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districts in this part of America, a discovery of the occurrence of this substance in large masses has been recently made in the Cretaceous deposits of Kreischerville, Staten Island, N.Y. The amber, which is being extensively worked for commercial purposes, occurs in a bed containing layers and masses of vegetable débris, together with lignite and pyrite. The bed appears to be lensshaped. Some at least of the amber is presumed to be the product of sequoias, but it is possible that a species of Pinus, and perhaps a representative of the AustroMalayan genus Dammara, may have contributed to its production. The remaining articles include one by Prof. Hallow on the structure of the vascular cylinder in hybrid catalpa trees; a second, by Messrs. Cushman and Henderson, on fresh-water rhizopods from New Hampshire; and a third, by Dr. F. W. Carpenter, on the behaviour of a fruit fly under certain stimulants.
A DESCRIPTION of the large diamond found recently in the Premier Mine, Transvaal, is given in the Geological Magazine (April) by Dr. F. H. Hatch and Dr. G. S. Corstorphine, with reproductions of four photographs which represent the diamond in its actual size from four
FIG. 1.-View of the Cullinan Diamond. Actual size. From a photograph by E. H. V. Melvill.
different points of view. One of these pictures is here given (Fig. 1), and it conveys a good idea of the size and shape of the crystal. The stone is bounded by eight surfaces, four of which are faces of the original crystal, and four an cleavage surfaces, which are distinguished from the original octahedral faces by greater regularity and smoothness. For a large stone the crystal is of remarkable purity, and the colour approaches that of a bluewhite. The complete crystal appears to have been a distorted octahedron,, with dodecahedral faces developed on
the edges; and the portions missing probably amount to more than half the original crystal. The stone, which has been named the Cullinan diamond, weighs 9600-5 grains troy, or 1.37 lb. avoirdupois; this is more than three times the weight of the largest diamond previously known.
SOME account of the Mount Morgan Gold Mine, Queensland, is given by Mr. E. J. Dunn (Proc. Royal Soc. l'ictoria, vol. xvii., part ii.). The hill, which rises to a height of 580 feet, is formed mainly of igneous rocks, within which are enclosed masses of decomposed rock, made up of siliceous and ferruginous material, and overlying these is a plug of Desert Sandstone, nearly 100 feet thick in places. The sandstone occupies a hollow in loose sandy beds overlying a ferruginous layer, and these beds yielded the rich secondary ore for which Mount Morgan has been celebrated. No naturally formed gold is known that more nearly reached chemical purity. At a much lower depth, in what is known as the sulphide zone, the gold is much alloyed with silver. The silver was got rid of in the transference of the leached ore to the enriched zone. The state of subdivision of the gold in this zone was so extreme that rich samples, in some cases those carrying 50 oz. per ton, showed no traces of gold that could be detected by the naked eye. The author attributes the formation of the secondary ore to the mechanical and chemical action of sea-water on the sulphide ore, there being evidence of considerable local erosion before the horizontal beds of Desert Sandstone were laid down.
THE Canadian Department of Marine and Fisheries has published the meteorological results obtained at the magnetical observatory at Toronto for the year 1904, with remarks, in a handy and useful form. The monthly means are in most cases compared with an average of sixty-four years, and are consequently of considerable value. The mean temperature of the year 1904 was 42°.2, being 2°.2 below the average. The maximum daily mean was 78°-9, on July 18, and the coldest day -8°.5, on January 14. The rainfall measured 30-04 inches (3.05 inches above the yearly average); this amount does not include 56-5 inches of snow, which is measured quite separately from rain.
