Eoanthropus, assigning this human form to the "latter half of the Pleistocene" and giving_its cranial capacity as "at least 1070 c.c. Dr. Smith Woodward came to the conclusion that Eoanthropus belongs to the older Pleistocene, and in his more recent reconstruction of the skull represents the cranial capacity as 1300-230 c.c. above his original estimate. Prof. Sollas sums up his final conclusion as regards human antiquity as follows: "that man, not only in the narrower, specific sense but also in the broader generic sense-Homo-is a product of the Pleistocene epoch, the latest child of time, born and cradled amongst those great revolutions of climate which have again and again so profoundly disturbed the equilibrium of the organic world." It will be seen from this extract that the author favours the older opinion that man made his first appearance at a comparatively recent date. The Body in Health. By Prof. M. V. O'Shea and J. H. Kellogg. Pp. ix + 324. (New York: The Macmillan Co.; London: Macmillan and Co., Ltd., 1915.) Price 3s. 6d. Of the making of books on elementary physiology and hygiene there seems to be no end, and the tendency to the multiplication of such manuals is specially marked in America. Perhaps this is an indication that our cousins across the sea are more alive to the importance of health in the wellbeing of a nation; they certainly make it a much more universal subject of school education than we do. The present volume has much to recommend it; it is clear, convincing and accurate; it is written in simple language and well illustrated; as a rule it is level-headed. The usual space, as in all American text-books of this kind, is devoted to the evil of alcohol; with that one has no quarrel; but tobacco also is regarded as nearly equally bad. The following is, for example, quoted with approval: "I know whereof I speak when I say that tobacco when habitually used by the young leads to a species of imbecility; that the juvenile smoker will lie, cheat and steal things he would not do had he let tobacco alone. Extravagant superlatives of this nature often do more harm than good. W. D. H. LETTERS TO THE EDITOR. [The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURE. No notice is taken of anonymous communications.] Ultra-Violet Excitation of the D Line of Sodium. IN a letter on this subject published in NATURE, May 13, I showed that sodium vapour, stimulated by the second line of the principal series at wave-length 3303in the ultra-violet, fluoresces with emission of the D line, which is the first member of the principal series. Each of these lines is a doublet. The interesting question arises, Supposing that stimulation were con fined to one member only of the ultra-violet doublet, should we get emission only of the corresponding member of the D line, or would both components of the D line be emitted? The first alternative seemed a priori more probable, taking into account the result of Wood and Dunoyer, that if sodium vapour is stimulated by D light, one component of the D line is not able to give rise to fluorescent emission of the other. I have, however, succeeded in carrying out an experiment which seems to decide fairly conclusively in favour of the second alternative. The zinc arc sodium doublet. My attention was directed to this spectrum shows an ultra-violet doublet very near the by reading Prof. Wood's account of his earlier attempts on the problem. Direct comparison of the spectra showed that the zinc doublet lay inside the sodium doublet, but that while one of the zinc components was situated at about one-twentieth of an Angström from one sodium component, and thus very nearly in coincidence, the other zinc component was four times as far from its sodium neighbour, and well clear of it. A zinc vacuum arc in quartz was used to illuminate the sodium vapour bulb, interposing the filter mentioned in the former paper, for the suppression of visible light. With currents of three or four amperes nothing could be seen. Increasing the current to six amperes, a faint emission of D light was observed. It was as yet too faint for spectroscopic examination, but was identified by the absorption methods described in the former letter. At 15 amperes, the light was bright enough for a specially designed spectroscope. and showed both components of the D line in about equal intensity. The current was increased in successive tests to about 100 amperes. These large currents were only kept on for two or three seconds so as to avoid destroying the lamp. For this short time the fluorescence was not inferior in intensity to the light of a moderately salted Bunsen flame, and the components of the D line were seen very bright. The intensity increases very rapidly with the current through the lamp. This is due partly, of course, to the greater brightness, but more to the broadening of the first zinc component, which makes it definitely overlap the first sodium component. Possibly at very large currents this cause may even bring the second zinc component on to the second sodium component, but plainly the first overlap must come in much