belief that my work does not throw any light upon the causes of variation. There are however many zoologists who believe that it has such a bearing, and indeed it seems only natural that writers (such as Dr. Romanes himself) who retain the Lamarckian conception of the direct influence of surroundings in causing the variations of the higher animals, should believe (as I think wrongly) that they see evidence for the soundness of their views in the results of experiments in which the colours of insects have been completely modified in a single generation by the action of environment. EDWARD B. POULTON

Oxford, July 15.

The Thunder-Axe.

THOSE who are interested in the study of anthropology need no reminder as to the European belief in a connection between ancient stone weapons and thunder. It would be mere waste of time if I quoted instances of this connection; but it may not be devoid of interest to some of your readers if I bring to their notice a modern account of the thunder-weapon, as described to-day by a New Zealander. The account may also be of service to those studying another branch of anthropology-that concerning the influence and value of ancient and modern creeds warring in the minds of semi-civilized peoples. I shall make no comment of my own, but proceed to give a translation of a tale printed (in Maori only) in the pages of the native newspaper, the Korimako. The few words in it which were not understood by those acquainted with the ordinary Maori speech, I referred to old men well versed in the dialect of that part of New Zealand.

"The finding of Te Awhiorangi.

"The tribes of this island have hitherto only heard of Te Awhiorangi, but have not seen it. We, Ngarauru-that is, the people descended from Rangitaupea, our ancestor who hid the axe-have never seen it until now. . . One of our settlements, called Okutuku, is near Waitotara. Twenty natives from this settlement proceeded in a party for the purpose of gathering the edible fungus (Hākekākeka) for the purpose of sale. With the party went a young woman whose name was Tomairangi (Dew of Heaven), the wife of Te Potonga Kaiawha. This girl was a perfect stranger in the district: she did not know where the sacred (tapu) places were; she belonging to the Ngaitahu (a South Island tribe), but her father was of us, the Ngarauru. The girl wandered away by herself, looking here and there, searching for trees on which the fungus grew. She saw a tree on which there was fungus, and laid her hand on it, but suddenly there came the flash of the Axe. Following with her eyes the direction of the flash, she saw the Axe close against the foot of a Pukatea tree; a cry of terror broke from her, and she fled screaming. At the same time the thunder roared, the lightning flashed, and blinding hail burst forth in sudden storm, increasing her terror almost to madness. Her husband heard her cries as she flew along: but an old man, called Te Rangi Whakairione, directly he heard her shrieks, understood the reason of the outcry, so he began to chant an incantation, and the fury of the storm abated. When the party had assembled together in the open land, the old priest asked which of them had been to Tieke; whereupon the girl asked Where is Tieke?' The old man answered that it was beyond the turn at Waione. Tomairangi replied, I have been there, but I did not know it was a sacred place: I saw something that looked like a spirit, and I am full of great fear.' Then all the party went to ascertain what it was, and then they found that it was indeed the lost sacred Axe, Te Awhiorangi. After Te Rangi Whakairione had chanted another incantation over it, they all took hold of the Axe, and wailed over it. When the crying had ceased, they brought the Axe back to the settlement. All the tribe knew that the Axe was somewhere in that vicinity, for our ancestor Rangitaupea had passed the secret on to his children in the words, Te Awhiorangi is at Tieke on the plain close above the Cave of the Dead.' Until now that place has been unvisited, being entirely sacred till this day, the 10th of December, 1887. Then gathered all Ngarauru and some of the Whanganui and Ngatiapa tribes, in number 300 persons, and at dawn the next day the sacred thing was hung up on a tree that all might see it. The priests, Kapua Tautahi and Werahiko Taipuhi were at the head of the procession as they approached the place: they reciting charms and incantations as they moved along with the people following. All the people carried green branches in

their hands as an offering to Te Awhiorangi. When the concourse drew near the place, successive peals of thunder and flashes of lightning rent the air; then came down a dense fog, making it dark as night. The Tohunga (priests) stopped the thunder and dispersed the darkness by their incantations. When the light again appeared, the people offered the green branches, together with a number of Maori mats, &c. ; then they made lamentations, and sang the old songs in which the ancient Axe was spoken of by their forefathers.

