vestigations on several Harcourt 10-candle pentane lamps and a number of Fleming large bulb standard electric glow lamps, which now form the working standards of candlepower. Intercomparisons have been made by means of glow lamps with the National Standards Bureau of Washington, the Electrical Standardising Laboratories of New York, and the Berlin Reichsanstalt.

In the general electrical department, Mr. Campbell has devised a method for obtaining for inductance measurements alternating currents having very high frequencies and a wave form almost a pure sine-curve. A large amount of new apparatus has been set up for testing purposes, much of it of a novel character.

The standard current balances and electrostatic voltmeters have been studied, and it has been found that the allegation that the Kelvin balance, when used with alternating current, is affected by eddy currents in the metal parts near the coils is without foundation for all ordinary frequencies.

Researches on the distribution of temperature in field coils of dynamos and motors, and on the behaviour of insulating materials under heat treatment, have been made by Mr. Rayner, and form the subject of a report to the engineering standards committee communicated to the Institution of Electrical Engineers at their last meeting.

In the department of metallurgy, Dr. Carpenter and Mr. Keeling, during the early part of the year, completed their work on the range of solidification and critical ranges of iron-carbon alloys, and an account of the work was read at the meeting of the Iron and Steel Institute in May last. The value of Dr. Carpenter's work was recognised by his election as Carnegie scholar. On Mr. Keeling's leaving the laboratory, Mr. Longmuir, also a Carnegie scholar, was appointed on the staff, and Dr. Carpenter and he have since been carrying on, in cooperation with Mr. Hadfield of Sheffield, an elaborate systematic research on the properties of the nickel-steels. In all, seventeen different kinds of physical, mechanical, and chemical tests have been performed on the different samples used, which contained varying amounts of nickel up to 16 per cent. The results obtained will shortly be submitted to the alloys research committee of the Institution of Mechanical Engineers.

An investigation on modern high-speed tool steels, such as those shown in use in the engineering department on Friday last, has also been completed by Dr. Carpenter, cooling curves and photomicrographs having been obtained showing clearly the various modifications in structure after different heat treatment.

The optical department is rapidly being organised, and, in addition to lens testing, the work has included the accurate measurement of the angles of prisms and determination of the optical constants of numerous samples of glass.

In the weights and measures department, the chief work has been the study of the master screw of the new leadingscrew lathe, which has been carefully calibrated throughout its entire length.

The foregoing serves to indicate the substantial progress made by the laboratory, and to prove that though it has only been at work a little more than three years, it has already begun to make its mark on the science and industry of the country, and to justify in a large measure the expectations of its promoters.

FUNGI.1

HAVING pointed out that the attempts to derive the word fungus from funere, or funus and ago, fungor, &c., have been shown to be failures-that it comes from the Greek ooyyʊs, and is the same word as sponge, the lecturer proceeded to give illustrations of the fungi known to the ancients. These were, of course, all of the larger kinds, since no knowledge of micro-fungi was possible. Nevertheless, references in the Old Testament show that certain diseases-mildew, smuts, &c.-were known to the Hebrews, but of course their connection with fungi was not suspected.

1 Abstract of a discourse delivered at the Royal Institution on February 24 by Prof. H. Marshall Ward, F.R.S.

The Greeks and Romans not only knew several forms of Amanita, Agaricus, Boletus, Polyporus, and of Truffles, Morels, &c., but they discriminated clearly between the poisonous and wholesome species.

Their ideas as to the nature and origin of such fungi seem childish to us, but they were consistent with the naif attitude of the Greeks towards natural objects. Theophrastus, about 320 B.C., Dioscorides, about 60 B.C., and Pliny, for example, argued that since truffles and other fungi had no roots, leaves, stems, &c., they are objects apart. They arise spontaneously from earth, or by fermentation from the sap of trees, or from water.

It is interesting to note that Polyporus officinalis was imported and used as an article of medicine not only during classical times, but also for centuries afterwards.

In mediæval times the herbalists chiefly copied from Galen, Theophrastus, &c., and as they had no figures the early herbals give us little information. In 1576, however, Clusius gave a series of wood-cuts which are well worth looking at, and in 1601 he made a series of water-colour sketches of eighty-two of the fungi of Austria-the first drawings of the kind known. Figures in Dalechamps, 1536, Dodoens, 1583, and Parkinson, 1640, may also be compared.

The next step forward was only possible after the microscope had come into use as a scientific instrument.

