NATURE 



[November g, 1905 



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 equi- 

 noctial 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 



The Aeger in the Tient. 



to i foot in height at Torksey, 35 miles from the 

 mouth of the river, and then graduallv dies out. 



The bore was to be seen under exceptionally favour- 

 able 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 

 ii.2i 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 z\ 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 -J 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 



NO. J 880, VOL. "]l\ 



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 

 4j 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 prob- 

 ably 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 break- 

 ing wave at the sides 6 feet or 

 7 feet. In summer, when the ebb 

 current is low, the aeger reaches 

 Naburn with a crest 1 foot 6 inches high. Since the 

 improvement of the channel of the river below Goole 

 these aegers have become smaller. 



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 congratu- 

 lations on the successful completion of the work. But 

 the difficulties that have been most readily appre- 

 hended 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 

 uud Erdc for August ' bringing these matters forward, 

 and making us familiar with the work which has 



1 " Die Vermessungs- und Absleckungs-Arbeiten (iir den Simplon 



