MEAN SCOTTISH METEOROLOGY. 275 



October. But there have been years, and Table XXVI. will show which they are, when 

 the heat-accession went on increasing up to, and even including, all December. 



(Table XXVI. concluded.) Again the absolute amount of botanical day-degrees of 

 heat, recorded through each annual cycle, is so very different in different years, that while 

 in the usual fulness of October, the average amount is 1727° — there have been some years 

 when it reached 2216°; and have also been others when it attained to no more than 

 971°; or something ruinous then to those very crops, which had been a distinguished 

 success in other years. 



4. Frost and Fire. 



(Tables XXVIa., XXVII. and XXVIII.) All the previous new therm ometrical Tables 

 from XXI. to XXVI. inclusive are founded on the means of shaded thermometers. But 

 there is another class of temperature observations, viz. of the exposed Black-bulb thermo- 

 meters, in their occasional excesses once a month, both by day and by night, which are far 

 more immediately suited to indicate some of the most trying influences to which all 

 open-air structures, whether natural or artificial, are liable, both on their outside surfaces, 

 and to some small depth within their substance according to its conductibility for heat. 

 The important dividing thermometrica] plane to measure from in this case, being, how- 

 ever, by no means the 42° F. of plant life, but the far more widely acknowledged 32° F., or 

 the very freezing point of all watery Nature ; and that which brings on the often sudden 

 change in water from its fluid, to its solid, condition, with all its then visible whitenings, 

 irresistible expansions, and splitting of rocks exposed to it, with hardening of soft ground, 

 and stoppage of building, agricultural and inland-navigation work. 



The efficient quantities therefore to be entered in these Tables XXVII. and XXVIII. 

 are, for the benefit of practical men, not so much the actual readings of even the said 

 exposed Black-bulbs by night and by day (as entered preliminarily in the large Table 

 XXVIa.), but the differentia] amount of such readings in degrees, under or over, — or 

 + , 32° F. And again they are not founded on the means of those exposed kind of read- 

 ings for every day, and every night of the month (when day-degrees in monthly sums 

 might be demanded, to show effects of long continuance ; and many an acute, if not crucial, 

 experience of a single hot day, or a single freezing night, might be concealed) — but on 

 the one extremest reading each way, or the highest one by day, and the lowest by night, 

 during each whole month, at every Black-bulb station, i.e., the mean of all of them. 



There is still therefore the effort, according to the whole tenor of all these 31 Tables, 

 to present such a return by a mean from a number of stations ; and not to risk the 

 character of the whole country and the interests of science on the unsupported testimony 

 of a single observer ; and this whether such solitary recorder's station should have been 

 arbitrarily chosen in preference to all the rest ; or whether the one, absolutely highest 

 reading of all the Black-bulb stations should be taken each month, and quoted anony- 

 mously, though it might appertain to a different station every month. 



Now this last plan was the method, for certain reasons, adopted from the beginning 



