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a con

(1)

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in the moving matter.

This means

a moving force mann has suggested that we are to look for the explanation - (L,/c,)oc. But if there is compression, a, probably in the mutual action between the molecules and the always varies intrinsically as well.

æthereal medium which surrounds them. I am afraid, It will be found that the omission of the auxiliary h however, that if we call in the help of this medium, we has the result of complicating instead of simplifying the shall only increase the calculated specific heat, which is force formulæ. Similarly the omission of e complicates already too great.'') It seemed to me, however, that the them. Now the use of e is founded upon the idea that difficulty was fully met by the numerical results arrived at the electric polarisation is produced by a separation of in chapter ix. of my book. ions under the action of E, for E, is the moving force on Suppose, to make the point at issue as definite as a moving unit electric charge. Analogously in, is the possible, we take a sample of air from the atmosphere, moving force on a moving unit magnetic charge or say at 15° C. Almost all the energy of this gas will be magneton. If there are really no such things, the inter- assignable to five degrees of freedom—so far as we know, pretation must be made equivalent in other terms. But three of translation and two of rotation. Let us surround the categorical imperative is not easily to be overcome. this gas by an imaginary perfectly reflecting boundary.

The application to plane waves I described in a recent The total energy of matter and æther inside this enclosure letter (NATURE, March 9) will be found to harmonise with will remain unaltered through all time, but this total the above in the special case.

energy may be divided conveniently into two parts :But a correction is needed. In the estimation of the (1) The energy of the five degrees of freedom, say A. moving force on “ glass " receiving radiation, the assump- (2) The energy of the remaining degrees of freedom of tion was made that the electric and magnetic energies in the matter plus the energy of the æther, say B. the transmitted wave were equal. So the result is strictly As Lord Rayleigh insists, the system is now limited by that condition. The conditions E=WB and servative system, so that according to the law of equiU=T are not coextensive in general, though satisfied partition, the total energy A+B is, in the final state of together in Lorentz's case. When U not =T, we have the gas, divided in the ratio instead of (8), p. 439,

A:B=5:00
P.v-p.0- Pow=w(T.-U.),

whereas observation seems to suggest that the ratio ought and the rate of loss of electromagnetic energy is

to retain its initial value 24H, H,u+(w - 1)(T-U,).

A: B=5:0 •

(2) Now this is zero when ero, or the polarisation is pro

This I fully admit, but a further point, which I tried to portional to the electric force. The question is raised how bring out in the chapter already mentioned, is that the to discriminate, according to the data stated above, between transition from the ratio (2) to the ratio (1) is very slow cases of loss of energy and no loss. To answer this ques- -if my calculations are accurate, millions of years would tion, let e and n in the above be unstated in form ; else hardly suffice for any perceptible change-so that, although the same.

Then, instead of (4), the activity equation (1) may be the true final ratio, it is quite impossible to will be

obtain experimental evidence of it.

If the sample of gas were initially at a much higher - ow=U + 1 + {}E?@cd/de) + ... + (899+8,u) - (EJ, +1G,), (5) temperature than we have supposed, the transition would where w is as in (4), whilst *, and f, are the forces

undoubtedly be much more rapid ; but even here we could derived from the stresses specified (not the same as F, and

not hope for experimental verification. For the assumed F,), and y,, G, are the electric and magnetic polarisation

boundary, impervious to all forms of energy and itself currents, thus, v=D, +Von, &c.

possessing none, ca be realised in practice, and as It follows that it is

soon as the energy of the enclosed æther becomes appreciupon e and h that the loss of energy depends in plane able, the imperfections of our apparatus would become of waves, when u and q are constant. For the stresses

paramount importance in determining the sequence of reduce to longitudinal pressures, so that by line integration events.

