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the phenomena of karyokinesis and their relation to fertilization will be reckoned hereafter as one of the most, if not the most, important of the biological discoveries of the past twenty years.

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Apart from Darwinism, the most remarkable development of biological studies during these "twice ten tedious years" is undoubtedly the sudden rise and gigantic progress of our knowledge of the Bacteria. Though the foundations were laid fifty years ago by Schwann and Henle, and great advances were made by Pasteur and by Lister just before our period, yet it is within this span that the microscope and precise methods of culture have been applied to the study of the vibrions," or "microbes," and the so-called "bacteriology" established. We now know, through the labours of Toussaint, Chauveau, Pasteur, and Koch, of a number of diseases which are definitely caused by Bacteria. We also have learnt from Pasteur how to control the attack of some of these dangerous parasites. Within these twenty years the antiseptic surgery founded by Sir Joseph Lister has received its full measure of trial and confirmation, whilst his opportunities and those of his fellow-countrymen for making further discovery of a like kind have been ignorantly destroyed by an Act of Parliament.

To particularize some of the more striking zoological discoveries which come within our twenty years, we may cite-the Dipnoous fish-like creature Ceratodus of the Queensland rivers, discovered by Krefft; the jumping wheel-animalcule Pedalion, of Hudson; the development and the anatomy of the archaic Arthropod Peripatus worked out by Moseley, Balfour, and Sedgwick; the Hydrocorallina of Moseley, an entirely new group of compound animals; the fresh-water jelly-fish Limnocodium of the Regent's Park lily-tank; the Silurian scorpion of Gotland and Lanarkshire; the protozoon Chlamydomyxa discovered by Archer in the Irish bogs; the Odontornithes and the Dinocerata of the American paleontologists; the intracellular digestion obtaining in animals higher than Protozoa, and the significance of the "diapedesis" of blood-corpuscles in inflammation, and the general theory of phagocytes due to Mecznikow; the establishment of the principle of degeneration as of equal generality with that of progressive development, by Anton Dohrn; the demonstration by Weismann and others that we have no right to mix our Darwinism with Larmarckism, since no one has been able to bring forward a single case of the transmission of acquired characters. Perhaps the attempt to purify the Darwinian doctrine from Lamarckian assumption will hereafter be regarded-whether it be successful or not-as the most characteristic feature of biological movement at the end of our double decade Its earlier portion was distinguished by the publication of some of Darwin's later works. Its greatest event was his death.

In botany, twenty years ago, the teaching in our Universities was practically sterile. In one of our earliest numbers, Prof. James Stewart defended with some vigour the propriety of intrusting botany to a lecturer at Cambridge who was also charged with the duty of lecturing on electricity and magnetism. It is startling to compare a past, in which botany was regarded as a subject which might be tacked on anywhere, with its present condition, in which there is scarcely a seat of learning in the three kingdoms which is not turning out serious work. The younger English school would be ungrateful if it did not acknowledge its debt to the eminent German teachers from whom it has derived so much in the tradition and method of investigation. Sachs and De Bary have left an indelible mark on our younger Professors. But it would be a mistake to suppose that English modern botany has simply derived from Germany. It has developed a character of its own, in which the indirect influence of Darwin's later work can be not indistinctly traced. There has been a gradual revolt in England, the ultimate consequences of which have still to be developed, against the too physical conception of the phenomena of plant life which has been prevalent on the Continent. Darwin, by his researches on insectivorous plants and plant movements from a purely biological point of view, prepared the way for this; Gardiner followed with a masterly demonstration of the physical continuity of protoplasm in plant tissues. This has thrown a new light on the phenomena studied by Darwin, and we need not, therefore, be surprised that his son, F. Darwin, has started what is virtually a new conception of the process of growth, by showing that its controlling element is to be sought in the living protoplasm of the cell, rather than in the investing cell-wall. On the whole, English botanists have shown a marked disposition to see in the study of protoplasm the real key to the interpretation of the phenomena of plant life. The complete analogy between the processes of secretion in animals and vegetables, established by Gardiner, and the essential part played by ferments in vegetable nutrition, illustrated by Green, are examples of the results of this line of inquiry. To Germany we owe a flood of information as to the function of the cell-nucleus, which it is singular has met with general acceptance but little detailed corroboration in this country.