AN important step for the promotion of New South Wales meteorology is recorded in the U.S. Monthly Weather Review (vol. xxxii., No. 11, p. 518). It seems that the principal newspaper of the colony, the Daily Telegraph, has commenced the publication of a daily weather chart. The origin of this step is stated in the following brief extract from the first number of the paper which contained this new information, a more complete account of which is inserted in the Weather Review referred to above :-" The inclusion of meteorology in the new public schools syllabus has directed special attention to consideration of weather conditions. Correspondents, including a number of public school teachers, have applied to the Daily Telegraph for amplified daily information on this subject, and the meteorological branch of the Sydney Observatory also has been requested to furnish details of the weather conditions and atmospheric pressures, the information upon which the weather forecasts are made. The Daily Telegraph has arranged to publish daily a chart showing the principal features of weather conditions, including the high and low pressure isobars. Where possible the rainfall area will be indicated and conditions on the coast will also be given. . . . The publication of isobaric charts will enable students with their local knowledge of physical surroundings to anticipate in detail their probable weather more completely than is possible at the central
solution the authors have constructed a voltameter which
office, where precise knowledge of local peculiarities is lacking." Those acquainted with Australian meteorology | is-according to their published results-more accurate will appreciate the importance of disseminating a knowledge of this valuable factor in Australian welfare. In many countries the absence of public interest in the science of the weather is due to its omission from all school instruction, and we in Great Britain are suffering from the same neglect.
THE current number of the Fortnightly Review contains an article by Major B. Baden-Powell, president of the Aeronautical Society, entitled Air-ships and M. Santos Dumont." Major Baden-Powell supplements and criticises a contribution by M. Santos Dumont to an earlier number of the same review on air-ships. He also points out some of the advantages to be gained by flying machines not dependent on a light gas to lift them, and directs attention to a few of the drawbacks inherent in the large gas-bag. The attainment of human flight, he contends, apparently presents no insuperable difficulties. "All that is wanted, so far as I can see, is a few thousand pounds and a clever and energetic inventor, and there is no reason why a machine could not be constructed within a year or two capable of rising and carrying a man in safety for, at all events, a short trip through the air.'
THE water jet affords a most convenient method of applying the power carried by high-pressure water, whether for driving wheels, such as are generally known as Pelton wheels, for conveying the water itself into burning buildings, or for the destructive process of breaking down a mountain side, as practised in hydraulic mining. All this is especially the case in mountainous country where water supply with almost unlimited head is available. As it is not always necessary that the jet should work at full power, regulation becomes necessary. Merely reducing the flow of water by throttling elsewhere than at the jet would be ruinously wasteful, for half the flow would the one-quarter and carry power, wheel driven would no longer run at the proper speed. The regulating nozzle described in a thesis entitled "An Investigation of the Doble Needle Regulating Nozzle," by H. C. Crowell and G. C. D. Lenth (printed by permission of the Civil Engineering Department of the Massachusetts Institute of Technology, Boston, and Tangential Water Wheels, Abner Doble Company), contains a spindle-shaped concentric needle which may be advanced so as to reduce the area of the orifice or withdrawn so as to enlarge it, but the form of the annular passage-way is always such as to lead the water to converge along easy stream lines, until a circular jet of corresponding size is the result. In this way a range of 10 to 1 in the area of the jet may be attained, while the full head is always available. Very beautiful photographs are given showing the jets like clear glass rods instead of the familiar opaque and spray-clothed stream of water. Efficiencies from 96.4 to 99.3 for the energy of the jet are found, which correspond to 98.2 to 99.7 for the velocity.
IN vol. vi. of the Transactions of the American Electrochemical Society, which has just been published, Messrs. A. G. Betts and E. F. Kern publish a paper on the "lead voltameter." Two years ago Mr. Betts found that lead could be deposited in a non-crystalline and dense form from solutions of lead fluosilicate to which had been added a small quantity of gelatin. The Canadian Smelting Company now manufactures more than twenty tons a day of refined lead from solutions of lead silicofluoride. Until Mr. Betts discovered this process it had not been found possible to refine lead electrolytically. By using the above
than the copper coulombmeter, and does not fall far behind the silver instrument. A glass beaker is used as the electrolysing cell, and a kathode of thin lead sheet is hung between two anodes of the same metal. The calculated value of the electro-equivalent of lead is 103.46. In this instrument, in which the electrolyte was 8.5 per cent. PbSiF, 2.5 per cent. H,SiF., and a small quantity of gelatin, the numbers found in six experiments ranged from 103.39 to 103.49. Among other papers of interest in the same journal we note the electrolysis of fused salts, by Dr. Lorenz; the electrical extraction of nitrogen from the air, by Mr. J. S. Edström; electrolysis and catalysis, by Dr. W. Ostwald.
