1 62 



NATURE 



{Dec. 13, 1888 



biology in its widest sense in this country. Indeed, it is not too 

 much to say that the remarkable improvement which has taken 

 place within the last few years must be ascribed either directly 

 or indirectly to his influence, and has been in many cases due to 

 his initiation. 



The Rumford Medal has been awarded to Prof. Pietro Tac- 

 chini for important and long-continued investigations, which 

 have largely advanced our knowledge of the physics of the sun. 



Prof. Tacchini occupies a foremost place among those who 

 have paid special attention to the physics of the sun. Since 1870 

 he has unceasingly observed, first at Palermo, and afterwards at 

 Rome, the so'ar prominences. The information at our disposal 

 at the present time, both as regards their distribution, their 

 spectra, and the changes which take place in them, and their 

 connection with other solar phenomena, rests to a large extent 

 upon his individual Efforts. His memoirs on this subject are 

 very numerous. He has been engaged in the observation of 

 four total solar eclipses, and from some of the phenomena therein 

 observed has drawn the important conclusion that many of the 

 so-called prominences are really descending currents. . 



A Royal Medal has been awarded to Sir Ferdinand von 

 Mudler for his long services in Australian exploration, and for 

 his investigations of the flora of the Australian continent. 



For more than forty years von Mueller has been working, 

 without intermission, at scientific botany and its practical 

 illu^trations. As a botanical traveller and collector, he has, to 

 quote the words of Sir Joseph Hooker, "personally explored 

 more of the Australian continent than any other botanist, except 

 Allan Cunningham." No one has investigated the Australian 

 flora and the geographical distribution of its components with so 

 much perseverance and success, and no one has enriched our 

 herbaria, laboratories, and gardens with materials for study to so 

 great an extent. The eleven volumes of the " Fragmenta 

 Phytographise Australia "" contain the descriptions of a great 

 series of new plants, and the unrestricted communication of his 

 collections and observations to the late Mr. Bentham rendered 

 possible the preparation of the " Flora Australiensis," in seven 

 voIumeSj the only account of the vegetation of any large 

 continental area which has at present been completed. 



He has especially devoted himself to the elucidation of the 

 most difficult though most characteristic groups of the Aus- 

 tralian flora ; and as a result of his labours in this direction, 

 his " Eucalyptographia " may be more particularly mentioned, 

 a work which will always be the standard of nomenclature for 

 the intricate genus Etualypltis. Of a similiar character are bis 

 descriptions and illustrations of the " Myoporineous Plants of 

 Australia," and his " Iconography of the Genus Acacia^ To 

 him is also due the foundation of the Government Herbarium 

 at Melbourne, the first great botanical collection formed in the 

 southern hemisphere, and the future centre of all scientific work 

 on the Australasian flora. 



A Royal Medal has been awarded to Prof. Osborne Reynolds 

 for his investigations in mathematical and experimental physics, 

 and on the application of scientific theory to engineering. 



Prof. Reynolds was among the first to refer the repulsion ex- 

 hibited in that remarkable instrument of Mr. Crookes's, the 

 radiometer, to a change in the molecular impact of the rarefied 

 gas consequent upon the slight change of temperature of the 

 movable body due to the radiation incident upon it ; and in an 

 important paper published in the Philosophical Transactions for 

 1879, he deduced from theoretical considerations the conclusion 

 that similar phenomena might be expected to be observed in 

 bodies surrounded by a gas of comparatively large density, pro- 

 vided their surfaces were very small. He verified this anticipation 

 by producing on silk fibres, surrounded by hydrogen at the 

 atmospheric pressure, impulsions similar to those which in a high 

 vacuum aff"ect the relatively large disks of the radiometer. 



