directions, more or less from a central point the place of impact.

There is a small crater in Arizona, Canyon Diabolo, which resembles closely a lunar crater, and in this instance there is no evidence of volcanic action having taken place. The earth's atmosphere has evidently been a good cloak of protection against extensive pitting by meteoric bombardment at some early epoch. This seems true, because. on examining the structure of rock formations, no indication of buried craters have been revealed, so far as the writer is aware.

The meteoric theory of the lunar craters has been objected to on the ground that there are too many circular craters, since with nearly grazing impacts which, from probability considerations, must have been numerous, there should be more signs of guttering or elongated ridges. There are, in fact, comparatively few very oval

craters.

at

To meet this objection, if it be valid (one cannot be dogmatic), the velocity meteoric impact, for reasons not difficult to imagine, may not have been so great as supposed, and the bodies might have been explosive in the ordinary sense of the term. This supplementary idea would make it unnecessary to assume very high velocities, so that the meteorites by virtue of gravitational attraction, would strike the body of the moon more frequently in a direction nearly at right-angles to her surface, and yet the disruptive violence would be sufficient owing to the bombarding material being explosive. This view is here mentioned, as it is in harmony with the theory that the asteroids resulted from a series of explosions in the material of an at-one-time single planet of appreciable size.

H. Jeffreys ("The Earth," 1924, p. 60), says, speaking of the formation of the asteroids (numbering over one or two thousand) "of their large eccentricities and inclination agree equally with the theories of explosion and tidal disruption. Some may have been captured; in particular, it is possible that the satellites of Mars are captured asteroids. Large variations in the eccentricities of the orbits would be set up by the perturbations. due to the planets, especially Jupiter, and the positions of the nodes and the anses would be continually varying." Furthermore, Jeffreys says: "Explosion is possible, though there is little evidence for it. If the planet contained enough radioactive matter to heat part of its interior up to the boiling

point, the disruptive stresses might come to exceed the small gravitative power of such a mass and permit explosion, and if one explosion took place, there is no reason why others should not follow, since gravity would diminish at every rupture. Tidal disruption by close approach to Jupiter is also possible; the small planet would have to approach very close to the surface of Jupiter, and might be repeatedly broken up during a single encounter." No mention is made of a chemically-explosive planet.

It must be remembered that the idea of the disintegrations or explosions, starting with a single planet, to account for the multiplicity of the asteroids, is not the only theory; for, according to the planetesimal hypothesis of Chamberlin and Moulton, "The fact that there over a thousand asteroids between the orbits of Mars and Jupiter merely tells us that there was no dominant nucleus in this region from the beginning; and the zodiacal light suggests that the process of aggregation is not yet fully completed to quote from W. D. McMillan (Science, July 24, 1925, particularly page 72. It may be noted that the

harmonic mean between the distances of the extreme asteroids Eros and Achilles comes out 20.6, which is close to the theoretical "B" value 21 (see Chemical News, 1923, CXXVII., p. 290), but what this means it is impossible to say at present. The dividing constant for the planet distances in miles is in this case 10,317,000.

These matters are of interest from the geological and mining side, because the distribution of valuable metals and certain non-metallic elements, e.g., diamonds, leads to inquiries as to their origin, which in turn leads to the consideration of physical phenomena of the kind here discussed with reference to the moon. For example, carbon monoxide has been found in meteorites, and the Canyon Diabolo meteorite is said to have contained black and transparent diamonds. Unusual minerals are of interest in this connection.

Before concluding this short survey, attention should be drawn to another feature of the moon's surface. One very remarkable fact is the observed radial streaks or rays, emanating from certain craters, which are of lighter colour than the general surface of the moon. While they appear to occur only in the case of a few craters notably that of Tycho-where they are observed clearly, they extend great distances, hundreds of miles in some

instances. They are from 5 to 10 miles wide or even wider in places-and they do not appear to be cracks in the moon's surface, as no shadows are seen; and, besides, they are lighter in colour, as just mentioned. They pass over and through craters, across the mountains, and for this reason it is difficult to imagine that cracks were originally formed which were filled practically flush with the adjoining surface by molten matter rising upwards from the moon's interior-due to hydrostatic pressure and SO filling them. Although magma forced upwards might have the lighter colour, it seems difficult to understand the absence of deep recesses at the highest places, unless the shrinkage of the moon's crust and the partial closing up of the cracks had forced the magma to the surface in these very high places.