sooner, for the interval to be bridged is four times less; and at the lowest current which brings out the D line brightly enough for examination, its components are approximately equal. Wood's failure to get any D emission is probably to be explained by his not having used a heavy enough current through the zinc lamp to secure an overlap of the zinc and sodium lines. R. J. STRUTT. Imperial College of Science, South Kensington, May 31. On the Sealing of Electrical Conductors through Glass. AT the present time there is great difficulty in obtaining soft glass with a comparatively high coefficient of expansion, suitable for sealing wires into glass tubes, bulbs, etc. The pre-war imported stocks of glass for this purpose are exhausted, and the recently published results of glass research committees do not contain formulas for its manufacture. About three years ago, Mr. George B. Burnside, of the natural philosophy department of the University of Glasgow, discovered a method of hermetically sealing electrical conductors through glass and other vitreous substances. The process is simple, and entirely obviates the use of a "flux" glass; and in view of the present needs, it seems advisable to bring this method again before the notice of those who may find it to their advantage to use it. A general description of the process appeared in the Electrician of July 4, 1913; but the method does not seem to have become so popular as might have been expected from the simplicity and ease of its application. As to the results obtained, the following facts from my own experience may be mentioned as affording proof of its absolute perfection. In the course of some research work which is being carried on at present in Prof. Gray's laboratory, involving the examination of certain resolved spectral lines, a Wehnelt electrolytic interrupter was used in connection with an 18-in. induction coil. This interrupter was employed on account of the fact that, with it, the discharge can be allowed to run for hours without attention. The positive electrode was simply a small length of platinum wire sealed through the end of a glass tube. The wire conveying the current dipped into mercury surrounding the upper end of the sealed wire. At first the sealing of the platinum wire into the glass tube was done by means of a "flux" glass in the usual way. It was noticed, however, that after a few hours' working, as a result of the disruptive action of the interruptions, this glass round the anode became pitted out, a crater being formed with the wire projecting from its centre. This action may go on until a leak occurs. Again, for the large currents used-more than 10 amperesa fairly heavy wire is necessary, and the heating effect frequently causes fracture of the glass, by small radial cracks starting from the wire, or even from the junction of the two glasses. Both these effects are, of course, undesirable. The pitting out of the glass exposes a greater amount of the conducting material, and consequently alters the frequency; while leakage due to fracture considerably increases the amount of "steady current," that is, current spent in mere ordinary electrolytic effects. To overcome both these defects, I used a piece of Jena glass tubing, with a small length of heavy platinum wire sealed directly into it by the Burnside method. This anode has been in use now for several hours daily for the past five weeks, and there is neither any fracture nor any sign of the pitting out of the glass as formerly. This hard glass is less liable than the soft sealing-in glass to be damaged by the disruptive action of the current, and the chilling process has the effect of toughening the skin of the glass as well as of perfecting the seal between the glass and the wire. re In connection with the same research, a large number of small vacuum discharge tubes were quired. In most of these tubes, the electrical conducting wire has been sealed in by the Burnside process, and in every case the result has been entirely satisfactory. The spectral lines under observation are of rather low intensity, and, in consequence, exposures of four or five hours' duration are required to give a good photographic presentment. Generally, each tube has been used for two photographs. Thus the discharge has been passed in one direction for four hours or more, continuously, and then in the opposite direction, for a similar continuous period of four or five hours. In many cases, during the process of exhaustion, the tubes have been strongly heated by means of a bunsen burner; during some of the exposures, when the vacuum has been high, the tube has become very hot; in some cases the discharge has fractured the glass near the discharge end of the kathode; but in no single case has cracking occurred at the seal, nor has there been any sign of leakage. Considering the large number of tubes used, I think these facts afford striking evidence of the trustworthiness of the seal. The essential part of Mr. Burnside's process of sealing consists of the repeated immersion of the leading-in wire and the glass surrounding it, in a bath of