Proceedings of the British Association. 93 



also the formulae which he had investigated and placed on the board in- 

 dicated it. 



< On the Progress of the Meteorological Observations at Plymouth, 

 with the Barometer and Thermometer,' by Mr. Snow Harris. — The 

 pressure of our atmosphere, as indicated by the barometer, being affec- 

 ted in these latitudes by many accidental circumstances, it is not without 

 difficulty we are enabled to trace the great periodical variations, and 

 exhibit them as they would appear in an undisturbed state. It is only 

 by a careful and extensive series of observations, such as those now 

 in progress in various places under the direction of the British Associa- 

 tion, that we can hope to examine successively great periodical variations 

 in atmospheric pressure, and bring them under the dominion of general 

 laws. The great periodical variation, as shown by the horary oscil- 

 lation, observed by Humboldt in the tropics, and by other philosophers 

 in different parts of Europe, is undoubtedly a phenomenon of high 

 interest in meteorology. In discussing the hourly observations with the 

 barometer at Plymouth, Mr. Harris has shown that this phenomenon 

 is distinctly traceable amidst a vast mass of accidental fluctuation. He 

 exhibited the mean hourly pressures for the years 1837 and 1838, and 

 the mean of the two years, and showed that a double wave was appar- 

 ent, when these points were connected by a continuous line. The points 

 in the waving kne thus produced had been each determined from 730 

 observations ; the whole number of observations from which the mean 

 pressure had been deduced being 17,500. The following general results 

 were then mentioned : — The mean height of the barometer at the Ply- 

 mouth dockyard, 60 feet above the level of the sea, and at a mean 

 temperature of 60° of Fahrenheit's scale, was from the latest results 

 29.8967. It occurred in the mean hourly progression four times in 

 the day, viz. at 2, 20, and 8, 10, a.m. ; 12, 30, and 6, 15, p.m., — at which 

 times the waves crossed the mean pressure line. The difference on 

 oscillation from 5 to 10 a.m. amounting to .0113 of an inch, between 10 

 a.m. and 3, 30, p.m. amounted to .0118. The hours of greatest pressure 

 were 10 a.m. and 9 p.m. The hours of least pressure, 5 a.m. and 3 p.m. 

 Of the diurnal semi-waves, the ascent in the morning is the least, and 

 the ascent in the evening the greatest. Of the descending branches of 

 the curves, that during the day is less than that during the night. The 

 times of the oscillations differ. The wave by day, viz. that between 

 5 a.m. and 3, 30, p. m. being ten hours and a half. That by night, viz. 

 between 3, 30, and 5 a.m. being thirteen hours and a half. The size 

 of the daily wave, therefore, so far as the observations hitherto proceeded, 

 was less than that of the wave at night. Mr. Harris proceeded then 

 to discuss the observations as applied to the different seasons, of spring, 

 summer, autumn, and winter, and showed that the general hourly 

 progress of the pressure was greatly interfered with at particular 

 periods ; the wave of autumn being that which coincided most nearly 

 with the general curve. Of the different monthly pressures, October 