Since the streaks are associated with

craters (some craters show radial rays numbering, say 13, if one were to show them in diagram, but there are, in detail, more, and they blend together centrally as a splash of ink would do), and the craters appear to have been formed by exploding meteorites, it is just conceivable that the explosions in certain circumstances gave rise to long vapourous streaks or heavy dust-like clouds, which deposited their whitish matter when they settled down in sweeping over the rough lunar surface.

Another explanation mentioned in Young's "Manual of Astronomy," is that the streaks have been formed by vapours ascending from rifts or cracks too narrow to be telescopically visible.

Jeffreys has discussed the origin of these lunar streaks in the chapter on surface features in his book cited above.

The surface of the moon presents other interesting characteristics. It is well known, for example, that there are long valleys or rills; deep cracks or clefts, some fairly straight and extending in a few instances several hundred miles, and quite unique is the Valley of the Alps, a straight deep wide gash 83 miles long and about 6 miles wide (see Heath's "Popular Astron

(Atlas) 3rd edition, page 76); also large plains (maria). Many of the big craters are about 10 times the diameter of terrestrial craters, the former being about 50 miles, but exceptional craters over 100 miles in diameter are known. Those 5 to 20 miles across are very numerous, running into hundreds. There are also some depressions without elevated outer rings. There

are, in short, a great many small depressions, holes, or craterlets. The heights of the mountains and peaks vary, the latter attaining to about 26,000 feet; this figure also representing nearly the total number of craters in the visible half of the moon. Taking the gravitational attraction at the surface of the earth as unity, it is only 0.16 on the moon (= }). The surface area of the moon as compared with that of the earth is in the proportion of 0.074 to 1.

In conclusion, a note of caution seems necessary, for some of the figures hereinabove given are only approximate, as will be realised when studying the photographic reproductions of the moon's very rough surface.

An article by the present writer on "Meteors," in the Chemical News, August 14 and 21, 1925, forms a companion to this

one.

A MUCH IMPROVED THERMO-
ELECTRIC GENERATOR.

In the Daily News, of September 4th, 1925, the following item appears :

"What may be a remarkable development of electric power production is foreshadowed in a preliminary report issued from Sheffield University last night of experiments carried out by Dr. T. F. Wall, of the research staff.

the

The idea appears to be based on theory of a German investigator before the war, who discovered a secret alloy and the junction when heated to 400 degrees centigrade developed great electro-motive force.

Dr. Wall states that he has obtained by a new special process a practical form of thermo-junction, capable of developing .05 volts at a given temperature. His proposal is to place such junctions together and One make a thermo-electrical generator. estimate places the cost of a thermo-electric generator at about half the price of a steam engine plant, and the cost of producing electricity at a third the present cost.

The new generator, it is claimed, will need no other attention to generate electricity than stoking the heating apparatus. underneath it with coal.

No steam boilers, engines or moving machinery will be needed. It is thought that the German scientist was killed in the war."

Dr. Wall is the author of the well-known book "Electrical Engineering," published

by Messrs. Methuen. Some time ago, Dr. Wall announced that he was making experiments with the view of breaking up atoms by subjecting matter to very intense magnetic fields; for if the atoms contain electrons describing orbits, in sufficiently strong magnetic fields they should be sufficiently deflected as to disrupt the atom. No results however have yet appeared to show that such disruption is possible by this method, although exceedingly intense fields were tried.

Referring to the new or improved thermo-electric junction, it will be remembered that with a bismuth wire and an antimony wire joined together, the E.M.F. of 0.0001 volt for one degree is obtained, that is to say, when the difference of temperature between the elements of the junctions is maintained at one degree Centigrade, within certain temperature limits. It would appear that Dr. Wall has raised this value to 0.05 volt, a most remarkable result if this is the interpretation of the announcement. Dr. Will has filed provisional applications for patents for thermoelectric generation, which are numbered 18154, 18438, 18645, and 20135 (July and August). Further developments will be awaited with interest. F. H. L.

