120 C. Barus — Counter-twisted Curl Aneroid. 



20e, so that the walls must have been reduced in thickness 

 from # 025 cm to about one-half this value, 



Diam. of curl, 2'8 cm Pressure, H'9 cm , Hg Deflection, 111° 



Turns of curl, 22 59'5 cm 97° 



Length of curl 14'7 cm 0-0 20° 



(later) 0-0 0° 



(next day) 0*0 —2° 

 Pressure per degree of arc per turn, 14*6 cm , Hg. 

 Pressure per degree per linear cm., 130 cm , Hg. 



There has therefore been a considerable gain in sensitive- 

 ness,* inasmuch as the deflection of one degree between the 

 ends of a linear centimeter of the coiled tube is now equivalent 

 to 130 cm of mercury. A new feature has been introduced in 

 the apparent occurrence of marked viscosity, as shown by the 

 gradual displacement of the " zero " reading for pressure dif- 

 ference. The cause of this will be further studied, but it is 

 probably due to the tendency of external pressure to quite 

 close the tube,f so that it takes the air some time to reenter. 



This curl was now cut in two parts, V a and Y 6 , of 9*5 and 

 11 turns respectively, in order to test whether the air had 

 quite reached the extreme parts of the tube. An examination 

 showed the following results : 



V, 



Pressure : 



Deflectio 



f Diameter of curl, 2'88 cm 72-O cm , Hg 



49-6° 



Turns of curl, 9-5 64'3 



43-7° 



I Length of curl, 55-8 



38-3° 



I 33-3 



o-o 



23-4° 



1-6° 



(later) 0-0 



o-o° 



Pressure per degree per turn, 14*0 cm . 





Pressure per degree per linear cm., ]22 cm . 





'Diameter of curl, 2'8 cra 62'7 cm , Hg 



56-3° 



Turns, 11 53'9 



49-6° 



Length, 46*2 



43-8° 



35-6 



35-3° 



o-o 



7'9° 



(later) 0*0 



0-0° 



Pressure per degree per turn, 14*3 cm . 





Pressure per degree per linear cm., 127 cm . 





V, 



These results agree substantially with the data for the uncut 

 curl, the discrepancies being due to the difficulties of estimat- 

 ing the number and diameter of the turns and to the occur- 

 rence of viscosity. It is seen that viscosity has in no way dis- 

 appeared, though it is much more marked in Y b than inV a . 



* Data of the table taken in accord with other similar experiments on the same 

 curl. 



f There may also be a displacement of the zero due to friction of the walls of 

 the tube on each other. Such displacement, however, would probably be per- 

 manent. 