It is a curious point that abundant and conspicuous as the powdery spores of the fungi are, no one seems to have observed their importance until Micheli, in 1729, collected and sowed a series of them, and with results, for he obtained mycelia, and in a few cases even sporophores; but it was not until a century later, 1820, that Ehrenberg, in his classical "De Mycetogenesi," traced the larger fungi to their my. celial filaments, collected and sowed spores, and grew several species of Moulds, and especially discovered the sexual act in Zyzygites. For although Micheli's ideas had been confirmed by Gleditsch in 1753 and by Schaeffer in 1762, Rudolphi and Persoon had more or less denied the germination of spores, and insisted on the spontaneous generation of the moulds.

However, before 1840 Nees von Esenbeck had cultivated a Mucor from spore to spore, and Dutrochet, 1834, and Trog, 1837, had seen the "puffing " of asci and practically established the doctrine of wind-distribution of spores. By these and similar successes the era of the Mould-fungi was initiated, and the labours of Corda, Tulasne, Prings heim, Cohn, and De Bary soon introduced system into their study, and especially the exact study of life-histories showed what important results for morphology lay in the biological investigations of these micro-fungi.

The lecturer here gave illustrations of the commoner types of mould fungi, with notes on their botanical importance, and some remarks on the points he wished to emphasise later.

An early outcome of the investigations of the moulds and their allies was the discovery of what curious substrata some

of them grow upon. A rapid survey of all saprophytic fungi shows that while the majority grow on the soil, on plant remains, or on dung of various kinds, peculiar forms or species occur on such bodies as resin, cork, bees' and wasps' nests, bones, limestone, insect-remains, horn, hair, feathers and hoofs, fats, and in chemical solutions such as picric acid, copper sulphate, arsenic, and poisons such as atropin, muscarin, and so forth.

Here, also, the lecturer gave some notes on details, of which the most striking was, perhaps, his own proof that the horn-destroying fungus will not act until its spores have been passed through the alimentary tract of an animal, or subjected to the influence of gastric juice.

In 1866, the year of publication of De Bary's book on mycology, a revolution in the study of fungi was brought about by the first morphological proof of parasitism and infection, and the clear distinction drawn between the saprophytic micro-fungi or "moulds" and the parasitic fung which induce diseases." The matter was of especial importance as explaining away prevalent erroneous ideas according to which these disease-fungi were outgrowths (exanthemata) from the moribund tissues of the host-plan itself.

De Bary's great service was to prove that a spore of a fungus arrived from outside, and after germinating on the

leaf or other organ of a plant, bored its way in, or through a stoma, and entered the tissues. Here it lived, as does a plant in any other medium, at the expense of the substances in the tissues, which it eventually kills. It then emerges and develops its spore on the outside.

Thus was founded the "germ theory" of disease.

The lecturer here gave illustrations of the kinds of parasites referred to, and showed how the spotting of leaves is brought about by various epiphytic and endophytic forms, such as Oidium and Erysiphe, Phytophthora, Ustilagineæ and Uredineæ, &c., and directed attention to certain special genera, such as Botrytis, Aspergillus, &c.

That the ancients were acquainted with the phenomena of rot in timber is attested by remarks of Theophrastus on hollow trees and the decay of oak; but it was not unti! about 1830 that any idea of connecting the phenomena with fungi can be traced, and even then Theod. Hartig, who discovered hyphæ in the rotten wood, thought they originated from the wood-fibres themselves. Schacht, in 1850 and 1863. figured many instances of hyphæ in wood, and showed that the fungus fed on the starch, pierced the cell-walls, and in some way induced their putrefaction; and to these and Willkomm's researches, in 1864, we may trace the origin of our knowledge of fungi as the causes of decay in timber. Meanwhile the palæontologists also were bringing forward examples of fungus-hyphæ in fossil woods.

But the real founder of this important subject was R. Hartig, who in his works, 1874 and 1878, proved that not only are there several kinds of wood-rots in different species of trees, each induced by different forms of fungi, but that the different woods show special markings, and break up in peculiar manner for each case, so that particular kinds of rot can be recognised by particular symptoms. Hartig, moreover, showed how the fungi got into the tree, and that these wound-fungi have special peculiarities. He traced their hyphæ into the vessels and wood-elements, showed how they pierce the cell-walls, and, most important of all, proved that they dissolve out from the wood-elements the lignified constituents to which their fundamental physical properties -as wood-are due, and either leave the delignified walls soft and cellulose in character or dissolve them to a jelly. Here the lecturer showed illustrations of the mode of action of dry rot, of Polyporus igniarius, and of other wooddestroying fungi, and referred to Czapek's recent discovery of Hadromal, the probable uniform constituent of wood hitherto vaguely known as Lignin.