J. H. JEANS. along a tube of energy flux we get (eli +1G = (U+T).

(6) Growth of a Wave-group when the Group.velocity is

Negative. Thus, when a pulse enters moving glass from stationary ether, the rate of loss of energy is 31 - eJ.). Ife is zero,

Tue following may be of interest in connection with the so is the loss, as in the special case above. There is also recent discussion on the flow of energy in such cases. agreement with the calculated loss in the other case. Let the energy of an element of a linearly arranged That the moving force on the glass should be controlled

mechanical system be by e is remarkable, for it is merely the small difference between the electric force on a fixed and a moving unit

{(dạylexdr)? +y}dx/2. charge. The theory is not final, of course. If the electro- Such a system can be approximately realised by taking magnetics of the ether and matter could be made very a bicycle chain, loading it so that the radius of gyration simple, it would be a fine thing ; but it does not seem of each link has the same large value, and suspending it probable.

OLIVER HEAVISIDE. by equal threads attached to each link so that the chain Ipril 5.

is horizontal and the axes of the links vertical. By the principle of least action we immediately find the equation

of motion to be d'y dx?dt = y. A simple harmonic wave The Dynamical Theory of Gases.

is given by y=sin (pt - x'p). The group velocity is -- pa, In a letter to NATURE (April 13) Lord Rayleigh makes a

and is negative. Let such a system, extending from x=0 criticism on my suggested explanation of the well known

to x=, be at rest in its position of equilibrium at time difficulty connected with the specific heats of a gas.

He

t=0, and then let the point x=o be moved so that its posiconsiders a gas bounded by a perfectly reflecting enclosure,

tion at any subsequent time is given by y = 1 -- cos t. and says “the only effect of the appeal to the æther is to

By application of the usual method vid Fourier's inbring in an infinitude of new modes of vibration, each of

tegral, the motion of the system is found to be given by which, according to the law (of equipartition), should have

either of the equivalent formula its full share of the total energy. The apparent difficulty before my mind when

y = {( - 1)"(?'x)"+"Jgn +22 1'(tx), writing my book. Indeed, as Lord Rayleigh remarks,

y=I - cos(1 + r) -1 + 31 – 1)"(x/t)"1942 (1x). something of the kind had already been indicated by Maxwell. (I think the passage to which Lord Rayleigh refers where the J's are Bessel's functions and the summations will be found in the Coll. Works," ii., p. 433 :-“ Boltz- extend from

n=0. There are

some doubtful

1

no

was

or

no

to

name.

points in the reasoning, however, and the proof consists of the proposed changes, and of others of a similar in showing (1) that y satisfies the differential equation, type, then, and then only, I venture to think, could they (2) from the second formula that y=1-cost when x=0, be regarded as obligatory. (3) from the first formula that y and dy/dt are both zero It may be added that the use of combinations, which when t=0, (4) from the first formula that when t is finite Mr. Stebbing has felicitously designated “comicalities in y is small for all large values of x. If, now, x is finite nomenclature," of the type of Anser anser and asina and t great, the second formula reduces to y=- cos (t+x), asinus (or, still worse, Asinus asinus asinus, which is 3 so that the motion now consists entirely of waves pro- possible contingency), is rapidly tending to discredit the ceeding towards the source of the disturbance-a most re- common sense of scientific zoologists among matter-of-lart markable result. If in the formulæ for y we change the men of the world.

Ř. LYDEKKER. sign of x, the J functions are replaced by I functions. The resulting value of y does not satisfy (4), and cannot be accepted as a solution of the problem.

A little known Property of the Gyroscope.
H. C. POCKLINGTON. To my surprise I have found that the property of the

gyroscope which I am about to describe, although perfectly The Transposition of Zoological Names.

elementary, appears to be little known to either physicists or astronomers.

Neither is it mentioned in the text-books Among the many radical changes in zoological nomen- so far as I am aware. That it has a very important beárclature proposed of late years, none appear to me more ing on the mechanism of the solar system has been showa open to objection than those where names which have in some of my earlier papers, but the laws which govern long been in general use for particular species or groups the rotation and the simple facts themselves seem to be so are transferred to others on the ground that they were little understood that I have thought it worth while to originally applied to the latter. One of the earliest of such

explain them more fully in this place. transpositions was suggested by Prof. Newton, of Cambridge, who urged that Strix is not the proper generic

