HARDWICKE'S SCIENCE-GOSSIP. 



to contain a very good British herbarium. At Kew 

 the cabinets employed are somewhat similar, but 

 their height is greater and the shelves are fixed. 



The above are the principal points connected with 

 the arrangement of a herbarium, considered as 

 distinct from the work of collecting. It is possible 

 that I may have omitted to touch upon certain 

 details which may occur to the amateur ; should 

 such be the case, I may add that I shall be happy 

 to supply any additional information, either by letter 

 or by word of mouth ; or to show the system adopted 

 at the British Museum to any one who may call 

 upon me there for further hints upon the subject. 



"FROST PHENOMENA," AND EVAPORA- 

 TION EROM ICE. 



EEFERRING to Mr. Mott's paper in Science- 

 Gossip, 1 have for many years been familiar 

 with the tendency of hoar-frost crystals to point 

 towards the wind, and, have mentioued it in, as well 

 as out of print. 1 have found, too, that most farmers 

 and sportsmen know that the windward side of a 

 hedge affords, on a frosty morning, a whiter back- 

 ground for a shot than the opposite side ; though 

 they have not in general been aware, until shown 

 the cause, that such superior whiteness was owing 

 to this behaviour of the frost-crystals ; and, on the 

 other hand, others would not believe in the piling on. 

 process, spite of clear proof ; but said the " wind 

 must have changed," &c. Even Professor Tyndall 

 seems to have been mistaken on, not exactly this, 

 but on a closely similar point ; for in the Saturday 

 Review, Jan. 1861, in speaking of the icy plumage seen, 

 in the late severe frost, on the exposed parts of the 

 huts on the top of Snowdon, he describes it as 

 "snow drawn out by the wind into the perfect 

 resemblance of feathers ; " but he evidently did not 

 see it in actual course of formation, as I was for- 

 tunate (?) enough to do in 1867 in manner now to 

 be described. 



Many of our readers will remember the severe 

 " Blackthorn winter " of that year, which after a 

 warm, almost hot, fit of spring, set in suddenly on 

 the 12th of May, and included Hermit's snowy Derby 

 day. On the 13th I fixed on the top of Y-Glyder- 

 fach, four "miles E.N.E. from, and 350 ft. lower than 

 the summit of Snowdon, an Elliott's minimum self- 

 registering thermometer ; which by the way, unlike 

 those fixed on Snowdon, is still unmolested and in 

 good order, its readings having been repeatedly taken 

 during the past seven years. 



In the ascent I had entered, at about 2,000 ft. 

 high, a dense cloud-stratum borne at a good 20 miles 

 an hour on the wings of a bitter nor'-easter, and 

 met with new-fallen snow, six or eight inches deep 

 on average, but as many feet deep in holes and 

 drifts. The temperature here was 32°, decreasing 



to 26° as I rose higher, still in dense cloud, but no 

 snow falling. Near to and at the summit, the won- 

 drous crag and block structure of this little-known 

 peak was profusely beset on the salient windward 

 angles with a beautiful growth of icy plumage in 

 rows and groups of feather-like crystals two or 

 three inches long, stouter in their build than those of 

 hoar frost, but, like the latter, set so point-blank 

 towards the wind, E.N.E., that I no longer needed 

 to use the compass. 



I send with this printed and other slips for edi- 

 torial satisfaction as to my having years ago recorded 

 the above-named tendency of frost crystals ; but I 

 may add that in dead calms,— e.g., the intense frost of 

 Dec. 21-25, I860,— the spiculee tend rather to radiate 

 a la bottle-brush, round twigs, &c, than to " fall to 

 the ground and thence grow upright." For some 

 days before the date last mentioned there had been, 

 owing to the increasing dryness of the air, but little 

 hoar frost ; yet the extreme cold of that Christmas 

 eve overtook and passed the dew-point, low as it 

 must have been ; and the result was a precipitation 

 of rime so profuse as to produce, in S. Derbyshire, 

 a fairy-like scene not to be forgotten. The fine old 

 elms overtopping the tower of the village church 

 were encrusted radially, not merely edged or fringed, 

 to their highest twigs, with a frost-growth nearly an 

 inch in diameter, their heads looking like huge growths 

 of white coral against the bluest of wintry skies. 



It is not necessary that hoar frost should always 

 accrete from an intermediate state of visible watery 

 particles, or mist ; the clearest air may, often does, 

 deposit its moisture as dew or (if frosty) rime, on 

 objects sufficiently cooled by radiation ; and there 

 need be no " falling of watery particles " so as to 

 cause "upright frost-growth," which may, of course, 

 take place under special conditions, though I never 

 saw it except as included in the radial growth of a 

 calm frost. 



Conversely, ice can, and often does pass (without 

 thawing I mean) from the solid to the invisibly dis- 

 solved state ; or in plainer English, ice evaporates 

 at temperatures below 32° Fahr. ; and at 21° to 26°, 

 with a brisk wind, the process is quicker than one 

 would expect. To convince an unbelieving scien- 

 tific friend, I once put it to direct proof by balancing 

 in a delicate pair of scales a piece of ice of about 

 two ounces weight and forty square inches surface, 

 in a north aspect and a stiff north-east wind at a 

 temperature not exceeding 26°. I have not the 

 figures at hand, but remember that in three minutes 

 the balance turned, and in three hours the ice 

 " kicked the beam." 



At school we used to make slides by pouring 

 water over a flagged pavement in a north aspect ; 

 and knew well how they would " dry up " in a strong 

 wind, though with hard frost, so that at noon it was 

 necessary to look out for trips where all was right 

 three hours before. H. B. Biden. 



