280 PROFESSOR C. PIAZZI SMYTH ON 



While if the geographical inquiry be pursued still further, to the smallest, the most 

 exposed, and the most wind-vexed of the Shetland Isles, — trees are not only said to be 

 non-existent there, in any size or shape ; but the local botany, if here and there larger 

 than mere grass or moss, assumes only a hummocky form, half-earth, half- compacted 

 leaves, roots, and water ; under which humps no man can hide his head from the possible 

 Sun, or shelter it from the ever-present whistling wind and shrieking blast ; while a lost 

 sea bird is wheeling in the dark grey sky above, and the white horses are prancing in 

 driving mist over the deep blue waves below. 



So far too is this inhospitable vegetation from being a necessary consequence of the 

 simple coldness of a high northern locality, that in the very same Latitude-parallel as 

 those bald and frowning islets of ours, but away to the East in the midst of the immense con- 

 tinent of Russia in Europe and Asia combined, — which has winters terribly more severe 

 by the thermometer, but keeps the winds of her sea-coasts far, far away, as magnificent 

 forests of trees in point of size (but usually with very small leaves), spread their branches 

 on high, and rear their spiry heads, as in any of the warmer parts of the world. But then 

 it is in an atmosphere where calms prevail for weeks, and almost months, at a time ; and 

 snow, once fallen, remains mechanically undisturbed for a large part of the season. 



In view, therefore, of this immense importance of the strength-of-the-wind element in 

 the climate of our rather over wind-swept country, Tables XXIX. and XXX. have been 

 constructed to call attention to the terrible significance, if true, of the few little figures often 

 employed, almost at hazard, to express the mean force of the wind, by day and by night, 

 and summer and winter, at many a station, of which better things might have been 

 expected ; but where, of course, choice plants cannot grow upwards and flourish, if they 

 have really something like 3000 day-pounds pressing them down to the earth on every 

 square foot of their surface, from one year's end to another. 



Einally, Table XXXI. does little more than sum up and take the means of each of the 

 preceding Tables of years, so as to present them for one point of time; as they were 

 already presented for one point of space; and they being clearly titled will explain 

 themselves without further letter-press, beyond a few words on the Humidity of the air. 



This curious but important technical name or quality, means little definitely, when by 

 itself ; but everything when taken in conjunction with the shade temperature and 

 Barometric Pressure. These quantities are no doubt given in Tables III. and I.; but the 

 derivation thence of what the " Humidity " return really means in absolute physics, is a 

 rather intricate calculation ; which every one is not always ready and willing to perform, 

 even with the help of Mr James Glalsher's very convenient " Hygrometrical Tables." 1 

 have therefore added here, and from thence in an approximate manner, to the Humidity 

 and Temperature, the other forms in which Moisture of invisible water-gas may be 

 chronicled ; and trust they will be found useful in comparing these tables of Scottish 

 Meteorology with those of other countries ; seeing that some Meteorologists concentrate 

 their Humidity expressions in one, and others in another, of these separate terms. 



