Border occasionally seen between Light and Dark Regions on Photographic Plates.

For a small installation, where light is the first consideration, it would probably be admitted that acetylene is highly satisfactory, but even for lighting the use of mantles has rendered gasoline a very severe rival. The

cases of schools the gas is required to meet both demands, and gasoline seems to possess the advantage.

F. J. ALLEN.

THE explanation of a well known phenomenon in photography, given by Sir Oliver Lodge in his letter to you last week (p. 5), does not take into consideration the following facts:

66

(1) The perceptible difference in thickness" between the acted-on and unacted-on portions of a negative is only perceptible to our unaided senses when certain developers are employed containing substances which act powerfully on the gelatin. Most modern negatives certainly have no perceptible difference in thickness, certainly not enough difference to give rise to so marked an effect as that referred to.

(2) The difference in thickness is most marked in the "carbon" transparencies from which many enlarged negatives are made. Here it can be both seen and felt; in the other case it cannot. We might therefore expect this cylindrical lens effect to be most marked when using such a transparency, but the careful comparison of a number of enlarged negatives made in these two methods reveals not the slightest difference between them. In my own mind I have always accounted for the phenomenon in the following way :-The sensitive film ordinarily can only be approached by the developer from its outward face, hence the action over an area where the light action has been the same is uniform. But if that area is bordered by one where there has been little or no light action, the developer absorbed by such parts is not spent in doing any or much work in those parts, and, so far as any lateral diffusion is concerned, is practically fresh developer. Hence the borders of an exposed portion, where it comes against an unexposed portion, are attacked by fresh developer diffusing both from the front and from the unexposed part, and we should therefore expect to find a border line of greater density there, as in fact we do. For a similar reason we should expect to find a less dense line on the border of the more transparent portion, as is the case, though it is not often so noticeable as the former.

That this is the true explanation is, I think, made manifest by the fact that the line in question can be quite easily distinguished on plates exposed in Spurge's actinometer, where there is certainly no opportunity of a cylindrical lens effect," and especially when_development has been pushed far. R. CHILD BAYLEY.

20 Tudor Street, London, E.C., November 6.

The Use of Gasoline in Chemical and Fhysical

Laboratories.

The questions for consideration are cost and efficiency. In reference to cost, estimates were obtained to supply the chemical and physical laboratories and to light the whole building, and showed that the initial cost of plant and fitter's work would be about fifty per cent. higher for acetylene than for gasoline, and the estimated cost of maintenance for the former was also much higher. Efficiency may be considered under the following heads (a) The relative simplicity of the generating plant; (b) the ease of manipulation;. (c) the nearness to which the gas approaches in use to coal-gas; (d) the risk of explosion.

(a) The plant used in the Llanberis School was supplied by the Walworth Manufacturing Co., of Boston, U.S.A., and consists essentially of three parts:-(1) A large shallow cylindrical copper tank, holding 250 gallons, buried some 30 feet or more from the building, which is filled with gasoline through a pipe and closed air-tight by a screw cap. Two other pipes, an inlet and outlet, are fitted into the top of the tank and pass under ground to the cellar of the building. (2) In the cellar a pump, worked by a weight on pulleys, forces air through the inlet pipe on to the surface of the gasoline in the tank. Evaporation is rapid (gasoline boiling from about 35° C. to 70° C.), and the mixture of vapour and air is driven through the outlet pipe into (3) an automatic mixer, by which a definite and known amount of air can be added, so that the proper proportion for burning may be constantly maintained. The whole plant is extremely simple, and was easily put up by a local gas-fitter under my direction.

(b) It requires very little attention. The weight has to be wound up about once a week; the mixer adjusted, by moving a small wheel along a rod, about once every two or three months; and the tank filled about every twelve or eighteen months. The frequency of the recurrence of these operations clearly depends on the size of the plant relative to the demands upon it.

