334 EEPOKT — 1889. 



so that tlieir motion is not equal or proportional to the motion of the 

 water — for a sufficiently slow motion of the water the ball would not 

 move ; so that if the ebb were just not sufficient to move the ball, and the 

 flood were stronger, the bail would be moved up each tide, or vice versa, 

 and the same resultant motion would follow, even though the ball might 

 be moved somewhat by both ebb and flood ; the strongest would carry 

 the ball farthest. In this way they furnished a very delicate test as to 

 the symmetry of the tides and the sufficiency of the balancing. 



Hxpefi'iments on the Movement and Equilibrmm of Sand in a Tide Way. 



Series 1. — Tide running in a uniform rectangular pan with vertical 

 sides and end, and a level bottom for the sand to rest on. 



Experiment 1 (tank A), commenced June 22. — Three cubic inches 

 of Calais sand were placed in a heap on section 17 and line Ir, and 3 cubic 

 inches of Hnna Bay shell sand similarly on section 17 and line 1,., the tank 

 being otherwise clean and empty. Then, with low water 0'083 of a foot 

 and high water '23' from the bottom, the tide was set running with a 

 period of 55 sec. After 3,000 tides, the white sand spread upwards from 

 section 16 '5 to 12 "7 in 7 ripples, having just painted the bottom 1 grain 

 thick down to section 22. 



The Huna Bay shell sand spread upwards from section 18 to 14'25 in 

 4 ripples, also having painted the floor down. 



Experiment 2 (tank A), commenced June 24. — Calais sand was 

 introduced as a uniform bank across the channel. 



Experiment 3 (tank A). — The Calais sand was arranged exactly as 

 for Experiment 2. 



Experiment 4 (tank A). — A repetition of Experiment 3, observa- 

 tipns being directed more closely to the motion of the sand after 

 starting. 



Experiment 5 (tank A), July 5 (Plans III. to VI.). — Calais sand 

 passed through a sieve into the tank, in which there was sufficient water 

 to cover the sand until there was enough sand to fill the tank from the 

 upper end to section 18, to a depth of 0"25 foot, terminating in a natural 

 slope from section 18 to the floor. Then the sand, which was in excess 

 at the upper end, was carefully levelled by means of a wooden float 

 guided on the sides of the tank, and having its straight edge completely 

 across the tank 0'25 foot from the bottom. The scummer was then 

 adjusted to keep the low water at 181 from the floor, and the crank 

 adjusted to give a rise of 0"166 over the whole tank. The actual rise at 

 starting, owing to the sand above low water, was 0*2' over the whole 

 surface. 



The tank was then started, and ran 12,607 tides at a period of 53 

 sees., when the speed was increased to 50 sees, and continued for 3,589 

 tides ; then, as the condition seemed very steady, the survey for Plan I. 

 was made. 



At the starting of the tank careful note was taken of the pi'ogressive 

 appearances, and during the interval of running, which occupied from 

 July 5 to July 15, sand gauges were introduced and read daily, as well 

 as other notes of progress made. The periods of rise and fall of the tide 

 were checked, and a curve taken which showed the rise and fall at the 

 generator to be symmetrical and nearly harmonic. 



The sand was found to descend down the tank towards the generator 



