COMPARISON OF I'l. ANNCM .\\l> UAS THKl;M i\li: I I ! C.'.i 



neck. This washer is tightly held in place by a brass clamp, which screws on to a 

 collar made in halves and fixed to the narrow part of the neck by a cement, which is 

 :i little less fusible than that employed for the joint proper. 



(b) Barometer m,-! Manometer. 



'I'd.- manoinetrie apparatus is mounted on a vertical iron girder, '_' metres high ami 

 of H -shaped cross-section, solidly bolted by three diverging iron feet to the massive 

 pillar previously descril>ed. The external faces of the girder are planed up as true 

 as possible ovei ili.-n entire length, and on \\\<-\\\ -Tnle ^uj.p..it- ti.i ilie manometrie 

 tubes, the Imrometer, and mercury reservoir. To increase the stability of the whole, 

 the top of the iron column is fixed to the wall by a transverse piece, which also serves 

 to support two brass tubes 011 which slide the observing telescopes. 



The barometer consists in its upper part of a tube of 15 inillims. internal diameter. 

 A point of black glass is fixed axially in the interior of this tube by fusion. This is 

 referred to subsequently as the barometer -point. Below the barometric chamber the 

 tube has a double bend, which brings the lower part of the tube 4 centims. to the 

 right of the upper portion. 



The kilometer tul>e is firmly fixed above to a carnage, r, which can be displaced 

 vertically by the movement of a screw 60 centims. in length, working in bearings 

 above and below, and engaging by bevel gearing with a horizontal shaft projecting 

 forwards. By turning the small handle m the barometer can be raised or lowered at 

 will. 



The piece which maintains the barometer tube on its support also carries suspended 

 between two points by one of its extremities a graduated brass scale 1*5 metres long, 

 whose axis is at a distance of 48 millims. from the barometer point. This scale shares 

 all the movements of the barometer carriage, and the glass point may be assumed to 

 have an invariable position with reference to the neighbouring divisions of the scale. 



The lower end of the barometer is immersed under mercury in a tube of 90 centims. 

 in length and 25 millims. in diameter, which serves as its reservoir ; this tube can be 

 fixed at different levels on the manometer support. 



Projecting from the front of this tube are four stop-cocks at intervals of 15 centima, 

 serving to establish communication between the barometer and manometer at any 

 beight 



The open branch of the Imrometer communicates below by means of a long steel 

 tul>e, a, with a reservoir, R, of large capacity filled with mercury, which can be 

 displaced vertically either rapidly by hand or slowly by a micrometer screw. 



(c) Manometer. 



The closet 1 luaiich of the manometer, the details of which are shown in the fig. 13, 

 i- composed of a rather thick-u ailed Hint glass tube 16 millims. internal diameter, 



