344 



Mr. Carl Barus on the 



15. The table contains five series of observations made at 

 the times (minutes) stated. Not more than two or three 

 minutes were allowed per observation. Comparing data on 

 the same or corresponding horizontal rows ; the maximum 

 difference is '40 centim., or 24 atmospheres. Comparing the 

 two zero readings of the last column (work intentionally 

 hastened), the difference of reading is '56 centim., or 33 

 atmospheres. This is the maximum index of error in case of 

 unreasonably hasty work (§ 18). 



16. A second point of view is obtained by comparing the 

 data of the pressure " on " and the pressure " off' - ' phases of 

 the above experiments. This is done in the chart, fig. 6 

 (PI. X.) No. 0. The accordance in the " on" phase is satisfac- 

 tory, since the errors are not above 10 atmospheres, and the 

 loci very nearly straight. The " off" data do not return in 

 the lines of the " on " data. Indeed the two curves, " on " 

 and " off," enclose a band the maximum width of which is 

 1*5 centim. or 90 atmospheres. 



17. To, interpret this curious phenomenon I compared the 

 gauges after several months' use. At least five minutes 

 were allowed per observation. Two complete series are given 

 in Table II. This table also gives some data on the con- 

 stancy of the zero after very high presssure. Slight shifting 

 equivalent to 5 or 10 atmospheres is observable after 2000 

 atmospheres. 



Table II. — Comparison of the Bourdon Gauge and the 

 Tait Gauge, No. 0, four months later. 





First Series. 



Second Series. 







High Pressure 



Large 

 Bourdon. 



Pressure 



Pressure 



Pressure 



Pressure 



Factor. 



Mean 

 Factor. 



Tes 



sts. 





" on." 



" off." 



" on." 



" off." 







Pressure, 

 atm. 



Eeading. 

 centim. 



atm. 



centim. 



centim. 



centim. 



centim. 



cm./atm. 



cm./atm. 



100 



6-40 



630 



6-35 



6-20 



•01715 



•01722 







4-90 



200 



8-10 



7-95 



8-03 



7-88 



•01725 





2110 



40-93 



300 



9-87 



9-70 



9-80 



9-60 



•01720 









5-10 



400 



11-57 



11-39 



11-50 



11-32 



•01728 





2160 



41-95 



500 



13-29 



13-23 



1320 



13-12 











5-20 



The character of Tables I. and II. is identical. Hence to 

 account for the apparent hysteresis it is necessary to construct 

 other Tait gauges. This I did with much care. 



18. The new gauges are No. 1, about of the same length 

 as No. 0, and No. 4, which is much shorter. The glass tube 

 (t t, fig. 4) is as close-fitting as practicable, and the capillary 



