•270 PROFESSOR C. PIAZZI SMYTH ON 



as the proper and acquired temperature in the shade of the atmosphere alone; which 

 for the day half of the 24 hours is 46*2 + 6*2 = 52°4 F. But as to the annual cycle 

 of these exposed Black-bulb day observations, its Max. occurs in July = 91 0, 4, and its 

 min. in December = 47°'6 F. 



Table VI. gives the monthly means, of the cold extreme, or nightly observations of 

 the same exposed Black-bulb thermometers, but now at night and the coldest part of 

 each and every night. Establishing that such Mean, of exposed night temperature in 

 Scotland, on the Mean as before of all the days of all the months of all the years and all 

 the stations, is down so low as 35° - l F.; and includes about 5° of negative radiation 

 effects from the open night sky. The shaded thermometers at night yielding on the 

 whole no lower result than 46°'2 — 6° '2 = 40°'0. But as to the annual cycle of these Black- 

 bulbs exposed by night, its Max. occurs in July = 44° - 9 and its min. between December 

 and January = 28°*3 F. 



Table VII. sets forth the Mean monthly Humidity of the air, as measured by the 

 depression of the wet, below the dry, bulb thermometer ; and computed according to Mr 

 Glaisher's well known and most practical tables. It is then found to amount on the 

 whole year and years to 85, where saturation = 100. While the number of grains of 

 moisture in a cubic foot of the earth's gaseous atmosphere, or any other direct and positive 

 expression of the amount of moisture has to be computed from that 85 of Humidity in 

 combination with the shade-temperature, and Barometric pressure at the time and 

 place. 



But these having been already given, for the one general mean of all the stations and 

 all the years, as 46° *2 and 29*846 inches, there results very nearly 3'1 grains of watery 

 vapour present in each cubic foot ; 0*5 grains further required to saturate the same bulk 

 of air ; and 0*26 inch for the elastic force of vapour present in the air. The depression 

 of the wet, below the dry, bulb being 2°*1 ; and the depression of the computed dew- 

 point below the observed dry-bulb being 4° "5. 



Or showing the general climate of Scotland to be usually within half a grain of 

 manifesting visible mist, instead of concealing it as invisible vapour, or water gas. But 

 taking the mere " Humidity" return just as it stands, its annual cycle has its Max. in 

 December=89, and its min. in May = 80. 



Table VIII. gives the mean number of days on which rain fell in every month ; and 

 which, on the whole year and years amounts to the round number of 1 5 for every month. 

 The annual cycle however shows itself in having a Max. = 17 in January, and a min. = 12 

 in April. 



Table IX. represents the still more important feature of rain-fall, viz. its quantity, as 

 measured by its depth when fallen. And while the table gives such depth for each 

 month, it likewise gives the accumulated depth for each year, and the mean of the years, 

 viz., 39*12 inches. A quantity however requiring immense alterations for individual 

 localities, sometimes 4- and sometimes — , according to local position, as will be taken up 

 in the second part of these Meteorological explanations. The annual cycle however 



