On Sal Nitnim and Nitro-Aerial Spirit 69 



light, as is shown in Plate V., Fig. i. Care, how- 

 ever, must be taken that the surface of the water 

 enclosed within the glass be at the same level as the 

 water without. But that this may be attained in the 

 present experiment, and also in those that follow, let 

 one leg of an inverted syphon be enclosed within the 

 cavity of the cupping-glass before it is put into the 

 water while the other leg projects outside, yet so that 

 the end of each leg may be above the surface of the water, 

 as is seen in the said figure. The use of the syphon is 

 to enable the air enclosed in the alembic, and com- 

 pressed by the underlying water while the glass is 

 being let down into the water, to pass out through the 

 cavity of the syphon, so that the water within may 

 not be depressed below the level of the water outside, 

 as it would otherwise be. But when the air ceases to 

 pass through the syphon (which will happen almost in 

 an instant) the syphon should be at once withdrawn, 

 that the air may not afterwards rush through it into 

 the glass. When these arrangements are made let the 

 cupping-glass be firmly fixed so that it may descend 

 no further into the water, and you will presently see, 

 while the light still burns, the water rising gradually 

 into the cavity of the cupping-glass. 



I will not deny that the ascent of the water arises in 

 part from the circumstance that when the light is 

 about to expire, the air enclosed in the cupping-glass 

 is less agitated and rarefied by the igneous particles 

 than formerly. But the rise of the water into the 

 glass must not be ascribed to this cause alone, since it 

 is partly due to this, that the lamp enclosed in the 

 glass is, by its own burning, deprived of nitro-aerial and 

 elastic particles so that the air there is not able as be- 

 fore to resist the pressure of the atmosphere. And this 

 will be further confirmed by the following experiment. 