THE latest number of the Journal of the Russian Physical and Chemical Society (1904, No. 9) contains the conclusion of an interesting study, by B. N. Menshútkin, on Lomonósoff as a chemist. natural philosopher and Lomonósoff's services in the creation of the Russian literary language and poetry are well known; but the remarkable work of this eighteenth century natural philosopher, of whom his friend and correspondent, Euler, always spoke with great respect, had hitherto found no proper appreciation in his mother country. His ideas upon the structure of matter, the atomistic theory of chemical changes, the mechanical theory of heat, his kinetic theory of gases, his views on the liquid and the solid state, and his theory of atmospheric electricity, which, he said, is always present in the atmosphere, and originates from the changes in the thermal potential of ascending and descending air currents-all these theories being based upon molecular movements within the bodies-were expressed in terms almost identical with those which are used now.
"It is," he wrote, "the inner, unseen motions of the corpuscles of which all bodies are composed which are the cause of every rise of temperature in a given body. These movements are rotatory. When a cold body is brought into contact with a hot one, the latter communicates. to the former the movements of its particles, which therefore are slackened in the hot body, and accelerated in the cold one. The greater these rotatory movements, the greater the repulsive forces, and the weaker the connection between them."
DR. A. C. HADDON, F.R.S., is delivering a course of lectures on Saturdays at the Horniman Museum, Forest Hill, S.E., on Magic and Primitive Religion."
THE first volume, that for 1904, has been received of a series of yearly publications to be issued by the Chemical Society under the title "Annual Reports on the Progress of Chemistry." The object of these reports is to present an epitome of the principal definite steps in advance which have been accomplished in the preceding year. The first volume contains articles on general and physical chemistry. by Prof. James Walker, F.R.S.; on inorganic chemistry, by Dr. P. P. Bedson; on the aliphatic division of organic the chemistry, by Mr. H. J. H. Fenton, F.R.S.; on aromatic and other cyclic divisions of organic chemistry, by Prof. J. B. Cohen; on stereochemistry, by Prof. W. J. Pope, F.R.S.; on analytical chemistry, by Mr. A. C. Chapman; on physiological chemistry, by Prof. W. D. Halliburton, F.R.S.; on agricultural chemistry and vegetable physiology, by Dr. J. A. Voelcker; on mineralogical chemistry, by Dr. A. Hutchison; and on radio-activity, by Mr. F. Soddy. These summaries of the chief advances in various branches of chemical science should prove of real benefit to students, teachers of chemistry, and professional chemists.
10 31 29 10 52 58 111311
+49 515... 01281... 00189 ... 0.32 O'0375... 0'28 0'0558 ... 0'24 0'0740. 0'21 0'18 .0*0919
+47 418 ... 0'1739
Tune i 1132 9 5... 11 49 51 COMETS 1905 II (1904 e) AND 1904 I.-A daily ephemeris for comet 1904 e, computed by Dr Strömgren, is given in
No. 4011 of the Astronomische Nachrichten. The comet is now very faint, and as seen by Dr. Palisa at the beginning of April it was 10" in diameter, and had a fourteenth-magnitude nucleus. During the present month it will apparently travel through the constellation Lynx in a south-easterly direction towards Leo Minor.
A bi-daily ephemeris for comet 1904 I, computed by Herren Nijland and van d Bilt, is given in the same journal. This comet is also faint, being 0-052 as bright as when first discovered, its magnitude then being about 90. It is likewise situated in the constellation Lynx, and is apparently travelling in a S.S.E. direction towards Cancer, although at the beginning of September it will only be about 3° south of 35 Lyncis.