If a gyroscope is mounted on gimbals so that it may

shift its plane of rotation freely about an axis passing designation of the barn-owl, and that while this species

through the plane of the revolving disc, we shall find it should be called Aluco flammeus, the tawny owl should is possessed of certain curious properties. To most persons take the generic title Strix, as S. aluco. I find, however, the notable characteristic of a gyroscope is the resistance that this emendation is not accepted in the British Museum it offers to any force tending to change the plane of its Hand-list of Birds," where the barn-owl figures under its rotation. This is true of it only, however, in case certain familiar title of Strix flammea. Uniformity is not, there- conditions are complied with. If these conditions are fore, attained by this proposal.

neglected, it will change its plane with the greatest facility. Another instance occurs in the case of the walrus, which If the wheel is properly balanced and mounted as above was long known as Trichechus rosmarus, until systematists described, and we set it spinning, it will continue tu discovered that the generic title refers properly to the rotate in one plane without change until it stops. Supmanati, to which animal they transferred the

pose that while it is spinning we set it upon a table, and Again, the Simia satyrus of Linnæus is now stated to be cause the stand supporting it to revolve slowly about its the chimpanzi, and not the orang-utan, and consequently vertical axis. Instantly the wheel will adjust itself so i Simia is made to stand for the latter instead of for the to revolve in a plane parallel to the surface of the table. former. As a fourth example of this transference of a Furthermore, the direction of rotation of the wheel upon familiar generic name may be cited the case of the mar- its axis will be the same as the direction of rotation of mosets of the genus Hapale, to which it is now proposed the stand. If we turn the stand in the opposite direction to apply the title Chrysothrix, despite its practically the wheel will at once shift its plane, and turn over, so immemorial use as the designation of the titi monkeys. as again to rotate in the same direction as the stand.

As an example of the transference of a species name, it Another way of showing the experiment is to hold the will suffice to take the case of the African antelope com- stand supporting the gyroscope at arm's length. The monly known as the white oryx (Oryx leucoryx). This

observer then slowly revolves upon his heels, first in one name, it is stated, properly belongs to the Arabian Beatrix direction and then in the other. Each time the observer oryx, tç which it is accordingly proposed that it should be shifts his own direction of motion the gyroscope will shift transferred, after being so long used for the former animal. its plane, and always in such a manner that its direction

Personally, I am very strongly of opinion that such of rotation shall be parallel and in the same direction as transpositions should not on any account be permitted, and its revolution in its orbit. that when a species or genus has been known by a par- It is a well known fact that according to the nebular ticular name for a period of, say, fifty years, this should, hypothesis all the planets should have rotated in a direcipso facto, give such an indefeasible title to that name tion opposite to that of their revolution in their orbits, just (altogether irrespective of its original application) as as Neptune does at the present time. This is because by ba its transference to any other group or species. It Kepler's laws the inner edge of a revolving ring must may, indeed, be deemed advisable that, as in the case of necessarily move faster than the outer edge. The fact that the walrus, the old name should not be retained in the Neptune is the only planet that even approximately fulfils generally accepted sense, but, if so, it should be altogether this condition has always been a source of trouble to the discarded, and not transferred. The practice of trans- adherents of the nebular hypothesis. No one has ever ferring names must, if persisted in, inevitably lead to much even attempted to explain the anomalous rotation of unnecessary confusion without the slightest compensating Uranus, in a plane practically perpendicular to the plane advantage. Indeed, it will render such works as Darwin's of its orbit. Origin of Species and Wallace's “Geographical Dis- The interesting property of rotating bodies illustrated tribution of Animals," which are certain to live as bio- above in the case of the gyroscope, and fully explained by logical classics, absolutely misleading to the next gener- its theory, now at once makes the matter perfectly clear. ation unless special explanatory glossaries are supplied. In the case of the planetary bodies, the force rotating the

Advanced systematists urge that those who refuse to stand of the gyroscope is supplied by the annual tide raised follow their lead in this and other kindred emendations in upon the planets by the sun. In former times, when the nomenclature are not only old-fashioned and behind the planets were large diffuse bodies, this tidal force was of times, but that they are absolutely doing their best to considerable importance. Neptune, however, is so remote hinder the progress of zoological science. This, however, from the sun that the tidal influence upon it has always is but the opinion of a comparatively small (and, shall we been small. The plane of its rotation, therefore, has been say, somewhat prejudiced?) section. What we really want but slightly shifted from that of its orbit-about 15° is the opinion of all those interested in zoology and Uranus being nearer the sun has had its plane shifted natural history, namely, professional zoologists, palæonto- nearly half-way over, or through 820. The plane of motilogists, geologists, physiologists, anatomists, zoogeo- tion of Saturn has been shifted through 153', while that graphers, amateur naturalists, and sportsmen. If the of Jupiter has suffered a nearly complete reversal, and the general consensus of opinion of all these were on the side planet now revolves approximately in the plane of its

