December 29, 192 1] 



NATURE 



577 



will give a lecture on "The Johnsen-Rahbek Electro- 

 static Telephone and its Predecessors " at 4 p.m. on 

 January 4 and at 8 p.m. on January 5. Mr. F. 

 Harrison Glew will give a lecture on '" Radium : Its 

 Application in Peace and War" at 8 p.m. on 

 January 4. Other discourses are being arranged. We 

 understand that invitations have been given to the 

 Institution of Electrical Engineers, the Institution of 

 Mechanical Engineers, the Chemical Society, the 

 Faraday Society, the Wireless Society of London, and 

 the Rontgen Society. Admission in all cases will be 

 bv ticket only, and therefore members of the societies 

 just mentioned desiring to attend the exhibition should 

 apply to the secretary of the society to which they 

 belong. Others interested should apply direct to Mr. 

 V. E. Smith, hon. secretary of the Physical Society, 

 Admiralty Research Laboratory, Teddington, S.W. 



A METHOD, which is to be tried at the London Air 

 Station, Croydon, of finding cloud heights at night by 

 means of a searchlight was referred to in the Times of 

 December 19. The method is, however, not new. At 

 South Farnborough observations were made in 19 16 in 

 connection with a searchlight station about two miles 

 distant from which a vertical beam was projected. The 

 spot of light on the clouds was first observed with a 

 theodolite, but it w-as often diflficult to locate the 

 brightest part in the telescope. A vertical scale was 

 therefore set up against which the light was observed, 

 the eye being placed in a fixed position. If observations 

 are always made from one place the scale may be 

 graduated to read heights directly ; it should be black 

 with white graduations. Heights may be determined 

 from lights of distant towns reflected on clouds. The 

 light from London may be seen fifty miles away on 

 very many moonless nights, and may occasionally be 

 photographed, but, as street-lighting is not always very 

 actinic, colour-sensitive plates are required at such dis- 

 tances, and very long exposures, four or five hours with 

 a lens working at f/4-5. The best conditions occur 

 with alto-cumulus clouds at ten to fifteen thousand 

 feet, but a faint glare extending to very considerable 

 altitudes may sometimes be seen on {perfectly cloud- 

 less nights. 



As a preliminary to the proposed standardisation 

 throughout the commerce and industries of France 

 the Government considered the question of the unifica- 

 tion of the methods of measurement at the time in 

 use, and issued in 1919 regulations for the intro- 

 duction of certain new units in the metre-ton-second 

 and centimetre-gram-second sj'stems. The text of 

 these regulations was reproduced in the Bulletin of 

 the Societe d'Encouragement pour I'lndustrie 

 nationale for November-December, 1919. In the issue 

 of the bulletin for October last the unit of density, 

 that of a body of mass one ton and of volume one 

 metre cube is explained and its relation to older 

 units set forth. The available methods of deter- 

 mining density are described and the errors liable to 

 occur pointed out. As a result of the discussion 

 methods of determination which depend on the balance 

 are recommended instead of those depending on 

 NO. 2722, VOL. 108] 



hydrometers. It is further recommended that to avoid 

 all confusion as to the unitg used the terms "specific 

 mass " be reserved for the density in the metre-ton 

 or centimetre-gram units, and be used in all com- 

 mercial and industrial statements and tables. The 

 Baume degree is to be discarded as obscure and 

 indefinite, and therefore prejudicial to French com- 

 merce. 



So much attention has been directed of late years 

 to the scientific work of Leonardo da Vinci that 

 any discoveries concerning him are bound to interest 

 those occupied with the study of the history 

 of science. Prof. De Toni has been engaged 

 on a biographical sketch of the physicist Gio- 

 vanni Battista Venturi (1746-1822), whose " Essai 

 sur les ouvrages physico-mathematiques de Leonardo 

 da Vinci " (Paris, 1797) was among the first 

 works to emphasise the importance of Leonardo's 

 ] scientific position. In the course of investigating the 

 remains of the correspondence between Venturi and 

 other men of science of his time. Prof. De Toni found 

 in the Reggio-Emilia Library three large volumes 

 of transcripts and digests which Venturi had copied 

 from the Leonardo manuscripts in Paris. It soon 

 became evident that these transcripts had been made 

 between 1796 and 1797 before the manuscripts, 

 generally known as A, B, and E, had had torn from 

 them a number of sheets which were afterwards dis- 

 posed of and man)' of which were believed to be 

 entirely lost. The manuscript A consisted of 114 

 sheets and has now only 63, while E consisted of 

 96 sheets and has now only 80. Much of this material 

 has now been recovered by Prof. De Toni, and con- 

 sists largely of descriptions of mechanical devices and 

 fortifications, together with biographical and political 

 notes. Prof. De Toni has already communicated an 

 outline of his results to the Comptes rendus of the 

 Paris Academy of Sciences (vol. 173, No. 15, October 

 10, 192 1, pp. 618-20). Further more detailed com- 

 munications by him will appear in the publications of 

 the Instituto Reale of Florence. 



At a joint meeting of the Royal Geographical 

 Society and the Alpine Club on December 20 Col. 

 Howard Bury gave an account of the work of the 

 Mount Everest Expedition. He was followed by Mr. 

 Mallory, who is again to take part in next year's 

 assault on the summit. Mr. Mallory described the 

 conditions which the climber w^ill probably have to 

 face and discussed the possibilities of success. The 

 summit of the mountain is formed by three aretes. 

 The faces between them are quite impracticable, and 

 the only possible line of advance seems to be to reach 

 the upper part of the north-east arete from the north. 

 Whether it is possible on account of reduced atmo- 

 spheric pressure to reach the summit is another 

 matter, and on this point Mr. Mallory spoke with 

 caution. He believed it possible for unladen moun- 

 taineers to reach 26,000 ft., and did not think the 

 last 3000 ft. would be so much more tiring as to exclude 

 the possibility of reaching the summit. The higher 

 one goes the less is the effect of any given rise, 

 since the atmospheric pressure diminishes less rapidly 



