210 On the Resistance of Air to the Motion of Vortex-rings, 



VIII. This column shows that the difference between the cor- 

 rected mean time and the calculated time in no case exceeds 



0*01 second. 



IX. The approximate velocities deduced by drawing tangents 

 to the curve. 



X. The true velocities calculated from the formula 



^=0-368(27-7-*). 

 XI. The retarding force, 



-|| =0-136(27-7 -*). 



Table of Experiments showing the retardation which a Vortex- 

 ring of air experiences when moving through air at the same 

 temperature and pressure. The vortex-ring is 9 inches in 

 diameter, and has an initial velocity of 10-2 feet per second. 

 The retarding force is proportional to the velocity ■ and after 

 234 seconds the ring has moved 16 feet, and its velocity is 

 reduced to 4'3 feet per second. 



'• 



II. 



III. 



Mean corre- 



IV. 



V. 



VI. 



Refer- 

 ence 



Distance of target 

 from orifice, 



sponding 

 reading of 



Correction 

 deduced by 



Corrected value 

 of mean chrono- 



Equivalent time, 



number. 



minus 4 feet, 

 s. 



chronoscope, 



minus 



6-5. 



graphical 

 construction. 



scopic reading. 



in seconds. 



1. 



2 feet 



1«6 



00 



1-6 



021 



2. 



4 „ 



3-4 



-01 



3-3 



043 



3. 



6 „ 



5-4 



-02 



5-2 



0-67 



4. 



8 „ 



7-3 



00 



73 



093 



5. 



10 „ 



102 



-0-7! 



9-5 



1-23 



6. 



12 „ 



12-0 



-0 1 



11*9 



1-54 



7. 



14 „ 



145 



+ 0-3 



14-8 



1-91 



8. 



16 „ 



182 



-01 



18-1 



2-33 





VII. 



VIII. 



IX. 



X. 



XI. 







Difference 

 between cal- 

 culated and 

 observed time. 



Approximate 



True velocity, 



Retarding force, 



Refer- 

 ence 

 number. 



Time calculated 

 by formula 



-6-25 log (277-s), 



velocity de- 

 duced from 

 graphical 

 construction. 



calculated by 

 ds 

 dt 



calculated by 

 d2 s 

 ~~dt* 











= 0-368(277-s). 



= 0-136(277-*). 



1. 



020 



-001 



93 



9-5 



3-5 



2. 



0-42 



-001 



8-4 



8-7 



3-2 



3. 



0-66 



-001 



77 



8-0 



30 



5. 



• 0-92 



-001 



73 



72 



2-7 



5. 



1-22 



-001 



6-4 



6-5 



2-4 



6. 



1-54 



000 



5-9 



5-8 



21 



7. 



191 



0-00 



52 



50 



1-9 



8. 



2-34 



+0-01 



4-4 



4-3 



1-6 