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orbit. The deviation amounts to but 3°, and its plane of rotation has therefore shifted through 177o. The explanation of the retrograde rotation of Phæbe is

also clear. Phæbe, the first-born of Saturn's numerous retinue, came into being while the planet itself still retained its original plane of rotation, that is, while it was still revolving in a retrograde direction. Before lapetus, Saturn's second satellite, reckoning from without inwards, was created, the mighty tides acting upon the planet in its then diffuse condition had shifted its plane of rotation more than 90°. Two forces then acted on the plane of the orbit of the new satellite, one from the sun tending to bring the orbit into the plane of the orbit of Saturn, the other from Saturn tending to bring the orbit of the satellite into the plane of the equator of its primary. At first both forces tended to produce the same result, namely, to diminish the angle of inclination of the plane of the orbit of the satellite. They are now pulling in opposite directions, as is the case with our own moon, the inclination of the orbit of Iapetus, 19o, ng less than that of the equatorial plane of its primary.

The inner satellites of Saturn inore powerfully affected by the equatorial expansion of the planet than by the action of the sun, the planes of their orbits, 270, coinciding nearly with the plane of the planet's equator.

WILLIAM H. PICKERING. Harvard Observatory, Cambridge, Mass., U.S.A.

are

proteids-have, on account of their complexity, critical temperatures of decomposition which lie very close to the normal temperature of the earth's surface.

If, now, by some means we proceed to add on atoms to such a molecule so as to make it more and more complex, we would steadily lower its critical temperature of decomposition, and by adding on a suitable kind and number of atoms we could reduce the critical temperature and pressure of the compound until they coincided with the normal temperatures and pressures which hold upon the earth's surface. Such a compound would be possessed of an extraordinary sensitiveness to external influences on account of the sharpness of the constants called above the critical temperature and pressure of the compound. The slightest increase of temperature or decrease of pressure would serve to throw it into a condition of rapid chemical decomposition, whereas a slight increase of pressure and decrease of temperature would cause it to cease to decompose. Even did we maintain the external temperature and pressure ex at the critical temperature and pressure of the compound, nevertheless the external impulses which are continuously pervading all space in the neighbourhood of the solar system, beating intermittently upon the sensitive substance, would be sufficient to throw it into a series of rapidly alternating states of decomposition and repose.

I suggest that the temperature range of animal life is probably nothing more or less than the range of the critical temperatures of decomposition of a series of certain very complex carbon compounds which are grouped together under the name “ protoplasm,” the external pressure of the atmosphere coinciding roughly with their critical pressures of decomposition. In fact, I suggest that just as a tuning-fork is set into motion by vibrations of a certain definite frequency and by no others, so living matter is so constructed as to respond continuously to the incessant minute fluctuations in the external conditions which hold upon the earth, the state of response being what is known as life. The temperature of animal life keeps remarkably constant, as it should do .on our supposition, a temperature too high exceeding the critical temperature of decomposition of living matter and so destroying its structure, while a temperature too low causes it to cease to decompose, and the living matter becomes inactive.

GEOFFREY MARTIN. University of Kiel, April 4.

[The writer of the above will see his “ suggestion " discussed in Lockyer's “ Inorganic Evolution,” book iii. Ep. NATURE.]

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HAVE

seen

Have Chemical Compounds a Definite Critical

Temperature and Pressure of Decomposition ? So far nobody seems to have considered the question whether to every chemical compound there exists a definite critical temperature and pressure of decomposition. Yet I think the following considerations show that such constants probably do exist. Suppose we place a given compound (say Caco) in a closed cylinder and subject it to a continually increasing temperature, keeping the pressure constant by means of a weighted piston. Then at certain definite temperature range the compound will begin to decompose. Suppose, now, we increase the pressure sufficiently; then the decomposition ceases, and the substance can now bear a higher temperature than before without decomposition.

