increased, as shown in the upward turn of the curve. rate of increase is maintained for a time, but only for a time. When the primary current attains a certain value the curve bends downward, indicating that the deflections of the galvanometer are now increasing less rapidly as the primary current is increased; if the primary current be still continually increased, the galvanometer deflections increase less and less rapidly. The magnetism of iron ships is of so much importance navigation that a good deal of the time of men of great power has been devoted to its study. It was the ientific study of Archibald Smith; and Airy and Thomson have added not a little to our practical knowedge of the disturbance of the compass by the iron of The ship. Sir W. Thomson, in addition to much valuable practical work on the compass, and experimental work on magnetism, has given the most complete and elegant athematical theory of the subject. Of late years the evelopment of the dynamo machine has directed #ention to the magnetization of iron from a different point of view, and a very great deal has been done by any workers to ascertain the facts regarding the magnetic properties of iron. The upshot of these many years of study by practical men interested in the mariner's compass or in dynamo machines by theoretical men interested in looking into the nature of things, is, hat although we know a great many facts about magnetism, and a great deal about the relation of these facts to each other, we are as ignorant as ever we were as to any reason why the earth is a magnet, as to why its magnetic poles are in slow motion in relation to its substance, or as to why iron, nickel, and cobalt are magnetic, and nothing else, so far as we know, is to any practical rent. In most branches of science the more facts we row the more fully we recognize a continuity in virtue of hich we see the same property running through all the various forms of matter. It is not so in magnetism; here the more we know the more remarkably exceptional does the property appear, the less chance does there seem to be of resolving it into anything else. It seems to me that cannot better occupy the present occasion than by recalling your attention to, and inviting discussion of, some Inaugural Address delivered before the Institution of Electrical Ene on Thursday, January 9, by J. Hopkinson, M. A., D.Sc., F.R.S., Frodott You ob This Now what I want to particularly impress upon you is the enormous difference which exists between soft iron on the one hand, and ordinary substances on the other. On this diagram I have taken the galvanometer deflections to the same scale for iron, and for such substances as glass or wood. You see that the deflections in the case of glass or wood, to the same scale, are so small as to be absolutely inappreciable, whilst the deflection for iron at one point of the curve is something like 2000 times as great as for non-magnetic substances. This extraordinary property is possessed by only two other substances besides iron-cobalt and nickel. On the same figure are curves showing on the same scale what would be the deflections for cobalt and nickel, taken from Prof. Rowlands's paper. You observe that they show the same general characteristics as iron, but in a rather less degree. Still, it is obvious that these substances may be broadly classed with iron in contradistinction to the great mass of other bodies. On the other hand, diamagnetic bodies belong distinctly to the other class. If the deflection with a non-magnetic ring be unity, that with iron, as already stated, may be as much as 2000; that with bismuth, the most powerful diamagnetic known, is o'999825-a quantity differing very little from unity. Note, then, the first fact which any theory of magnetism has to explain is: Iron, nickel, and cobalt, all enormously magnetic; other substances practically non-magnetic. A second fact is: With most bodies the action of the primary current on the secondary circuit is strictly proportional to the primary current; with magnetic bodies it is by no means so. You will observe that the ordinates in these curves, which are proportional to the kicks or elongations of the galvanometer, are called induction, and that the abscisse are called magnetizing force. Let us see a little more precisely what we mean by the terms, and what are the units of measurement taken. The elongation of the galvanometer measures an impulsive electromotive force -an electromotive force acting for a very short time. Charge a condenser to a known potential, and discharge it through the galvanometer: the needle of the galvanometer will swing aside through a number of divisions proportional to the quantity of electricity in the condenser that is, to the capacity and the potential. From this we may calculate the quantity of electricity required to give a unit elongation. Multiply this by the actual resistance of the secondary circuit and we have the impulsive electromotive force in volts and seconds, which will, in the particular secondary circuit, give a unit elongation. We must multiply this by 108 to have it in absolute C.G.S. units. Now the induction is the impulsive electromotive force in absolute C.G.S. units divided by the number of secondary coils and by the area of section of the ring in square centimetres. The line integral of magnetizing force is the current in the primary in absolute C.G.S. units -that is, one-tenth of the current in amperes-multiplied by 4. The magnetizing force is the line integral divided by the length of the line over which that line integral is distributed. This is, in truth, not exactly the same for all points of the section of the ring-an imperfection so far as it goes in the ring method of experiment. The absolute electro-magnetic C.G.S. units have been so chosen that if the ring be perfectly non-magnetic the induction is equal to the magnetizing force. We may refer later to the permeability, as Sir W. Thomson calls it; it is the ratio of the induction to the