262 REPORT—1874. 
the gradual meeting of the side streams which had bounded it : from this point 
to about 7 or 8 feet further. sternwards there rose vertically a central wall 
of water, the crest of which, in its side elevation, had a parabolic form (as 
far as could be estimated by the eye), the highest part of the ridge being 
certainly over 2 feet above the natural water-level ; its sectional form was 
tolerably discernible when it was looked at endways, and was not unlike that 
of an ordinary fountain issuing from a circular orifice ; the thickness increased 
as the upward velocity lessened, till at the crest the water spread laterally in a 
kind of mushroom form, and fell in streams on either side. These streams 
in side view formed ragged sheets, through which the central wall of water 
could be seen at intervals. 
The disarrangement of forces which at high speeds took so intensified a 
form would of course produce results of sensible magnitude at smaller speeds ; 
but it seemed that a tolerably effective remedy would be supplied by the 
application of the water-deck which has been already described. 
This was so arranged that the depth of its immersion could be varied 
within moderate limits. If too little immersed it would not sufficiently re- 
strain the surface-disturbances, or might allow the intrusion of air. If too 
deeply immersed it might produce stream-line forces of its own, though its 
under surface was plane from end to end and truly horizontal. Eventually 
it was found to produce least disturbance when its underside was immersed 
about Z of an inch, and at this level it was maintained during the subse- 
quent experiments. The area of the deck was 19 inches in length and 
14 inches in width. 
One valuable purpose which the deck served was to give additional steadi- 
ness to the tube. Some collateral experiments showed distinctly that the 
pressure in a long tube of small diameter underwent most abnormal dis- 
turbances ; and though it can hardly be said with confidence that tremor 
would account for these, it is the only condition which suggests itself as a 
possibly relevant “vera causa;” and even in the experiments which are 
reported, there are certain discordances which may possibly be attributable 
to the same cause, though the tubes used were stiff and were pretty rigidly 
held at the deck level: the discordances or unintelligible differences were 
felt, not in the maximum pressure delivered on an aperture exactly facing 
the line of motion, but in the pressure exhibited in the experiments relative 
to the position of the neutral point and to the negative pressures. 
In performing each experiment the aperture was set in the required direc- 
tion and the apparatus clamped. The zero of the pressure-scale was brought 
to a convenient level according as a negative or positive pressure was to be 
expected. The zero was recorded; andthe mean height attained by the water 
in the tube was also recorded when the steady speed was attained. 
Partly because time did not permit the extended variation of conditions 
which was desired, partly because, at higher speeds, increase of tremor (or of 
the unknown cause of irregularity whatever it may be) was to be appre- 
hended, the speed adopted throughout the tabulated experiments was 360 feet 
per minute. 
After these explanations, the details of the tabulated statement must be 
allowed to speak for themselves. It does not, however, contain the record 
of the experiments with the pipe-end flush with the underside of the deck, 
or of those made with the hole in the stopped end of the ordinary pressure- 
tube, because the particulars were not readily reducible to the form of the 
table. The results were therefore fully stated in the prefatory matter. 
The series of experiments requires extension in many directions which 
