43 SECTION PHYSICS. 



the precipitation of a real cloud denser than any fog you have ever seen 

 in London, and still in no case did the fog or fumes exert any sensible 

 influence upon the waves of sound. The sensitive flame was as much 

 affected by the sound passing through these smoky media as when the 

 smoke was absent, whereas a couple of candles or a couple of gas 

 burners, placed within the chamber, in half a minute stilled the waves 

 of sound by virtue of a state of things perfectly invisible to the eye, 

 that is to say, layers of air of different densities produced by these 

 burning bodies. We have made artificial showers of snow, artificial 

 showers of hail, and artificial showers of rain. We have had showers 

 of bran, showers of grain of various kinds, and showers of sand ; 

 showers of real water and showers of pieces of paper to imitate flakes 

 of snow, and you will be prepared from what you have seen to 

 acknowledge the reasonableness of my statement that none of them 

 had the slightest influence upon the waves of sound. You told me, 

 Mr. President, that I had half-an-hour, and I do not think I have 

 exceeded the time which you allotted to me. 



The PRESIDENT : Ladies and Gentlemen, I will express once more 

 on your behalf our very sincere thanks to Professor Tyndall for his, in 

 the first place, extremely clear and interesting account of these remark- 

 able experiments, which he terminated some little time ago. We have 

 secondly to thank him for bringing the apparatus here and arranging 

 them so successfully as he has done, a thing certainly which could not 

 be done without great labour and great thought, especially at the dis- 

 tance which his usual laboratory and usual lecture room are from this 

 place. We have to thank him for filling this room with an atmosphere 

 of such intellectual transparency, that I feel there is not one trace of 

 fog, not one intellectually opaque cloud, if I may judge at all from the 

 intelligence and attention which has been shown by the audience, re- 

 maining in any corner of this room. Professor Tyndall has shown 

 himself to-day not only a successful experimental philosopher, but also 

 a great moral philosopher in restricting his remarks, of which we should 

 have been glad to have heard more if time had permitted ; to the time 

 which I had ventured to indicate to him, and thereby giving other gentle- 

 men who are kind enough to offer communications, an opportunity of 

 making them, and us hearing them. I beg to move our sincere thanks 

 to Professor Tyndall, and to call upon Dr. Stone for his communication 



