76 Royal Society. 



Head light-ship. Precisely fifteen minutes after we had separated 

 from them the flag was hoisted. The sound, as anticipated, had at 

 length succeeded in piercing the body of air between the boat and 

 the shore. 



"On returning to our anchored boat, we learned that when the 

 flag was hoisted the horn-sounds were heard, that they were suc- 

 ceeded after a little time by the whistle-sounds, and that both in- 

 creased in intensity as the evening advanced. On our arrival of 

 course W T e heard the sounds ourselves. 



"The conjectured explanation of the stoppage of the sounds 

 appeared to be thus reduced to demonstration ; but we pushed 

 the proof still further by steaming further out. At 5| miles we 

 halted and heard the sounds. At 6 miles we heard them distinctly, 

 but so feebly that we thought we had reached the limit of the 

 sound-range ; but while we waited the sound rose in power. We 

 steamed to the Varne buoy, which is 7| miles from the signal- 

 station, and heard the sounds there better than at 6 miles distance. 



" Steaming on to the Varne light-ship, which is situated at the 

 other end of the Varne shoal, we hailed the master, and were in- 

 formed by him that up to 5 p.m. nothing had been heard. At that 

 hour the sounds began to be audible. He described one of them 

 as ' very gross, resembling the bellowing of a bull,' which very accu- 

 rately characterizes the sound of the large American steam-whistle. 

 At the Varne light-ship, therefore, the sounds had been heard 

 towards the close of the day, though it is 12| miles from the 

 signal-station." 



Here we see that the very conditions which actually diminished the 

 range of the sound were precisely those which would cause the 

 greatest lifting of the waves. And it may be noticed that these 

 facts were observed and recorded by Prof. Tyndall with his mind 

 altogether unbiased with any thought of establishing this hypothe- 

 sis. He was looking for an explanation in quite another direction. 

 Had it not been so he would probably have ascended the mast, and 

 thus found whether or not the sound was all the time passing 

 over his head. On the worst day an ascent of 30 feet should 

 have extended the range nearly J mile. 



The height of the sound-producing instruments is apparently 

 treated as a subordinate question by Prof. Tyndall. At the com- 

 mencement of his lecture, he stated that the instruments were 

 mounted on the top and at the bottom of the cliff ; and he sub- 

 sequently speaks of their being 235 feet above him. He does not, 

 however, take any notice of the comparative range of those on the 

 top and those at the bottom of the cliff ; but wherever he men- 

 tions them he speaks of them as on the cliff, leading me to suppose 

 that for some reason those at the bottom of the cliff had been 

 abandoned, or that they were less efficient than those above. If 

 I am right in this surmise, if the sounds from below did not range 

 so far as those from above, it is a fact in accordance with refraction, 

 but of which, I think, Prof. Tyndall has offered no explanation. 



[Besides the results of Prof. Tyndall's experiments there are 

 many other phenomena which are explained by this refraction. 

 Humboldt could hear the falls of Orinoco three times as loud by 