In morphology a review would be ineffective which did not go somewhat deeply into detail. The splendid hypothesis of Schwendener, of the composite nature of lichens as a commensal union of Algae and Fungi, has gradually won its way into acceptance. In England there is little of the first rank which calls for note except the researches of Bower on the production of sexual organs on the leafy plant in ferns without the intervention of an intermediate generation.

In vegetable physiology there seems a pause; the

purely physical line of inquiry, as already suggested, to the University Colleges throughout the country, of seems to have yielded its utmost. The more biological which last it is to be hoped that a fair proportion will be line of inquiry has only yet begun to yield a foretaste devoted to the promotion of research rather than to the of the results which will undoubtedly ultimately flow reduction of class fees. from it.

Something must be added as to systematic and geographical botany. The " Genera Plantarum" of Bentham and Hooker, the work of a quarter of a century at Kew, affords a complete review of the higher vegetation of the world, and has been accepted generally as a standard authority. To Bentham also we owe the completion of the "Flora Australiensis," the first complete account of the flora of any great continent.

In geographical botany, perhaps the most interesting results have been the gradual elaboration of a theory as to the distribution of plants in Africa, and the botanical exploration of China, of the vegetable productions of which, twenty years ago, almost nothing was known.

In the classification of the lower plants, perhaps the most interesting result has been the happy observations of Lankester upon a coloured Bacterium, which enabled him to show that many forms previously believed to be distinct might be phases of the same life-history.

In geology probably the greatest advance has been in the application of the microscope to the investigation of rock structure, which has given rise to a really rational petrology. All except the coarser-grained rocks were only capable of being described in vague terms; with modern methods their crystalline constituents are determinable, however minute, and the conditions under which they were formed can be inferred.

It is impossible, even in a brief review of this kind, to think only of what has been won, and to ignore the loss of leaders who were once foremost in the fray. In England three names which will never be forgotten have been removed from the muster-roll. Darwin, Joule, and Maxwell can hardly be at once replaced by successors of equal eminence. As the need arises, however, men will no doubt be found adequate to the emergency, and it is at least satisfactory to know that they will appeal to a public more capable than heretofore of appreciating their efforts.

The support afforded by the Governments of Western Europe to scientific investigation has been markedly increased within the period which we survey. France has largely extended her subsidies to scientific research, whilst Germany has made use of a large part of her increased Imperial revenue to improve the arrangements for similar objects existing in her Universities. The British Government has shown a decided inclination in the same direction the grant to the Royal Society for the promotion of scientific research has been increased from £1000 to £4000 a year; whilst subsidies have been voted to the Marine Laboratory at Plymouth, to the Committee on Solar Physics, to the Meteorological Council, and quite recently

Twenty years ago England was in the birth-throes of a national system of primary instruction. This year has seen the State recognition of the necessity of a secondary and essentially a scientific system of education, and the Technical Instruction Act marks an era in the scientific annals of the nation.

The extension of scientific teaching has gone on rapidly within and without our Universities. Twenty years ago the Clarendon Laboratory at Oxford was approaching completion, and was the only laboratory in the country which was specially designed for physical work. Now, not only has Cambridge also its Cavendish Laboratory, but both Universities have rebuilt their chemical laboratories. both have erected buildings devoted to the study of biology. and the instruction of students in both zoology and botany has taken a characteristic practical form which we owe to the system of concentrating attention on a series of selected "types" introduced by Rolleston and by Huxley. Oxford has been furnished with an astronomical observatory by the liberality of Warren De la Rue, and Cambridge has accepted the noble gift of the Newall telescope. Nor have such proofs of the vitality of science been confined to the Universities.

