360 Mr. J. Glaisher's Remarks on the Weather 



The mean temperature of evaporation at Greenwich — 



For the month of July was 56'*2; for August was 57^*3; 

 and for September was 54-°-6. These values are l°-3 less, 

 0°'4 less and 0°vl greater, respectively, than the averages of the 

 same months in the preceding eight years. The mean value 

 for the quarter was 56°*0. which is 0°'5 below the average of 

 the corresponding quarters of the eight preceding years. 



The mean temperature of the dew-point at Greenwich — 



For the months of July, August and September, were 51°*1, 

 53''-0 and 5l°-0 respectively. These values are 3°-6, 2°'4 and 

 l°"6 below the average of the same months in the preceding 

 eight years. The mean value for the quarter was 51°*75 being 

 of less value than in the same quarter of each of the eight pre- 

 ceding years, and less than their average by 2°'5. This implies 

 that less water has been mixed with the air during this period 

 than in any of the corresponding quarters for eight years. 



The mean elastic force of vapour at Greenwich for the quarter 

 balanced a column of mercury O'^OO inch in height. Its 

 average value for the corresponding quarter of the eight pre- 

 ceding years was 0*433 inch. The difference implies great 

 dryness of the air. 



The mean weight of vapour in a cubic foot of air for the 

 quarter was ^'S grains. The average from the eight preceding 

 years was 4*9 grains. 



The mean additional weight of water required to saturate a 

 cubic foot of air was 1'6 grain. This value, from the eight 

 preceding years, was 1*1 grain. 



The mean degree of humidity in July was 0'711, in August 

 was 0-772, and in September was 0*772. The averages for 

 the eight preceding years were 0*798, 0*837, and 0*858 re- 

 spectively. 



The mean reading of the barometer at Greenwich in July was 

 29*789 inches, in August was 29-841, and in September was 

 29*767. These values are respectively O'Oll less^ 0*060 

 greater, and 0*048 less than the averages of the same months 

 for the preceding eight years. 



The reading of the barometer was 30*03 inches at the begin- 

 ning of July. It decreased to 29*56 on the evening of the 

 4th, when it began to increase, and passed the point 30 inches 

 during the afternoon hours of the 8th, and was 30*25 on the 

 11th at 9 A.M. This was the highest reading in the month. 

 The reading decreased below 30 inches on the 15th, and to 

 29*40 by the morning of the 20th ; it then increased to 29*94 

 by noon on the 23rd; it then decreased to 29*31 on the 25th, 

 and this was the lowest reading in the month ; it then increased 

 to 29*80 by the evening of the 28th ; then decreased to 29*52 

 at 3 P.M. on the 30th ; and after this increased to 29*80 at 



