324 Royal Society: — Prof. 0. Reynolds on the 



" On the Refraction of Sound by the Atmosphere." By Prof. 

 Osborne Reynolds, Owens College, Manchester. 



This paper may be said to consist of two divisions. The first 

 contains an account of some experiments and observations under- 

 taken with a view to ascertain how far the refraction of sound caused 

 by the upward variation of temperature may be the cause of the 

 difference in the distances to which sounds of the same intensity 

 may be heard at different times. 



Some rockets, capable of rising 1000 feet and then exploding a 

 cartridge containing 12 oz. of powder, having been procured, an 

 effort was made to compare the distance at which the rockets could 

 be heard with that at which a gun, firing | lb. of powder and 

 making a louder report than the rockets, could be heard under the 

 same conditions of the atmosphere. In the first instance the rockets 

 and the gun were fired from a spot in Suffolk around which the 

 country is tolerably flat, observers being stationed at different 

 distances. Owing, however, to the effect of the wind and the time 

 required for the observers to proceed to the distant stations, these 

 experiments were not successful in establishing the comparative 

 merits of the gun and the rockets. They were, however, important 

 as showing that on hot calm days in July the reports of the rockets 

 never failed to be distinctly audible at distances of 4 and 5 miles, 

 although the sun at the time was shining with full force on the 

 ground and rendering the air near the surface so heterogeneous 

 that distant objects seen through it appeared to wave about and 

 twinkle. 



The next attempt was made during a cruise on the east coast. 

 After three weeks cold and windy weather, the 19th of August was 

 a fine day ; and some experiments were made in Lynn Deeps, which 

 revealed a very extraordinary state of the atmosphere as regards 

 the transmission of sound. A party rowed away from the yacht 

 in one of her boats, it having been arranged beforehand that either 

 a rocket or a large pistol was to be fired from the yacht when sig- 

 nalled for ; also that when those on the yacht heard those in the 

 boat call they should answer. The boat proceeded to a distance of 

 5 miles, until those on the yacht had completely lost sight of it ; 

 but all the time the calls from the boat were distinctly heard by 

 those on the yacht, although after they had lost sight of the boat 

 they ceased to answer the calls. On the boat also not only were 

 the reports of the pistol and rockets distinctly heard, but every 

 answer from the yacht was heard plainly. The last came after an 

 interval of 35 seconds, which gave the distance 3| miles. Nor was 

 this all ; but guns, and on one occasion the barking of a dog, on 

 the shore 8 miles distant were distinctly heard, as were also the 

 paddles of a steamer 15 miles distant. 



The day was perfectly calm, there was no wind, the sky was quite 

 clear, and the sun was shining with great power — conditions which 

 have been described as most favourable to the stoppage of the sound 

 by the heterogeneity of the atmosphere, and which may also be 

 described as most favourable for great upward refraction. On 

 this day, however, it was observed that all the time distant objects 