In another direction activity was turned to the fungi which attack insects, and which are now known often to become epidemic, to the great advantage of areas devastated by locusts, cockchafers and other grubs, caterpillars, &c.

It is a remarkable fact that whereas the diseases of plants due to fungi are numbered by their thousands, only some two hundred or so of animal maladies due to fungi proper are known. Whether this is due to the more acid nature of vegetable sap, to the high temperature of animal tissues, or to the greater abundance of the anti-bodies in animals cannot be decided.

The lecturer gave illustrations of caterpillars with their destroyers, Cordyceps, Isaria, &c., growing from their mummified bodies, and referred to Torrubia's "Vegetable Wasp "legend of 1749. He also showed photographs of the "plant-worms used in Chinese medicine, and rapidly surveyed the work of Cesati, Pasteur, De Bary, Cohn, &c., on Muscardine, Entomophthora, Empusa, Saprolegnia, and other insect-killing fungi.

But these entomophagous fungi are merely particular cases of mycoses. Every group of animals from the Protozoa and Infusoria upwards have their fungus parasites; hyphæ penetrate the ceratin of sponges and the calcareous walls of corals, and fishes and amphibia are by no means immune.

Birds and mammals suffer particularly from certain mycoses due to fungi which we have been in the habit of regarding as harmless moulds, e.g. Aspergillus, and even man is sometimes in danger from such fungi.

When, in 1869-70, Grohe and Block showed that small doses of the spores of Penicillium and Aspergillus are fatal to kittens, their statements were emphatically disbelieved; but Grawitz confirmed them, and the body of evidence showing that Aspergillus contains poisons toxic to birds and higher animals can no longer be overlooked. Some of these forms of aspergillosis are very serious diseases indeed.

While the new era of mycology was stimulating observers to new investigations into the life-histories of moulds, and of the parasites of animals and plants, and into the ætiology of the timber-destroying fungi, and so forth, on the one hand, it was, on the other, gradually attracting to its domain areas of investigation which had grown up independently out of the past, and which the older thinkers could never have dreamed of associating with fungi.

A conspicuous example was the study of fermentation, which, since Janssen in 1590 had brought forward a microscope of several lenses, and Leeuwenhoek had applied an improved form of it to the animalculæ in putrefying liquids, had undergone the initial stage of passage into the hands

of the naturalists.

The lecturer then sketched in rapid outline the history of the thecry of fermentation, from the early days when the lees or sediment (yeast) were known as the" Faeces Vini "apparently owing to the shrewd suggestion of a Venetian doctor, who, in 1762, said putrefactive and fermentation processes are due to the vital activity of minute worms, the excreta (faeces) of which induce the turbidity and mal-odour of the liquid-to the days when the living plant-nature of these "faeces" was gradually established by the work of Astier, 1813, Desmazières, 1826, Quevenne, 1838, and Persoon, and especially by Erxleben, 1818, Kützing, 1834, Cagniard Latour and Schwann, 1837.

At the same time, the sketch included an outline of the first great controversies regarding abiogenesis or spontaneous generation, brought forward from its ancient strongholds in the ignorance of the classical and mediæval writers--e.g. Pliny, Bock, Van Helmont-by Needham in 1745, and confuted by Spallanzani, 1765-76, Schultze, 1836, Schröder and Dusch, 1854; and to which the coup de grâce was given by the work of Pasteur, 1862, Cohn, 1870-75, and Tyndall. Information derived from the brewing of quass, saki, pulque, kava, toddy, koumiss, mead, metheglin, spruce and other beers and wines by peoples all over the world has only confirmed the ideas, of Pasteur especially, that all such fermentations are due to the presence of fungi; and although the discussions as to the process itself being due to catalytic actions and the communication of internal movements to the molecules of sugar broken up, initiated by Stahl in 1697, and revived in various forms by Liebig, 1839, and Naegeli, 1879, culminating in Buchner's views on the discovery of zymase in 1896-97, have modified the older forms of the vitalistic theory of Cagniard Latour and Pasteur, they have not dissociated fermentation from the life of the cell.