Thus far the native account. Then follows an enumeration of the articles offered up as propitiation; then a description of the axe, which appears to be a huge and beautiful specimen of the stone weapon, so highly polished that the face of the beholder may be seen reflected in it. Afterwards, the pedigree, or rather the mythological history, of the axe, showing how (name by name) it had been handed down from the first Maori chief who came to New Zealand (Turi), and that it had descended to him, through the great god Tane, from the primeval pair, Heaven and Earth (Rangi and Papa). But our chief interest in it is the thunder heralding its finding.

Wellington, N.Z., June 11.

EDWARD TREGEAR.

The Dispersion of Seeds and Plants.

I HAVE read with much interest Mr. Morris's communication on the above subject (NATURE, vol. xxxvii. p. 466), and can corroborate most of what he states from personal observation. I can also remove his doubt respecting the germination of the seeds of the Guava and Passiflora, to which may also be added the Tomato.

I have adopted the "earth system" in my w.c., and from the place where the earth is deposited may always be gathered fine young plants of the three genera named above.

Thousands of acres of pasturage have been destroyed in this island by the distribution by birds of the Lantana, which was unfortunately introduced here by the first Roman Catholic missionaries, to form a hedge for their property at St. Louis or Conception. The " Gendarme plant " (an Asclepiad) was brought here in a pillow by a gendarme from Tahiti. It was a seed attached to a wing of silk cotton. The gendarme shook out his pillow; the wind carried the seed to a suitable spot, and now it vies with the Lantana in destroying our pastures.

I have shot the Great Fruit Pigeons of Fiji and this island with several seeds of the Canarium (?) in their crops, as Mr. Morris says, as big as hen's eggs. The seeds of water-plants are conveyed, with the eggs of fresh-water Mollusca, to vast distances, adhering to the hairs and feathers of the legs of water birds-ducks, herons, and waders of all sorts. In London the basins of the fountains in Trafalgar Square were peopled by Lymnea brought thither from the Serpentine, attached to the feathers of the sparrows who bathed, first in one, and then in the other.

I

Another plant which occurs to me as being largely indebted to man for its distribution, is that known as the "Cape Gooseberry," which is a native of South America (I forget its botanical name). The Kaffirs call it the " White man's plant," and say it follows the white man everywhere. I know it is found in India, Ceylon, Africa, Fiji, New Caledonia, New Hebrides. really believe boiling it into jam does not destroy the vitality of the seeds. We have just got a plant here, bearing a lovely flower, but whence it comes no one knows. It has hard wooden seed capsules, each furnished with two hooks as hard as steel and as sharp as needles, this size and shape. These, hooking

into the hide of any animal, would be carried for days until forcibly dislodged.

The Bathurst burr" (Xanthium spinosum) was introduced into the Cape in a cargo of wool wrecked at Cape Lagulhas, and spread out to dry, first there, and then at Simon's Town, at both of which places the "burr" sprang up. I believe and hope I destroyed the first and last plant of it that sprang up in New Zealand some twenty-five years ago. The seed had been

July 26, 1888]

The owner of brought in the living fleece of a fine merino ram. the pasture was cherishing the "wonderful new plant," and was not a little horrified when I took out my knife and carefully cut it down. He was more horrified when I told him what it was.

The seeds of some of the Indian banians, I believe, require to pass through the bodies of birds to enable them to germinate. A minute bird (Diceum) feeds on them, and is so small that its dropping cannot fall clear of the branch on which it sits, conseSometimes this quently is glued to the bark and takes root. takes place on a palm tree; the roots then run down the trunk, and finally smother their host.

British Consulate, Noumea, May 15.

Indian Life Statistics.

