118 Popular Science Monilih/ 



An Easily Made Mercurial Barometer 

 ^HE accompanying diagram, Fig. i, 



T' 



shows a useful barometer of simple 

 construction. The baseboard A may 

 be of mahogany, 38 ins. long, 2^^ ins. 

 wide in the central part and 4 ins. at the 

 ends. A straight glass tube B is needed, 

 36 ins. long and about }4 in- in bore. 

 After filling by the simple method about 

 to be described, it may l)e fastened to 

 the center of the board by means of 



A mahogany base, a glass tube and a mer- 

 cury cistern comprise this barometer 



neat brass saddles. The cistern (', to 

 be described in connection with the 

 method of filling, is provided with a 

 wider saddle at the lower end of the 

 board. This may be hidden, for the 

 sake of appearance, by means of the 

 [xilishcd mahogany disk M. The appear- 

 and' will be impro\cd by lurning the 

 disk, or providing a small beveled mirror 

 in the center. The upper end of the 

 tube may also be concealed by means 

 of an ornamental disk of turned wood. 

 It is in filling the lube with mercury 

 that most amateur barometer makers 



experience the principal difficulty, owing 

 to the necessity for exc-luding air. The 

 regulation method is fairly easy in 

 experienced hands, but the following 

 will be found much simpler. The tube 



B, Fig. 2, is of soft glass with walls of 

 medium thickness. It is therefore a 

 simple matter to make a constriction at 

 X, 3 ins. from one end, by softening the 

 tube in the flame of an alcohol lamp 

 and drawing the ends gently apart. To 

 the open end above the constriction 

 should be attached a short length of 

 India rubber tube D, capable of being 

 closed with a brass clip or pinchcock E. 

 The other end of the tube should be 

 passed through an India rubber cork, 

 fitting tightly into a wide glass tube 



C, forming the cistern. A bent tube F, 

 previously passed through the cork 

 towards the side, serves for connection 

 with a cycle-pump and valve, with thick- 

 walled rubber tube. 



Let the tube be supported vertically, 

 the cistern being rather more than half 

 filled with mercury — before inserting the 

 cork, of course — and force a little air 

 in with the pump so as to drive mercury 

 into the tube to about two-thirds of its 

 length. Without removing the cycle- 

 valve attached to F, that is, without 

 letting any air escape, lower the tube 

 gradually in a slanting direction. The 

 mercury will rise still higher until it 

 passes the constriction and fills the 

 India rubber tube. Then close the pinch- 

 cock, remove the valve from F, and 

 replace in the vertical position. The 

 mercury will come to rest somewhere 

 near the end of the tube, as shown in 

 Fig. 2. The space above it is a vacuum 

 siiu^e the air has been dri\en out and 

 prevented from re-entering. The upper 

 end of the tube above the constriction 

 is no longer required and may be 

 removed by directing the alcohol lamp 

 flame against the narrowest portion with 

 a mouth blowi>iiH', (or even an odd 

 piece of thin lube), the same operation 

 serving to close the top of the barometer 

 tube with ,1 neat and pcrfeclK- airtight 

 seal. 



A scale of inches ami tenths must be 

 made on glazed cardboard or imitation 

 ivory and attached to the top of the 

 board, a sinu'lar scale being fixed on the 

 other side of the tube to show the words 



