( 214 ) 



to piesi-urt'S of alout 60 atiiiosplicris), made an al solute nuiiiomcter 

 a real want for a long time past. It it impossible to place there 

 open large manometers "with a single continuous mercury-column fol- 

 lowing the example of Regnault, Cailletet and Amagat. Only in 

 special cases there will be an opportunity for doing this and generally 

 one will have to have recourse to the principle (first applied by 

 EiCHAKDS in 1845 and afterwards by others) to shorten the open 

 maEcnieter by dividing it into several not very high manometers placed 

 side by side in which the pressure to be measured causes the column 

 of mercury in the first manometer to rise, while a pressure is applied 

 above the mercury which pressure again is measured by transferring 

 it to the second manometer where it causes the mercury to rise 

 under an excess of pressure which is measured by the third mano- 

 meter, etc. Richards and his followers have the pressure transferred 

 by water. This means is also given by Thiesen ^) and his design 

 has been taken as a basis in constructing the normal-manometer of 

 the Physikalisch-Technisehe Reichsanstalt, an apparatus which though 

 made after the principle of those formerly mentioned fulfills far 

 higher conditions by its whole construction. 



In the (diagrammatic) serpentine syphon of upright and reversed 

 U's when in equilibrio the upper D parts contain water, the 

 lower U parts contain mercury and if a pressure is applied to 

 one end, all the menisci are set in motion at the same time, so 

 that the pressure might be deduced from the moving of one of 

 the menisci. Adjustments however are made on all the menisci sepa- 

 rately, and in this way only, as Wiebe rightly remarks ^), a 

 standard instrument is obtained. Yet the moving of all the menisci 

 together has been one of the difficulties which checked the operations 

 with the standard-manometer in the Phys. Techn. Reichsanstalt. 

 For there, although the apparatus was intended also for determinations 

 of higher pressure, they have contented themselves with attaining 

 20 atmospheres, a limit not even high enough for testing the mano- 

 meters of the Government Survey of Steam Boilers in this country by 

 direct comparison with the absolute manometer. (Among the manometers 

 which I have tested by means of the open manometer for the Chief 

 Government Surveyor of Steam Boilers, there were some to 30 atmo- 

 spheres ; among those tested by me for the Chief Constructors of H. M. 

 Navy there were some to 60, and others even to 100 atmospheres). 



') Zeitsclirift f. Instrumeutenkuude. 1881, p. 114. 



-) Compare his interesting im])ev in the Zeitsolirift I'iir ('ompriiuirte üase 1S97, 

 p. '.)8, 25, S2, 101. 