E. L. LAYARD.

ALTHOUGH Mr. Hill (in NATURE of July 12, p. 250) refers to the Holi festival as among possible influences in causing variations of births, he does not say whether he considers lucky and unlucky months and years, which so largely affect marriages in India, as incidents which may have an effect.

HYDE CLARKE.

IG. 31-To the left is a pair of leaves of the Scotch pine, with the blisterlike Ecidia. a. of Peridermium Pini (var. acicola) projecting from their tissues: these blisters are orange-yellow in colour, and contain Between the blisters are the minute spores, as shown in Fig. 33. To the right is a small branch, killed at a aa by

b

spermium Pini (var. corticola), the blister-like yellow Ecidia of

the fungus being very conspicuous. (Reduced, after Hartig.) yellow vesicles the lens shows certain smaller brownish or almost black specks. Each of the vesicular swellings is a form of fungus-fructification known as an Ecidium, and each of the smaller specks is a fungus-structure called a Spermogonium, and both of these bodies are developed from a mycelium in the tissues of the leaf. I must employ these technical terms, but will explain them more in detail shortly the point to be attended to for the moment is

1 Continued from p. 272.

FIG. 33.-Vertical section through a very young Ecidium of Peridermium Pini (var. acicola), with part of the subjacent tissue f the leaf. h, the mycelium of the parasitic fungus running between the cells of the leaf: immediately beneath the epidermis of the leaf, the ends of the hyphæ give rise to the vertical rows of spores (6), the outermost of which (p) remain barren, and form the membrane of the blister-like body. The epidermis is already ruptured at by the pressure of the young Ecidium. (After R. Hartig: highly magnified.)

arranged in vertical rows, each row springing from a branch of the mycelium: the outermost of these sporesi.e. those which form a compact layer close beneath the epidermis-remain barren, and serve as a kind of membrane covering the rest (Fig. 33, ). It is this membrane which protrudes like a blister from the tissues. The hyphæ of the fungus are seen running in all directions between the cells of the leaf-tissue, and as they rise up and form the vertical chains of spores, the pressure gradually forces up the epidermis of the leaf, bursts it, and the mass of orangeyellow powdery spores protrude to the exterior enveloped

in the aforesaid membrane of contiguous barren spores. If we examine older Ecidia, it will be found that this membrane bursts also at length, and the spores escape. Similar sections across a Spermogonium exhibit a structure which differs slightly from the above. Here also the hyphæ in the leaf turn upwards, and send delicate branches in a converging crowd beneath the epidermis; the latter gives way beneath the pressure, and the free tips of the hyphæ constrict off very minute sporelike bodies. These minute bodies are termed Spermatia, and I shall say no more about them after remarking that they are quite barren, and that similar sterile bodies are known to occur in very many of the fungi belonging to this and other groups.

Sections through the Ecidia and Spermogonia on the cortex present structures so similar, except in minute details which could only be explained by lengthy descriptions and many illustrations, that I shall not dwell upon them; simply reminding the reader that the resemblances are so striking that systematic mycologists have long referred them to a mere variety of the same fungus. Now as to the kind and amount of damage caused by the ravages of these two forms of fungus.

In the leaves, the mycelium is found running between the cells (Fig. 33, h), and absorbing or destroying their contents: since the leaves do not fall the first season, and the mycelium remains living in their tissues well into the second year, it is generally accepted that it does very little harm. At the same time, it is evident that, if very many leaves are being thus taxed by the fungus, they cannot be supplying the tree with food materials in such quantities as if the leaves were intact. However, the fungus is remarkable in this respect that it lives and grows for a year or two in the leaves, and does not (as so many of its allies do) kill them after a few weeks. It is also stated that only young pines are badly attacked by this form: it is rare to find Ecidia on trees more than twenty years or so old.

