74 SECTION PHYSICS. 



the year 668, when Theodore was made Archbishop of Canterbury, 

 and Adrian was sent with him to watch him, because he was a 

 Greek, and might introduce some practices of the Eastern church 

 which were not sanctioned in Rome. We find that Saint Aldhelm, 

 who died in 705, began his " Praise of Virginity " with these words : 



" Maxima millennis auscultans organa flabris." 

 (Listening to the greatest organs with a thousand bellows), 

 Wolstan fully describes an organ of the loth century in the cathedral of 

 Winchester, with 400 pipes, and it required many men to blow it. I 

 am indebted to Dr. Stone for having made this model of the action 

 of the hydraulic organ from my description in the History of Music. 

 Here are two glass vessels, one inverted inside the other, and when 

 we inject air into the inner one, water is expelled, and rises in the 

 outer ; and when we sound the pipe, the air escaping, the water 

 returns to seek its own level. There are many erroneous descrip- 

 tions of the hydraulic organ. Some say it was worked with boiling 

 water, but that idea arose from the bubbling of the water. Thus 

 when the cork which now floats sinks to the bottom, it shows that 

 the vessel is filled with air, and if we continue to blow, the surplus 

 air will ascend in bubbles outside, and thus give it the appearance 

 of boiling. 



The object of this invention of the Egyptian Ctesibius was to prevent 

 the possibility of overblowing the instrument, to which the pneumatic 

 organ was then subject. It proves that he understood the law that 

 " Liquids transmit pressure equally in all directions, and the pressure 

 they produce by their own weight is proportionate to the depth." 



The CHAIRMAN : I am sorry that we have not time to discuss this 

 interesting subject, but I must now call on Mr. Baillie Hamilton. 



AEOLIAN INSTRUMENTS. 



Mr. J. BAILLIE HAMILTON : I am going to bring before your notice 

 the last result of three years' work, and I select this particular one 

 because it to a great extent embodies all the rest. I hold in my hand 

 a small object, consisting of the following parts. There is a vibrator, 

 consisting of the tongue of a reed, and above it there is a double 



