172 



NATURE 



[October 15, 19 14 



in my paper {Phil. Mag., December, 19 13) would 

 be capable of emitting similar series. This atom can 

 be shortly described as a rotating Thomson atom, 

 capable of executing elastic vibrations. If the nega- 

 tive electron is constrained to remain on the surface 

 of a sphere of radius r within the atom (radius a), it 

 will have a frequency v given b\' the formula 

 v = A— N(f/a)^, where A depends on the boundary 

 conditions, and the homogeneous radiation emitted 

 will be of amount hv, where h is the quantum 

 constant. 



Reasons are given in the paper for showing that 

 if the atom were executing radial vibrations the 

 electron would be imprisoned on a nodal sphere and 

 usually on the smallest nodal sphere of a given 

 mode. Thus if the radii of the nodal spheres were 

 given by the formula r = a{n/m), where n and m 

 are integers (n<w), then in the formula for r we 

 take for a series n=i and m = 3, 4, 5, ... . For 

 the enhanced spectra it is only necessary to suppose 

 that the electrons may be on the second nodal 

 sphere of each mode, i.e. putting n = 2. 



Arthur W. Conway. 



Elsinore, Dalkey, Co. Dublin, October i. 



Theodore Schwann and the University of Louvain. 



It might not be altogether inappropriate at this 

 time when the world of true culture is grieving in- 

 consolably over the destruction of the University of 

 Louvain, to be reminded that the originator of the 

 famous cell-theory, Theodore Schwann (1810-82), was 

 for nine years a professor at that University. To 

 biologists this fact is probably the most interesting 

 association which the mention of Louvain arouses. 

 Schwann went to Louvain as professor of anatomy in 

 1838, and left it for a chair at Liege in 1847. It was 

 in 1839 that he gave to the world the cell-theory in a 

 treatise, "Microscopical Researches into the Accord- 

 ance in the Structure and Growth of Animals and 

 Plants," as the title runs in the translation made by 

 Henry Smith in 1847 for the Sydenham Society. 



This great generalisation was made public, there- 

 fore, while Schwann was in his chair at Louvain. It 

 is perhaps not so well known that after he had been 

 seven years at L'lhge, he invented a self-contained 

 respiration apparatus in which carbon dioxide was 

 absorbed and oxygen liberated. It was the precursor 

 of the rescue apparatus so much used in coal mines at 

 the present day, for Hales's apparatus (1726) was too 

 crude to have been of any real value. 



It is interesting to know now that, through a crime 

 no expiation can ever atone, the University of Louvain is 

 no more than a memory, its name will be associated 

 with one of the most far-reaching generalisations ever 

 made in the nature of living things — the cell-theory of 

 Schwann of Louvain. D. Fraser Harris. 



Dalhousie University, Halifax, N.S., 

 September 18. 



Filtering Power of Sand. 



To those who wish to repeat the experiments on 

 the filtering power of sand, mentioned by Prof. 

 Trouton at the recent meeting of the British Associa- 

 tion, I would strongly recommend a solution of the 

 aniline colour known as "Nachtblau." A strongly 

 coloured solution of this substance passed through 

 Fontainebleau sand issues from it absolutelv colour- 

 less for a much longer time than does that of potassic 

 permanganate. C. J. Watson. 



' The Midland Institute, Birmingham, October i. 



NO. 2346, VOL. 94] 



FLIGHT OBSERVATIONS IN INDIA.^ 



VARIOUS theories have been proposed by 

 different *vriters to account for the fact that 

 birds are able, in certain countries, to remain 

 suspended or even rise in the air without any 

 apparent exertion and without flapping- their 

 wings. This action appears to have become 

 known as "soaring flight," notwithstanding the 

 fact that in two English dictionaries now before 

 us the verb " soar " is defined as meaning to rise 

 in the air, without any reference to the means 

 adopted. On the other hand, the action in ques- 

 tion does not necessarily imply rising, but it may 

 exist equally when a bii'd maintains the same 

 level for an indefinite time. We prefer to de- 

 scribe this action as "sailing flight." 



Now while writers innumerable have attempted 

 to offer explanations of this apparently paradoxical 

 phenomenon, very little has been done to obtain 

 systematic records, extending over long periods^ 

 of the conditions under which soaring or sailing 

 flight takes place. This is probably due to the 

 fact that in northern Europe, where most scien- 

 tific work is done, sailing flight rarely occurs. 

 During his residence at Agra, Dr. Hankin has 

 had specially favourable opportunities for observ- 

 ing large birds in sailing flight, and his present 

 record of observations should do much to syste- 

 matise our knowledge of the subject. 



The principal birds which figure in Dr. Hankin 's 

 observations are as follows : — 



Span Load in lb. 



. in feet. per square foot 



Cheel (Milvus govinda) 4 ... 055 



Scavenger {Neophron gingianus) 5 ... 087 

 Common Vulture {Pseudogyps 



bengalensis) 7 ... 1-13 



Black Vulture {Otogyps calvus) 65 ... 1-23 



Adjutant {Leptoptilus dubius) ... 9-1 1 ... 1-54 



Dr. Hankin distinguishes a number of different 

 sailing actions, some of them continuous, others 

 alternating with flappings of the wings. These 

 he designates by such names as ease circling, 

 flap circling, flap gliding, flex gliding. A large 

 portion of the book is occupied with illustrated 

 descriptions of the positions of the wings, tail, 

 and body in different kinds of flapping and sailing 

 flight (c/. Figs. I, 2, 3). 



The principal theories that have hitherto been 

 advanced attribute sailing flight to irregularities 

 in wind velocity (c/. Langley's "Internal Work 

 of the Wind ") or upward air currents (Maxim 

 and others). Dr. Hankin attempts to prove that 

 neither of these causes is sufficient to account for 

 the phenomena as they occur in India, and that 

 the explanation must be sought in some other 

 unknown cause. In particular he uses the term 

 " soarability " to designate the state of the atmo- 

 sphere when sailing flight is possible, and so far 

 as his observations tend to define when and under 

 what conditions this state exists, they constitute 

 a first step in the solution of the problem. 



Now Dr. Hankin observes that in fine weather 

 there is a definite time in the morning, varying" 



, 1 " Animal Flight," a Record of Observation. By Dr. E. H. Hankin. 

 . Pp. 405— Index. (London : Uiffe and Sons, Ltd., n.d.) Pfice i2j. td. neU 



