336 



liquid due lo the small gas-bubbles emerging from the capil- 

 lary tube. 



The regulation of the velocity of flow of the gas was obtained 

 l)j means of the stopcock E already mentioned, in combination with 

 two accurately adjustable pinch-cocks B, which were inserted between 

 the reservoir N and the appai-atus R, carrying the capillary tube 

 and its adjustments. With this arrangement no undesirable cooling 

 of the surface, nor any lack of adjustment of the gas-velocity^ need 

 be feared as a considerable source of error. 



h. The apparatus R consists of an upright rod H (fig. 2a), about 

 1 meter high, and made of brass heavily plated with nickel. It rests 

 on a heavy iron tripod fitted with three levelling screws. The vertical 

 rod can be rotated about its axis by means of two gliding discs 

 at the foot of the pillar; they may be clamped fast when desired. 

 In this way it is possible to bring the horizontal arm, bearing the 

 adjusting arrangements and the movable counter-weight / into any 

 desired azimuth, and to fix its position by means of the clamps at 

 and the collar at H. With the aid of a handle provided with a 

 vertical rack and pinion, this horizontal arm can be raised to any 

 height and fixed there with proper clamps. This arm can also be 

 moved horizontally, in order to vary its length. Moreover it appeared 

 to be necessary to prevent a slight bending of the pillar H under 

 certain circumstances, by means of three steel supports attached to 

 H and to the iron tripod ^). 



Just over R, it has at its end a rectangularly bent steel support, 

 to which are attached the spiraltubes 6^, made of gas-tight aluminium- 

 tubes, nearly 3 millimeters wide, and also the similar tubes U, which 

 however consist of much wider spirals. The latter form the continu- 

 ation of the aluminiumtubes G, and their ends are firmly fastened 

 to the horizontal beam, which is fixed in the laboratory just above 

 the whole apparatus. The two sets of spiraltubes appeared to be 

 necessary to ensure the desired mobility of the apparatus with regard 

 to the manometer-connecting tubes, and also to render an effective 

 operation of the adjusting devices possible. The great sensitiveness 

 of the manometer makes it necessary, that all the connecting tubes 

 of the instrument, as well as the spirals G and U, should be wrapped 

 with a thick layer of white flannel or asbestos, in order to avoid 

 the disturbing influence of slight oscillations of temperature. 



^) In the construction of this apparatus the mechanics D. Vonk and A. van 

 DER Meulen, and the amanuensis J. J. Folkers, all of Groningen, have aided in a 

 most practical and effective way. 