OBSERVATIONS OF JUPITER.-The results of their observations of Jupiter during the 1904-5 opposition are given by MM. Flammarion and Benoit in the May number of the Bulletin de la Société astronomique de France. Numerous points of change in the colours and forms of the various features are noted, and some of them are illustrated on the four drawings accompanying the article. Among the other conclusions derived from these observations the writers state the following:-(1) the estimations of the coloration of the equatorial bands do not confirm Mr. Stanley Williams's views as to periodical changes therein; (2) the appearance of the Great Red Spot has not changed since the previous opposition; (3) the large variation of the longitude of this feature between March and June, 1904, was probably due to the passage alongside it of the dark region of the tropical zone; (4) a clear spot situated in longitude o° of system ii., and dividing the south equatorial band, appears to be a permanent feature which it will be well to observe assiduously. They further urge that careful attention should be paid at the end of this year to observations of the movements of the red spot, of the bright spots on the southern edge of south temperate band announced by Mr. Denning, and of the dark region situated in the south tropical zone.
THE ELECTRIC CHARGE OF THE SUN.-In No. 1, vol. x., of Terrestrial Magnetism and Atmospheric Electricity is reprinted the address "On the Electric Charge of the Sun" delivered by Prof. Svante Arrhenius before the International Electrical Congress held at St. Louis last September.
After briefly discussing the various theories regarding the nature of the sun's repulsive action, the author shows that the theory which explains the phenomena, by premising that the repulsion is due to radiation pressure acting on negatively charged particles, is in accordance with observational records. The particles having a specific weight of 1-0 and a radius of 0.08 μ are those which are repelled at the greatest speed, and would reach our atmosphere in about 45-9 hours, an interval of the same order as that obtained by Riccò for the time intervening between the probably correlated soiar and terrestrial phenomena. These particles are negatively charged in accordance with Mr. C. T. R. Wilson's proof that such particles are more Pasily condensed on negative than on positive ions, the
ionisation of the solar atmosphere resulting, as Lenard has shown, from the action of the sun's strong ultraviolet radiation. By a simple calculation Prof. Arrhenius shows that the remaining positive charge is balanced, and the balance maintained, by the attraction of negative electrons emitted by other celestial bodies which are negatively charged and lose their charge under the influence of their ultra-violet rays. All such rays coming within a mean distance of 0.063 light-years of the sun will be attracted thereto, and by this means the supply of negative electrons becomes just proportional to the defect thereof.
VARIABILITY OF MINOR PLANET (15), EUNOMIA.-Circular No. 94 of the Harvard College Observatory is devoted to an account of Prof. Wendell's observations of the minor planet Eunomia, from which he established a variation of magnitude of about 0.5. The observations were made with a photometer having achromatic prisms and attached to the 15-inch telescope. As the planet was near its stationary point it was compared with the same star, +13° 1875 (mag. 9.0), from March 15 to April 1, and the corrected differences varied from -0.77 to -III. The formula J.D. 2416920-116+0-1267 E. expresses the phase and period of the changes. The period is very similar to that found for minor planet (7), Iris, viz. o.1295d., and in both cases it is still doubtful as to whether the period requires doubling or not.
FAINTNESS OF PLANETARY NEBULA.-Some interesting results of calculations appertaining to the luminosity of the surfaces of several planetary nebulæ, as compared with the surface luminosity of the sun or the moon, are given in a letter written by Mr. J. E. Gore to the current number of the Observatory.
Dealing with the nebula H, iv. 37, situated near to the pole of the ecliptic, he finds that the ratio of its surface luminosity is to that of the sun's as 1:43196.7 × 10o. The similar ratios for the nebulæ h 3365, 5, and G.C. 7027 are 1: 245.3 X 10", 1: 1095.5 × 10o, and 1: 434 X 10° spectively; thus the brightest of them, i.e. h 3365, has a surface luminosity of only 1/400 that of the moon.