magnetizing force causing it, and is usually denoted by μ. There is a further difference between the limited class of magnetic bodies and the great class which are nonmagnetic. To show this, we may suppose our experiment with the ring to be varied in one or other of two or three different ways. To fix our ideas, let us suppose that the secondary coil is collected in one part of the ring, which, provided that the number of turns in the secondary is maintained the same, will make no difference in the result in the galvanometer. Let us suppose, further, that the ring is divided so that its parts may be plucked from together, and the secondary coil entirely withdrawn from the ring. If now the primary current have a certain value, and if the ring be plucked apart and the secondary coil withdrawn, we shall find that, whatever be the substance of which the ring is composed, the galvanometer deflection is one-half of what it would have been if the primary current had been reversed. I should perhaps say approximately one-half, as it is not quite strictly the case in some samples of steel, although, broadly speaking, it is one-half. This is natural enough. for the exciting cause is reduced from-let us call it a positive value, to nothing when the secondary coil is withdrawn; it is changed from a positive value to an equal and opposite negative value when the primary current is reversed. Now comes the third characteristic difference between the magnetic bodies and the nonmagnetic. Suppose that, instead of plucking the nng apart when the current had a certain value, the current was raised to this value and then gradually diminished o nothing, and that then the ring was plucked apart and the secondary coil withdrawn. If the ring be nonmagnetic, we find that there is no deflection of the galvanometer; but, on the other hand, if the ring be of iron, we find a very large deflection, amounting, it may be, to 80 or 90 per cent. of the deflection caused by the withdrawal of the coil when the current had its full value Whatever be the property that the passing of the primary current has imparted to the iron, it is clear that the iron retains a large part of this property after the current has ceased. We may push the experiment a stage further. Suppose that the current in the primary is raised to a great value, and is then slowly diminished to a smaller value, and that the ring is opened and the secondary coil withdrawn. With most substances we find that the galvanometer deflection is precisely the same as if the current had been simply raised to its final value. It is not so with iron; the galvanometer deflection depends not alone upon the current at the moment of withdrawal, but on the current to which the ring has been previously subjected. We may then draw another curve (Fig. 2) representing the galvanometer deflections produced when the current has been raised to a high value and has been subsequently reduced to a value indicated by the abscissa. This curve may be properly called a descending curve. In the case of ordinary bodies this curve is a straight line coincident with the straight line of the ascending curve, but for iron Is a curve such as is represented in the drawing. You observe that this curve descends to nothing like zero when he current is reduced to zero; and that when the current 15 not only diminished to zero, but is reversed, the galvanometer deflection only becomes zero when the reversed current has a substantial value. This property possessed by magnetic bodies of retaining that which is impressed upon them by the primary current has been called by Prof. Ewing "hysteresis," or, as similar properties have been observed in quite other connections, "magnetic hysteresis." The name is a good one, and has been adopted. Broadly speaking, the induction as measured by the galvanometer deflection is independent of the time during which the successive currents have acted, and depends only upon their magnitude and order of succession. Some recent experiments of Prof. Ewing, however, seem to show a well-marked time effect. There are curious features in these experiments which require more elucidation. It has been pointed out by Warburg, and subsequently by Ewing, that the area of curve 2 is a measure of the quantity of energy expended in changing the magnetism of the mass of iron from that produced by the current in one direction to that produced by the current in the opposite direction and back again. The energy expended with varying amplitude of magnetizing forces has been determined for iron, and also for large magnetizing forces for a considerable variety of samples of steel. Different sorts of iron and steel differ from each other very greatly in this respect. For example, the energy lost in a complete cycle of reversals in a sample of Whitworth's mild steel was about 10,000 ergs per cubic centimetre; in oil hardened hard steel it was near 100,000; and in tungsten steel it was near 200,000-a range of variation of 20 to 1. it is, of course, of the greatest possible importance to keep this quantity low in the case of armatures of dynamos, and in that of the cores of transformers. If the armature of a dynamo machine be made of good iron, the loss from hysteresis may easily be less than 1 per cent; if, however, to take an extreme case, it were made of tungsten steel, it would readily amount to 20 per cent. In the case of transformers and alternate-current dynamo machines, where the number of reversals per second is great, the loss of power by hysteresis of the iron, and the consequent heating, become very important. The loss of power by hysteresis increases more rapidly than does the induction. Hence it is not well in such machines to work the iron to anything like the same intensity of induction as is desirable in ordinary continuous current machines. The quantity O A, when measured in proper units, as already explained-that is to say, the reversed magnetic force, which just suffices to reduce the induction as measured by the kick on the