REFRACTION OF SOUND BY THE ATMOSPHERE. 
317 
II. On the 16th of July, at 3 p.m., the day being very hot with no wind, a single 
rocket was sent up, an observer being stationed at four miles and a half on the Wood- 
bridge road. The explosion was very distinct, but the hiss was not heard. 
III. On the 18th a series of rockets were compared with the discharges of a gun 
capable of firing \ lb. of powder, and which made a much louder report than the 
rockets. The observers drove along the Framlingham road, the times of the discharges 
having been determined beforehand. This road was chosen because at the commence- 
ment of the experiments the wind was blowing almost at right angles to it. The wind 
was very light when the start was made, but before the first gun was fired it had consi- 
derably strengthened and changed in direction so as to blow against the sound. It was 
to this cause I attribute the fact that the first two guns were not heard at a distance of 
a mile and a half and two miles respectively. After this the direction of the wind again 
changed, and the two next guns were heard distinctly, although at greater distances ; 
but, strange to say, the rockets at the same distance were not heard. The wind remained 
constant in this direction until the end of the experiments, and a rocket was heard at 
four miles. Owing to the changes in the wind the results of these last experiments have 
shown nothing as regards the refraction of sound, although they show (what was, indeed, 
shown by the previous ones) that it is possible on a very hot day when there is little or 
no wind to hear the discharge of a small cartridge, such as that carried by the rockets, 
distinctly for a distance of four or five miles, and this when the lower stratum of the 
atmosphere was so heterogeneous that all distant objects near the ground appeared to 
waver and twinkle as they do when seen over the top of a furnace. 
In the hope of improving the conditions of the experiments, I accepted the invitation 
of my friend Major Hare, of Docking in West Norfolk, to accompany him in his yacht 
the 4 Feronia ’ during a cruise on the east coast, taking rockets with me. Here I spent 
three weeks without having a single calm day. 
Experiments in Lynn Deeps. 
On the evening of the 18th of August, however, the weather improved; and being 
then in Lynn Deeps, I made some preliminary experiments so as to get the men into the 
way of firing the rockets. The yacht was at anchor in what is called the Upper Hoad, 
and at 9.50 p.m. I rowed with two men in a direction slightly to leeward of the yacht. 
The wind was very light : at a distance of two miles they fired a large pistol ; the interval 
between the flash and the report was eleven seconds (which gave us our distance) ; the 
report was loud and accompanied with prolonged reverberation ; a rocket was also heard 
distinctly, but was not so loud as the pistol, and was not accompanied with any echoes 
or reverberation. The hails from the yacht were heard by us in the boat quite distinctly, 
but our answers were not heard on board the yacht. As there was a light mist it was 
not thought safe to go further away from the yacht, so we returned and waited in hope 
of being able to do something the next day. In this we were not disappointed ; for on 
MDCCCLXAVI. 
2 Y 