The lecturer then passed to a survey of the enzymes, those remarkable bodies which, though not themselves living, are capable of breaking up organic substances apart from the protoplasm of the cells which secrete them, and showed that since the discovery of diastase in malt by Payen and Persoz in 1833, of pepsin in gastric juice by Schwann in 1836, and of invertase in yeast by Berthelot in 1860, numerous other special enzymes have been isolated, and all the principal forms of sugar-inverting, starch-saccharifying, cellulose-dissolving, fat-splitting, proteid-converting, and oxidising enzymes occur in the fungi. Bourquelot has shown the presence of nine such enzymes in Polyporus sulphureus and of seven in Aspergillus alone.

The presence of certain deadly poisons in putrefying fish, flesh, &c., and the researches consequent on the increasing knowledge of septic poisoning of wounds-with which Lister dealt so practically at the time-led to researches which, in the hands of Brieger, Sonnenschein, Armand Gautier, Selmi, and others resulted in the isolation of more or less specific bodies, such as sepsin, cadaverine, ptomaines, leucomaines, &c. In 1876 Neucki obtained an unusually pure form, and the doctrine of ptomaine poisons may be regarded as thereby established.

For us, the point of interest here is that these poisons proved to be analogous, if not identical as a class, with a number of vegetable poisons, such as atropine, brucine, nicotine, strychnine, or at any rate presented striking resemblances to them in their physiological actions.

As close, or even closer, resemblances were found in the poisons extracted from the fungi; amanitin, bulbosin, cornutin, sphacelotoxin, &c., all came under the same general category. In 1880 Pasteur showed that fowl cholera could be produced by means of the poison excreted by the bacilli, from which the bacilli themselves had been removed; and

Brieger, in 1885, then showed the same to be true for tetanus and typhoid. Löffler, 1887, and Hankin, 1890, then showed the same to be true for diphtheria and for anthrax, and the toxins of tetanus, cholera, &c., were obtained shortly afterwards.

Thus was founded the doctrine of toxins. The bacilli of disease do not merely induce the formation of ptomaine poisons in the decomposing tissues; they form the toxins in their own cells, and then excrete them.

The lecturer then referred to the similarities of the venenenes of snakes, scorpions, and spiders; of the toxins in eels' blood; and of the vegetable toxins ricin, robin, &c., emphasising the fact that all these bacterial, animal, vegetable, and fungal poisons belong to one and the same great family of toxic bodies.

The horribly intoxicating and poisonous drink made by certain Siberian and Kamschatkan peoples from the fly Agaric, the dry gangrene and paralysis due to ergotism, now a rare disease in western Europe, and the effects of the toxins of tetanus, diphtheria, and other bacilli, all have points in common with the poisons of snakes, of certain seeds, and so on-certain Australian species of Swainsonia impel horses which have eaten it to behave as if trying to climb trees, or to refuse to cross a twig as if it were a large log, reminding one of the effects of Amanita muscaria on man.

In great part, if not entirely, owing to an experiment of Nuttall's in 1888, in which he found that normal blood has bactericidal properties, researches were undertaken which resulted in the discovery that the sera of animals, either normally or if rendered immune by minimal doses of toxins, contain antidotal substances to the toxins. Behring and Kitasato, in 1890, who demonstrated the antitoxic power of blood immunised with diphtheria or tetanus to the toxins of these bacilli, were followed in rapid succession by Brieger, Ehrlich, Pick, and others, and the doctrine of the antienzymes and antitoxins was established.

The lecturer then gave two illustrative cases. Dunbar, in 1903, showed that hay-fever, as already maintained by others, was not only due to the pollen of grasses, but he isolated from the pollen-grains a toxin which itself induces all the symptoms of the malady.

Not only so. He showed that the serum of horses, &c., to which the hay-fever is communicated becomes antitoxic to the malady. This antitoxin has been distributed, and the statistics uphold the accuracy of Dunbar's views.

That pollen-grains contain enzymes has long been known, and the experiments of Darwin and others have shown that some pollens are poisonous to the stigmas of the wrong plant. Another suggestive illustration is that given by Woron, in which, bees having conveyed pollen, together with the spores of a Sclerotinia, to the stigmas of certain species of Vaccinium, the pollen-tubes and the fungus-hyphæ race each other down the style, and the latter usually win, and destroy the ovules. Moreover, everyone knows how corrosive and destructive the pollen-tubes of pines, &c., are in the tissues, and we must not forget that pollen-grains are spores.

The second case dwelt on by the lecturer is that of pellagra, a disease to which the ill-nourished peasantry of maizegrowing countries are liable in bad seasons, when the crops are poor and mouldy.

