Polytechnic Association. 715 



which wind I heard ; but there was certainly a coincidence between 

 the sound and the motion of the aurora. 



Dr. P. H. Van der "Weyde — If the aurora was 600 miles high, it 

 would take an hour for the sound to reach the earth. 



Mr. W. E. Partridge— In the winter of 1860, 500 miles north of 

 here, with the thermometer twenty degrees below zero, the snow two 

 or three feet deep, on a perfectly quiet night, during a brilliant 

 aurora, I heard sounds very like the clacking of two pieces of horn. 

 I was watching for sounds from the aurora, and sounds I heard ; but 

 whether from that or from the movement of the snow in the extreme 

 cold weather, I cannot say. 



Mr. Hudson — During one of the finest auroras I have ever seen, 

 in 1866 or 1867, when it was perfectly still, and I was entirely alone, 

 with no wind, no snow, no ice, no intense cold, it seemed to me that I 

 could hear a crackling sound. Still, I could not be sure that it was 

 not imagination, having so often heard it described. 



Dr. Parmelee — "We have had three witnesses who have heard three 

 different sounds, the clacking of two pieces of horn, the wind sighing 

 through the boughs, and a crackling sound. I venture to say that any 

 person, on any perfectly still night in the country, if he will listen, 

 will hear a great variety of sounds, some of them perhaps in his own 

 ears. Throwing the head back, may itself cause a rush of blood to the 

 head, which will produce a roaring noise. 



Mr. Partridge — I have listened for the same sounds on other 

 nights, but failed to hear them. 



Explosion of Steam Boilers. 



The President — In the paper of Judge Hayes, read at our last 

 meeting, the explosion of steam boilers is ascribed to electrical influ- 

 ences. Pie asserts that the evaporation of water produces electricity ; 

 but he does not give any reason why the electricity should remain in 

 a metallic boiler having metallic connections with the earth. In the 

 next place, he believes that the water is decomposed ; that the gases 

 are mixed inside the boiler, and that they are fired by the electric 

 current. Steam discharged from a boiler will produce frictional 

 electricity ; but we have no evidence of the existence of electricity 

 within a boiler. 



Dr. P. II. Van der Weyde — The idea of electricity in the boiler has 

 given rise to a patent for a lightning rod inside of the boiler. On 

 the end of the rod magnets were placed, not only to prevent the 

 boiler from exploding, but to prevent scale from forming. Another 



