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NA TURE 



[April 15, 1922 



west, and the direction is from south-west or west- 

 south-west in the afternoon. The land breezes at 

 night blow from north-west or north. Sea breezes 

 generally blow more strongly than land breezes. A 

 normal sea breeze at Barcelona corresponds with 4 

 or 5 on the Beaufort wind-scale, whilst at Montpellier 

 the breeze is rather lighter, not exceeding force 3 or 4. 

 Land and sea breezes are said to be essentially surface 

 currents and they are supplemented by a return 

 circulation in high atmosphere. These points have 

 been tested by pilot balloons and the results given are 

 decidedly instructive. 



United States Temperatures. — The U.S. 

 Monthly Weather Review for November 1921 has an 

 article on " Some Characteristics of United States 

 Temperatures " by Prof. Robert De C. Ward, of 

 Harvard University. The author has had access to 

 ihaps prepared by the U.S. Weather Bureau for the 

 new Atlas of American Agriculture. The tempera- 

 tures are not reduced to sea level. In the opinion 

 of the author the isothermal maps of the United 

 States will supersede all previous maps and will 

 for years to come remain the " standard set." Iso- 

 thermal lines are given for each 5° F., and those for 

 midwinter and midsummer run fairly smoothly and 

 symmetrically to the east of the Rocky Mountains, 

 but the effects of the Appalachian topography warp 

 the local irregularities of the lines. Over the western 

 plateau and mountain area, the isotherms are most 

 irregular, and it is there that the new charts, which 

 show actual temperatures, are so great an advance 

 on those previously drawn. The greatest differences 

 in temperature in different parts occur in the winter. 

 In January, going southwards the temperatures 

 increase about 2°-5 for each degree of latitude. Very 

 different conditions exist in midsummer, when the 

 distribution of temperature is far more uniform and 

 the difference of temperature for each degree of 

 latitude amounts only to about 1° F. Highest and 

 lowest " record " temperatures are given on separate 

 maps produced from the results at about 600 stations. 

 These extreme temperatures are of considerable 

 interest, and if they do not show the world's highest 

 and lowest readings, they give very valuable results. 

 In the United States, especially in the eastern parts, 

 very low temperatures commonly penetrate far to 

 the south into latitudes where the winters are 

 distinctly mild. 



Submarine Periscopes. — The current number of 

 the Transactions of the Optical Society contains a 

 paper by Dr. Alexander Gleichen on the path of rays 

 in periscopes having an inverting system comprising 

 two separated lenses, in which results are given of 

 a theoretical investigation carried out by the author 

 for Messrs. C. P. Goerz of Berlin-Friedenau. The 

 paper is devoted generally to the design of periscopes 

 as regards the best arrangement and sizes of the 

 various optical parts involved, with the object of 

 making the best possible use of the available space, 

 which in the case of submarine periscopes particularly 

 is very limited. The characteristics of these instru- 

 ments are their. comparatively great length and small 

 diameter. In particular it is shown how the magni- 

 fication, the field of view, and the illumination in the 

 centre and at the edge of the field of view, depend 

 on the length and diameter of the instrument, in 

 order to derive therefrom the most advantageous 

 optical arrangement. A feature of submarine peri- 

 scopes which limits the design to an important extent 

 is the reduction of the diameter of the upper portion 

 which may be extended above the surface. Formulae 

 for the determination of the path of the rays in peri- 

 scopes of this type are given and also a brief statement 

 regarding the external form of the submarine periscope. 



NO. 2737, VOL. 109] 



Crystal Structure of Common Elements. — 

 In a paper published in the Journal of the Franklin 

 Institute for February under this title, A. W. Hull 

 gives a very useful summary of the results of X-ray 

 crystal analysis. The methods of analysis which were 

 first developed (analysis by means of a Laue photo- 

 graph, or with the X-ray spectrometer) can be used 

 only if a single homogeneous crystal of appreciable 

 dimensions is available. It was impossible to 

 examine the structure of a large number of the 

 elements and simple compounds, which could be ob- 

 tained only in a finely divided crystalline form, 

 until the " powder method " of analysis was developed 

 by Debye and Scherrer, and by Hull. A mass of 

 powdered crystalline material is placed in the path 

 of a narrow beam of monochromatic X-rays and 

 the crystal structure is deduced from the manner in 

 which the rays are diffracted. The technique of the 

 powder method of analysis has been brought to a very 

 high degree of perfection by Hull, who has examined 

 a large number of elements and compounds. We 

 now know the crystalline structure of thirty-five of 

 the elements, twenty-nine having been determined 

 by Hull himself. A number of binary compounds 

 have recently been analysed by Davey, using the 

 Debye - Hull method. A list of all crystals whose 

 structures have been completely determined is given 

 by Hull. The powder method of analysis will cer- 

 tainly become a most powerful means of studying the 

 structure of solid bodies. It can be applied to any 

 crystalline substance, and in addition, it can be used 

 to analyse constituents of a mixture of crystalline 

 bodies, so that to the metallurgist it will be of the 

 highest importance. The paper concludes with an 

 interesting discussion of " atomic diameters." 



The Lighting of Public Buildings. — An interest- 

 ing paper on this subject was read by Messrs. E. H. 

 Rayner, J. W. T. Walsh, and H. Buckley of the 

 National Physical Laboratory, at the meeting of the 

 Illuminating Engineering Society on March 28. The 

 paper was devoted mainly to experiments undertaken 

 in co-operation with H.M. Office of Works, one note- 

 worthy installation being the semi-indirect lighting 

 in the new Pensions Offices at Acton. The tabulated 

 data show that the level of illumination provided 

 in public buildings has arisen considerably during 

 recent years, values from 3 to 4-5 foot-candles now 

 being general. Another section of the paper was 

 devoted to some experiments on the lighting of picture 

 galleries, where the avoidance of reflected images in 

 the glass on pictures is a difficult problem. Diagrams 

 were presented showing a new arrangement of the 

 skvlights which, while occasioning some loss in light, 

 seems to give a much more satisfactory distribution 

 of illumination. The authors also described a special 

 building erected at the National Physical Laboratory 

 for the purpose of experiments on illumination, 

 which has some interesting features. Following the 

 presentation of the paper Capt. J. W'. Liberty, 

 Public Lighting Inspector to the City of London, 

 showed a number of photographs of recent lighting 

 installations in certain public buildings, where 

 architectural and decorative considerations play an 

 important part. Amongst such interiors may be 

 mentioned the Guildhall, the Marylebone Town Hall, 

 and the new Port of London building. Some of these 

 interiors, notably those panelled in very dark walnut, 

 present interesting lighting problems. The arrange- 

 ment adopted in the main office at the Port of London 

 building, where gas-filled lamps giving 20,000 c.p. are 

 assembled in a vast white dome, is particularly 

 striking, and it is hoped to present fuller details of this 

 installation when completed. 