Proceeding in this way, it is, I think, obvious from the finite nature of the mass of the atoms, and from the limited intensity of the forces holding them together in the molecule, that ultimately at some definite finite temperature the external forces tending to drive the atoms apart will become equal to the maximum internal forces that the atoms can exert on each other in the molecule. It therefore follows that above a certain definite temperature, depending upon the nature of the molecule, no pressure, however great, can prevent the substance from completely decomposing. This temperature and pressure, above which a compound is incapable of existing, we will call the critical temperature and pressure of decomposition of the compound. The critical temperature and pressure of decomposition would therefore be completely analogous to the critical temperature of liquefaction of a compoundonly in the latter case we are dealing with the temperature whereat a certain molecular condition of existence disappears, and in the former case with the temperature whereat a certain atomic condition of existence disappears.

Since atoms are a very much more finely divided form of matter than molecules, it is clear that the critical temperature of decomposition of a compound must be a very much sharper and clear-cut constant than its critical temperature of liquefaction. The critical temperature and pressure of even very unstable compounds is usually very high, provided there exist but a few atoms in the molecule. For example, AuCi,, ozone, and the oxides of nitrogen, although very unstable at ordinary temperatures, seem capable of existing at very high temperatures. In general, the greater the number of atoms contained in the molecule the lower the critical temperature of decomposition, as is evident from the general observation that the more complex a compound is the easier it is to decompose. Many of the very complex carbon compounds-for example, the

as

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Experiment on Pressure due to Waves. I

both in the Physikalische Zeitschrift (January) and in the Physical Review (February) an account of an experiment by Prof. R. W. Wood to demonstrate the pressure due to waves, and which he suggests

lecture demonstration of the effect observed by Lebedeff and by Nichols and Hull. The same experiment is quoted by Prof. Poynting in his address on this subject to the Physical Society of London (Phil. Mag., April). I venture to suggest that the experiment, which consists in setting a small windmill in motion by means of Leyden jar discharges maintained by a transformer, will bear a different explanation. It was shown long ago (1793) by Kinnersley, of Philadelphia, in his “ Electrical Thermometer," that a jar discharge produces in air a violent explosive effect, which we should now explain by the repulsion between constituents of the current in opposite phase to one another. The repulsive force may be very great. I think it is this explosive effect that Prof. Wood shows in the experiment, and not the pressure due to reflection of a continuous train of waves, I do not think that the suggestion is new, but it appears to me that the same cause may account for the disruption which occurs when lightning strikes a building, an instance of which is recorded in NATURE of April 13 (p. 565) in the displacement of some of the blocks of the small pyramid.

SIDNEY SKINNER. South-Western Polytechnic, Chelsea, April 15.

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TANTALUM.

for three days, and at the end of the time had only

made a depression 0.25 mm. deep, while the diamond has again borne fruit in the isolation and pre very probably lead to its being used for drills in place paration of tantalum. Dr. Werner von Bolton, of of the diamond. the firm of Siemens and Halske, published the results The metal melts between 2250° and 2300°. The of his very interesting research upon the preparation atomic heat agrees with the law of Dulong and Petit, of tantalum in the Zeitschrift für Elektrochemie being 6.64. The specific gravity is 14.08.When twn (January 20). Although the existence of tantalum electrodes of tantalum are placed in a bath of dilute was pointed out by Hatchett in 1801, it does not sulphuric acid, the tantalum becomes passive, and appear up to the present to have been prepared in even with an E.M.F. of 220 volts at the terminals the pure condition. Moissan, indeed, in 1902 pre- no current passes. When placed opposite an electrode pared the metal by reducing tantalic oxide (Ta,0,3) of platinum only one phase of an alternating current in the electric furnace. But the metal was extremely passes; it may thus be used for rectifying an alterhard and brittle, a property which Dr. Bolton now nating current in the same manner that aluminium shows only belongs to the impure product; Moissan's

can. metal probably contained some carbide. Dr. Bolton In the form of wire, sheet or ingots, the metal is has succeeded in obtaining the metal by an electrical unacted upon by sulphuric, hydrochloric, or nitric and by a chemical method.

acid, and even by aqua regia.