Twenty years ago the Owens College was a unique institution: now, united with two thriving Colleges in Leeds and Liverpool, it forms the Victoria University; while science is studied in appropriate buildings in Birmingham, Newcastle, Nottingham, and half a dozen towns beside. A race is thus springing up which has sufficient knowledge of science to enforce due recognition of its importance, and public opinion can now, far more than in the past, be relied on to support its demands. Fortunately, too, these can be authoritatively expressed. The Royal Society wields, if it chooses to exercise it, an enormous power for good. Admitted on all hands to be the su preme scientific authority in this country, its decisions are accepted with a deference which can spring only from respect for the knowledge and scrupulous fairness by which they are dictated. If sometimes it moves slowly, pur se muove, and it is delightful to turn from the babble of the politicians to the study of an institution which does its work well, and perhaps too noiselessly. But even the House of Commons, hitherto ignorant and therefore apathetic in matters scientific, is awakening to the fact that there are forces to be reckoned with and impulses to be stimulated and controlled which are of more enduring import to the national welfare than mere party politics. And the people, too, are beginning to see that it is to the economic working of these forces, and to the right direction of these impulses, that their representatives are bound to give attention. True it is that

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MODERN VIEWS OF ELECTRICITY.

Modern Views of Electricity. By Oliver J. Lodge, D.Sc.,
LL.D, F.R.S. (London: Macmillan and Co., 1889.)

IN this interesting book Prof. Lodge gives a very lively
and graphic account of many of the most recent
speculations about the nature of electrical phenomena.
A work with this object was urgently needed, as the
method of regarding these phenomena given in popular
treatises on electricity is totally different from that used
by those engaged in developing the subject.

The attention called by Faraday and Maxwell to the effects produced by and in the medium separating electrified bodies has had the effect of diverting attention from the condition of the charged bodies in the electric field to that of the medium separating them, and it is perhaps open to question whether this of late years has not been too much the case. To explain the effects observed in the electric field we should require to know the condition not only of the ether, but also of the conductors and insulators present in it; just as a compiete theory of light would include the state of the luminous bodies as well as of the ether transmitting the radiations excited by them, Since matter is more amenable to experiment than the ether, it seems most probable that we shall first gain an insight into the nature of electricity from a study of those cases where matter seems to play the chief partsuch as in the electric discharge through gases, and the phenomena of electrolysis-rather than from speculations, however interesting, as to what takes place in the ether when it is transmitting electrical vibrations. Prof. Lodge, however, in the work under consideration, devotes most of his space to the consideration of the ether. In his preface he says, "Few things in physical science appear to me more certain than that what has so long been called electricity is a form, or rather a mode, of manifestation of the ether;" and he proceeds to give precision to this somewhat vague statement by developing a theory that electricity is a fluid, and a constituent of a very complex ether. In the first few chapters he supposes that all insulators, including the ether, have a cellular structure the cells being filled with a fluid which is electricity, and which is not able to get from one cell to another unless the walls of the cells are broken down; in conductors, however, there are channels between the cells, so that the electricity is able to flow more or less freely through them. A flow of this fluid is an electric current. But if this is the case, anything which sets the ether in motion will produce an electric current. Now, Fizeau's experiments show that moving bodies carry the ether with them to an extent depending on their index

of refraction; so that a disk made of glass or other refracting substance, if set in rapid rotation about an axis through its centre, and at right angles to its plane, ought to act as if currents were circulating in the disk, and produce a magnetic field around it. In order to observed which indicates that a magnet or a current avoid the allied difficulty that nothing has ever been flowing through a coil possesses gyroscopic properties, Prof. Lodge assumes, in subsequent chapters, that the fluid in the cells of the ether is a mixture of two fluids, and that these two fluids are positive and negative electricity and that, in order to exhibit any electrical effect, the compound fluid has first to be decomposed into positive and negative electricity by the application of an electromotive force. A current of electricity, on this view, consists of the flow of equal quantities of positive and

