MEAN SCOTTISH METEOROLOGY. 273 



explained that they are prepared to satisfy a want, often expressed in public, as to having 

 these extreme quantities, or limits in either direction for the daily cycle of that kind of 

 temperature clearly set before the eye, without giving the head of the reader the trouble 

 of deducing them by simple arithmetic from the old Tables III. and IV. Where Table III. 

 is the mean Temperature of the 24 hours in the shade, and Table IV. the daily cycle or range 

 of differences of the said shade Temperature in the same length of time. One half therefore 

 of this latter quantity has been added to the old Table III. to form the new Table XXI; and 

 one half subtracted from the same Table III. to produce the new Table XXII. ; and both 

 of them for every month, of every year from 1856 to 1887 inclusive. 



According to which new Tables XXI. and XXII. , it will be seen as a first step, that the 

 daily shade temperatures at any hour of the day in the coldest month, or January, will be 

 on the average of 32 years, somewhere between 32°'5 and 41°'5. And similarly for the 

 hottest month, or July, the daily shade temperature will then be anywhere between 50°'0 

 and 64°"9. Which four quantities give a mean of 47°'2; indicating July to be more in 

 excess by solar influences above its neighbouring months, than January is in defect below 

 its neighbours ; or again it gives a useful warning, much required in Meteorology, that 

 the mean of the two extremes of a cycle, is by no means necessarily the mean of all the 

 smaller component portions thereof. For, taking the means for all the 12 months, 

 instead of for 2 only, there comes out again the 46° "2 that appeared in our account of the 

 old Table III., as the Mean Temperature of the whole year. 



Table XXIIL, of Rain- fall depth, is based on the former Table IX.; but instead of 

 beginning each month's chronicle of depth from zero, goes on accumulating it, month 

 after month from the beginning to the end of the year; and this is believed to be a 

 form of representing the rain-fall much approved by both agriculturists and engineers. 



Table XXIV., of " day-degrees" of useful Plant-growth Temperature, sets forth per 

 month the resulting number of Fah. degrees in the mean shade temperature of the month, 

 either above or below the newly supposed botanical dividing plane of 42 o, F., multiplied 

 into the number of days in each month, agreeably with the new method practised by the 

 Meteorological Office in London; and evidently giving the duration, as well as the 

 intensity, of such or such a plant temperature in any and every month. 



In this first Table (XXIV.) therefore of this kind of return, we see that the average 

 number of such positive day-degrees of possible botanical activity, performance and result 

 in an average month of the whole year is 129°. 



Or again that the negative affects, which are — 155 day-degrees in an average January, 

 have become +478 in an average July, and sink down again to —133 in an average 

 December. 



This Table XXIV. will therefore serve conveniently to compare any month in one 

 year, with the same month in another year ; but will not suffice to show instantly 

 how the vegetation of any year, at some particular epoch of it, is getting on upon the 

 whole ; and whether towards the end of it the plants have received all the stimulus and 

 all the time they require for perfecting their growth and ripening their seeds. 