THE COWTHORPE OAK.
IN the Transactions and Proceedings of the Botanical Society of Edinburgh (vol. xxii., part iii., 1904, p. 396) we notice a very interesting article on the Cowthorpe Oak from the pen of Mr. John Clayton. This venerable tree, which stands near the church of Cowthorpe, a small village near Wetherby, is unique among oaks in that its girth is greater than that of any other known tree of its species. Recorded measurements taken about 1700 show that it had at that time a height of 80 feet with a girth of 78 feet on the ground. Since then various observers have recorded its dimensions and noted at the same time the gradual process of decay, damage by storm, and other points likely to be of interest. The latest measurements were taken by Mr. Clayton himself, and they show that the height is now reduced to 37 feet including dead wood, while the girth on the ground has diminished to 54 feet 3 inches. In 1893 a crop of acorns was produced, from one of which a seedling was reared, and is now planted near its parent as a memorial.
The tree stands in a warm, sheltered spot in a field which has a gentle slope to the river, and near enough to get a constant supply of water. The process of decay has been going on for the last 200 years. Between 1703 and 1722 much damage was done by various storms; nevertheless, new leaves are put forth annually. The acorns produced in 1893 were on long stalks-hence the species is Quercus pedunculata. As regards the age of this giant opinion seems to differ. The trunk, being now hollow, precludes all possibility of ever ascertaining the number of year-rings, and no trustworthy data are available before the year 1700-hence the author has been compelled to rely upon a comparison with the age of other trees. In a tree the duration of life may be taken as composed of
three periods, one of growth, one of maturity, and lastly one of decline and decay. Between the number of years in each period a certain ratio is found to exist, and, taking this as a basis, together with what is known of the tree since 1700, Mr. Clayton arrives at the conclusion that its age is not more than 500 years-certainly much nearer the mark than the age of 1600 years assigned to it by Prof. Burnett in 1842, who based his calculation on the theory of the elder De Candolle that a tree increases by one-twelfth of an inch in diameter annually, an altogether untrustworthy basis of calculation.
There is quite a number of other interesting historical trees dealt with in the article, for example, the Greendale Oak in Welbeck Park, which belongs to the Duke of Portland. Its height was recorded by John Evelyn in 1846 as 88 feet, while the altitude of the highest twig at the present day is only 54 feet. In 1724 a roadway was cut through the trunk, which girths 30 feet 1 inch at 4 feet from the ground. The height of the archway was
sacred edifice, such as this yew and the Cowthorpe Oak, and the association no doubt affords them protection. Another notable veteran is the great chestnut of Tortworth, Gloucester, which girths 49 feet 2 inches at 4 feet from the ground. It also stands about 100 yards from a very old and beautiful church.
As regards the longevity of trees, the theory was promulgated at the beginning of the nineteenth century by De Candolle that the duration of life in trees was practically unlimited, neglecting accidents due to unfavourable external conditions, such as the ravages of parasites, injuries from storms, lightning, and other causes. Passing in review the vegetable kingdom, we find there are some lowly organised plants, such as certain algae and fungi, the whole life cycle of which may be completed within the short space of a few days, or even hours. Among the higher plants we have annuals and biennials the existence of which terminates with the production of seed. Then we have the agave and certain palms, the
Cowthorpe Oak, seen from North. The tree is supported by twenty-five props, disposed mostly on the South and East sides. There is a paling about 5 ft. high, which seems as if it had been put up from twenty to forty years ago.
then 10 feet 2 inches, but recent measurements show that the highest point is now only 9 feet 3 inches, and the lowest 8 feet 6 inches. This shows conclusively that a subsidence of the trunk must have taken place within the last 200 years, and, by assuming that a similar sinking into the ground has occurred in the case of the Cowthorpe Oak, Mr. Clayton explains the apparent discrepancies between the earliest and latest recorded girth dimensions of the veteran. The trunk being somewhat tapering, the diameter naturally lessens as the sinking in proceeds. Mr. Clayton adds a note on the testimony of a Cowthorpe man named Oates, who said, "The tree has shrunk very much in my time, and in shrinking the tree has twisted-the Eastern branches towards the South."
