SECTION PHYSICS (including Astronomy). 



May 19/7^, 1876. 



The PRESIDENT : Ladies and Gentlemen, as it is now the hour of 

 commencement I think I need make no preface whatever in the case 

 of our first communication, but have only to mention the name of 

 Professor Tyndall to insure an attentive audience. I therefore call 

 upon Dr. Tyndall to give us his communication upon his remarkable 

 experiments upon the Reflection of Sound. 



Professor TYNDALL, D.C.L., LL.D., F.R.S. : If gas be permitted to 

 issue from a nipple with a circular orifice, such as I now hold in my 

 hand, and if it issue under a very low pressure and in a very calm at- 

 mosphere the column of unignited gas will rise to a height, or can be 

 made to rise to a height of from eight inches to a foot or more. Great 

 calmness on the part of the atmosphere is required to accomplish this, 

 and if with the gas, smoke, or some other floating matter be associated 

 you can see the column rising through the air to this height. If you 

 augment the pressure a little very soon that column breaks up and you 

 have the gas issuing from the nipple thrown into tourbillons or vortices. 

 If you ignite that gas then those vortices instantly disappear, and a 

 flame more or less tall arises from the burner. You can then go on 

 augmenting your pressure, doubling it, trebling it, or even quadrupling 

 it, and it may be even more than this, the flame at the same time be- 

 coming taller and taller. You can in this way, with appropriate gas, 

 raise your flame to a height of eighteen inches or two feet. But if you 

 go on augmenting the pressure you come to a point where the ignited 

 jet also breaks up into those vortices, or tourbillonsj the gas flares, 

 to use a common term, but if, before the gas jet or flame reaches 

 this point, you bring it just to the verge of flaring, then by an 