Much more disastrous results can be traced directly to the action of the mycelium in the cortex. The hyphæ grow and branch between the green cells of the true cortex, as well as in the bast-tissues beneath, and even make their way into the medullary rays and resin-canals in the wood, though not very deep. Short branches of the hypha pierce the cells, and consume their starch and other contents, causing a large outflow of resin, which soaks into the wood or exudes from the bark. It is probable that this effusion of turpentine into the tissues of the wood, cambium, and cortex, has much to do with the drying up of the parts above the attacked portion of the stem: the tissues shrivel up and die, the turpentine in the canals slowly sinking down into the injured region. The drying up would of course occur if the conducting portions are steeped in turpentine, preventing the conduction of water from below.

The mycelium lives for years in the cortex, and may be found killing the young tissues just formed from the cambium during the early summer of course the annual ring of wood, &c., is here impoverished. If the mycelium is confined to one side of the stem, a flat or depressed spreading wound arises; if this extends all round, the parts above must die.

When fairly thick stems or branches have the mycelium on one side only, the cambium is injured locally, and the thickening is of course partial. The annual rings are formed as usual on the opposite side of the stem, where the cambium is still intact, or they are even thicker than usual, because the cambium there diverts to itself more than the usual share of food-substances: where the mycelium exists, however, the cambium is destroyed, and no thickening layer is formed. From this cause arise cancerous malformations which are very common in pine-woods (Fig. 34).

Putting everything together, it is not difficult to explain the symptoms of the disease. The struggle between the

mycelium on the one hand, which tries to extend all round in the cortex, and the tree itself, on the other, as it tries to repair the mischief, will end in the triumph of the fungus as soon as its ravages extend so far as to cut off the watersupply to the parts above this will occur as soon as the mycelium extends all round the cortex, or even sooner if the effusion of turpentine hastens the blocking up of the channels. This may take many years to accomplish.

So far, and taking into account the enormous spread of this disastrous disease, the obvious remedial measures seem to be, to cut down the diseased trees--of course this should be done in the winter, or at least before the spores come-and use the timber as best may be ; but we must first see whether such a suggestion needs modifying, after learning more about the fungus and its habits. It appears clear, at any rate, however, that every diseased tree removed means a source of Ecidiospores the less. Probably everyone knows the common groundsel, which abounds all over Britain and the Continent, and no doubt many of my readers are acquainted with other species of the same genus (Senecio) to which the groundsel belongs, and especially with the ragwort (Senecio Jacobea). It has long been known that the leaves of these plants, and of several allied species, are attacked by a fungus, the mycelium of which spreads in the leaf-passages, and gives rise to powdery masses of orange-yellow spores, arranged in vertical rows beneath the stomata: these powdery

FIG. 34. Section across an old pine-stem in the cancerous region injured by Peridermium Pini (var, corticola). As shown by the figures, the ster was fifteen years old when the ravages of the fungus began to affect the cambium near a The mycelium, spreading in the cortex and cambium on all sides, gradually restr.cted the action of the latter more and more: at thirty years old, the still sound cambium only extended half-way round the stem-no wood being developed on the opposite side. By the time the tree was eighty years old, only the small area of cambium indicated by the thin line marked 80 was still alive; and soon afterwards the stem was completely "ringed," and dead, all the tissues being suffused with resin. (After Hartig.)

masses of spores burst forth through the epidermis, but are not clothed by any covering, such as the Æcidia of Peridermium Pini, for instance. These groups of yellow spores burst forth in irregular powdery patches, scattered over the under sides of the leaves in July and August: towards the end of the summer a slightly different form of spore, but similarly arranged, springs from the same mycelium on the same patches. From the differences in their form, time of appearance, and (as we shall see) functions, these two kinds of spores have received different names. Those first produced have numerous papillæ on them, and were called Uredospores, from their analogies with the uredospore of the rust of wheat; the second kind of spore is smooth, and is called the Teleutospore, also from analogies with the spores produced in the late summer by the wheat-rust. The fungus which produces these uredospores and teleutospores was named, and has been long distinguished as, Coleosporium Senecionis (Pers.). We are not immediately interested in the damage done by this parasite to the weeds which it infests, and at any rate we might well be tempted to rejoice in its destructive action on these garden pests: it is sufficient to point out that the influence of the mycelium is to shorten the lives of the leaves, and to rob the plant of food material in the way referred to generally in my last article.