Hydrofluoric acid reacts very
The Electrolytic Method.

slowly, unless the metal is in As is well known, Nernst found that when a thin

contact with platinum, for rod of magnesia (MgO) is heated to whiteness it example, in a platinum dish, becomes able to conduct the electric current, the

when it dissolves readily with magnesia being split up into its components, mag

evolution of hydrogen. 'Fused nesium and oxygen; the magnesium, however, alkalis have no action upon it. immediately re-combines with oxygen, the process of

When made the kathode in electrolysis therefore becoming continuous. Other an acid electrolyte it absorbs metallic oxides, such zirconium, ytterbium, hydrogen, which is only parthorium, calcium, and aluminium, &c.,' likewise be tially given up, even when have in a similar manner. If, now, a rod of mag

the metal is fused. The metal nesium is strongly heated in vacuum and the electric may be heated to red heat in current passed through it, the oxygen given off is so

the air without taking fire. dilute that re-combination does not take place, and

At 400° it turns slightly

110 the rod becomes powdered.

Dr. Bolton, working yellow, at a low red heat it along somewhat similar lines, found that the coloured

turns blue, and finally beor lower oxides of vanadium, niobium (columbium),

comes coated with a white and tantalum will conduct the electric current with protective coating of the pentout the necessity of being heated to very high a white heat, and unites with

oxide. It absorbs nitrogen at temperatures. Strange to say, the colourless or higher oxides have not this property.

sulphur when melted with it

FIG 1,- View of Tantalom In order to prepare tantalum in this manner

under fused potassium Lamp. Hall-size linear filament of the brown tantalum tetroxide (Ta,O) was

chloride. Tantalum apparprepared and fixed into an evacuated globe, which ently forms no amalgam with mercury, although it was connected with a vacuum pump, so that it oxygen produces alloys with most other metals. When united was given off, on heating, it could be pumped out.

with i per cent. of carbon it becomes hard and brittle. On passing a current through this filament, at first

and can no longer be drawn into wire. the two ends of the filament became white hot, and

As already stated, the original idea in working with

tantalum then gradually the incandescence travelled along the

was to find a new material to be used for filament until the whole of it became incandescent.

incandescent electric lamps. The first experiments A large quantity of oxygen was given out, and the columbium); the coloured or lower oxides of these

were tried with the oxides of vanadium and niobium filament, which at the commencement was brown, metals were found to conduct the current and to give became metallic grey. The tantalum so obtained showed on analysis a purity of 99 per cent.

up their oxygen when thus heated in vacuum. Vanadium so obtained was found to melt at 1680

and niobium at 1950°; but owing to these comparaThe Chemical Method.

tively low melting points they could not satisfactorily Details as to how the chemical method is carried be employed for electric lighting purposes. Tantalum, out are not given. Dr. Bolton simply says that the however, which melts between 2250° and 2300° has metal can be obtained by fusing a mixture of potas been successfully employed for this purpose by Messrs. sium tantalum fluoride with potassium by means of Siemens and Halske. the electric arc furnace in a vacuum. This method

Filaments of the metallic tantalum are fused into is a modification of that used by Berzelius in 1824.

a globe, which is then evacuated in the usual manner.

The first lamp was made with the usual bow-shaped Properties of the Metal.

filament, and required 0.58 ampere with a pressure

of 9 volts, giving 3 candle-power. It was then found One of the most remarkable properties of the metal that in order to produce a 22 candle-power lamp suitis its extreme ductility combined with extraordinary able to being placed on a 110-volt circuit more than hardness. The red-hot metal can readily be rolled 20 inches length of filament was required. The diffiinto sheets and foil, and easily drawn into wire. culty presented was to get this great length of filaWhen the sheet is again heated and hammered it ment conveniently into the ordinary sized globe. The becomes so extremely hard that it was found im- illustration (taken from the Electrical Magasine for possible, by means of a diamond drill, to bore a hole March) shows how the difficulty was got over. The through a sheet i mm. thick. The drill, rotating central support is a rod of glass, having a number of 5000 times to the minute, was worked day and night wires radiating from it to act as supports. This

a

lamp gives 22 candle-power with an energy consump- such reservoirs might make us chary of crediting tion of 1.7 watt per candle-power, or about half that prehistoric man with such scientific methods. required by the ordinary incandescent lamp. The An exposed position innocent of springs was weight of a single filament is 0.022 gram, so that selected, and straw or some other non-conductor of i kilogram of metal would be sufficient for 45,000 heat spread over the hollowed surface. This was such lamps.

