NA TURE 



[August 19, 1909 



surface, while the inner surface, which is inclined and 

 plane in one direction, serves to reflect the light that 

 enters the system down the axis of the vertical tube that 

 carries the lens at its upper part. A reflecting prism 

 enables a horizontal eye-piece to be used. The lens has 

 already been approved by the Admiralty for use in the 

 conning towers of submarines. A photograph taken by it 

 gives a well-defined annular picture of the view as seen 

 in every direction around it. 



We have received a copy of a paper, by Mr. Louis 

 Derr, on a photographic study of Mayer's floating magnets 

 (Proceedings of the American Academy of Arts and 

 Sciences, vol. xliv.. No. 19, May). Although it is now 

 recognised that inferences made in regard to the structure 

 of matter from the exact behaviour of such floating 

 systems must be received with caution, yet the groupings 

 obtained are so suggestive that any fresh study of them 

 is of interest. Mr. Derr has endeavoured to obtain a 



Mr. Irwin G. Priest. The method depends on the 

 measurement of the diameter of one of the circular rings 

 of the Fabry-Perot interferometer when seen through the 

 lens by reflected homogeneous light. If viewed without 

 the intervention of the lens, the ring system is localised 

 at infinity, and with the lens a real image will be formed 

 in the focal plane of the lens. The outer edges of the 

 rings are sharp, and admit of accurate measurement of 

 diameters by means of a micrometer. From two measure- 

 ments of the diameters of the same ring with different 

 distances between the interference plates, the focal length 

 of the lens can be found with an accuracy of about half 

 per cent., and if with the interference plates a fixed 

 distance apart the constant of the apparatus be determined 

 once for all, a single measurement of the diameter of a 

 ring is all that is necessarv. 



The four numbers of the Journal of the Roval Society 

 of Arts issued in July contain the Cantor lectures on the 



^2 3 45 678 







public supply of electric power delivered 

 by Mr. G. L. Addenbrooke before the 

 society in January and February last. 

 After describing with great clearness the 

 present position of affairs, the lecturer 

 points out in what directions we may 

 reasonably look- for improvements in the 

 future. Whatever the improvements in 

 prime movers, he believes that electrical 



flSSl wSOn IIBm flmn fiSSu j^TBI f^^W factories. This power will, when gas 



^■plr \^^ \SS^ ^9S^ ^BS^ \jgfF S^ff^ engines and producers have been rendered 



more suitable and trustworthy, be pro- 

 duced by internal-combustion engines of 

 the four- or si.x-cylinder type. He con- 

 siders that the time now required to obtain 

 a provisional order in the case of a power 

 scheme should be greatly reduced, and 

 wishes to direct the attention of legislators 

 to the importance of facilitating the supply 

 of cheap electric power. 



None of the formulae in common use 

 connecting the pressure and temperature of 

 saturated steam can be regarded as satis- 

 factory. Any empirical formula should 

 cover the whole range, give a fair repre- 

 sentation of those experimental results 

 which probably approximate most closely 

 to the true relation, and should be easy 

 of calculation. Mr. S. Godbeer, in an 

 article in Engineering for August 6, pre- 

 niuch more complete series, which he has photographed sents a new formula which should be useful. For various 

 in order to show the progression from one form to another reasons, a table given by Holborn in iqoS, ranging from 0° 

 more clearly than can be done by tables. The magnets to 205° C., together with experiments by Cailletet covering 

 were clear J-inch steel balls, floated on freshly filtered a range up to the critical temperature, have been used as 

 mercury, as described by Prof. R. W. Wood, but initially data. A few irregularities have been corrected, and the 



Photographs of systems of flcating magnets. 



magnetised by placing them one by one between the poles 

 of an electromagnet. In the plate (part of which we 

 reproduce) the balls as photographed have been connected 

 together afterwards by lines, in order to bring out more 

 obviously to the eye the formation in concentric groups. 

 Many of the forms differ from those calculated by Sir 

 J. J. Thomson ; since the stability depends upon the exact 

 law of force between the magnets — and in the experi- 

 ments this is different from the law assumed in the 

 calculations — the divergence is not to be wondered at. 



The May number of the Bulletin of the Bureau of 

 Standards contains a description of a new method of deter- 



formula is as follows : — 



log/ = '3'9 if + 226) (M^229g2-_ 



30-203, 



19202S (z + iioS) (^ + 329) 

 where p is the pressure in millimetres of mercury and t is 

 the temperature centigrade. If pressure and temperature 

 curves be drawn for the experiments of Cailletet, Battelli, 

 and Knipp, it becomes evident that there is a sudden dis- 

 turbance in the general trend of the curve between 240° 

 and 270° C, and the author suggests that further experi- 

 ments in this region of temperature would be interesting. 



Metal-cutting by means of oxygen is now finding a 

 place among- engineering operations, and several interesting 

 mining the focal length of a converging lens system, by ! applications are given in Engineering for August 6. The 

 VOL. 81] 



NO. 2077, 