(c) The burners differ slightly from the ordinary coal-gas bunsens, but give an excellent flame for ordinary laboratory purposes. The most noticeable difference is that the flame is more easily blown out. This gives a little trouble with an ordinary foot blowpipe, but a slight modification, which I hope to carry out, suggested by my friend Mr. B. B. Turner, of Storrs Agricultural College, Connecticut (who has used gasoline for some years, and who brought it to my notice), will probably get over the difficulty. The plant supplies enough gas to light the whole building as well as for laboratory purposes.

(d) The risk of explosion is very slight, as any escape is at once detected by the strong smell, and the limits of explosion are narrower than those of coal-gas and very much narrower than those of acetylene. The absence of any heating arrangements to aid the evaporation, such as are proposed by some makers, considerably reduces the risk of explosion. J. R. FOSTER.

THE AEGER IN THE RIVERS TRENT AND OUSE.

bore, or aeger as it is locally called, in the River Trent at Gainsborough during the recent high equinoctial tides, which did so much damage all along the east coast, I send you the following description, which may interest some of your readers, more especially as I am not aware of any trustworthy account of this bore that has yet been published.

The Trent is a tributary of the Humber, and joins that river about 16 miles above Hull and 40 miles from the North Sea. The width of the Trent at the junction is from 2500 feet to 3000 feet at high water, diminishing to 700 feet 1 miles from the

junction. This wide space is encumbered with a mass of sand banks. The width of the Humber below the junction averages about 4500 feet, and this channel also feeds the Ouse, which is a continuation of the Humber. This width is double that of the Trent and Ouse combined. The rise of ordinary spring tides at Trent mouth is 15 feet, increasing at equinoctial tides to 19 feet. The tide has a run of 47 miles up the Trent, and reaches to 87 miles from the North Sea, the flood lasting three hours and the ebb nine hours.

The bore, or aeger, is caused by the check of the tidal flow through the shoal water of the sand banks and the contraction of the waterway, the tidal current overrunning the transmission of the foot of the wave. It first assumes a crest somewhere between Burton Stather, 3 miles from the mouth of the Trent, and Amcotts, 2 miles further on, depending on the condition of the tide, the water rising almost simultaneously 3 feet. In ordinary spring tides the bore does not extend more than 7 or 10 miles above Gainsborough. In high spring tides it diminishes

FIG. 1.-The Aeger in the Trent.

to foot in height at Torksey, 35 miles from the mouth of the river, and then gradually dies out.

The bore was to be seen under exceptionally favourable conditions on September 30 and October 1 last, being the second and third days after the new moon. The tides were laid down in the Admiralty tide tables for the Humber as the largest of the year. The moon was in perigee on September 29, and had 11.21 degrees south declination. The wind was from N.E. to N.W., a direction which brings the largest tides, and was blowing at Spurn with a force of from 6 to 7. Inland the force was only about 3 on the Beaufort scale. There was a limited quantity of fresh water running down the river, the velocity at low water being 2 miles an hour. The depth in the channel between Gainsborough and the Humber is now about 6 feet, but there are several shoals with not more than 2 feet to 2 feet over them. The tide was exceptionally high, rising in the Humber at Hull nearly 3 feet higher than ordinary spring tides, and within 10 inches of the record tide of March, 1883.

The bore could be heard approaching about half a mile from the place of observation, and passed with a crest in the middle of the river of from 4 feet to 4 feet extending across the full width of the river, which is here about 200 feet at high water. At the sides the breaking wave rolled along the banks 6 feet or 7 feet high. The crest was followed by five or six other waves of less height, terminating in a mass

of turbulent broken water for a distance of 100 yards. The velocity of the wave, as nearly as it could be measured, was about 15 miles an hour, the current running up after the bore had passed at the rate of 4 miles an hour, and at its maximum, about half flood, 5 miles an hour. The tide rose 4 feet in the first four minutes after the arrival of the bore, 5 feet in the first half hour, and 8 feet in two hours, when it attained its maximum height and commenced to fall; but the tide continued running up the river for another hour after this, at the reduced velocity of 2 miles an hour. There were some steamers and barges lying at the wharves, and a row-boat in the middle of the river. These rose with the wave and suffered no harm.

