t 349 ] 



XLIX. An Account of the Water -Barometer constructed and 

 erected by Alfred Bird, Experimental Chemist, Birmingham. 



[With a Plate.] 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



AT the Meeting of the British Association which has just 

 been held at Birmingham, I had the pleasure to show a 

 water-barometer which has been in perfect action for six years. 

 A general desire having been expressed that some account of the 

 instrument should appear, I have the pleasure to send you the 

 following particulars and drawings. 



In the construction of a water- barometer four things have to 

 be attended to: — 



1st. The water must be deprived of air ; 



2nd. The air must not again enter the water; 



3rd. The water must go into the barometer, to the exclusion 

 of the air ; and 



4th. The instrument must be so constructed that, while the 

 atmospheric pressure within the instrument shall be uninter- 

 rupted, no air shall penetrate into the vacuum-chamber. 



I begin by describing the material. The tube is composed of 

 metal and glass, and the three taps are those which go by the 

 name of " Lambert taps." The size of the metal part is half an 

 inch internal diameter, and is that sort of white-metal tube 

 which is in universal use by gas-fitters, called "compo." I 

 believe it is an alloy of lead and zinc. 



I recommend that which is made by Messrs. Stock Brothers 

 and Co., in Birmingham, as their compo tube will stand an 

 internal pressure of fifty pounds of air to the inch without leaking : 

 it is also very cheap. The glass tube to show the " readings " is 

 1 inch internal diameter and 6 feet long. The brass Lambert 

 taps are half an inch internal diameter. These taps are con- 

 structed internally with a cushion of india-rubber, pressed down 

 by means of a brass plate acted upon by a screw, which makes 

 them absolutely secure. 



I now proceed to describe the upper and lower parts of the baro- 

 meter in reference to the drawings. Plate IV. A A is the compo 

 tube, having two enlarged sockets B, B, \\ inch in diameter 

 and 3 inches deep. These sockets were made of brass, and their 

 office is to receive the ends of the glass tube. To fix the glass 

 tube C, about six inches of the compo tube was soldered to the 

 bottom of the socket, and being inverted and fixed very steady, 

 enough dry sand was poured into the compo tube to fill it up to 

 the bottom of the socket B. The using of the sand was to pre- 



