weij^hts have once been set rotating by the hand or in another 

 way, the apparatus may be left to itself. The kinetic energy of the 

 rotation is so great tliat the apparatus continues rotating for a 

 considerable time, at any rate long enough to perform a pressure 

 measurement. Only on account of this circumstance it is possible 

 fully to avail oneself of the absence of friction in consequence of 

 the rotation, for it appears that any, also the lightest, touch of the 

 apparatus brings about increase or decrease of the pressure in C, 

 as it is not possible in doing so not to exert a force on the piston 

 B in vertical direction. If the space C is connected with a sensible 

 manoscope (and the volumenietei' itself served as such in our expe- 

 riments) every touching of the piston, also the slightest, betrays 

 itself immediately by a deviation of the manoscope. Measurements 

 may, therefore, only be made when the apparatus is in rotation, and 

 entirely left to itself. 



A second circumstance, on account of which in our opinion 

 ScHAFFER and Budenberg's pressure balance may claim to be considered 

 as an improvement compared with Amagat's manometer, is this that 

 the differential piston as well as the cylindre consist of one piece, 

 and can therefore be completely finished as a whole on the lathe. 

 As is known Amagat's manometer makes use of two pistons of 

 different section, which are connected with each other. In the vessel 

 where the great pressure which is to be measured, pre\'ails, there is 

 a small piston, accurately ground in, and the force with which it 

 is expelled is transmitted to a large piston, which can move in a 

 second vessel ; the pressure in this latter vessel is measured by 

 means of mercury. In this construction it is, however, not to be 

 avoided that the cixes of the two pistons are not entirely each other's 

 prolongation, which must give rise to wrenchings and frictions. To 

 prevent these the pistons must, of course, not be so tightly ground 

 in as would otherwise be possible. It is known that Amagat there- 

 fore uses molasses as transmission liquid in his manometer, because 

 else the transmission liquid would flow away too quickly, whereas 

 in ScHAFFER and Budenberg's pressure balance thin machine oil sufHices. 



On the other hand Schaffer and Budenberg's pressure bahxnce 

 shares a drawback with Amagat's manometer, which as far as I 

 know, Wagner ^) was the first to point out in his investigation of 

 an Amagat manometer. Amagat himself took as effective area of 

 the piston, i. e. as area on which the pressure acts to the outside, 

 simply the section of the piston itself. Wagner, however, points out 

 that the liquid which is pressed through between piston and cylindre 



1) Thesis for the Doctorate. Müiichen i90i. Ann. d. Phys. (4) 15, p. 906. 



