4(V2 



tW ooiineclioii between tlie mean Velocity (tlie volume) and the 

 pressure cüiikl lie represented t»y a paraltolic curve. So it was 

 possible to reduce observations at a pressure yHo a standard pressure 

 (for wliicli 2,14 k.g. cm" was cliosen) by multiplying the shift of 



2.14 



the interference fringe, measured a( the pressure u, bv I or 



I' 

 graphically l)y means of the curve. 



Before relating the obtained results I shall give in extension an 

 arbitrary example of one of the 32 determinations of the change 

 of phase. The four cocks in Fig. 2B (tirst communication) will be 

 called A, B, C, D respectively. 



Photo n°. 154 wavelength 4580 A.U. 



Photo (I. Photo h. 



B, D open; A, C shut. A, C open ; B, D shut. 



Pressure on manometer. Pressure on manometer. 



2.12 2.15 



2.14 2.14 



2.14 2.15 



2.17 2.18 



2.18 2.17 

 2.18 2.16 

 2.16 2.18 



Mean : 2.16 2.16 



Mean pressure during the experiment 2.16 k.g./cm\ 



We have mentioned already that the given pressures refer to the 

 times Ü, 30", 60" etc. 



Mcasiireinent of photo N°. 154 a. Readings with the Zeiss-compa- 

 rator in m.m. 



on the interference fringes. on the fixed wire. 



54.217 53.591 52.689 



224 591 686 

 220 599 688 



218 593 692 



225 599 689 



219 594 688 

 225 598 52iJ89 

 223 600 



Mean • 5021 53.596 thus middle : 53.908 



52.68 9 



Distance between j _ n ,^05 Distance from I ^ 219 



the fringes j '— "^ " the fixed wire \ 