oil, fat, or wax. If a wire is to be led into a tube, the tube should be drawn down until the bore is just large enough to admit the wire. The conductor having been inserted, the glass around it is strongly heated in the blow-pipe flame until perfect cohesion has taken place between the metal and the glass. The wire should then be drawn out slightly, carrying the adhering glass with it, and this glass heated again. This may be repeated until a "neck' of glass about two or three millimetres long, and having the end well rounded, is formed around the wire. The seal is then withdrawn from the flame, and, when the red glow has entirely disappeared, the end of the tube carrying the wire is cooled by several immersions in the oil. This may best be done by bringing the bath containing the oil-a short, wide test-tube, say-up round the seal. Each immersion should last about two or three seconds. The depth of immersion is increased with each successive dip, until the seal is completely cooled out. In the case of vacuum tubes where the electrode requires a small inner support tube, the conducting wire can first be fused into the support tube, leaving a fairly long thick neck of glass in contact with the wire. support is then well fused into the bulb of the vacuum tube in the usual way, and, finally, the seal is cooled out as described above. Not only does this cooling process render perfect the seal between the metal and the glass, but it also improves the junction of the glass of the inner tube with that of the outer. The leading-in wire of one of the vacuum tubes, immediately after being cooled out in oil, has been suddenly heated in the blow-pipe flame until it was at a bright red heat up to within about 1 mm. from the glass, without the seal being affected. This Compared with previous methods of sealing in electrodes, where a special "flux" glass had to be used, where care had to be taken to prevent the ordinary glass of the tubes from coming directly into contact with the metal, and where, unless special precautions as to annealing were observed, fractures frequently ensued, the present method is much simpler and easier, and more effective. It also enables us to make discharge tubes of Jena or other hard combustion glass. This was formerly quite impossible on account of the fact that no "flux' was known which was suitable for sealing wires through glass of this nature. Mr. Burnside recommends that sperm oil be used, and that it be heated slightly before the glass is immersed in it. For the above work, I used the ordinary machine oil from the workshop-simply because it was most readily obtainable-and used it at room temperature. In cases where the position of the seal prevents its being conveniently immersed in a bath of oil, the process may be effected by bringing vertically upwards a piece of fat or wax cut to a suitable size and shape, and pressing it against the hot seal. It may be mentioned also, that not only can platinum be sealed directly through Jena or other hard resistance glasses, and through fused quartz, but that perfect seals may be made between the more easily oxidisable metals, such as copper or iron, as well as platinum, and glasses having comparatively low fusion points, e.g. lead glass and German glass, or any glass of this nature. For large currents the conductor should be tubular, because it can be more effectively cooled out by repeated immersions than would be the case if a solid conductor of the same cross-sectional area were employed. The cases to which the process is applicable in scientific work are obvious and numerous, and it is needless to specify them. In view of the number of applications of a commercial and industrial value, as e.g. in the manufacture of incandescent electric lamps, mercury-vapour lamps, etc., the process has been protected by patent in Great Britain and abroad; but I understand that this protection is not intended to restrict in any way its use in research laboratories or its application to any purposes of a purely scientific and unremunerative nature. F. F. S. BRYSON. Natural Philosophy Institute, University of Eryonicus-Polycheles. In a recent publication on the Crustacea of Ireland, "Decapoda Reptantia of Ireland," Part I., by C. M. Selbie (Fisheries, Ireland, Sci. Invest., 1914, I. (1914)), the question of whether the peculiar forms known as Eryonicus are larvæ of the crayfish-like deep-sea crustaceans Polycheles is answered to the effect that they are independent animals constituting a genus related to Polycheles. As these animals since the days of the Challenger Expedition have enjoyed a special interest as the modern survivors of a group almost until then believed to be confined to Jurassic and Cretaceous times, I thought it might possibly interest some of your zoologist readers to learn about some of the results obtained through the study of the material collected in the North Atlantic by the Michael Sars in 1910 during the cruise undertaken by the late Sir John Murray and Dr. Johan Hjort. To begin with, it must be mentioned that the best specific characters both in Polycheles and