42 



KNOWLEDGE 



[Februaby, 1902. 



devised by the author would be necess;iry to lead to a correct 

 identification. Having discovered, by the key, the suppofcd 

 name of the bird seen, we are referred to a brief dcscrii)tiou of 

 it in the second part of the book. Here Mr. Price has come 

 sadly to grief regarding many species. His idea has been to 

 deal with "habitat. Might and characteristic habits rather than 

 details of plumage." Then why does be not, for instance, 

 differentiate the brown and barn owls by their distinctive notes 

 rather than by the colour of their plumage, which is seen rarely 

 when thej' are abroad V Some of the author's descriptions are 

 very good, and in these the correct characteristics in habits or 

 plumage which will lead to identification have been jiointed out. 

 But Mr. Price is evidently a i)Oor observer, and in many 

 instances shows a lamentable want of knowledge of his subject. 

 He says, for example, tliat the cock house sparrow has a red- 

 brown cap, and surely of all birds the familiar sparrow could 

 have been described correctly. That the red brown ctip belongs 

 to the tree-sparrow, and is one of its distinguishing marks is not 

 mentioned. Agiiin the plumage of the wheatear is described 

 as pale brown. The female wheatear, and even the male in early 

 winter, may be so described, but the conspicuous and beautiful 

 grey of the cock bird in spring and summer is not referred to. 

 Nor do we think the author's selection of the commoner birds 

 altogether wise. The guillemot, for instance, is described ; but 

 the razor-bill, which in winter, in any case, might easily be 

 mistaken for it, is ignored. 



BOOKS RECEIVED. 



Text-Book- of Elemeiitari/ Botany. By Charlotte L. Laurie. 

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Jixperimental Chemistry. By Lyman C. Newell, PH.D. (Heath.) 58. 



"Stops": or Hoio to Punctuate. By P. AUardyce. (Fisher LTuwin.) 1?. 



Britain and the British Seas. By H. J. Mackinder, jr. A. 

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Lamarck : His Life and Wurl: By Alpheus S. Packard, M.D., 

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Concise Dictionary of Egyptian Archceology. By M. Brodiick 

 and A. Anderson Morton (Methuen.) Illustrated. 3s. 6d. 



Mosquito B'iyades and How to Ori/anise Them. By Konald Ross, 

 F K.C.S., D I'.n., P R.s. (George Philip & Son ) Ss. net. 



Ouide to the Practical Elements of Electrical Testing. By J. 

 ■Warren. (Rentell.) Illustrated. 3s. 6d. 



Practical Electrician's Pocket Book and Diari/, 1902. (Rentell.) Is. 



French History Jsl-,-lS73. By Henry Hn-sdiiis.A. (Blackie ) ls.6d. 



History of Oeology and Palceoutology. By Karl Alfred Tou Zittel. 

 Translated by Maria M. Ogilvie-Grordon. (Walter St-ott.) Cs. 



In Memory of W. r. By William Tanton. (Dent) 39. fid. net. 



Discussion on the Teaching of Mathematics. (British Association.) 

 Edited by John Perry. (Macmillan.) 2s. net. 



Annuaire Asfronomique et Metc'orologique pour 1902, By Camille 

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Underground Watering of Plants and Gardens. By John Gi'aut. 

 (■Ward, Lock.) Is. ' 



Bird-Killing as a Method in Ornithology. By Reginald C. 

 Robbiiis. (Cambridge, Mass. : Wheeler.) 



THE FLIGHT OF A HAILSTONE. 



By Aethur H. Bell. 



