On Barometric Pressure. 87 



a considerable descent of tlie column of water within ir, evident 

 by the depression of the upper and distant surface : if they were 

 liberated beneath, they did not affect it until they had reached 

 the orifice, and then acted as before: if the bubbles were li- 

 berated at a little distance above the orifice, the effect was not 

 so great, and at a certain distance was not sensible. 



Perhaps I may commit an error in comparing the inelastic 

 dense medium of water, to the elastic rare one of air : however, 

 I shall venture to do so ; for I am not aware that any circum- 

 stance could take place, were the exjieriment repeated in the 

 latter, which would give results differing in their nature from the 

 above. The strength of the forces brought into action in the 

 two media cannot of course be considered equal, but they ap- 

 pear to nie to be of the same kind. 



It occurred to me also, whilst making tlie above experiment, 

 that the descent of a body in any medium should increase the 

 pressure beneath it; and in water, I easilv succeeded in elevating 

 a column above its ordinary level, bv letting a bodv descend to- 

 wards the lower extremity of it. Thus, bv permitting a leaden 

 weight to sink on to the end of the tuije ; or, by thiusting a solid 

 body towards it ; or (as I at last made my experiments) by de- 

 pressing a circular plate of metal attached to the end of a stout 

 wire, 1 caused a rise in the column of water inclosed in the 

 tube. 



I have not had time further to consider the effects ; and as 

 it v/ould be an easy task to many of vour readers to solve what 

 to me would be difficult, I ve:iture to ask a few questions on the 

 subject. 



A barometer l)eing placed under a balloon ; does it not indi- 

 cate a diminished pressure on its ascent ? does not the pressure 

 increase as tlie balloon recedes? and in what ratio ? 



A balloon or any large bodv dcscendi;ig in the atmosphere ; 

 should it not on approaching the earth increase the pressure be- 

 neath ? and in what proportion ? 



A barometer on the earlh't' surface being affected by the as- 

 cent of a balloon from tlie spot where it is placed ; how should 

 a barometer be affected in the car of a balloon ? should it not 

 mark a dimitiished pressure whilst rising, and an increased pres- 

 sure whilst descending, to what it would do in the same situa- 

 tions were no balloon present ? 



The above questions might be put more generally, as on the 

 motion of bodies in media; and many others might be asked: 

 but were these answered, I should be able to solve the rest my- 

 self, and I prefer putting them in this form because they refer 

 piore directly to the conversation I have before noticed. IShouUl 

 F 4 tl)Q 



