mean reading of the barometer was Ji9-867 in. ; the highest reading 

 was 80-862 in., on February 11, 1849; the lowest 28-38'2 in., on 

 December 0, 1847. The two latter results shew the state of the 

 barometer on the days named at the ordinary time of reading, but at 

 10 p.m. on the last named day the reading was 28*154 in., making the 

 extreme range for the seven years 2*708 in. We have no self-registering 

 barometer, and therefore the true range is probably greater. The mean 

 pressure of dry air reduced to the level of the sea was 29*589 in. 

 The mean temperature of the air 50*0" ; the highest reading of the self- 

 registering maximum thermometer in the shade, was 82*3° on the 19th 

 June, 1846; the lowest reading of the self-registering minimum ther- 

 mometer, was 20*8° on the 29th January, 1848. The extreme range 

 of temperature for the seven years was 61*5°; the mean daily range 

 was 8*9°. The mean annual fall of rain was 28*39 in, ; the largest 

 annual fall was 32*20 in. in 1852, and the smallest 21*46 in. in 1850; 

 the average number of days in the year on which rain fell was 174. 

 The mean amount of cloud was such as to cover 6*8 of the sky, the 

 largest mean amount in any one year was 7*3 in 1851, and the smallest 

 6-3 in 1849. 



The mean temperature of the dew-point for the seven years was 450°, 

 being 5° lower than the mean temperature of the air. The mean elastic 

 force of vapour, or mean amount of water mixed with the air, was 0*325 

 of an inch. The mean weight of vapour in a cubic foot of air was 3*70 

 grains, and the mean additional weight required to saturate a cubic 

 foot of air, 0*67 of a grain. The mean degree of humidity (complete 

 saturation=l) was 0*851. The mean amount of vapour mixed with the 

 air would have produced water, if all had been precipitated at the same 

 time on the surface of the earth, to the depth of 4*48 inches. The 

 mean weight of a cubic foot of air, under the mean pressure, tem- 

 perature, and humidity, was 5*385 grains. 



In the autumn of 1851 Mr. Follett Osier erected a self-registering 

 machine for the purpose of recording the force and direction of the wind, 

 the amount of horizontal motion of the air, and the fall of rain. At an 

 elevation of thirty feet above the roof of the observatory, a pressure 

 plate of four superficial feet is kept facing the wind by means of a set of 

 small vanes. This plate is urged in opposition to the wind by eight 

 springs, so arranged that a slight spring comes into play with a light 

 wind, and stronger springs are made to act in conjunction with the first 

 successively as the plate is driven back by the force of the ^vind. A 

 chain from the pressure plate passes over a pulley and communicates 



