66 MR ROBERT COCKBURN MOSSMAN ON 



but little from readings taken at 9 a.m. and 9 p.m. so that no corrections were made. 

 With reference to the monthly means from 1769 to 1816, it was not considered desirable 

 to attempt any reduction to 9 a.m. and 9 p.m., as the hours of observation could not be 

 ascertained for some periods. The limit of error arising from this disturbing factor 

 must be small, as the Edinburgh observations were checked against the isobars drawn 

 month by month for the E. of Scotland. In any case, the departure from the true 

 mean due to this deficiency would not exceed 0*012 inch. 



Table I. shows the means of each month and year reduced to 32° and mean sea-level, 

 as well as decadal and monthly means for the whole period, viz., 1770 to 1896. The 

 annual mean was 29*858 inches, being highest (29*962 inches) in 1864 and lowest (29*706 

 inches) in 1789, showing a difference of 0*256 inch in the annual means. The highest 

 monthly mean was that of May, which is 29 "940 inches, and the lowest that of December, 

 which is 29 "800 inches, there being thus a difference of 0'140 inch between the highest 

 and lowest monthly means. It is to be observed that the average pressure of November 

 is practically the same as that of December, the difference being only 0*001 inch. 



The highest mean pressure of any month was 30'361 inches in March 1840, and the 

 lowest was 29*186 inches in January 1791, the difference being 1*175 inch. The month 

 showing the greatest range among the means is February, the highest mean being 

 30*337 inches, in 1891, and the lowest 29*202 inches, in 1776, a difference of 1*135 inches. 

 The least variation is in July, the highest mean being 30*153, in 1825, and the lowest, 

 29*633 inches, in 1798, a difference of 0*520 inch. 



The absolutely highest barometric pressure during the 127 years under review was 

 31*071 inches, at 9 a.m. on January 9, 1896, and the lowest 27*451 inches, at 10 p.m. 

 on January 26, 1884, giving a difference of 3*620 inches. The highest and lowest pres- 

 sures are given for each month since 1840 in Tables II. and III. Table IV. gives the 

 extreme range of pressure during the last fifty-seven years, for each month. The greatest 

 monthly range was 3 03 5 inches in January 1884, and the lowest 0*515 in July 1852. 

 The mean monthly range is greatest (1*611 inch) in January and least (0*935 inch) in June 

 and July. It is to be observed that the differences between the values given in Tables 

 II. and III. do not always agree with the values in Table IV. This is due to the entry 

 in the former tables of extra readings taken during periods of high and low pressure, 

 whereas the table of monthly range has been compiled from the bi-diurnal observations 

 taken at 9 a.m. and 9 p.m. The results given in Tables I. to IV. are further summarised 

 in Table V., while Table VI. shows all the sea-level pressures above 30*90 inches or 

 below 28*20 inches experienced in Edinburgh from 1770 to 1896. 



Mean Temperature of the Air. 



Table VII. shows the mean temperature of the air in shade, 4 feet above grass, and 

 at a height of 250 feet above mean sea-level, from 1764 to 1896. From 1764 to June 

 1781 the values given are those taken by Hoy at Hawkhill House, St Andrew Square, 



