32 



J. Waterhouse — An Account of the Tidal 



[No. 1, 



To^cScw 



He soon devised a simple method of expelling the air and restoring the 

 requisite identity of level, by fixing a stop-cock for the exit of the air at the 

 vertical bend, where the iron piping, after rising from the bottom of the 

 well to within a few inches of the surface of the ground, begins to slope 

 downwards towards the sea. This bend has necessarily to be made at a 

 point a little below the level of the lowest high-water tide, and, consequently, 

 on opening the stop-cock at high-water, all the air inside the pipe is of 

 course immediately expelled, and then the water inside the well at once 

 assumes the same level as that of the sea. But for this expedient it would 

 have been impossible to carry on the operations continuously for any length 

 of time, as there was found to be a decided tendency for air to collect in the 

 pipes. It was most fortunate that this was discovered during the experi- 

 mental observations at Bombay, for there stop-cocks could be readily con- 

 structed and attached to the piping, which could not possibly have been 

 done at either of the stations in the Gulf. 



At Okha Captain Baird found some difiiculty in keeping the stop- cock 



dry and having access to it. He 

 therefore had a water-tight box 

 3 feet long and 1 foot square 

 made in halves and fitted over 

 and under the stop- cock, holes 

 having been cut to admit the 

 pipes, and carefully caulked up 

 after the box had been fitted 

 over the pipe (see figure); in this 

 way no water could get at the 

 stop-cock except over the top of 

 the box. Underneath the first 

 7 or 8 feet of the pipe leading 

 to the sea, a layer of mud and 

 stones of considerable thickness 

 was made, and a wall of similar 

 material built all round the 

 stop-cock, lea\dng a sjmce about 3 

 feet square for standing in and 

 steps for getting down to it ; also 

 mud and sand were thrown down 

 between the iron cylinder and the masonry wall right up to the level of the 

 stop-cock bend. It was found that by this means the stop-cock was quite 

 dry and access could be had to it at any time however high the tide was. 



Captain Baird spent the recess of 1873 at Bombay in preparing for the 

 operations of the field season of 1873-74. Cylinders as above described 



