( 2ir, ) 



by tlie oidiuai y means offerer! by the laboratory. It can easily be taken 

 to pieces and cleaned, leakages can easily be detected and repaired 

 and it admits of a high degree of accuracy in reading. Even in use 

 it answers expectations better than I dared to expect. It now seems 

 to me that a shortened manometer consisting of a tube of every- 

 where equal bore which is alternately filled with water and mercury 

 would offer more difficulties and admit of less accuracy than this 

 apparatus consisting of parts which each can be used either as 

 manometer or as differential manometer, of which each has a size 

 of bore agreeing with the pressure te be determined therein, and to 

 which more partial manometers for higher pressures can be added 

 without any alteration being made in those which exist already. 



2. The separate manometers. At first I had thought of using 

 tubes of 12 atmospheres length and to fasten these on a wall of a 

 staircase. On nearer consideration of several sources of error in the 

 observations it seemed to me desirable however to arrange the whole 

 apparatus at least to pressures of 60 atmospheres in one and the 

 same room along the wall. Quick reading, so desirable in many 

 respects, was only possible when the single tubes were not longer 

 than 3.14 M. so that the height of the mercury in the tubes could 

 be 3.04 M., corresponding to 4 atmospheres. 



Every separate manometer consists of one single piece of glass, 

 made of tubes sealed together, which can be properly cleaned and 

 dried. The mercury once brought into the manometer-tube remains 

 there and has contact only with the carefully cleaned glass and the 

 dry gas which causes the pressure. Where a meniscus is to be 

 adjusted the manometer-tube should be wide enough for sufficiently 

 obviating the uncertainty resulting from the capillary depression, 

 and for the rest so wide as the pressure which the separate 

 manometer shall have to resist will admit of. The manometer is 

 on both ends provided with suitable contrivances by means of 

 which it may be connected with the other parts of the apparatus, 

 and the tubes of which it consists are bent in such a way that 

 these joints together with the others can be brought very near to 

 each other at the bottom of the apparatus near the stopcocks. 



I used three different types of glass tubes. The first type is repre- 

 sented by tube A in fig. 1. One leg of the U-shaped wider tube 

 (12 m.m. diameter) is half the length of the other, to both legs 

 capillary tubes have been sealed on which are bent downwards and 

 reach below the lower part of the U. Tubes of this kind A may 

 generally be used where we want to read a whole range of positive 

 pressures from to 4 atm., (from o to m^' — m^ on tlie same tube. 