What we are here more directly interested in is the

following. A few years ago Wolff showed that if the spores from the Ecidia of Peridermium Pini (var. acicola) are sown on the leaf of Senecio, the germinal hypha which grow out from the spores enter the stomata of the Senecio leaf, and there develop into the fungus called Coleosporium Senecionis. In other words, the fungus growing in the cortex of the pine, and that parasitic on the leaves of the groundsel and its allies, are one and the same: it spends part of its life on the tree and the other part on the herb.

If I left the matter stated only in this bald manner, it is probable that few of my readers would believe the wonder. But, as a matter of fact, this phenomenon, on the one hand, is by no means a solitary instance, for we know many of these fungi which require two host-plants in order to complete their life-history; and, on the other hand, several observers of the highest rank have repeated Wolff's experi ment and found his results correct. Hartig, for instance, to whose indefatigable and ingenious researches we owe most that is known of the disease caused by the Peridermium, has confirmed Wolff's results.

It was to the brilliant researches of the late Prof. De Bary that we owe the first recognition of this remarkable phenomenon of heteræcism-i.e. the inhabiting

FIG. 35.-A spore of Peridermium Pini germinating. It puts forth the long, branched germinal hyphæ on the damp surface of a leaf of Senecio, and one of the branches enters a stoma, and forms a mycelium in the leaf: after some time, the mycelium gives rise to the uredospores and teleutospores of Coleosporium Senecionis. (After Tulasne: highly magnified.)

more than one host-of the fungi. De Bary proved that the old idea of the farmer, that the rust is very apt to appear on wheat growing in the neighbourhood of berberry-bushes, was no fable; but, on the contrary, that the yellow Ecidium on the berberry is a phase in the life-history of the fungus causing the wheat-rust. Many other cases are now known, eg. the Ecidium abietinum, on the spruce firs in the Alps, passes the other part of its life on the Rhododendrons of the same region. Another well-known example is that of the fungus Gymnosporangium, which injures the wood of junipers: Oersted first proved that the other part of its life is spent on the leaves of certain Rosaceæ, and his discovery has been repeatedly confirmed. I have myself observed the following confirmation of this. The stems of the junipers so common in the neighbourhood of Silverdale (near Morecambe Bay) used to be distorted with Gymnosporangium, and covered with the teleutospores of this fungus every spring in July all the hawthorn hedges in the neighbourhood had their leaves covered with the Ecidium form (formerly called Ræstelia), and it was quite easy to show that the fungus on the hawthorn leaves was produced by

sowing the Gymnosporangium spores on them. Many other well-established cases of similar heterocism could be quoted.

But we must return to the Peridermium Pini. It will be remembered that I expressed myself somewhat cautiously regarding the Peridermium on the leaves (var. acicola). It appears that there is need for further investigations into the life-history of this form, for it has been thought more than probable that it is not a mere variety of the other, but a totally different species.

Only so lately as 1883, however, Wolff succeeded in infecting the leaves of Senecio with the spores of Peridermium Pini (acicola), and developing the Coleosporium, thus showing that both the varieties belong to the same fungus.

It will be seen from the foregoing that in the study of the biological relationships between any one plant which we happen to value because it produces timber, and any other which grows in the neighbourhood there may be (and there usually is) a series of problems fraught with interest so deep scientifically, and so important economically, that one would suppose no efforts would be spared to investigate them: no doubt it will be seen as time progresses that what occasionally looks like apathy with regard to these matters is in reality only apparent indifference due to want of information.