negative electricity in opposite directions. Thus this, the most "modern view of electricity," is in its most important features almost identical with the old two-fluid theory published by Symmer in 1759. We confess we do not think the theory in its present form advances the science of electricity much it does not suggest new phenomena, nor does it lend itself readily to explain the action of matter in modifying electrical phenomena; it demands, too, a very artificial ether. It would seem that the first steps required to make a theory of this kind a real advance on the old two-fluid theory would be the discovery of a structure for the ether, which would possess the same kind of properties as the mixture of the two electricities on that theory. A great deal, too, is left indefinite in the theory: thus, for example, we are not told whether for a given current these streams are moving slowly or with prodigious velocities. In fact, there is throughout the book rather a want of definite conclusions, and this is rather hidden by the vigorous style in which Prof. Lodge writes: he develops his ideas in such an enthusiastic and interesting way that on the first reading they seem to be a good deal more definite than they prove

to be on calmer reflection.

But whatever may be thought of Prof. Lodge's theory of electricity, there can be, we think, no two opinions of the value of the numerous models illustrating the properties of electrical systems which he has invented. These must prove of the greatest assistance in enabling the student to gain a clear and vivid idea of electrical processes, and ought to be largely employed by all teachers of electricity.

In a work dealing so briefly with such a multitude of different and difficult subjects it is natural that there should be many statements to which exception might be taken. Prof. Lodge disarms criticism by his frank admission of this; sometimes, also, by an amusing vagueness of statement: thus, on p. 206, in speaking of the condition of the ether in-ide a strongly-magnetizable substance, he says: "Perhaps it is that the atoms themselves revolve with the electricity; perhaps it is something quite different." There are, however, some statements of a less theoretical kind which seem to us likely to mislead the student. Thus it is stated that the amount of the Peltier effect shows that the difference of potential between zinc and copper is only a few micro-volts. The Peltier effect, however, without further assumption, cannot tell us anything about the absolute magnitude of the difference of

potential between the metals; it can only give us the value of the temperature coefficient, which is equal to the Peltier effect divided by the absolute temperature. Then, again, the pyro-electricity of tourmaline is explained by the unilateral conductivity of a tourmaline crystal whose temperature is changing, discovered by the author and Prof. Silvanus Thompson. If this unilateral conductivity is regarded as proving the existence of an electromotive force in a crystal which is increasing or decreasing in temperature, the explanation is valid, but in the text nothing is said about an electromotive force, and the student might be led to infer that a mere difference in resistance could explain pyro electricity. The way in which a current flows past an insulating obstacle, the lines of flow closing in on the obstacle, and leaving nothing corresponding to "dead water" behind it, is given as a proof that the electric current has no mechanical momentum; but unless the corners of the obstacle were infinitely sharp, a slowly-moving fluid might flow in the same way as electricity, even though it possessed inertia, so that the proof is not conclusive. It is also stated that the effects on light produced by a magnetized body, discovered by Dr. Kerr, of Glasgow, have been deduced by Prof. Fitzgerald from Maxwell's theory of light. As a matter of fact, however, the results deduced from this theory by Fitzgerald do not coincide with those observed by Dr. Kerr and Prof. Kundt. The production in an unequally-heated conductor of an electromotive force is explained by supposing the atoms in such a body to be moving faster in one direction than the opposite, and therefore, since they are supposed to drag the ether with them, producing a flow of ether in the direction in which they are moving fastest; but, on the dualistic theory of electricity adopted in this book, this ether stream would consist of equal quantities of positive and negative electricity moving in the same direction, and this would not produce any electrical effect.

At the end of the book are three popular lectures de. livered by Prof. Lodge, the first on the relation between electricity and light, the second on the ether and its functions, and the third his admirable one at the Royal Institution, on the discharge of a Leyden jar, which is a model of what such a lecture ought to be.

Taken as a whole, we think that the book is one which ought to be read by all advanced students of electricity; they will get from it many of the views which are guiding those who are endeavouring to advance that science, and it is so stimulating that no one can read it without being inspired with a desire to work at the subject to which it is devoted.