Cene and Beste, in 1902, referred the malady to the presence of an Aspergillus in the bad grain. They also extracted from this mould a highly toxic body. Mariani, in 1903, then showed that the blood of patients cured of pellagra is antitoxic to the poison of the disease.

The lecturer pointed out that, without committing ourselves to any premature opinion as to the absolute accuracy of these views, there are two increasing classes of evidence which support his suspicion that numerous as yet insufficiently examined cases of this kind will turn out to be due to what he calls "lurking parasites" in bad grain and fodders.

The first is the large class of mycoses now referred to the poisonous action of such a "mould as Aspergillus, a fungus shown to abound in enzymes and toxic bodies. The second is the increasing number of cases of poisoning by fodder and grain-plants, normally wholesome, but found to be deleterious in certain circumstances or years.

Cases of poisonous wheat, oats, &c.-the "Taumel

99 66

Getreide, 'Taumel-Roggen" of the Germans-have long been known, and the lecturer quoted cases where similar noxious effects are traced to the presence of Ustilagineæ, Helminthosporium, Cladosporium, and other fungi.

A notable case is that of the Darnel, a tiresome weed in some countries. The ancients-e.g. Galen-knew that darnel in bread causes dizziness, headache and sickness, and thought that neglected wheat, &c., was transformed into darnel. Hofmeister, in 1892, examined and extracted the toxic bodies, and confirmed the repeated statements as to their deleterious and even fatal action on animals.

Yet it was not until 1898 that Vogl discovered the existence of a mycelium in the seed-coats of the poisonous darnel, and in the same year this was confirmed by Hanausek and Nestler, though they did little beyond recording the presence of a fungus.

In 1903, Freeman, in the lecturer's laboratory at Cambridge, worked out the details, and left no doubt that the poisonous property is due to the fungus.

The lecturer then pointed out that a whole series of questions concerning these and similar diseases now being investigated in his laboratory lie under suspicion of connection with grain-poisoning, or at any rate with poisoning of fungi introduced as food.

To say the least, we want further and extensive researches from this point of view into the ætiology of Acrodymia in Mexico, Algeria, &c., and of the Colombian Pelade, of the "trembles of cattle and sheep, and of the "milk sickness" of the North American prairies, and even diseases like beri-beri, &c.

The conclusions, the lecturer pointed out, to which we are driven may be thus summarised :

(1) Fungi, like animals and other plants, including bacteria, excrete enzymes, and utilise them in the same way and for the same purposes.

(2) The poisons of the fungi are toxins, not only similar in character to the poisonous alkaloids, toxalbumens, &c., of the bacteria, and of the higher plants, the venenenes of the snakes, &c., but their poisonous actions in the paralysis of nerve-ends, &c., are essentially the same.

(3) These poisons, &c., introduced into the blood of animals, call forth the activities of antitoxins and antienzymes, as do the toxins of animals, bacteria, &c., in similar circumstances.

(4) The presumption is, therefore, justified that the action of the enzymes and toxins of parasitic fungi on the proteid cell-contents of their plant-hosts is similar in principle to that on animal proteids, and that the host reacts by means of anti-enzymes and antitoxins.

The lecturer then adverted to the difficulties of obtaining the toxins and antitoxins from sap, and concluded by showing in specific cases-the rusts of wheat and grasses— how probable it is that, since no anatomical features explain the facts of predisposition and immunity, and the latter cannot be referred to climatic conditions or to peculiarities of soil, &c., the above considerations will be found to apply, a matter dealt with elsewhere by the lecturer.

TRYPANOSOMIASIS AND EXPERIMENTAL MEDICINE.1

THE greater portion of the first Report deals with the subject of human trypanosomiasis, particularly in the Congo district. The trypanosomata are flagellated protozoa, which have been found to be parasitic in many animals, sometimes causing no symptoms, as in the rat, but sometimes associated with serious effects, as in the tsetse-fly disease of the horse. During the last few years trypanosomata have been found to be parasitic in man in various districts of West and Central Africa. If the infected person shows irregular fever without other marked symptoms the condition has been termed trypanosomiasis; if in addition there is somnolence and stupor, and later wasting, convulsions, and fatal coma, the condition is the

1. Reports of the Trypanosomiasis Expedition to the Congo, 1903-1904.” Liverpool School of Tropical Medicine. Memoir xiii. Pp. 111. (1904-) Price 155.