These bores were considered by the men on the river as fair specimens of those which come with high tides, and as never exceeded in height to any extent. When the river is full of fresh water and the ebb is heavy the bore is less pronounced, and does not show at all on neap tides. It was reported that at Owston Ferry, which is 8 miles nearer the Humber

than Gainsborough, the crest of the aeger was 8 feet, but this was probably at the side of the river. A boat which was in the middle of the river when the wave came was for an instant completely out of sight of a spectator on the bank.

The photograph from which the illustration is taken is by Mr. E. W. Carter, of Gainsborough, and is copyright.

In the Ouse during spring tides there is a less pronounced bore. In ordinary spring tides it commences at a shallow reach in the river at Sand Hall, 2 miles above Goole, attains its greatest height 4 miles above Selby, and then gradually dies out. The crest of the bore is from 2 feet to 3 feet, and the breaking wave at the sides 6 feet or 7 feet. In summer, when the ebb current is low, the aeger reaches Naburn with a crest I foot 6 inches high. Since the improvement of the channel of the river below Goole these aegers have become smaller.

WE

W. H. WHEELER.

SURVEY OF THE SIMPLON TUNNEL. E have appreciated many of the difficulties the engineers encountered in the construction of the Simplon Tunnel and have offered our congratulations on the successful completion of the work. But the difficulties that have been most readily apprehended have been those arising from the outburst of water from the hot springs in the track, the high temperature, and the mechanical boring and removal of the rock. In the happy completion of a task of great magnitude, which at one time threatened to end in a catastrophe, people are apt to forget the onerous preliminary work necessary to set out the line of the tunnel, to arrange the gradient so as to provide not only for efficient drainage at either end, but to secure the continuity of the separate tunnels at the point of junction, and so render it possible to work simultaneously at both ends. We are therefore glad to see an article by Prof. C. Koppe in Himmel und Erde for August bringing these matters forward, and making us familiar with the work which has 1 Die Vermessungs- und Absteckungs-Arbeiten für den Simplon Tunnel."

1

been so efficiently carried out by Prof. Rosenmund of Zurich.

Before the work of boring and perforation can be begun, there are three elements which have to be determined with an accuracy which must be greater in proportion to the difficulties of construction. These are the direction, the length, and the altitude above sea-level. Assuming that the places of entrance and exit of the tunnel have been marked by suitable pillars, the determination of these three elements begins; and that of the level is the least difficult, because the surveying engineer trusts to direct measurements. By the aid of accurate levelling instruments, it is possible to derive the difference in altitude of two stations 50 kilometres apart with no greater error than 3 cm. This is effected by the use of the levelling staff, which is read by means of an accurate level, the staff being placed vertically at two stations a convenient distance apart, and the sum of the differences of each pair of readings being taken. The surveyor apparently trusts entirely to the accuracy with which his theodolite can be levelled. Several

determinations of the difference of level of the two ends of the tunnel were made, but between the two last there was a discrepancy of only 2 cm., a more than sufficient degree of accuracy. The actual difference of level between the two ends was 52.439 metres. The second element, that of the length of the tunnel, is to be derived indirectly from triangulation, the length being reckoned from the same points

that have served for the determination of difference of level, and, as a matter of fact, these points are at some distance from the actual openings. A base line being given, the construction and the solution of the triangles present little difficulty, for here great accuracy is not required, and the probable error that Prof. Rosenmund was content to leave in his work amounted to 10.7 metre. The distances measured are as follows:-

The length between the columns mark-
ing the axis of tunnel...
Distance of northern column from

...