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causes" of an observed event, or the ways in which might have happened, by means of the calculus of prob abilities, it is usual to make certain unwarranted assump tions concerning the so-called a priori probability of those causes. Suppose that a number of black and white bils have been drawn at random from an urn, and from th datum let us seek to determine the proportion of black and white balls in the urn. It is usual to assume, without sufficient grounds, that a priori one proportion of balls. one constitution of the urn, is as likely as another. Or suppose a coin has been tossed up a number of times, and from the observed proportion of heads and tails let it be required to determine whether and in what degree the coin is loaded. Some assumption must be made as to the probability which, prior to, or abstracting from, our observations, attaches to different degrees of loading. The assumptions which are usually made have a fallacious character of precision.

Again, M. Bertrand points out that the analogy of ums and dice has been employed somewhat recklessly by Laplace and Poisson. It is true that the ratio of male to female births has a constancy such as the statistics games of chance present. But, before we compare boyand girls to black and white balls taken out at random from an urn, we must attend not only to the average proportion of male to female births, but also to the deviations from that average which from time to time or from place to place may be observed. The analogy of urns and ballis more decidedly inappropriate when it is applied to determine the probable correctness of judicial decisions The independence of the judges or jurymen which the theory supposes does not exist.

"Quand un juge se trompe il y a pour cela des raisons il n'a pas réellement mis la main dans une urne où le hazard l'a mal servi. Il a ajouté foi à une faux te moignage, le concours fortuit de plusieurs circonstances a éveillé à tort sa défiance, un avocat trop habile l'a ému, de hautes influences peutêtre l'ont ébranlé. Ses collègues ont entendu les mêmes témoins, on les a instruits des mêmes circonstances, le même avocat a plaidé devant eux, on a tenté sur eux la mê.ne pression."

With equal force does M. Bertrand expose the futility of the received reasoning by which it is pretended to determine the probability that the sun will rise to-morrow from the fact that it has risen so many days in the past.

These reflections are just and important; but their value is somewhat diminished by the fact that they have been, for the most part, made by previous writers with whom our author seems unacquainted. Thus Prot Lexis has more carefully considered the extent of the error committed by Laplace and Poisson in applying to male and female births and other statistics rules derived from games of chance. The fundamental principles of Probabilities have been more fully explored by Dr. Venn. M. Bertrand, like Laplace, starts by defining the prob ability of an event as the ratio of the number of favourable cases to the number of possible cases. He does not explain what constitutes a "favourable case "—that, when a die is thrown, the probability of obtaining the 3 of 4 is one-sixth, because as a matter of fact each side in the long run turns up once out of six times. Accordingly when he argues that in a great number of trials each event is most likely to occur with a frequency correspond

ing to its probability, he lays himself open to the charge of circularity which Dr. Venn has brought against Bernouilli's theorem. Without pronouncing on this delicate question, we may safely say, with respect to the first principles of the subject, that no point which has been left obscure by Dr. Venn has been cleared up by M. Bertrand.

It is with respect to the purely mathematical portion of the calculus, or that part of its metaphysics which is inextricably mixed with mathematics, that we expected and have found most assistance from M. Bertrand. Hitherto the study of Probabilities has been barred by the dilemma which M. Bertrand thus states:

"On ne peut bien connaître le calcul des probabilités sans avoir lu le livre de Laplace; on ne peut lire le livre de Laplace sans s'y préparer par les études mathématiques les plus profondes."

Much of Laplace's analysis which must have affected many eager students like stickjaw has been simplified by M. Bertrand. He is in general more readable than Poisson. Several of the theorems which he gives seem to be new. His methods of determining from a given set of observations the characteristic, or modulus, appertaining to the source of error are specially interesting.