Eryonicus' are derived from the arrangement of the spines on the carapace. Now a peculiar correspondence is observed in several species of the two genera," making it possible to "pair" several of the Eryonicus species each with one of the Polycheles species, as will be seen from the following formula representing the position of spines in the median line of the carapace. In these formulæ, 1 and 2 denote single and double pointed spines, while 3 denotes a single blunt spine, and c the position of the cervical groove, the rostral spines being to the left : : ... ... P. sculptus pacificus, Faxon Now, I ask, is it possible to explain the above correspondences as mere accident, or are they not to be taken as evidence of the Eryonicus species being in fact larval Polycheles? One of the commonest objections to this theory is the giant size presented by some of the Eryonicusspecimens compared with the smaller Polychelesindividuals, though this need not signify much. Like so many other plankton animals, the Eryonicus are of a nearly jellyfish-like consistency, and it may as well be conceived that an Eryonicus can shrink into a small Polycheles, as that the Leptocephali, when turning into montée," lose about 78 per cent. in weight (in dry matter they lose over 32 per cent.), according to Dr. Johs. Schmidt, the Danish specialist on eels. If Eryonicus were adult animals, it would be rather remarkable that not a single egg-bearing female has been found among the fifty-nine specimens known to have been captured (Mr. Selbie, op. cit., mentions thirty-five specimens, and the Michael Sars got twenty-four). It cannot matter much that secondary male sexual characters in different stages of development have been found in a few of the largest specimens. Finally, it must be mentioned that one is at a loss where to seek the larvæ of Polycheles, which do not seem to be very rare animals (the Irish research steamer Helga, for instance, obtained thirty-two specimens) if these larvæ are not represented by Eryonicus. For literature and details of the species in question, see Mr. Selbie's paper quoted above. OSCAR SUND. Bureau of Fisheries, Bergen, Norway, May 8. The Age of the Earth. IN NATURE of May 6, Mr. C. E. Stromeyer states that two conclusions in my letter published in your issue of April 22 are not correct; he claims, first, that the amount of energy lost by the earth is not compensated by the heat received from the sun; secondly, that meteoric bombardment of the sun has been left out of account as a source of energy. As to the first point, the amount of energy lost in consequence of the temperature gradient in the earth's cal crust is of the order 133× 10−6. As this is 6000 cm. sec. times less than the total amount radiated, no useful purpose would be served by taking it into account. As regards the second point, any heat due to meteoric bombardment up to date has been taken into account, as the sun's mass as it is known to-day was inserted in the calculation. Perhaps the purport of my letter was not as clear as I could have wished. It was not so much my intention to weigh the evidence for or against an age of some twenty million years, as to emphasise the point that neither radio-activity nor any other known cause will account for a longer period. I have lately had the advantage of discussing the subject with Prof. Strutt, and must admit that the conclusions he has drawn from the helium contained in rocks appear unanswerable. It would seem, therefore, that the origin of the sun's heat cannot be referred to any known cause. Farnborough, May 15. F. A. LINDEMANN. Modern Substitutes for Butter. THE issue of NATURE dated April 8 contains an article relating to " Modern Substitutes for Butter." which gives a highly interesting impression of the technical and scientific state to which the margarine industry has developed in recent years. Towards the end of the article, the author deals with the influence of vitamines, and indicates that, while these substances are present in butter, they would not be met with in margarine This characteristic would meet the case as regards certain butter and margarine products, but by far the largest quantities of butter now on the market are made from pasteurised cream, and the pasteurisation would no doubt have reduced the original quantities of vitamines very considerably. On the other hand, large quantities of margarine contain, among other fats, cold-pressed oils (such as ground-nut oil) which, like the better grades of olive oil, do not undergo any refining process whatever, and would therefore lend to the margarine their original content of vitamines. If vitamines are produced in the lactic acid fermentation of milk, an abundance of these precious substances would be imparted to both butter and margarine, as in buttermaking the ripening takes place after the cream has been pasteurised, and in the manufacture of margarine the ripened skim milk is churned with the fat after the latter has been refined. Hence in both cases the vitamines produced in the fermentation process are not subsequently subjected to any harmful