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Scientific Proceedings, Royal Duhlin Society. 



generally speaking, found, near the velocities expected. We liad better, 

 perhaps, postpone the consideration of the possible causes of this second 

 critical stage until we have given a resume of the facts regarding its 

 production. First, a remark may be made as to the appearance of the effect. 

 Curves nos. 2, 4, 6, 7, 8, 11, and 16 all have the discontinuity due to 

 the effect. It occurs at the velocities 46, 75, 96, 118, 145, 79, 39, 

 respectively. In many cases it is remai-kable that the course of the curve 

 could be prolonged from a little before where this discontinuity occurs, so as 

 to pass into the subsequent part. We may also remark that the irregularity 

 produced on the curve is usually much less marked than in the case of 

 turbulence. These two cliaracteristics seem to indicate that the effect is 

 due to some phenomenon that does not influence the flow of the main body 

 of gas, and would therefore seem to have its seat at the surface of the tube. 



The general facts regarding this second * discontinuity ' are given in 

 Table V. (The last set of numbers refers to au experiment for which no 

 curve is given).' 



Table V. 



The first six lines refer to experiments on air. These results are given 

 graphically in fig. 3, where the abscissae represent the tube-diameters, 

 and the ordinates the velocities. With one exception, the points lie very 

 well on a straight line. This line cuts the axis of velocities at a point 



' It was found that this discontinuity was very indistinctly marked in the case of the two 

 smallest tubes. I have marked ths critical yelocities as doubtful. 



