352 Mr. A. Bird on a Water-Barometer. 



of the gutta-percha pipe Y is a -|th-inch tap, terminating with a 

 -§ th-inch female screw union-joint Z. The gutta-percha pipe 

 being in position, and hanging down as seen in the drawing, 

 became a siphon; and the air being sucked out, the water at 

 once came over, and was stopped from running away by turning 

 the small tap Z. The female union- screw at Z being tightly 

 screwed on to the male screw-joint 0, the water was ready to 

 enter the barometer. 



The first thing to be done was to displace the air in the bend 

 of the tube, reaching from the tap N at the bottom, to the 

 extreme end of the compo tube in the cistern R. This was done 

 in the following manner : — The cistern or bottle was taken clean 

 away and filled quite full to the very brim with best olive oil ; 

 the three Lambert taps being all open, and, the bottom end of 

 the " compo " tube hanging down, the small gas-tap Z was 

 opened ; the water then began to ascend both legs of the baro- 

 meter, and when it reached the tap P, it passed over and ran 

 out of the end of the tube which was hanging down. At that 

 instant the stream was stopped with the thumb, and, the tap Z 

 being turned off, the bottle full of oil was brought to the thumb 

 which stopped the end of the compo tube and kept-in the 

 water. The thumb supporting the tube was now put into the 

 oil, and the end of the tube slipped down to the bottom of the 

 oil. The bottle was then put into its place on the stand S, and 

 the surplus oil being siphoned out, there remained in the cis- 

 tern R about 3 inches in depth of olive oil, the compo pipe dip- 

 ping into it nearly to the bottom. 



The next thing was to fill the longer part of the barometer, 

 which was accomplished as follows : — The tap P being closed 

 and the small tap Z opened, the water rapidly rose in the baro- 

 meter; when the water had reached the opening M at the top, 

 it was allowed to run a minute or two to carry any traces of air 

 away which might have lingered in the tube. Tap L at the top 

 and tap N at the bottom being then securely closed, tap P was 

 opened, and the column of water began to descend and to accu- 

 mulate in the cistern R under the stratum of olive oil. As the 

 column fell it was narrowly watched in the glass tube, but not 

 a bubble of gaseous matter was observed. On examining the 

 cistern R, it was found that the oil did not quite reach the zero- 

 point E, more oil therefore was poured in till the zero-point E 

 and the level of the oil were coincident. The graduated scale 

 was now looked at, and it showed that the column of water was 

 400 inches high, the mercurial barometer being 30*4 inches, 

 and the temperature 67°. 



In order to test if gaseous matter would accumulate in the 

 vacuum-chamber, the gutta-percha siphon was allowed to remain 



