500 



Mr. J. D. Fry on a JSfeiv Micromanometer . 



12*5 cm. on the scale. Curve II. was obtained with the 

 manometer near the limit of its working sensitiveness, and 

 shows deflexions of the order of 75 cm. per dyne per cm. 2 , 

 so that pressure differences as small as a thousandth of a 

 dyne per cm. 2 may be readily detected. 



The form of calibrator described above is one which 

 obviously enables the manometer to be used as a zero instru- 

 ment, the manometer acting as an indicator and the pressure 

 differences being obtained from the calibrator. 



Curve II. 



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The following table gives references to various recognized 

 types of sensitive manometer, and serves as a rough com- 

 parison in relative sensitiveness. For the purpose of this 

 comparison the numbers in the last column have been deduced 

 from the available data, and are all expressed in the same 

 units. They can only be regarded as approximate values,, 

 as it has not been possible in every case to determine from 

 the published records the value of the smallest pressure 

 which the various instruments are capable of detecting. 



