August 2, 1895.] 



SCIENCE. 



121 



THE 'BALL AND NOZZLE' FHENOMENON. 

 The interest which has been recently 

 shown in the phenomena of the ' ball and 

 nozzle ' must be the excuse for the present 

 publication of some experiments which were 

 made and described about eighteen years 

 ago, while a sophomore at college. At that 

 time I was of course ignorant of Bernoulli's 

 well known theoretical conclusion that in 

 such cases the pressure is always least 

 where the velocity is greatest. The experi- 

 ments with the water su.rface could be so 

 modified as to be shown in a projection lan- 

 tern. I have preferred to print the text 

 and figures without alteration. 



William Hallock. 



Physical Laeoeatoey, 



Columbia College, N. Y. 



It is an apparently inexplicable fact that 

 if we take two cards as A B and C D, Fig. 

 1, and through the middle of the lower C 

 D, bring a tube G, as shown in Fig. 1, A 

 B being held about one-fourth of an inch 

 from C D by four tacks, or some such 

 means, that if a current of air is set in 

 motion through G, no matter how slight, 

 or how strong, A B, instead of being imme- 

 diately blown up and carried away upon 

 the current, retains its position and is even 

 drawn down closer to C D and held there 

 by a force directly in proportion to the ve- 

 locity of the current in G. Even a quick, 

 strong puff can not remove it, and, in fact, 

 we can in no way remove A B from over 

 C D by blowing through the tube G. 



The explanation of this fact seems to con- 

 sist of two parts : First, why A B is not 

 blown ofi" as soon as a current starts in G 

 and before any eddies, or whirlpools 

 could be formed between A B and C D. 

 Second, what currents are formed between 

 A B and C D, and what action of theirs 

 holds A B over C D. The first of these 

 two actions is that of the first instant, the 

 second is that of the subsequent time until 

 the current in G ceases. During the first 



instant we have the current from G press- 

 ing upon a small circle of A B directly over 

 the mouth of G. This surface is repre- 

 sented as included between E and F, Fig. 

 1. Hence all the force tending to raise 

 the card is applied to the surface E F and 

 by the very compressible and yielding col- 

 umn of air from G. The resisting forces 

 which tend to hold the card down are its 

 weight and inertia applied over its whole 

 surface, and add to these two the fact that, 

 in order to raise A B suddenly by pressure 

 over E F, we must either lift all the air 

 above A B along with it, thus rarefying the 

 air between A B and C D, or we must com- 

 pel the air just above A B to rush around 

 it ; even if the air G should fill the space 

 left under A B as it is lifted up, still we 

 should have to overcome the weight and 

 inertia of a large quantity of air. Thus 

 upon comparing the conflicting forces at 

 work upon the card A B we find only the 

 slight force of the current upon E F tend- 

 ing to raise A B resisted by the weight and 

 inertia of A B and also the weight or in- 

 ertia, or both, of a large quantity of air ; 

 and it would seem quite reasonable that the 

 latter should prevail. The brevity of the 

 time and the delicacy of the forces make 

 experimenting very difficult. 



In experimenting to confirm the theory 

 of this first action, the lifting force applied 

 at E F remained constant, and the resist- 

 ing forces were lessened by reducing the 

 size of the card, since by so doing its 

 weight and inertia were lessened, and also 

 the amount of air set in motion. Making 

 A B smaller and smaller, a size is finally 

 reached when A B would be lifted off" by 

 the first puff, but if held a second or two 

 until the currents are all started it stays on 

 of itself, i. e., the lifting force at E F is now 

 able to overcome the above mentioned re- 

 sisting forces ; this inferior limit to the 

 size of A B is shown in Fig. 2. If we pass 

 below this limit, as Fig. 3, A B will be 



