276 PROFESSOR C. PIAZZI SMYTH ON 



by the Registrar General in Scotland ; so that in that Officer's quarterly returns, while 

 the Black-bulb observations which we have utilised for Tables V. and VI. are the means of 

 the readings for every day, at every Black-bulb station, — the extreme readings entered 

 alongside them, refer to only one day and at some one, or any, station, whose name does 

 not transpire, and may be different every month. 



As such a return would not suit the present 32 year discussion of means only, — Mr 

 Heath, First Assistant, has been at the pains of going back over all the years of all the 

 stations, and picking out the max. and min. readings of each, for every month, of every 

 year ; and taking the means rigidly, according to the varying number of stations at work 

 at the time. 



This proceeding, however, has brought into prominent view, not only the terrible 

 differences between the extreme readings of one station and another, as for instance 30° 

 or 40° (and which may be characteristic of Black-bulb exposed thermometer observa- 

 tions) ; but has also shown the utter defalcation from the original published plan of the 

 Scottish Meteorological Society and the Registrar General as to the number of stations 

 combined to give the Meteorology of the country. For while, for Barometric Pressure, 

 Temperature in Shade and other important returns, the one mean quantity finally given 

 out, represents seldom less than 55 stations, — the Black-bulb returns. 



Began in 1857 



with 



3 Stations, 



Increased in 1860 



to 



16 



)> 



1864 



to 



23 



55 



1870 



to 



24 



55 



Decreased in 1873 



to 



20 



55 



1876 



to 



18 



55 



1880 



to 



16 



5) < 



1887 



to 



10 



55 



and 



It seems therefore fairest for the public, and most honouring to the enterprise and 

 devotion of those enthusiastic observers who did cultivate this extra branch of Meteor- 

 ology, that their individual stations should be known by name, so long as they alone con- 

 tributed the sparse items, which have hitherto passed as the condensed work of more than 

 twice, or thrice their number of stations. To this end therefore Mr Heath's great table 

 XXVI A., with his valuable and indeed unique collection of results of Black-bulb observa- 

 tions, names of stations, and summations as well as means for every month, has been in- 

 troduced entire; and forms the solid foundation on which the next two Tables XXVII. 

 and XXVIII. have been prepared. They show too precisely, on the testimony of all the 

 data of the kind, available over the whole country, the extreme temperatures in Fahrenheit's 

 Scale, to which exposed surfaces are liable by day and by night in Scotland, during any 

 cycle of 24 hours. 



To distinguish these deductions from such extreme returns, effectually from all shaded 

 Thermometer readings, and also from the simple mean readings of the exposed Black-h^lbs 



