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NA TURE 



[August 26, 1922 



able for a hot country, this amount having actually 

 been exceeded in England. The mean annual evapo- 

 ration exceeds the rainfall by i inch — a balance fairly 

 typical of this type of climate. Rain falls on 136 days, 

 and thunderstorms occur on as many as 68 days. The 

 mean annual humidity is 78-3 per cent., with little 

 monthly variation, whilst the vapour tension follows 

 closely the monthly mean temperature. The general 

 subject of the geographical and seasonal variation of 

 absolute humidity is deserving of more study, but it 

 seems almost inevitable that, except perhaps in arid 

 continental interiors away from sources of vapour 

 supply, the dominating factor controlling the varia- 

 tions must be temperature. 



Current Meters. — A pamphlet by Dr. M. A. 

 Hogan on " Current Meters for use in River Gauging " 

 has been issued by the Department of Scientific and 

 Industrial Research for the committee on gauging 

 rivers and tidal currents (London : H.M. Stationery 

 Office, 15. 6d. net). The pamphlet gives in vi +33 pp. 

 a useful summary of information relating to the con- 

 ditions affecting the design and use of current meters. 

 Several meters in common use are described, and 

 sections are devoted to a discussion of the effects of 

 oblique and varying velocities, and also of turbulence. 

 Theoretically, the best type of meter is the screw 

 type fixed on a rod, with blades or guard rings 

 specially designed for the good measurement of oblique 

 velocities. But the main disadvantages attached to 

 this type of meter concern the practical details, such 

 as the supporting of the rod during measurement, 

 and in this respect it is concluded that the cup-type 

 meter, being supported by a cable, is more easily 

 manipulated. The results of tests of meters in 

 turbulent water and also for low velocities are collated. 

 The author concludes that in favourable circum- 

 stances most meters will give results of sufficient 

 accuracy for river gauging, but that when the condi- 

 tions are unfavourable, as when turbulence is present, 

 the crude results given by a single meter of any 

 existing type are likely to be considerably in error. 

 The most important effects of turbulence arise through 

 the variations in direction of velocity rather than in 

 magnitude. With the cup type of meter turbulence 

 causes over-registration, while with the screw-type 

 meter it causes under-registration, so that a combina- 

 tion of the two types can be used to measure turbulent 

 flow. 



Telescopes vzksus Field Glasses. — Although 

 almost every text -book which deals with optical 

 instruments describes the astronomical or Kepler 

 and the Galilean telescopes, and explains how the 

 former may be converted into an erecting telescope 

 like the latter, few of them direct attention to the 

 decrease of luminosity of the field due to the erecting 

 devices, and still fewer give anv information as to 

 the relative extents of the fields of view of the two 

 instruments. It is. however, on account of the small 

 field of the Galilean instrument that it is no longer 

 used in astronomical observatories, and some ex- 

 planation of this restriction of the field should be 

 given in any modern text-book on optics. To fill 

 the gap in present-day text-books Dr. A. Sonnefeld, 

 of Jena, contributes an article on the subject to the 

 issue of />i, Nalurwissenschaften fur fuly 28. From 

 the point of view of the instrument-maker wishing 

 to widen the field, the subject has been treated 

 recently by .Messrs. Hughes and Everitt, Transactions 

 ol Hi'- Optical Society, 22, p. 15, and bv Mr. T. 

 Smith in the same volume, p. 84. 



Spectra on the Quantum-Orbit Theory. — This 

 theory has been so successful in describing the known 

 facts as to the spectra of elements constituted of a 

 single nucleus and a single electron, that there is 

 considerable justification in the hope that it may 



NO. 2756, VOL. Iio] 



help to explain the spectra of more complicated 

 elements. An approximate solution of the larger 

 problem has been given by Sommerfeld in his 

 " Atombau und Spcktrallinien, " but there are assump- 

 tions made by him as to actual spectral observations 

 which l'n if. Hicks points out in a paper on the subject 

 in the August issue of the Philosophical Magazine 

 are not justified. In the first instance the expression 

 for the frequencies of the lines of a series which 

 results from taking the atom to consist of a central 

 nucleus, a ring of equally spaced electrons and out- 

 side it a single electron obeying the quantum laws, 

 is not general enough to cover all known series. In 

 the second instance observation lends no support to 

 Sommerfeld's deduction that the different types of 

 spectra are obtained by giving one of his constants 

 successive integral values. Lastly, many small and 

 often irrelevant points are referred to as striking 

 confirmations of the theory, which, when examined 

 more carefully, are found to afford no support to it. 



IIixosamines and Mucins. — Dr. P. A. Levene, 

 in Monograph No. 18 of the Rockefeller Institute, 

 gives the interesting results of his work on constitu- 

 tion of these substances. He shows that the nitrogen 

 in the amino-sugars is present as a primary amino 

 group, in analogy with the other glucosides. A large 

 number of derivatives are described and many of 

 the hexosamines were synthesised. As regards the 

 mucins, it is shown that there are two groups, from 

 one of which chondroitin-sulphuric acid is obtained, 

 from the other mucoitin-sulphuric acid. They differ 

 in the fact that the former, obtained from cartilage, 

 aorta, and sclerotic, contains the amino-hexose, 

 chondrosamine ; the latter, obtained from umbilical 

 cord, vitreous humour, and cornea, contains in its 

 place chitosamine. This latter amino-sugar is some- 

 times called glucosamine. The chitosaminic acid 

 derived from it turns out to be 2-amino-mannonic 

 acid, whereas chondrosaminic acid is 2-amino-talonic 

 acid Apart from this difference, the two conjugated 

 sulphuric acids are similar and consist of the amino- 

 hexose, glucuronic, acetic, and sulphuric acids in 

 equi-molecular proportions. The amino-sugar . and 

 glucuronic acid are combined as a disaccharide. The 

 acetyl group is linked to the amino group. Finally 

 two molecules of the whole are joined as glucoside 

 by their glucuronic acids. There appears to be a 

 slight difference in the place of attachment of the 

 sulphuric acid to the amino-sugar. 



The Composition of Phosphorite. — Mr. A. F. 

 Rogers (Amer. Journ. Sci., vol. 203, p. 269, April 

 1922) writes of " Collophane, a much neglected 

 mineral," and shows that this name deserves a more 

 general recognition. It was given by Fridolin Sand- 

 berger in 1870 to an amorphous calcium phosphate and 

 carbonate, with some water, from Sombrero. Sand- 

 berger eliminated the carbonate ; but the material 

 has been shown by Lacroix to consist almost exactlv 

 of 3Ca 3 (POj) 2 .CaCO a . Dahllite is clearly its crystal- 

 lised representative. The author regards the varia- 

 tions in composition as due to solid solution, calcium 

 fluoride and sulphate being sometimes concerned. 

 Collophane becomes important if we recognise that 

 a large part of the ordinary phosphorite of commerce, 

 rock-phosphate and the rest, consists of this material. 

 When the author states that, " like most other 

 amorphous minerals, it is of colloidal origin," he 

 probably means that it once was in a colloidal state. 

 Dahllite has, of course, been previously recognised as 

 forming the concretions of phosphorite in Podolia, 

 which show internal radial crystallisation. Carbon 

 dioxide varying from 2-40 to 11-72 per cent, is recorded 

 by J. Samojlov (Comple rendu Congr. internat. geol., 

 I2 mo session, Canada, 1913, p. 850) as a constituent 

 of the widely spread Jurassic and Cretaceous phos- 

 phorites of Russia. 