treatment. It therefore appears that, so far as the presence or absence of vitamines is concerned, margarine would rank as equal to butter. There are, in fact, qualities of margarine on the market which contain a small proportion of fresh egg yolk, and such qualities would doubtless be of high standing as regards vitamines. S. H. B. On the other hand, if the present writer's memory is not at fault, the work of American investigators has shown that of several oils investigated, butter fat alone contained vitamines. There is also evidence to indicate that vitamines are closely associated with lipoids, and it is doubtful whether they would be formed during lactic fermentation. It is evident should vitamines be present in nut oils as suggested, that nuts might form a valuable preventative of beriberi, or scurvy; the writer is unaware if this has been tested in practice. As stated in the original article, probably sufficient vitamines are present in the rest of the dietary to enable them to be dispensed with in the fat. THE WRITER OF THE ARTICLE. May 20. THE EXTINCTEUR AND ITS THE There are, of course, one or two other forms of portable chemical liquid fire-extinguishers, i.e., certain forms of less than a gallon capacity containing carbon tetrachloride or some combination thereof, intended for use on small petrol fires, and where the capacity is sufficient, say, from 2 quarts to 1 gallon, and the chemical is discharged automatically by some capsule of compressed air or the like, effective results are obtained from such appliances on small spirit fires. Where, however, the appliance only has the capacity of a pint or quart of carbon tetrachloride or some combination thereof, and has to be applied by manual action, the limit of effectiveness is certainly very small, a quart of chemical applied, say, by a double action squirt being able to deal at the most with a 2 gallon tin of petrol spilt over a motor-car or in some vessel of no great area. A weak spot in the use of carbon tetrachloride and its combinations, by the bye, is the fumes it gives off when in contact with fire. For this reason its use in enclosed spaces should in any case be avoided, and people suffering from liver complaint should in any case keep clear of this chemical when used on fires. But to revert to the ordinary portable chemical liquid extinguisher of 2 to 3 gallons' capacity, as seen in many public buildings, and thus considered by the general public as something acceptable for every-day purposes. We are desirous of warning the public as to unsuitable purchases of such appliances. To begin with, in a very general way a portable liquid chemical fire-extinguisher is not the alpha and omega of first-aid fire-extinguishing, although there is no doubt that these appliances as such are popular. They look so bright and neat. Their presence advertises the owner's forethought. If finished on copper they are quite ornamental. For the ordinary householder and for the ordinary business establishment where fire appliances are not under constant inspection, we would, however, rather pin our faith in the ordinary bucket of water energetically applied, and the ordinary miniature manual hand-pump or corridor engine. A few dozen buckets and a couple of hand-pumps, involving together perhaps an expenditure of 51. to 6l., will work wonders in a quite substantial fire, whilst the same 61. will only produce three or four 2-gallon extinguishers, which require, as a rule, practice to discharge. properly and time to re-charge at intervals; they require also most careful maintenance, and at the best will give the user some 6 or 8 gallons of chemically prepared water as against, say, the 50 gallons of water immediately available for continuous application and rapidly replenished without intervals. A small stirrup hand-pump of the London type, by the bye, can be worked singlehanded to supply 4 to 5 gallons per minute at an effective range of 25 to 40 ft. The whole principle of putting out a small fire is the cooling effect of water applied in fair bulk continuously and under pressure; and the cooling effect can be best obtained by a copious supply of water continuously applied in fair force and bulk from buckets and hand-pumps. The possibility of applying water in bulk continuously with a good cooling effect cannot be obtained from the ordinary householder's supply of extinguishers. Of course, in public buildings where there are many extinguishers immediately at hand, where they are thoroughly maintained, and are handled by skilled or trained men, they are most useful. They are the most handy of water economising minor fire appliances in the hands of a professional fire brigade, although we observe the London brigade only used them in 577 instances last year, whilst they used buckets in 1248 cases. They are essential makeshifts for conditions where buckets and hand-pumps cannot be equally well stowed or applied, as, for instance, on trains, in small boats, or for other awkward places, as, for instance, on the aeroplane in flight, but, to repeat, the alpha and omega of fire extinguishing is not to be