next covered with a thick layer of well puddled clay, Whether it will be possible to obtain sufficient which was closely strewn with stones. The pond mineral to produce tantalum on a really large scale would gradually fill, and provide a constant supply remains to be seen, because if it is possible there of pure water, due to condensation during the night should be hardly an end to the usefulness of this of the warm, moist air_from the ground on the metal, which possesses the properties ductility and surface of the cold clay. Evaporation during the day hardness in such an extraordinary degree, leaving is less rapid than this condensation, and the only entirely out of question its employment in electric danger is that the straw should be sodden by leakage. lamps.

F. MOLLwo PERKIN. It is for this reason that springs or drainage from

higher ground are avoided, as running water would

cut into the clay crust. PRIMITILE WATER-SUPPLY.1

Some ponds of this kind, no doubt of very early and THE HE mighty earthworks that still crown so many perhaps of Neolithic date, may still be seen in working

of our hills fill the archæologist alike with order : others are of modern construction; but to and wonder and despair-wonder that prehistoric man, from the ancient dew-ponds (or their sites) can somewith the most primitive tools, was equal to the task times be traced the hillside tracks along which the of raising them, and despair that so little can ever be known about them, despite the most laborious and costly excavation. Plenty of books, however, of the kind now under notice would do much to solve the mystery and increase our admiration for Neolithic man, for it is to the period before bronze was known in Britain that the authors assign the stupendous works of Cissbury and Chanctonbury on the South Downs.

This is an open-air book that gives life to the dry bones of archæology, and reads like the record of a well-spent holiday. A keen eye for country is one of the qualifications possessed by one or both the authors, and evidence of ramparts long since levelled is wrung from the very daisies as they grow. The construction of dew-ponds by the early inhabitants of Britain' has often been glibly asserted, but few, if any, have fur- Fig. 1.-Cattle-ways leading down to Dew-pond at the North of Cissbury Ring. nished such clear and cir

“Neolithic Dew.ponds and Cattle-ways.” cumstantial evidence as the authors of this short treatise. The water supply herds were driven, one leading from the camp, or for the occupants of our huge prehistoric “camps

cattle-enclosure hard by, the watering-place, has always been somewhat of a mystery, and it another leading back, to avoid confusion on the road. has been suggested that they were only tem- These and other details as to guard houses and posts porary refuges, when the country was up," so of observation are brought to notice in the that a permanent supply was not regarded as description of selected strongholds in ‘Sussex and necessity. But the watering of men and animals on Dorset; and verification, if, indeed, such is demanded, the scale indicated by the areas enclosed would be a must be sought on the spot by any who have doubts formidable task even for a day, and another explana- or rival theories. tion must be sought. The late General Pitt-Rivers, The banks, that enclosed pasture-areas sometimes for example, held that the water-level of the combes of vast extent, were no doubt stockaded against man was higher then than now, and streams would have and beast, and may be compared with the basebeen plentiful on the slopes; but, feeling the court defences of the Norman burh ; but the excavator inadequacy of this view, he also had recourse to the of Wansdyke had an alternative theory that such dew-pond theory. To those familiar with the banks were sometimes erected for driving game. process, this might seem an obvious expedient, but

Incidentally, the authors discountenance the view that the interesting account given of the formation of the “camps," not to mention the outworks, were

ever efficiently manned. Their extent would 1 "Neolithic Dew-ponds and Cattle-ways." By A. J. Hubbard and G. Hubbard. Pp. x+69; illustrated. (London: Longmans, Green and Co.,

necessitate for this duty a vast number of fighting 1995.) Price 35.

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From Hubbards

to

our

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men within call.

60. net.

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