"The Thompson-Yates and Johnston Laboratories Report." Vol. vi. (New Series), Part i., January, 1905. Pp. 205. (University Press of Liverpool; London: Williams and Norgate.) Price 12s. 6d.

PROF. W. JAMES, of Harvard University, has accepted, Science reports, the acting professorship of philosophy at Stanford University. He will lecture at Stanford during the second half of the next academic year, and will organise a department of philosophy for the university.

A GENERAL meeting of the Association of Teachers in Technical Institutes will be held on Saturday, March 25, at the Regent Street Polytechnic, London, when an address, to be followed by a discussion, will be delivered by Mr. W. J. Lineham, head of the engineering department, Goldsmiths' Institute, entitled "Technical Training-a Teacher's Views."

IN connection with the International Exposition to be held at Liége, Belgium, from April to November during the present year, it is proposed to hold an International Congress of Childhood on September 17-20. The congress will be organised in four sections, as follows: (1) education of children; (2) study of children; (3) care and training of abnormal children; (4) parents' associations, mothers' clubs, and other supplementary agencies for the improvement of youth.

THE Council of Liverpool University has accepted an offer from the president, Mr. E. K. Muspratt, to provide for an extension and equipment of the chemical laboratories at an estimated cost of 10,500l. The following contributions for the extension and maintenance of the chemical department have also been acknowledged by the council:100l. per annum for five years from the United Alkali Company, Ltd., 100l. each from Mr. George Wall, West Kirby, and Mr. T. Threllfall, London.

A NEW technical college and secondary school at East Ham was opened by the Prince and Princess of Wales on Saturday. The building has been erected and equipped at a cost of about 24,000l., towards which the Essex County Council has contributed 6000l., and the remainder has been made up by the East Ham Corporation. The accommodation includes a botanical room, chemical class-room and

laboratory, physics laboratory, carpenter's shop, and provision for the pursuit of various crafts-plumbing, metalwork, brickwork, &c. In replying to the address presented by the Mayor of East Ham, the Prince of Wales said :It is difficult to realise that only ten years ago these crowded streets were green lanes, that your population has multiplied nearly twentyfold in the last thirty years, and that within your borough one industry alone employs more than 10,000 men. You have very rightly recognised that this remarkable growth carries with it serious responsibilities. The vast and rapidly increasing population of the borough necessitates the provision of suitable secondary and technical education, and in this institution you are furnishing that educational equipment for the rising generation which is indispensable if we intend to maintain our place in the great struggle for commercial supremacy. My heart is with you in all such undertakings as that which we are about to inaugurate, and I trust that every success may attend your useful and patriotic efforts.

Royal Society, February 16.-" Further Observations on Slip-Bands.-Preliminary Note." By Walter Rosenhain. Communicated by Prof. Ewing, F.R.S.

The paper describes what the author believes to be a novel method of investigating the micro-structure of metals, and some preliminary results obtained by its aid. The method was devised in order to throw further light on the true nature of slip-bands, and the preliminary results relate mainly to this question.

A direct means of examining the surface configuration of a piece of metal upon which slip-bands have been produced would be presented by a transverse section of such a specimen, provided that the section could be produced with an absolutely sharp edge, but no useful result can be obtained by cutting the specimen through and simply polishing the exposed section. The edges of specimens prepared by the usual methods of polishing are always rounded off, so that it becomes impossible to focus upon any definite defect, there would be no guarantee that the edge reedge with high-power lenses; and even apart from this presented a true section of the pre-existing surface.

FIG. 1.-Transverse Section of Slip-bands. Vertical illumination X 1000 diameters.

The author has adopted the principle sometimes used in optical work of supporting the surface, which in section becomes the edge, by means of an adherent layer of hard material; but the conditions which such a layer must satisfy for the purposes of metallography are very stringent. In order to satisfy them, the author uses a deposit of another metal obtained by electrolytic means, and this method has proved satisfactory.

The specimens used consisted of strips of the mildest steel, and after preparation an electro-deposit of copper was applied to them. By first bending the strips into a flat U shape, short portions of their length could be polished in the usual manner for microscopic examination; subsequently the strips could be readily strained in tension. The slip bands and other features of the specimens having been satisfactorily observed, electro-deposition was proceeded with, care being taken to avoid chemical action on the prepared surface by the preliminary use of a bath of copper cyanide.

The specimens were then cut across. In order to obtain a satisfactory polish, the ordinary method of polishing had to be modified; it was found that polishing with rouge rapidly eroded a deep groove between the copper and iron,