CHROMITE.

By EDWARD SAMPSON and H. M. MEYER. (U.S.A. Geological Survey.)

Chromite is among the few industrially essential minerals used in large quantity in the United States of which the supply is normally obtained in distant lands. Therefore, any disturbance of international trade relations greatly affects the industry. In 1922, for the first time in seven years, there was a promise of return to a stable condition, and in 1923 this promise was fulfilled.

Domestic deposits furnish only an insignificant part of the chromite used in this country, for there is no known deposit of massive chromite in the United States comparable in size to the great deposits in several foreign countries. The transportation costs to which domestic chromits is subjected are high, for the deposits distant from existing lines do not warrant the construction of special railroads, and the few deposits that are favourably situated with respect to railroad transportation are far removed from the chief markets. In addition to these difficulties, most of the domestic ore is of low grade. Of our annual consumption of about 100,000 tons,

only a few hundred tons comes from domestic sources.

In 1923, 227 long tons of chromite were shipped from the mines, as compared with 355 tons in 1922. These figures are of the same order of magnitude as pre-war figures, and it seems improbable that there will be a substantial increase in the near future. The 227 tons of chromite shipped in 1923 averaged 47 per cent. of chromic oxide (Cr,O), as compared with 49.7 per cent. in 1922. These figures compare favourably with the content of the imported grades. The shipments in 1923 were equivalent to 214 tons of 50 per cent ore. Besides this high-grade ore, 335 tons of 35 to 45 per cent. ore were mined but not shipped. The shipments were the smallest since 1912.

It appears that while Rhodesia is sending more chromite to the United States she is having to meet increased competition from India for European markets. Production in Rhodesia increased from 85,000 metric tons in 1922, to 88,000 tons in 1923. Probably the imports recorded as from British South Africa and Portuguese Africa cover the Rhodesian imports into the United States. The imports of chromite into the United States from British India in 1923 (29,238 long tons) were considerably larger than the total production for that country in 1922 (22,777 long tons). The increase in imports was due largely to the greatly increased activity in Mysore. In 1923 more than 14,000 tons of ore from the Mysore field were imported into the United States for use in refractories, whereas in 1922 almost the entire output of India came from Baluchistan. Imports from Greece increased from 8,600 long tons in 1922 to 10,550 tons in 1923. The prices of imported chromite in the U.S.A., range from 20 dollars to 25 dollars per ton.

SCIENCE COURSES AT PRAGUE. from We have received the Charles University of Prague the Prospectus of Courses in research and other work for foreign students in the Faculty of Science.

Foreign students are eligible for experimental research work in Natural Science provided they have already completed a course equal to that of a Science Degree at a recognised University, or have had special training in the particular branch of science which they intend to study.

The degree of the Faculty is Doctor Rerum Naturalium. Candidates for the

CHEMICAL INDUSTRY.

After a series of slight reductions the price of sulphate of ammonia has begun to rise, very largely owing to the depression in the coal and steel industries having restricted the output. On the other hand, the contemplated expansion of the plant for the production of the synthetic material may well be expected to give rise to an in crease in production.

From the Board of Trade returns, it appears that the exports of bleaching powder were nearly 50 per cent. greater during the first seven months of this year than during the corresponding period last year, and the position generally was hopeful. There was a decided decrease in the exports of benzol, but this is to be accounted for by the remarkable increase in the home demand. The materials in which there was an in

crease in the quantities imported were in general raw materials.

Among fine chemicals there has been considerable reduction in the price of salicylic acid owing to Continental competition, and at 1s. 2.d-1h. 3 d., the British product is holding its own. British manufacturers of methyl salicylate, having reduced their prices, are able to sell at 1s. 44d., against Is. 9d., which is charged for the imported article. There has been strong Continental competition in benzol products, with a fall in price.

NEW STEELS AND THEIR
PROPERTIES.

An interesting exhibit was prepared by Sir Robert Hadfield, Bart., F.R.S., for a recent Conversazione of the Royal Society. Micro-photographs and specimens of various steels were exhibited. Regarding manganese steel, the exhibits illustrated its property of deformation hardness, i.e., the extraordinary increase in hardness in this steel which is caused by strain and accounts for its remarkable resistance to wear and also the difficulty met with in machining the substance. Specimens were shown of manganese and nickel steels, both magnetic and non magnetic.