M. Bertrand's mathematical power enables him to carry the torch of common-sense to those perplexed parts of the subject where less qualified critics, awed by the imposing mass of symbols, have hesitated to differ from Laplace or Poisson. Of this kind is the simultaneous determination of several quantities from a great number of equations. When Laplace computes that the odds are a million to one against the occurrence of an error of assigned magnitude in the determination of Jupiter's mass, M. Bertrand shows reasons for suspecting the accuracy of such computations. In fact, he carries out Poinsot's witty direction:

"Après avoir calculé la probabilité d'une erreur il faudrait calculer la probabilité d'une erreur dans le

calcul."

The true import and proper application of the theory of errors of observation are thus well expressed :

"On peut accepter sans crainte le résultat, mais il est téméraire d'évaluer en chiffres la confiance qu'il doit inspirer."

M. Bertrand teaches with authority-and not like those who have not followed the higher mathematical reasonings of the calculus-in what spirit its conclusions should be accepted.

Still, even with regard to those parts of the subject where a first-rate mathematician has so great an advantage, we venture to think that the work would have been much more valuable if the writer had taken the trouble to acquaint himself more fully with what his predecessors had done. For example, in discussing the reasons for taking the arithmetic mean of a set of observations (presumed to be equally good) re'ating to a single quantity, M. Bertrand does not dwell on the argument that the probability-curve -with which the arithmetic mean is specially correlated-is apt to represent the grouping of errors for this reason, that an error may be regarded as a function of a great number of elements each obeying some definite law of facility, and that the values of such a function conform to the probability-curve. It is true that Laplace, from

whom this argument may be derived, has not himself used it very directly. But in a writer on the method of least squares we may expect some conversance with more recent works, in particular with Mr. Glaisher's classical paper in the Memoirs of the Astronomical Society (London). Moreover, Laplace does employ the mathematical theorem which we have indicated, not indeed to prove that the law of facility for errors of observation in general is the probability-curve, but that, whatever that law of facility be, the most advantageous combination is a certain linear function. A treatise in which this celebrated argument is not discussed cannot be regarded as exhaustive. But it is remarkable that with respect to the combination of observations, M. Bertrand seems to defer more to Gauss than to his own eminent countryman.

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M. Bertrand has indeed slipped in a doctrine for which the authority of Laplace may be quoted, that in choosing the best combination of a set of observations "there is essential difference between the most probable value of a quantity and the value which it is best to adopt" (Bertrand, Art. 138); the latter being the mean (first power) of the observations (Art. 155)—which M. Bertrand rather awkwardly terms "la valeur probable." M. Bertrand does not seem to realize the gravity of the assumption which is contained in the latter clause. Later on he employs Gauss's criterion of erroneousness—namely, the mean square of error. But the ground, nature, and relation of these two principles are not very clearly explained by the writer. With respect to the philosophical foundation of the method of least squares he has not superseded the necessity of studying Laplace.

With these reservations, M. Bertrand's work may be regarded as one of the most complete treatises on the subject. Nowhere else are the two elements so peculiarly combined in the science of Probabilities-commonsense and mathematical reasoning-to be found existing F. Y. E. together in such abundance.

ARGENTINE ORNITHOLOGY.

Argentine Ornithology. By P. L. Sclater, Ph.D., F.R.S., and W. H. Hudson, C.M.Z.S. Vol. II. (London: W. H. Porter, 1889.)

THE

HE completion of this important work is an event of considerable importance to every lover of neotropical zoology, and the authors have both performed their parts well, while the ten plates by Mr. Keulemans are beautifully drawn and admirably coloured. Among the increasing number of Englishmen who settle in the Argentine Republic, there are sure to be many who will pursue natural history studies, and to all such a well-executed book like the present will be invaluable. The joint authors of the work are happy in their association, for while Dr. Sclater brings to the work a vast experience, and a sound scientific knowledge of his subject, it is certain that never was there a better describer of the habits of birds than Mr. Hudson. Although of English parentage, he is a native-born Argentine, and he has grown up among the birds whose life and history he so well knows how to portray. In turning over the pages of this volume, we have found many interesting extracts which we should have liked to present to our readers,

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