510 Mr. L. F. Vernon-Harcourt. 



tidal rise and fall, was made at an angle of about 50 to a line running 

 from east to west in the model, so that the tidal flow approached the 

 estuary from a point only about 5 to the west of north-west. The 

 tray was made of zinc, enclosed by strips on three sides to the height 

 of the sides of the estuary ; and it was hinged to the model, at its 

 open -end, by a strip of india-rubber sheeting along the bottom and 

 sides, so as to make a water-tight joint with sufficient play at the sides 

 to admit of the tray being tipped up and down from its outer end. 

 The rise and fall of the tray was effected by the screw of a letter 

 press, from which the lower portion had been detached, by raising and 

 lowering the upper plate of the press, half of which was inserted 

 under the tray. After the requisite amount of sand had been intro- 

 duced to raise the bottom to the average level, the model was filled 

 with just enough water for the surface of the water to represent low 

 water of spring tides when the tray was down and the screw at its 

 lowest limit ; and the tray was made of such a size that, when the 

 screw was raised to its full extent, the water in the model was raised, 

 by the tipping of the tray, to the level representing high water of 

 spring tides. The water representing the fresh-water discharge of 

 the Seine was admitted into the upper end of the model from a tap 

 in a small tin cistern ; and the efflux of a similar quantity of water 

 was provided for at the lower extremity of the estuary, on its northern 

 side near the tray, by a cock with a larger orifice placed at such a level 

 as to allow the water to flow out into a second cistern, of similar size, 

 during the higher half of the tide. 



First Results of Working the Model. The construction of the model 

 was commenced in October, 1886, and its working was commenced in 

 November. Though the Portland cement was convenient for mould- 

 ing in a small space and in the absence of appliances, it did not prove 

 satisfactory for retaining water at first. The model was purposely 

 made in two halves, and the straight joint was subsequently made 

 water-tight ; but, nevertheless, cracks occurred at various places 

 through which the water leaked, and they had to be repaired as they 

 appeared ; and the bottom of the model was eventually coated with 

 thick varnish, and after a time the leaks ceased. The flexible india- 

 rubber hinge, from which I had anticipated some trouble, leaked very 

 little from the beginning, and on being fitted with greater care in 

 introducing a tray of somewhat different form, no leakage occurred. 



Silver sand was used in the first instance for forming the bed of the 

 estuary. From the outset, the bore at Caudebec, indicated by a 

 sudden rise of the water, and the reverse current just before high 

 water near Havre, called the " verhaule" were very well marked. 

 The verhaule is evidently a sort of back eddy, on the northern 

 shore, occasioned by the influx of the tide, and by the final filling of 

 the estuary from the southern channel ; whilst the bore appears to 



