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PROFESSOR OSBORNE REYNOLDS ON THE 
often exist was proved by Mr. Glaisher’s balloon ascents in 1862, in which he found 
that when cloudy the mean rate of diminution for the first 300 feet was 0 o, 5 for each 
100 feet, and that when clear it was 1°, and that on some occasions it was greater and 
on others less than this. A variation of 1° in the temperature of the air alters the 
velocity of sound nearly 1 foot per second, so that with a clear sky the sound instead of 
moving horizontally would move upwards on a circle of 110,000 feet radius, and with 
a cloudy sky on a scale of 220,000 feet radius. This rate of refraction is very small 
compared with that caused even by a very moderate wind ; and consequently in order to 
verify it by experiment it is necessary to observe sounds at much greater distances. This 
renders the experiment very difficult to carry out ; and to make it worse we have no 
means of determining what the upward variation of temperature is, which therefore 
can only be surmised by the behaviour of the sound. 
The method of experimenting which first suggested itself was the same as that which 
I had previously employed for wind — namely, to obtain a means of producing a sound 
of certain intensity, and proceeding to such a distance that it could no longer be heard 
at the ground or on the level, and then ascertaining whether the range was extended by 
attaining a greater elevation or elevating the source of sound. 
The difficulty in every item of the experiments was greatly enhanced by the increased 
distance. For the wind an electric bell had answered very well, the range on the level 
being always less than a quarter of a mile ; but where the range was to be measured in 
miles, something in the nature of an explosion was the only sound available. A place 
in which to make the experiments was also difficult to find ; for it involved a range of 
several miles of level and unobstructed country, and thus the time occupied in moving 
from place to place became a matter of serious inconvenience. The greatest difficulty 
of all, however, was the effect of the wind ; since this was much greater than any thing 
to be expected from the temperature, it w r as absolutely necessary that the air should be 
quite calm, a circumstance which no precaution will insure, and for which, as I know 
from experience, one may have to wait a long while. These various circumstances 
rendered the results of the first series of experiments less conclusive than I had hoped 
they might prove. 
Experiments with rockets. 
I obtained a quantity of rockets capable of rising to a height of 1000 feet and 
exploding a charge of 12 ounces of powder. The first experiments with these rockets 
were made at Debach, a village lying between Ipswich and Framlingham, where the 
country is tolerably flat and traversed by roads in all directions. 
I. On the 14th of July, at about 3 p.m., three rockets and three cartridges were fired 
from the same spot, observers being stationed at three quarters of a mile and a mile 
and a half respectively. There was no wind, but the sky was covered with a thick 
haze, the day being very hot. All six discharges were heard at the nearer station, but 
only the rockets the distance of a mile and a half, although these w r ere heard very 
distinctly, even their hiss as they ascended. 