Another notable tree as regards size and age is the Crowhurst Yew, which girths 34 feet 4 inches on the ground. It stands in the churchyard of that place. The church must be very old, as it contains monuments of Saxon and Norman workmanship. The author points out that the oldest trees are usually in close proximity to a
aerial portions of which may live from ten to forty years until the production of flower and fruit terminates their span of life, their place being taken by new aerial portions developed from lateral buds at the base of the plant. In the case of trees and woody shrubs, on the other hand, new growing points are formed annually, but this vegetative process does not end in the production of flower and fruit, so that, excluding accidents, there is no reason why that vegetative process should not be continued for an unlimited time.
The giant Wellingtonias of California are well known examples of the age and dimensions which trees may attain. A stem in the British Museum shows 1330 yearrings with a diameter of about 15 feet. On the other hand, certain Japanese dwarf trees are known to be of very great antiquity, although lacking the size of the Wellingtonias. At the same time, one must not lose sight of the fact that the living cells are continually being renewed, and that in a tree like the Cowthorpe Oak the living parts are at most but a few years old.
FISHERY INVESTIGATIONS IN THE
DR. NORDGAARD has collected the results of investigations made in some of the fjords of northern Norway in the winters of 1899 and 1900, during the course of researches in the fishing waters of Lofoten, carried out at the expense of the Bergen Museum and the Norwegian Government. Two expeditions" were made. The first, January to May, 1899, included the Vest Fjord and the sea beyond Lofoten, Vesteraalen, Sengen, and Finmarken, besides a large number of fjords, as the Kirk, the Øgs, the Kanstad, the Sag, and many others. The second, in the winter of 1900, was made so as to obtain material from the fishing banks which would compare with that of the previous year, and it included visits to the Morsdal, Salten, Skjerstad, and Folden fjords.
The hydrographical observations, which are numerous, have been made according to recognised standard methods, and are therefore comparable with observations made further out at sea, in the regions in which the full explanation of many of the facts brought to light here is doubtless to be found. The chief hydrographical result arrived at by Dr. Nordgaard is that the northern fjords can be divided into two groups, those in which the bottom temperature is 6° C. to 7° C., and salinity about 35 pro mulle, and those in which the bottom temperature is below 6C, and salinity less than 35 pro mille. As examples of the former, the Salten, Folden, Tys, Ofot, and Vest fjords are given, and as examples of the latter the Malang, Lyngen, Kvaenang, Porsanger, Tana, Varaanger, Skjerstad, Skjomen, Kanstad, Øgs, and Kirk fjords. It is Suggested that while in some cases, as the Skjerstad
fjord, the inflow of ocean water is cut off by a submarine ridge, the occurrence of the two typical groups may be accounted for by the distribution of rainfall. The heavy winter rainfall in western Norway affords a large supply of fresh water to the surface layers of the fjords, which accordingly remain specifically light, notwithstanding the fall of temperature. In northern Norway the rainfall is much less, hence the surface waters retain a high salinity, and as their temperature falls they sink to considerable depths.
Dr. Nordgaard also discusses at some length the varying influence of different amounts of rainfall on the currents within the fjords. Heavy rainfalls, which raise the surface level of the water, are for the most part the result of winds from the ocean, which produce a similar effect; it is difficult to separate the effects of the two causes, but a rainfall above the average is taken as a fairly certain index of abnormal strength in the oceanic streams.