:

Returning once more to the particular case in question, it is obvious that our new knowledge points to the desirability of keeping the seed-beds and nurseries especially clean from groundsel and weeds of that description on the one hand, such weeds are noxious in themselves, and on the other they harbour the Coleosporium form of the fungus Peridermium under the best conditions for infection. It may be added that it is known that the fungus can go on being reproduced by the uredospores on the groundsel-plants which live through the winter. H. MARSHALL WARD.

(To be continued.)

EARTHQUAKES AND HOW TO MEASURE THEM

PROF EWING explained that the study of earthquakes

had two aspects, one geological and the other mechanical, and it was of the latter alone that his lecture was to treat. The mechanical student of earthquakes concerned himself with the character of the motion that was experienced at any point on the earth's crust, and with the means by which an earthquake spread from point to point by elastic vibration of rock and soil. The first problem in seismometry was to determine exactly how the ground moved during an earthquake, to find the amount and direction of every displacement, and the velocity and rate of acceleration at every instant while the shaking went on. He was to deal with the solution of that problem, and to describe some of the results which had been obtained in the measurement of earthquakes in Japan, where earthquakes happened with a frequency sufficient to satisfy the most enthusiastic seismologist. Most early attempts to reduce the observing of earthquakes to an exact science had failed because they were based on a false notion of what earthquake motion was. It had been supposed that an earthquake consisted of a single or at least a prominent jerk, or a few jerks, easily distinguishable from any minor oscillations that might occur at the same time. The old column seismometer, for instance, recom mended in the Admiralty Manual of Scientific Inquiry, attempted to measure what was called the intensity of the shock by means of a number of circular columns of various diameters which were set to stand upright like ninepins on a level base. It was expected that the shock 1 Abstract of a Lecture delivered at the Royal Institution on Friday evening, June 1, by Prof. J. A. Ewing, F.R.S.

would overthrow the narrower columns, the broadest that fell serving to measure its severity, and that the columns would fall in a direction which would point to the place of origin of the disturbance. In fact, however, such columns fell most capriciously when they fell at all, and it was impossible to learn anything positive from their behaviour in an earthquake. The reason was that there was no single outstanding impulse: an earthquake consisted of a confused multitudinous jumble of irregular oscillations, which shifted their direction with such rapidity that a point on the earth's surface wriggled through a path like the form a loose coil of string might take if it were ravelled into a state of the utmost confusion. The mechanical problem in seismometry was to find a steady-point-to suspend a body so that some point in it, at least, should not move while this complicated wriggling was going on. The steady-point would then serve as a datum with respect to which the movement of the ground might be recorded and measured. The simple pendulum had often been suggested as a steadypoint seismometer, but in the protracted series of oscillations which made up an earthquake the bob of a pendulum might, and often did, acquire so much oscillation that, far from remaining at rest, it moved much more than the ground itself. The lecturer illustrated this by showing the cumulative effect of a succession of small impulses on a pendulum when these happened to agree in period with the pendulum's swing. The fault of the pendulum, from the seismometric point of view, was its too great stability, and its consequently short period of free oscillation. To prevent the body whose inertia was to furnish a steady-point from acquiring independent oscillation, the body must be suspended or supported astatically; in other words, its equilibrium must be very nearly neutral. Methods of astatic suspension which had been used in seismometry were described and illustrated by diagrams and models, in particular the ball and block seismometer of Dr. Verbeck, the horizontal pendulum, and a method of suspension by crossed cords based on the Tchebicheff straight-line link-work.