In an important paper published in the Philosophical Trans- 

 actions for 1883, he has given an account of an investigation, 

 both theoretical and experimental, of the circumstances which 

 determine whether the motion of water shall be direct or sinuous, 

 or, in other words, regular and stable, or else eddying and un- 

 stable. The dimensions of the terms in the equations of motion 

 of a fluid when viscosity is taken into account involve, as had 

 been pointed out, the conditions of dynamical similarity in 

 geometrically similar systems in which the motion is regular ; but 

 when the motion becomes eddying it seemed no longer to be 

 amenable to mathematical treatment. But Prof. Reynolds has 

 shown that the same conditions of similarity hold good, as to the 

 average eflect, even when the motion is of the eddying kind ; 



and moreover that if in one system the niotion is on the border 

 between steady and eddying, in an:ither system it will also be on 

 the border, provided the system satisfies the above conditions of 

 dynamical as well as geometrical similarity. This is a matter of 

 great practical importance, because the resistance to the flow of 

 water in channels and conduits usually depends mainly on the 

 formation of eddies ; and though we cannot determine mathe- 

 matically the actual resistance, yet the application of the above 

 proposition leads to a formula for the flow, in which there is a 

 most material reduction in the number of constants for the 

 determination of which we are obliged to have recourse to 

 experiment. 



There are various other investigations of Prof. Reynolds's 

 which time would not allow me to enter into, and I therefore 

 merely mention his investigation of the relation between rolling 

 friction and the distortion produced by the rolling body on the 

 surface on which it rests, that of the effect of the change of 

 temperature with height above the surface of the ground on the 

 audibility of sounds, and his ercplanation of the effect of lubrica- 

 tion as depending on the viscosity of the lubricant. 



The Davy Medal has been awarded to Mr. Crookes for his 

 investigations on the behaviour of substances under the influence 

 of the electric discharge in a high vacuum. 



Mr. Crookes's remarkable series of researches which conducted 

 him to the invention of the radiometer led him to work with 

 excessively high vacua. In connection with this he found that 

 an electric discharge in such vacua is capable of exciting effects 

 of phosphorescence apparently quite different in their origin from 

 those produced in the ordinary way by such discharges. The 

 latter are clearly referable to the action of the ethereal undulations 

 which are propagated from the seat of the di- charge. But the 

 former involve in some way the effect of the actual transference 

 of the molecules of ponderable matter. These phenomena in 

 the hands of Mr. Crookes opened up a new means of discrimina- 

 tion between different bodies, and he has applied them as a test 

 for the discrimination of groups of rare earths, not yet fully 

 investigated. The test went hand in hand with processes of 

 chemical separation. But here a great difficulty presented itself. 

 So very closely allied in their chemical properties are the 

 members of the groups, that it was only by an excessively 

 tedious and laborious system of fractional precipitation that Mr. 

 Crookes was able to effect a pretty fair separation. Even still, the 

 separate existence of some members of the groups is more or less 

 problematical. It is for these most painstaking researches that 

 the medal has been awarded. 



The existence, or apparent existence, of so many earths of 

 such close chemical relationship led Mr. Crookes to speculate on 

 the possibility that after all the molecules of what is deemed a 

 chemical element may not be absolutely alike, as chemists have 

 almost universally believed, but only very approximately so, and 

 that what is deemed the molecular weight of the substance may 

 really be that of the average of its molecules. Should such 

 groups exist, it is conceivable that by processes of very delicate 

 chen ical separation they might be split up a?ain into sub groups, 

 the molecules of which still more nearly match one another ; io 

 that according to this view the number of groups into which an 

 element, or what is deemed such, might be split up, not, be it 

 observed, by any dissociation, but merely by a sorting of the 

 molecules which are very nearly alike, may be somewhat 

 indefinite. 



Chemists will not probably be disposed to give up the idea of 

 the perfect similarity of the individual molecules of elementary 

 bodies ; but it is surely legitimate for one who has worked so 

 assiduously at these difficult separations to suggest, merely as a 

 matter for chemists to think about, a possible view of the nature 

 of elements different from that to which they have been accus- 

 tomed. 



MOTIONS OF THE SOLAR SYSTEM.^ 



V[0 other hypothesis has been suggested which offers such 

 -'-^ direct and complete answers to most of the questions which 

 relate to the origin, structure, and unity of the universe, as 

 Newton's law of gravity. It is but natural, therefore, that the 



' Abstract of an Address before the Section of Mathem itlcs and 

 Astronomy of the American Association for the Advancement of Science, 

 at Cleveland, O., August 15-22, 1888, by Ormond Stone, Vice-President of 



the Section. 