Heat-resisting and non-scaling steels are of extreme importance in to-day's industrial development in the field of high temperature operations, especially in regard to valves and nozzles. These steels of iron, nickel, and chromium alloy resist scaling even at 1,000° C., in oxidising atmospheres ; interesting specimens were on view. Noncorrodible steels which have been developed under Angle-French auspices were shown in conjunction with an exhibit which well illustrated the development of what may be regarded as anti-corrosive measures. First there was the protective coating, either metallic or paint; then came the pure iron; thirdly, what is known as copper steel-that is, a small proportion of copper added to mild steel-fourthly, the non-rusting

chromium steel which marked a distinct step forward; and finally the special steels which do not depend upon heat treatment or special preparation of surfaces for their resisting powers. Micro photographs of one of these special steels were shown and also many applications of the same to ordinary trade purposes-for instance, turbine blades.

A further interesting section dealt with

silicon steel and X-ray spectograms of silicon steel and pure iron were exhibited. These show, as was first discovered by Professor K. Honda, that the crystalline structure of the two materials is indistinguishable and tends to prove that the remarkable magnetic properties of silicon steel are not due to any special crystalline formation, but that the magnetic properties reside in the individual atoms.

THE ASBESTOS INDUSTRY OF

CANADA.

The effort to bring about a general merger of the asbestos-producing companies of Canada has not yet met with success, the terms not being satisfactory to the Asbestos Corporation of Canada, Limited. It had been hoped that by effecting a merger of the Canadian producers, conditions would be established that would eliminate keen competition among themselves and enable them better to meet the competition of foreign producers. There has been marked decline in the average value of asbestos per ton during the last five years. Returns shew 225,744 tons of materials sold and shipped during 1924, valued at £1,378,937.

a

Exports of unmanufactured Canadian asbestos in 1924 amounted to 204,749 tons. The great proportion of the total output is consumed outside of Canada. This is an indication of the importance in Canadian affairs of any move that may be made towards holding the foreign markets.

THE INDUSTRIAL APPLICATIONS OF COAL TAR PRODUCTS.

Written for Messrs. Ernest Benn, by Messrs. Bunbury and Davidson, this work should be particularly useful at the present juncture to the heavy chemical industry. The aim of the work is to draw the attention of manufacturers, chemists, tar distillers, etc., to the full range of the materials which can be profitably isolated from coal tar, and to discuss their uses and potential uses in a thoroughly practical manner. Even to-day, the full possibilities of the coal tar products-crude, intermediate, and refined-are not too well known, and in this critical examination of them the authors have endeavoured to render a really practical service to the industry.

The Industrial Applications of Coal Tar Products was published on the 10th inst.

THE SIR JOHN CASS TECHNICAL
INSTITUTE.

JEWRY STREET, ALDGATE, LONDON, E.C.3.

The Session 1925-26 will commence on Monday, September 21st.

Students will be enrolled on Wednesday, Thursday and Friday, September 16, 17, and 18, from 6 to 8.30 p.m.

Instruction is given in the following subjects-Pure and Applied Mathematics, Physics, Chemistry, Fermentation Industries, Petroleum Technology, Gas Manufacture, Metallurgy, Arts and Crafts, Modern Languages and Trade Classes.

The courses of instruction are held from 6 to 10 p.m., and meet the requirements of those engaged in chemical, metallurgical, electrical, petroleum and the fermentation industries and in artistic crafts and the tailoring trade.

The following courses will be included in the syllabus-Differential equations and vector analysis; colloids; alternating currents and electrical oscillations; electrolytic analysis; anthracene and its derivatives; technical gas analysis; gas manufacture; brewing and malting; bottling and cellar management; micro-biology petroleum technology; metallography, pyrometry and heat treatment of metals and alloys; mechanical testing of metals and alloys; fuel refractories and furnaces; electro-metallurgy; dental metallurgy; mineralogy; foundry practice and metals relating thereto; mining and surveying; applications of engineering.