The complete analysis of the ground's motion was effected by a seismograph which resolved it into three components, two horizontal and one vertical, and recorded each of these separately, with respect to an appropriate steadypoint, by means of a multiplying lever, on a sheet of smoked glass which was caused to revolve at a uniform rate by clock-work. The clock was started into motion by the action of the earliest tremors of the earthquake on a very delicate electric seismoscope, the construction of which was shown by a diagram. In this way a record was deposited upon the revolving plate which gave every possible particular regarding the character of the earth's motion at the observing-station. A complete set of the instruments as now manufactured by the Cambridge Scientific Instrument Company was shown in action. Prof. Ewing also described his duplex pendulum seismograph, which draws on a fixed plate of smoked glass a magnified picture of the horizontal motion of the ground during an earthquake. Apparatus was shown for testing the accuracy of the seismographs by means of imitation earthquakes, which shook the stand of the instrument, and drew two diagrams side by side upon the glass plate one the record given by the seismograph itself, and the other the record derived from a fixed piece which was held fast in an independent support. The agreement of the two records with one another proved how very nearly motionless the "steady-point" of the seismograph remained during even a prolonged shaking resembling an earthquake. This test was applied to the instruments on the table, and the close agreement of the two diagrams was exhibited by projecting them on the lantern-screen. A large number of autographic records of Japanese earthquakes were thrown on the screen, including several which have been already reproduced in this journal (NATURE, vol. xxx. p. 174, vol.

xxxi. p. 581, vol. xxxvi. p. 107); and particulars were given of the extent of the motion, and the velocity and rate of acceleration, in some representative examples. To deter mine the rate of acceleration was of special interest. because it measured the destructive tendency of the shock. The lecturer explained that some of the seismograms exhibited on the screen had been obtained since he had left Japan by his former assistant, Mr. Sekiya, who now held the unique position of Professor of Seismology in the Imperial Japanese University. Prof. Sekiya had recently taken the pains to construct a model representing, by means of a long coil of copper wire carefully bent into the proper form, the actual path pursued by a point on the earth's surface during a prolonged and rather severe shaking. This model of an earthquake had been made by combining the three components of each successive displacement as these were recorded by a set of seismographs like those upon the lecture-table. The appearance of Prof. Sekiya's model (a description of which will be found in NATURE, vol. xxxvii. p. 297) was shown to the audience by means of the lantern.

In the

Prof. Ewing drew attention to the small tremors of high frequency which characterized the beginnings of earthquake motion, and which were apparent in a number of the diagrams he exhibited. These generally disappeared at a comparatively early stage in the disturbance. early portion they were generally found at first alone, preceding the larger and and slower principal motions; and then when the principal motions began, small tremors might still be seen for some time, superposed upon them. In all probability these quick-period tremors were normal vibrations, while the larger motions were transverse vibrations; and a reference to the theory of the transmission of vibrations in elastic solids served to explain why the quick-period tremors were the first to be felt. The whole disturbance went on for several minutes, with irregular fluctuations in the amplitude of the motion, and with a protracted dying out of the oscillations, the period of which usually lengthened towards the close. The record of a single earthquake comprised some hundreds of successive movements, to and fro, round fantastic loops. Each single movement usually occupied from half a second to two seconds. Earthquakes were quite perceptible in which the greatest extent of motion was no more than 1/100 of an inch. In one case, on the other hand, Prof. Sekiya had obtained a record in which the motion was as much as an inch and three-quarters. Even that was in an earthquake which did comparatively little damage, and there was therefore reason to expect that in a severely destructive shock (such as had not occurred since the present system of seismometry was developed) the motion might be considerably greater.

Prof. Ewing concluded his lecture by pointing out that seismographs might find practical application in measuring the stiffness of engineering structures. He exhibited, by the lantern, seismographic records he had recently taken on the new Tay Bridge, to examine the shaking of the bridge during the passage of trains. The instrument had been placed on one of the great girders, two-thirds of a mile from the Fife end, at a place where there was reason to expect the vibration would be a maximum. The extent of motion was remarkably small. It was less than an eighth of an inch, even while the train was passing the seismograph-a fact which spoke well for the stiffness of the structure. Nevertheless, by watching the index of the seismograph he had been able to tell whenever a train came on at the Dundee end of the bridge, a distance of 1 mile from the place where the instrument was standing. One could then detect a vibratory motion, the extent of which was probably not more than 1/500 of an inch. This began in the longitudinal direction, and for some time longitudinal vibration only could be seen. As the train came nearer, lateral vibration also began, and the amplitude of course increased. It reached a maximum