Dec. 22, 1887] 



NATURE 



177 



Society may well excite their sympathy. A moment's consider- 

 ation will show that the progress of horticulture is largely 

 based on the correct application of scientific principles. What 

 is not so familar tp most people is the extent of the obligation 

 under which science generally lies to horticulture. Should any 

 reader require an illustration of this, let him turn to the "Origin 

 of Species," and specially to the " Variation of Animals and 

 Plants under Domestication." There is scarcely a page in the 

 chapters of those volumes relating to plants that does not abound 

 in references to the practices and the discoveries of horticul- 

 turists. Fertilization, cross-breeding, hybridization, selection, 

 grafting, the limits and nature of variation, are only a few of the 

 subjects on which horticulture furnishes the largest and in many 

 respects the most trustworthy body of evidence yet available. 

 That these subjects are studied, and that the experiments are made, 

 not so much from a scientitic as from a utilitarian point 

 of view, is surely no matter of reproach. On the contrary, 

 it is the business of horticulturists to act as they do, but 

 without the aid of a Society much of the experience 

 gained would be lost to science. All this might be admitted as 

 a general principle, but yet its concrete application to the Royal 

 Horticultural Society might be from various causes inappropriate. 

 The Society in question has, however, distinct and undoubted 

 claims to recognition for the good work it has done in science for 

 a long period of years. The services it has rendered to science 

 by its collectors, and the still greater value of its work in all 

 departments of practical horticulture, should have secured for it 

 more sympathetic and respectful treatment from its landlords. 

 Among Societies deserving of national support and encourage- 

 ment on the ground of public utility, there are few, indeed, that 

 have greater claims than this. For years it has unfortunately 

 been hampered by the necessity of providing amusement for 

 a body of Fellows and visitors who cared nothing whatever for 

 horticulture in its higher aims. Now there is a chance of the 

 Society bursting its bonds and confining itself to its proper work 

 — the promotion of scientific and practical horticulture. The plan 

 of catering for fashionable idlers has proved disastrous. While 

 horticulture proper was starved, and thousands upon thousands 

 of pounds were utterly wasted, the landlords retain the whole of 

 the property on which their tenants expended so much, and the 

 Society has to seek a new home. In spite of all this, however, 

 a valiant attempt has been made throughout long years of 

 depression to maintain the scientific traditions of the Society. 

 There has always been a small body of Fellows who have been 

 mindful of the obligation w hich Thomas Andrew Knight, so long 

 the President of the Society, imposed upon his successors. Lindley 

 for forty years maintained the scientific interests of horticulture 

 in the Society, and he was assisted by Royle, by Bentham, 

 and many others. Twenty years ago, or more, a Scientific Com- 

 mittee was appointed, an1 this body, recruited by new accessions 

 each year, still continues its labours. Under its guidance experi- 

 ments have been performed in the Society's Experimental Garden 

 at Chiswick ; under its sanction have been published numerous 

 Reports of very great scientific interest and importance ; and much 

 more might and could have been done but for the lack of 

 means, or rather their diversion for more questionable purposes. 

 The Committee in question consists of some twenty or thirty 

 naturalists of all denominations — botanists, chemists, geologists, 

 entomologists— associated with amateur and professional gardeners 

 interested in science. To this body are referred for discussion 

 and investigation the most varied objects of natural history and 

 vegetable pathology ; before this body and its sister committees are 

 brought all new introductions, whether of natural origin, or pro- 

 duced by the skill of the gardener, and which have any scientific 

 interest. Sir Joseph Hooker is the Chairman of this Committee, 

 the Rev. M. J. Berkeley was for many years its Secretary, and 

 a large number of the most eminent biologists, chemists, and 

 geologists have been or still are among its members, giving 

 their services without fee or reward, simply in the interests 

 of scientific horticulture. On these grounds, therefore, the 

 sympathy and cooperation of those interested in science 

 may be claimed on behalf of the Royal Horticultural 

 Society. A new programme has been decided on in prin- 

 ciple, a new home must be provided at once, for the purpose 

 of the Society's meetings and for housing the Lindley Library. 

