152 . REPORT — 1861. 



The experiments were made in the open air, in a field adjacent to a corn- 

 mill belonging to Mr. Henry Neeson, in Carr's Glen, near Belfast. The 

 water-supply was obtained from the course leading to the water-wheel of the 

 mill, and means were arranged to allow of a regula^pd supply, variable at plea- 

 sure, being drawn from that course to flow into a pond, in one side of which the 

 weir-board with the experimental notcli was inserted. The inflowing stream 

 was so screened from the part of the pond next the gauge-notch, as to prevent 

 any sensible agitation being propagated from it to the notch, or to the place 

 where the water level was measured. For measuring the water level, a vertical 

 slide-wand of wood was used, with the bottom end cut to 

 the form of a hook (as shown in the marginal figure), the 

 point of which was a small level surface of about one- 

 eighth of an inch square. This point of the hook, by 

 being brought up to the surface of the water from below, 

 gave a very accurate means for determining the water 

 level, or its rise or fall, which could be read oflF by an 

 index mark near the top of the wand, sliding in contact 

 with the edge of a scale of inches on a fixed framing which 

 carried the wand. 



By other experimenters a sharp-pointed hook, like a 

 fishing-hook, has sometimes, especially of late, been used 

 for the same purpose, and such a hook affords very accu- . r t i 

 rate indications. The result of my experience, however, jg ^^^ii^ ^S^^^f^^ 

 leads me to incline to prefer something larger than the 

 sharp-pointed hook, and capable of producing an effect on 

 the water surface more easily seen than that of a sharp-pointed hook ; and 

 on the whole I would recommend a level line like a knife-edge, which might 

 be from one-eighth to half an inch long, in preference either to a blunt point 

 with level top or a sharp point. The blunt point which I used was so small, 

 however, as to suit very perfectly. If the point be too large, it holds the 

 water up too much on its top as the water in the pond descends, and makes 

 too deep a pit in the surface as the water ascends and begins to flow 

 over it. The knife-edge would be free from this kind of action, and would, 

 I conceive, serve every purpose perfectly, except when the water has a sen- 

 sible velocity of flow past the hook, and in that case, perhaps, the sharp point, 

 like that of a fishing-hook, might be best. 



To afi"ord the means for keeping the water surface during an experiment 

 exactly at a constant level, as indicated by the point of the wooden hook, a 

 small outlet waste-sluice was fitted in the weir-board. The quantity of water 

 admitted to the pond was always adjusted so as to be slightly in excess of 

 that required to maintain the water level in the pond at the height at 

 which the hook was fixed for that experiment. Then a person lying 

 down, so as to get a close view of the contact of the water surface with 

 the point of the hook, worked this little waste or regulating sluice, so as to 

 maintain the water level constantly coincident with the point of the hook. 



The water issuing from the experimental notch was caught in a long trough, 

 which conveyed it forward with slight declivity, so as to be about seven or 

 eight feet above the ground further down the hill-side, where two large 

 measuring-barrels were placed side by side at about six feet distance apart 

 from centre to centre. Across and underneath the end of the long trough 

 just mentioned, a tilting-trough 6 feet long was placed, and it was connected at 

 its middle with the end of the long trough by a leather flexible joint, in such 

 a way that it would receive the whole of the water without loss, and convey 

 it at pleasure to either of the barrels, according as it was tilted to one side 

 or the other. 