metres

20,091.33

The third element, that of direction, at all times presents some difficulty, and, in the case of mountains, where local attraction enters as a disturbing factor, the problem requires very delicate treatment. In a tunnel 20 kilometres long, an error in direction of one minute, which is usually the limit of accuracy sought in technical work, would produce an error of 6 metres, and the tenth part of such an error would be too great. Recourse is necessarily had to triangu lation, and the angular measurements must be made with the greatest care. Well-defined signal posts must be erected to mark the angles of the selected triangles, and the points of reference in these pillars defined with the utmost accuracy. The form which Prof. Rosenmund preferred consisted of cylindrical towers of brick about eight feet high, of which the axis was an iron tube the upper edge of which reached the top surface of the tower. A wooden pole carried this iron tube vertically upwards, and the whole was surmounted by a conical tin covering, the highest point of which was vertically over the centre of the iron axis. Eleven of these piers were erected, and when signals were made from any pillar the conical top was removed, and the theodolite was placed centrally over the middle of the iron tube in the cylindrical tower, which afforded a solid support for the

instrument and permitted accurate observation of the other stations. With the care exercised, it might have been anticipated that the sum of the angles of any triangle would differ from 180° by the known amount of the spherical excess, within the errors of observation. But the discrepancies were much larger, varying from 4 to 8.5 seconds, and these deviations could be explained only by attributing to the mountain an attractive force, which sensibly displaced the direction of the plumb-line. In other words, the theodolite was not placed horizontally. The amount of the deviations from the vertical, with the azimuths in which they occur, is shown in the following table :

Assuming these deviations from the vertical to arise

from the attraction of the mountain mass, an hypothesis which was confirmed by rigorous astronomical observation, it was found possible to reduce the closing errors of the triangles very materially. The solution of the whole network of triangulation showed that the tunnel's axis was fixed with a probable error of ±0.7, and that the direction of the tunnel could be fixed with sufficient accuracy by pointing the telescope, placed on one of the piers at the entrance of the tunnel, to any other signal tower, and revolving the telescope through a known angle.

66

It would be interesting to enter into the details by which the path of the tunnel was checked as the work progressed, more especially as curious refractive effects, akin to those seen in mirage," occurred to render the observations somewhat difficult and uncertain. These disturbing effects were more noticeable when observing towards the north end of the tunnel, where the difference of temperature between the internal and external atmosphere was greatest. On the southern side, the external air being warmer than on the north side, the " mirage was not so conspicuous. But we have only space to refer to the degree of success which resulted from the care bestowed on this difficult undertaking a success which could not be adequately tested until the junction of the engineering parties in the middle of the tunnel was effected. To take the three elements in order, it was found that the level agreed within 0.1 metre of the calculations. The length as measured differed 2 metres from the calculated value, but, as mentioned, this was a factor in which great accuracy was not needed, because, if the direction were given correctly, it was only necessary to continue the borings until the engineers from the south and north sides met in the middle. The direction was most satisfactory. The wall of one tunnel was absolutely continuous with the wall of the other; an attempt was made to compare the opposite walls of the tunnel for confirmation, but this attempt was frustrated by a projecting piece of rock. No better result could have been anticipated, and the utmost credit attaches to Prof. Rosenmund and his assistants.

W. E. P.

In 1860 he furthered his military studies at the Staff College at Sandhurst, passing the examinations in 1861. At this date geology was taught in the Royal Military College by Prof. T. Rupert Jones, and Hutton, who had taken up the subject with enthusiasm, contributed in 1862 to the Journal of the Royal United Service Institution (vol. vi.) an essay on The Importance of a Knowledge of Geology to Military Men. The importance, strange to say, does not appear to be so fully recognised nowadays. Hutton became captain in 1862, and served for a time as Deputy-Assistant Quartermaster-General at Dublin; but in 1866, having retired from the Army, he emigrated to New Zealand, and devoted himself to the study of natural history, and especially to zoology and geology. In 1871 he was appointed assistant geologist on the Geological Survey of New Zealand, in 1873 provincial geologist of Otago and curator of the Otago Museum, and in 1877 professor of natural science in the Otago University. In 1880 he settled at Christchurch, having become professor of biology and geology in the University of New Zealand, a post which he held until 1893, when he became curator of the Canterbury Museum at Christchurch. He was elected a Fellow of the Royal Society in 1892.