A HAILSTONE, when dissected, is found to be au aggregate 

 of tiny crystals disposed in concentric rings or zones ; 

 zones which, if rightly cross-examined, will have much 

 to tell concerning the wonderful journey of the hail- 

 stone as it plunged through the atmosphere on its way 

 to the earth. A snowfiake makes this same journey 

 through the air in a more leisurely fashion, and it does 

 not arrive at its destination with the noise and rattle 

 that announces the descent on the eai-th of hailstones ; 

 but the two travellers axe very nearly related, for they 

 are both the offspring of aqueous vapour. It is part of 

 the work of the meteorologist nowadays to discover, if 

 he can, why the moisture in the air sometimes takes 

 the form of a snowflake, while at others it crystallizes 

 as a hailstone. To merely record the size of a hailstone 

 is insufficient, for these frozen pellets of moisture liave 

 more interesting attributes. 



At the heart of every hailstone is a tiny atom of dust, 

 which may be considered to be the very foundation of 

 tho whole icy structure. These atoms of dust pervado 

 every part of the atmosphere. Not only are they found 

 in tho lower strata of the air, but the winds can-j' thcni 

 far above the highest mountains, and no matter whether 

 samples of air obtained by balloonists or by mountain 

 travellers are examined, minute particles of dust arc 

 always everywhere to be found. Indeed, it is becoming 

 understood that without an atom of dust upon which 

 tho moisture of the air could settle there would be no 

 rain-drops, no snow, no fog, dew, clouds or hail. Without 

 these minute platforms, as they may be called, upon 

 which the moisture as it condenses could alight, rain 

 wovdd be continually pouring down upon the earth, and 

 it is these motes that keep the moisture buoyed up in 

 the atmosphere until such times as circumstances compel 

 them to yield up tho aqueous supplies which thcv so 

 industriously collect. Supposing, then, that a little 

 vapoiu' should happen to condense on a particle of dust 

 floating aimlessly through the air, there is a beginning 

 made of what, under favourable conditions, may 

 ultimately gi'ow to a full-sized hailstone. 



It is highly probable that, for a hailstone to have 

 fitting opportunity of growing to maturity, it must take 

 its plunge to the earth from a great height. The clouds 

 which float at the greatest distance from the earth are 

 those known as the cirrus, which are often seen many 

 miles above the tops of the highest mountains. If. then, 

 an incipient hailstone can only dive towards the eai-th 

 from this dizzy height it will in its headlong flight 

 pass through strata of air differing very much as regards 

 moistui-c and temperature, and these are the circum- 

 stances most favourable to its development. 



But before the growing hailstone can launch itself 

 downwards it must by some means or other contrive 

 to get itself carried up to these serene and chilly heights. 

 Briefly, it makes the journey by stepping, as it were, 

 into one of the strong ascensional cuiTents of air which 

 spring upwards from almost every part of the earth's 

 surface. These cm'rents are revealed by the cumulus 

 clouds which are but the visible tops of columns of air. 

 As these rising currents of air rush upwards they 

 presently arrive ati a height where the air is rare and 

 cold, so that the aqueous vajjour they carry with them 

 condenses and promptly assumes the form of a cloud ; 

 a process that may be likened to a rocket which bursts 

 into a visible cloiul of fire at the end of its upward 

 flight. If, then, the dusty atom with its tiny load of 

 moisture that is subsequently to form the nucleus of a 

 hailstone can succeed in entering such a rising stream of air 

 it will ere long find itself at a height that will ultimately 

 prove to be an admirable coign of advantage. In this 

 position it resembles nothing so much as an oak apple 

 dancing at the top of a jet of water, for in each case au 

 ascending current keeps the object buoyed up. 



But it often happens that yet loftier heights are 

 necessary for the growth of a hailstone. Supposing, then, 

 that a further upward flight is desirable, there is a con- 

 venient motive force ready to hand. It is well known 

 that whenever condensation of moisture takes place 

 latent heat is set free, so that when the aqueous vapour 

 is actively engaged, say, in condensing into the form of 

 a cloud, it is probable that great supplies of warmth 

 spring into being. This warmth, of course, raises the 

 temperatiu-e of the aii% and as the latter becomes 

 warmed it rises and another form of ascending current 

 is thereby produced. Such a cru-rent provides the hail- 

 stone with a means of conveyance to those exalted 