In the "biological notes" which accompany the tables a number of points are brought out showing and defining the connection between fauna and hydrography. shown that whereas in the first or warm-water group of fjords the deep-water fauna is chiefly boreal, in the second group, where cold water of lower salinity makes its way downwards, the predominant forms are Arctic. The effect of the increased precision of modern methods of investigation in greatly reducing the number of so-called cosmopolitan species is also emphasised.
The section of this memoir which deals with fisheries is specially important and suggestive. In discussing the Lofoten fisheries, Dr. Nordgaard adopts the view that the currents in the Norwegian Sea are controlled by the winds, and that, as already explained, abnormal movements of the currents off-shore or on-shore can be associated with rainfall above or below the average. Again, he says, "It is clear that during the movements to or from the coast of the surface water, a compensating current must be set in motion in the deep water; it has long been a remgnised phenomenon in the fjords, that the surface and under currents go in contrary directions." From an examination of the observations, Dr. Nordgaard concludes that herrings move coastwards specially in the surface layers, while the cod travels along in the deeper layers. Bergens Museum. "Hydrographical and Biological Investigations in Norwegian Fjords." By O Nordgaard "The Protist Plankton and the Diatoms in Bottom Samples." By E. Jørgensen. Pp 254; with 21 plates and figures in the text. (Bergen: John Grieg, 1905.)
The statistics of the yield of the cod and herring fisheries for some years are discussed and compared with corresponding values of rainfall, with results which appear to support the hypothesis brought forward. It would of course be easy to suggest difficulties, such as the extension of the current régime observed in fjords to areas which can hardly be regarded as such, and may therefore have a different system of movements. But as the whole question is at present under investigation on the large scale by the International Council, we content ourselves with an attempt to summarise Dr. Nordgaard's results, deferring fuller discussion of them until the more abundant data are available.
A NEW SLIDE RULE.
MESSRS. JOHN DAVIS AND SON, of Derby, the well known instrument makers, are bringing out a variation of the slide rule which is likely to increase its value for certain classes of calculation without interfering with the simplicity and convenience of the form with which we are all familiar. The lower groove on the outside of the rule, which ordinarily is only wide enough to hold the inturned edge of the cursor, is made wider, so as to take one of the tongues of a spare slide, and this slide is held in place when required by two light aluminium clips which grasp the ends of the rule and of the spare slide while leaving the usual slide free to An extra cursor is also provided which is long enough to grasp both the rule and the extra slide. By this means any rare or special scales upon the extra slide are for the time being equivalent to scales upon the rule, and these may be read against scales upon the other slide by means of the long cursor. If desired, the extra slide can take the place of the ordinary slide, or may be removed altogether when the rule, if provided with an ordinary cursor adapted to the altered lower groove, becomes an ordinary slide rule. In the example submitted, the extra slide carries what are called E and E scales. The E scale is a log log scale, and is always being re-invented; it was called a P line or power line by Lieut. Thomson, who showed it at the Inventions Exhibition, and it was long before invented by Dr. Roget. This P or E line is very handy, for it at once enables the logarithm of any number on any scale, i.e. to any base, to be read according to its position against an ordinary A line, while fractional or high powers of numbers are read with equal facility. Compound interest, pressures and volumes of gases under isothermal or adiabatic conditions are readily evaluated with the aid of the E line read against an A line. If, however, a pair of E slides are used, one in the usual position and one attached below the rule by means of the clips, then against any value, say of v, on one, the cursor will show the value of Y on the other, y having any desired value according to the relative position of the two slides.
The slide rules made by Messrs. Davis and Son are too well known for their accuracy and finish for it to be necessary to refer more to such points, but by some curious perversity or accident there is one little fault in the rule sent for examination which only needs to be pointed out to be put right. On the feather edge a scale of inches in 16ths is provided; on the lower face outside the rule there is no scale at all, while inside, to be used like a hat measure, there is a scale of millimetres beginning at 550. If, therefore, the rule is required for the prosaic but very useful purpose of measuring a length, this can only be measured in inches if it is 20 inches or less, or in millimetres if it lies between 550 and 1040 millimetres. If,