One of his earliest geological papers, a sketch of the physical geology of Malta, was published in the Geological Magazine (1866). From this date his work related mainly to the country of his adoption. He prepared official reports on the Lower Waikato district and on the Thames gold-field in 1867, and a report on the geology and gold-fields of Otago (with G. H. F. Ulrich) in 1875. To the Geological Society of London he contributed in 1885 an excellent sketch of the geology of New Zealand, which gave a comprehensive summary of the knowledge attained at that time, and in 1887 he sent to the same society an account of a recent eruption of Mt. Tarawera in North Island. He contributed many other geological papers to the Geological Society and Geological Magazine. While distinguished as a geologist, the importance of his researches on zoology was early recognised, and he was elected a corresponding member of the Zoological Society in 1872.

gravitation and the theories of electrodynamics and radiation; a Royal medal to Prof. C. S. Sherrington, F.R.S., for his researches on the central nervous system, especially in relation to reflex action; the Davy medal to Prof. A. Ladenburg, of Breslau, for his researches in organic chemistry, especially in connection with the synthesis of natural alkaloids; the Hughes medal to Prof. A. Righi, of Bologna, on the ground of his experimental researches in electrical science.

THE following is a list of those who have been recommended by the president and council of the Royal Society for election into the council for the year 1906, at the anniversary meeting on November 30-President, Lord Rayleigh, O.M.; treasurer, Mr. A. B. Kempe; secretaries, Prof. Joseph Larmor and Sir Archibald Geikie; foreign secretary, Mr. Francis Darwin; other members of the council, Dr. Shelford Bidwell, Sir T. Lauder Brunton, Prof. J. Norman Collie, Prof. W. R. Dunstan, Prof. J. B.

Farmer, Prof. F. Gotch, Dr. S. F. Harmer, Sir William Huggins, K.C.B., O.M., Prof. E. Ray Lankester, Dr. J. E. Marr, Mr. G. B. Mathews, Mr. H. F. Newall, Sir W. D. Niven, K.C.B., Prof. John Perry, Prof. E. H. Starling, Prof. W. A. Tilden.

Ar a meeting of the council of the British Association on November 3 it was decided that, in consequence of strong representations by the local committee, the meeting at York next year shall be opened on Wednesday, August 1, which is earlier than the usual date of the opening meeting.

THE Council of the British Association has received a gift of 5ol. from Mrs. John Hopkinson, to be devoted to some investigation which may be suggested at the next meeting by the committee of recommendations.

THE Paris Academy of Moral and Political Sciences has awarded a prize of the value of 600l. to Dr. Calmette, of Lille, in recognition of his work in bacteriology and preventive medicine.

WE regret to see the announcement of the death, at forty-five years of age, of Prof. Walter F. Wislicenus, professor of astronomy in the University of Strasburg and editor of the "Astronomischer Jahresbericht."

A CHRISTMAS course of lectures, adapted to a juvenile

was

an

66

After an absence of nearly forty years he paid a visit to this country, and received a hearty welcome from his many scientific friends. He was returning to his home at Christchurch when the announcement of his death on October 27 was received by telegram from the Cape. We are indebted to an obituary in the Times for some of the above particulars. H. B. W.

NOTES.

THE Royal Society has this year made the following awards of medals. The awards of the Royal medals have received the King's approval:-The Copley medal to Prof. D. I. Mendeléeff, of St. Petersburg, for his contributions to chemical and physical science; a Royal medal to Prof. J. H. Poynting, F.R.S., for his researches in physical science, especially in connection with the constant of

on

H. H. Turner, F.R.S., astronomy, December 28 of this year to January 9, 1906.

from

DR. MAURITS SNELLIN informs us that he has resigned the directorship of the section of terrestrial magnetism and seismology at the Koninklijk Nederlandsch Meteorologisch Instituut. Dr. Snellin's private address is now Apeldoorn, Holland, and any papers intended for him personally should be sent to this address.

AT the inaugural meeting of the eighty-seventh session of the Institution of Civil Engineers, held on Tuesday, November 7, Sir Guilford Molesworth, K.C.I.E., the retiring president, formally introduced to the members his successor in the chair, Sir Alexander Binnie, who delivered an address to the members, in which he traced the influence of scientific thought and investigation upon the development of engineering practice. The president subsequently presented the medals and premiums awarded by the council for papers dealt with at the institution in the course of the past session.