 This library, it may be added, is held in trust for the benefit of 

 the Society, and is from lime to time enriched by donations and 

 by purchase, so far as the very meagre income of the Trustees 

 permits. The donations would be much more numerous were 

 it generally known that the library, though primarily intended 



for the Fellows, yet is under certain restrictions available to 

 outsiders, so that, though housed in the Society's rooms, it can- 

 not be sold or made away with in any financial catastrophe which 

 might overtake the Society. Such a fate, however, seems to be 

 averted at present ; the Society's debt is not large, and some 

 members of the Council, or other friends, have made a good 

 beginning by inaugurating a fund, to be used for the housing of 

 the Society, so that ere long we may hope to see the old Society 

 established on a more secure basis, and more potent than ever to 

 advance those interests of science committed to its special 

 keeping. Maxwell T. Masters, 



Classification of Clouds, 



As one who has been engaged for nearly forty years in working 

 up the materials for a monograph on clouds, I suppose I de- 

 serve the name of a " specialist in clouds " as much as any one. 

 Yet I decline, for reasons which I will hereafter state in an 

 appendix to my volume, to be altogether bound by the outlines 

 of classification which my friends Prof. Hildebrandsson and the 

 Hon. Ralph Abercromby appear to lay down (Nature, 

 December 8, p. 129 el set/.), although they adopt several 

 of the names which come from my mint. I fully adopt the 

 opinion implicitly held by Mr. Abercromby, and stated by my 

 friend Captain Barker [ibid.) — from whose classification, however, 

 I differ in one important point — that all ordinarily careful ob- 

 servers will readily comprehend the broad and simple distinc- 

 tions expressed in any fairly good classification. Nevertheless, I 

 believe that the apparently slow progress of this branch of re- 

 search, and the tediousness of the work thrown upon the classi- 

 fier, are matters on which we should congratulate ourselves, 

 since every year adds something to our knowledge of those 

 physical and structural processes which form the basis of all true 

 classification ; and I trust that some years may pass before an 

 International Congress may attempt finally to set its seal upon 

 any nomenclature or classification of clouds. 



W. Clement Ley, 



Effect of Snow on the Polarization of the Sky, 



The polarization of the sky has been shown experimentally 

 by Tyndall and theoretically by Lord Rayleigh to be due to fine 

 particles suspended in the atmosphere. According to both, the 

 sunlight scattered at right angles to its original direction by very 

 small particles is completely polarized in a plane through the 

 sun. In observation, however, we find the light from a region 

 of the sky distant 90" from the sun is only partially polarized. 

 This is due to that portion of the atmosphere being illuminated 

 not merely by the sun, but also by the rest of the sky and the 

 surface of the earth, and partly also no doubt to some of the 

 particles not being sufficiently small compared with a wave-length. 

 From these considerations we may expect that a fall of snow 

 would cause a considerable diminution of the polarization. 

 This expectation has been fulfilled in some recent observations 

 of mine here at 6000 feet above sea-level. My polarimeter con- 

 sists essentially of two piles of glass plates to depolarize the sky 

 light ; and a crystal and Nicol prism to test the depolarization. 

 Owing to the strength of the polarization at this altitude, I find 

 it necessary to use two piles of glass plates separated by two or 

 three inches. This arrangement diminishes the number of double 

 internal reflections, and so is a much more powerful polarizer 

 or depolarizer than the same number of plates combined into one 

 pile. As I have not seen this important practical consideration 

 noticed before, I may point out that, in addition to the light 

 refracted directly through the pile, there are a number of portions 

 twice reflected. One of these for instance is reflected first at the 

 second surface of the last plate, and secondly at the first surface 

 of the last plate. The number of such twice-reflected portions 

 for n plates is n (2« - i). When, as in my instrument, the fixed 

 pile is much inclined, no light can reach the edge after being 

 reflected first by one pile and then by the other. If the two 

 piles were combined into one, I should have 120 portions twice 

 reflected ; as it is, I have only 60. This increases the polarizing 

 power of the instrument by at least one-third. 



The crystal is a thick plate of Iceland spar cut so that the 

 light passes along the optic axis. The fixed pile of three plates 

 has its normal inclined at 47° to the axis of the crystal. The 

 movable pile of five plates has an index attached, which gives 

 the inclination of its normal to the axis of the crystal. This 

 inclination is the reading of the polarimeter. 



