266 Proceedings of the Royal Society. 
‘The last of the tables shew the consistency of the circle of 
Dublin in the places of the stars as determined by it after the in- 
terval of a considerable number of years, without any such ten- 
dency to the south, as is supposed to have been observed at 
Greenwich. 
Thursday, March 18. 
An Account of Experiments on the Velocity of Sound, made in Holland, 
by Dr..G. Moll and Dr. A. Van Beck, was communicated to the 
Society. 
After noticing the difference between the celerity of sound, as 
deduced by theory, and found by experiment, and La Place’s 
explanation of the cause of that difference, and his corrections of 
the Newtonian formula, the authors proceeded to consider the in- 
fluence of the variable force of wind upon its velocity, and state 
their mode of annihilating such cause of error, They then detailed 
their own experiments, for which they selected two open and 
elevated spots in the plains of Utrecht, distinctly visible from each 
other, and distant about 96.64 fathoms: they measured the interval 
between seeing the light and hearing the sound, by clocks, with 
conical pendulums, which divide the 24 hours into 10 million 
parts, andone of the indexes of which give ;4, part of a decimal 
second. Each station was also furnished with a good barometer, 
several accurate thermometers and excellent telescopes, and the 
humidity of the air was determined by Daniell’s hygrometer.: The 
authors then described the means which they adopted to ensure the 
simultaneous firing of the shots at both stations, and by which 
they succeeded in bringing them within 1” or 2” of each other, and 
entered at considerable length into the details of their different ex- 
periments, the results of which are given in several tables annexed 
to this paper, among which will be found one, exhibiting a general 
view of the results of the experiments of those different philosophers 
who have investigated this subject. 
In conclusion, it appears from their researches that at the tem- 
perature of 32° the velocity of sound is 1089.7445, English feet 
per sexagesimal second, 
