TBANSACTIONS OF SECTION G. 677 



metres in depth. The observations were taken 

 sometimes at every metre of depth, but more generally at 0-5 metre below the sur- 

 face, at mid depth, and at 0-2 metre above the bottom. The position of the metre 

 in depth was changed after each observation. Curves were shown giving the 

 velocities near the surface, at mid-depth, and at the bottom daring two ebb tides and 

 during a period extending from the end of one ebb, through the period of flow, and 

 into the next period of el)b. 



The calculation of the discharge of the river at different periods, and its com- 

 parison with the amount of upland water, cannot be given without tables, but the 

 following general facts are interesting. 



1. The change in the river-depth at the turn of the tide begins markedly 

 earlier than the change in the direction of flow. 



2. The relation of the surface and subsurface velocities is similar to tliat in a 

 non-tidal river at all periods of ebb and flow. 



3. The velocities could not be observed exactly at the turn of the tide, but 

 within a very short period after that instant the bottom water was in motion witli 

 a velocity bearing the same relation to the surface velocity as at other periods of 

 the tide. 



4. The change of velocity for the half-hour before and after the turn of the tide 

 is extremely rapid. 



The observations were made at Putney and "\\'ostminster, and the greatest 

 velocities observed were a little less than one metre per second. 



4. An Apparatus for recording the results of experiments with Railway Brakes. 

 By Sir Frederick Bramwell, F.B.S. 



This apparatus mainly consists of a train of wheelwork set in motion by a 

 spring, which can be wound up by hand. The motion of the wheelwork causes a 

 continuous strip of paper, of about an inch in width, to travel endways at a regular 

 speed, under a pencil moved alternately to the right and to the left, at right angles 

 to the direction of motion of the paper, the motion of the pencil being produced 

 by connection with an axle of tlie locomotive drawing the train to which the 

 brakes are attached, a motion of the pencil to the right, and one to the left, being 

 made for each revolution of the axle. It is essential that the axle giving motion 

 to the pencil should neither be driven by the engine nor should its wheels have 

 brakes upon them. 



A second pencil is provided, capable of being moved by hand, also at right 

 angles to the direction of motion of the paper. Each of the pencils can be placed 

 in contact with, or removed from, the paper at the will of the operator. 



The mode of working is as follows : — 



The apparatus being lixed on the locomotive, and the pencil coupled up with 

 the rod of an eccentric placed on the axle, the spring controlling the wheelwork is 

 wound up, and the continuous strip of paper set in motion. Then the pencil 

 is put into contact with the strip of paper, and as the paper moves endways, the 

 pencil makes a series of marks upon it, each of these representing one revolution 

 of the axle, and each representing therefore a forward motion of the locomotive, 

 and of the carriages attached to it, equal to the circumference of the wheels on 

 that axle. The speed at which the paper moves was regulated when the apparatus 

 was constructed, but this speed is ascertained, with absolute accuracy, for each 

 experiment by means of the hand-worked pencil making a second mark upon 

 the paper, and being moved alternately to the right and to the left at any interval 

 of time. 



Upon the signal for the shutting off of the steam and the putting on of the 

 brakes being given, a further mark is made by the hand-worked pencil, and this 

 pencil is kept at its then position until the locomotive and the carriages attached 

 to it have come to rest, when a further mark in the opposite direction is made. 



Upon considering the diagram thus produced it will be seen that it shows — 



1st. The number of revolutions of the driving wheel, and therefore the distance 