found in the extinguisher for the ordinary man in the street. His vade mecum should be the bucket and hand-pump, although they are less showy. These observations, however, should not preclude the purchase, and, in fact, should not discourage the purchase of well-made mechanical portable liquid fire-extinguishers, where there is a probability of their being properly maintained and looked after, as, for instance, in public and semi-public buildings, in large industrial establishments, or estates having private fire brigades, etc., especially if their attempted application can be immediately followed by the application of a hydrant or fire engine. In such places, if of good make in the first instance, and regularly looked after, they are neither likely to burst and injure the operator nor are they likely to get clogged up and fail at the critical moment. The danger of bursting is no small danger, and has resulted in fatalities as well as many personal injuries, whilst in the large majority of establishments where these appliances are not properly looked after they will be found defective at the time they are to be used. Thus at the initial stage of purchase, some standard as to safety for extinguishers is essential to limit the risk of careless users. It is very much to the credit of the British Fire Prevention Committee, to whose work we have had frequent occasion to refer, that it has for some years been pressing towards obtaining a sound standard of manufacture in chemical fire-extinguishers, and that it has further succeeded in getting these standards adopted as necessary standards by the Government and other principal purchasers at home and in the colonies. One of the first results of the Committee's propaganda in 1911-12 was that the fire insurance companies early in 1913 adopted an American. specification which had been long in force in the United States, and started listing extinguishers that complied with this form. The American model, however, being insufficient for British conditions, the British Fire Prevention Committee, which had been making exhaustive tests both with new appliances and appliances in actual use, issued its own provisional specification later in that year, which form was immediately adopted by several authorities of importance in their purchases. Extinguisher construction accordingly commenced to improve. Next, the Fire Prevention Committee suggested some form of conference with the Government departments on the matter, so that the Government departments might be specifying either on the committee's provisional specification or some similar-preferably stronger-specification. The result of this conference has been that, in turn, H. M. Office of Works last summer, the Metropolitan Police last autumn, the Board of Trade this March, and other departments have either Issued their own specifications, which are now practically identical, or have adopted the improved form of the British Fire Prevention Committee's specification of January 1, known as the 1915 standard. The only corporations which still keep to the lower standard are the insurance companies, but no doubt they will also come into line as time goes on, whilst in the meantime they benefit from the fact that the more responsible makers are now all making their appliances to either the Fire Prevention Committee's 1915 specification or to those of the Government departments named. The recent War Office contracts, for instance, are all for extinguishers to the Office of Works' specification, whilst half-a-dozen other departments are specifying their war emergency supplies to the Committee's schedule. A point has, of course, been made by the traders that the existence of several specifications makes it difficult for makers to keep suitable stocks, but this is not the case in actuality, inasmuch as it will be found that any maker who will stock cylindrical extinguishers made to the 1915 specification will meet the requirements of either one of the authorities and the committee. All this, of course, touches the great corporations, the great public authorities, and the public when using establishments controlled by public authorities, be they theatres, factories, or the like. The misfortune, however, is that the general public, the householder, the ordinary estateowner, the ordinary motor-car owner, etc., are still subject to the cheap-jack extinguisher and the specious tout who sells nothing more than a dangerous "tin can" at an exorbitant price-a can which probably costs somewhere around 10s. to manufacture, and for which he asks anything he can get-frequently as much as 2l. to 31. It is an open secret that the best-made chemical fire-extinguishers can be produced in large quantities and sold according to external finish, and after allowing for a fair profit, from, say, 175. to 20s., to comply with the specifications named, and they should thus be obtainable in lesser quantities of handsome finish at 25s. or less. The whole myth of purchasing extinguishers at prices varying from 21. to 31., holding 2 gallons of liquid, gaudily furbished, is bad enough when the |