galvanometer to nothing after the material has been submitted to a very great magnetizing force-is called the "coercive force," giving a definite meaning to a term which has long been used in a somewhat indefinite sense. The quantity is really the important one in judging the magnetism of short per manent magnets. The residual magnetism, O B, is then practically of no interest at all; the magnetic moment depends almost entirely upon the coercive force. The range of magnitude is somewhat greater than in the case of the energy dissipated in a complete reversal. For very soft iron the coercive force is 16 C.G.S. units; for tungsten steel, the most suitable material for magnets, it is 51 in the same units. A very good guess may be made of the amount of coercive force in a sample of iron or steel by the form of the ascending curve, determined as I described at first. This is readily seen by inspection of Fig. 3, which shows the curves in the cases of wrought iron, and steel containing o'9 per cent. of carbon. With the wrought iron a rapid ascent of the ascending curve is made, when the magnetizing force is small and the coercive force is small; in the case of the hard steel the ascent of the curve is made with a larger magnetizing current, and the coercive force is large. There is one curious feature shown in the curve for hard steel which may, so far as I know, be observed in all magnetizable substances: the ascending curve twice cuts the descending curve, as at M and N. This peculiarity was, so far as I know, first observed by Prof. G. Wiedemann. I have already called emphatic attention to the fact that magnetic substances are enormously magnetic, and that non-magnetic substances are hardly at all magnetic : there is between the two classes no intermediate class. The magnetic property of iron is exceedingly easily destroyed. If iron be alloyed with 12 per cent. of manganese, the kick on the galvanometer which the material will give, if made into a ring, is only about 25 per cent. greater than is the case with the most completely nonmagnetic material, instead of being some hundreds of times as great, as would be the case with iron. Further, with this manganese steel, the kick on the galvanometer is strictly proportional to the magnetizing current in the primary, and the material shows no sign of hysteresis. In short, all its properties would be fully accounted for if we supposed that manganese steel consisted of a perfectly non-magnetic material, with a small percentage of metallic iron mechanically admixed therewith. Thus the property of non-magnetizability of manganese steel is an excellent proof of the fact-which is also shown by the non-magnetic properties of most compounds of iron-that the property appertains to the molecule, and not to the atom; or, to put it in another way, suppose that we were to imagine manganese steel broken up into small par ticles, as these particles became smaller there would z: length arrive a point at which the iron and the manganese would be entirely separated from each other: when this point is reached the particles of iron are non-magnetic By the magnetic molecule of the substance we mean the smallest part which has all the magnetic properties of the mass. The magnetic molecule must be big enough to contain its proportion of manganese. In iron, then, must have a collection of particles of such magnitude tha it would be possible for the manganese to enter into each of them, to constitute an element of the magnet. Ma ganese is, so far as I know, a non-magnetic elemen Smaller proportions of manganese reduce the magne property in a somewhat less degree, the reduction be greater as the quantity of manganese is greater. appeared very possible that the non-magnetic property of manganese steel was due to the coercive force being very great-that, in fact, in all experiments we were st on that part of the magnetization curve below the rapid rise, and that if the steel were submitted to greater forces it would presently prove to be magnetic, like other kinds of steel. Prof. Ewing, however, has submitted manganese steel to very great forces indeed, and finds that its magnetism is always proportional to the magnetizing force. No single body is known having the property of capacity for magnetism in a degree which is neither very great nor very small, but intermediate between the two extremes. We can, however, mix magnetic and nonmagnetic substances to form bodies apparently intermediate. It is, therefore, interesting to consider what the properties might be of such a mixture. It depends quite as much on the way in which the magnetic part is arranged in the mass, as on its actual quantity. Suppose, for example, it is arranged as in Fig. 4-in threads or plates having a very long axis in the direction of the magnetizing force-we may at once determine the curve of magnetization of the mixture from that of the magnetic substance by dividing the induction for any given force in the ratio of the whole volume to the volume of magnetic substance. If, on the other hand, it is as in Fig. 5-with a very short axis in the direction of the force, and a long axis perpendicular thereto-we can equally construct the curve of magnetization. This is done in Fig. 6, which shows the curve when nine-tenths of the material is highly magnetic iron, arranged as in Fig. 5, whilst the other curve of the same figure is that when only one-tenth is magnetic, but arranged as in Fig. 4. You observe how very differen is the character of the curve-a difference which is reduced by the much less proportion of magnetic material in the mixture in the one case than in the other. One peculiarity of these arrangements of the two materials in relation to each other is, that the resulting material is not isotropic: that is, its properties are not the same in all directions, but depend upon the direction of the magnetizing force in the material. Of course, this is not at all a probable arrange ment but it is instructive in showing the character of the |