654 



THE POPULAR SCIENCE MONTHLY. 



itself anew, a second contraction is followed by a new disk in the 

 same plane as the first tongue, and so on ; the disks alternating in 

 the two vertical planes of breadth and depth, as in a paper fidibus. 

 In the photographs reproduced in Figs. 16 and 17, a mirror fixed 

 at an angle of 45 in the vertical plane gives, besides the front 

 view of the vein, its image as seen in profile. A mechanical 

 demonstration can be given of the movement of which the vein is 

 the seat by a parallelogram of basket-work, which we press upon 

 while holding it horizontally, and making it pass, by alternate 

 compression of the extremities, from the oblong to the square 

 shape, and then to the oblong the other way, return to the square, 

 etc. The example of the fidibus is not quite exact. We compre- 

 hend at first that, in consequence of the acceleration, the disks 

 will continue lengthening and deviating more and more we can 

 easily distinguish eight of them, sometimes twelve or more till 

 at last the molecules of water yielding to this dissociating action 

 of weight group themselves in little cohesion-drops. There is 

 another difference, in that the disks are not superposed as in the 

 fidibus, but are boxed into one another that is, one begins to 

 form by deviation before the preceding one has done contracting. 

 This is the necessary consequence of a third difference : that the 

 disks are not plainly flat, but are thin in the middle, like the 

 primitive tongue from which they are derived, and are flanked 

 by thick cords on the edges (Fig. 8, xviii). We can, therefore, 

 regard each disk as formed by the shock of the two cords of the 

 disk above it. If this shock is exerted in a horizontal plane, the 



new disk will spread out 

 equally in every direction, 

 having its center at the point 

 of the shock. Acceleration be- 

 coming a factor, the spread- 

 ing is prolonged farther down 

 than up ; the disk is thrown 

 out of center, but does not for 

 that cease to encroach upon 

 its predecessors. The case is 

 like that of the links of a 

 chain, which enter within 

 one another. Nowhere, then, not even at the point of minimum 

 surface, can the jet be cylindrical ; at the minimum, it assumes 

 the form of a rounded cross (Fig. 8, xix). 



Thus we find that, in the phenomenon so simple in appearance 

 of a fall of water, all the complications that arise one after another 

 under the fullest examination are explained logically down to the 

 most minute details. We can already draw one important con- 

 clusion : every mass of falling water, if it is not rigorously cylin- 



Fio. 12. 



