July 15, 1922] 



NA TURE 



93 



but differing in volume by ioo c.c. The density of the 

 liquid is thus obtained directly by weighing and is 

 compared with the hydrometer under investigation. 

 The balance is of special construction and is provided 

 with inertia bobs at the ends of the arms to counteract 

 the damping due to the movement of the plummets 

 through the liquid. Other exhibits in the Metrology 

 Department included a series of instruments for the 

 precision measurement of engineers' gauges and a 

 vertical interference apparatus for testing the flatness 

 of surfaces, line standards and comparators. 



In the Froude National Tank experiments to 

 determine the resistance of a ship form in artificially 

 created waves, and the method of taking con- 

 tinuous records of resistance, pitching angle and 

 pitching period were demonstrated. The object of 

 this work is to obtain data as to the loss of speed of 

 different designs of ships under service conditions. 

 It is interesting to note in this connexion that 

 observations of full size ships have been taken by 

 members of the staff in voyages across the Atlantic 

 in three tvpes of vessels, liners, cargo steamers, 

 and oil tankers. Apparatus was also shown for deter- 

 mining forces on a ship's rudder, the manoeuvring 

 power of a ship's form, and the resistance of a seaplane 

 model on the surface of the water. 



Many interesting exhibits were on view in the 

 various sections of the Electricity Department. The 

 Photometry Division showed a method of determin- 

 ing the spectral distribution of energy in arcs having 

 cores of different materials, and of measuring the 

 transmission ratios of coloured glasses intended as 

 standards for ships' navigation lights. 



The Alternating Current Section demonstrated the 



speed regulation of a D.C. motor by means of a rela- 

 tively small phonic motor directly coupled to it. 

 The Direct Current Section showed apparatus for 

 experiments on moulded insulators and other insulat- 

 ing materials, tests on buried cables and on energy 

 losses in a 3-core cable with three-phase current. 



In the Standards Section, an air gap for dielectric 

 tests on mica and thin sheet materials was shown. 

 This consists of very accurately flat steel plates 12 

 cms. in diameter, separated by distance pieces of 

 quartz, so as to give an accurately parallel gap. The 

 apparatus can be taken apart and the gap reproduced 

 to within o-oooi mm. In connexion with the above- 

 mentioned apparatus, a machine of the optical lever 

 type has been evolved for measuring the thickness 

 from point to point of sheets of mica or other thin 

 material. 



A standard multivibrator apparatus for radio- 

 frequencies was shown by the same section. In this 

 apparatus a wave with a sharp peak is produced, 

 having a frequency of 1000 per sec. From this, by 

 the help of a highly resonant circuit, every harmonic 

 up to the hundredth may be picked out, thus provid- 

 ing a series of accurately spaced radio-frequencies. 

 The fundamental is kept constant to 1 part in 100,000 

 by a tuning-fork control. A second multivibrator, 

 which can be controlled from the first one, has a funda- 

 mental of 30,000 per second and gives a further series 

 up to 1,000,000 per second. 



In the Wireless Section, directional measurements 

 of spark and continuous wave stations were shown, 

 the photographic reception of signals on a string 

 galvanometer, and a new type of thermo-j unction 

 ammeter for high frequency. 



Agricultural Research in Great Britain. 



THE "assistant principal" at the Ministry of Agri- 

 culture, Mr. V. E. Wilkins, has prepared a 

 valuable pamphlet, 1 which gives a useful account 

 of the various forms of agricultural research that are 

 being supported financially by the State. As is well 

 known, the Ministry decided to concentrate research 

 at definite institutions ; Rothamsted is concerned 

 with plant nutrition, soil problems, and plant 

 pathology ; Cambridge has entrusted to it plant 

 and animal breeding, and animal nutrition ; Long 

 Ashton, a branch of the University of Bristol, deals 

 with fruit growing and preserving ; plant physiology 

 is dealt with at the research institute attached to 

 the Imperial College of Science ; dairying at Reading ; 

 animal pathology at the Royal Veterinary College ; 

 agricultural zoology at Birmingham ; helminthology 

 at the London School of Tropical Medicine ; agri- 

 cultural economics in Oxford ; plant breeding, with 

 particular reference to Wales, at Aberystwyth ; fruit 

 growing and hops at East Mailing ; and nursery 

 and market gardening at Cheshunt. Besides these 

 research institutes and stations the Ministry has set 

 up a svstem of advisory centres from which informa- 

 tion in respect of specific subjects is disseminated by 

 advisory officers who also, in many cases, undertake 

 a certain amount of research. 



(a) The Soil and its Effect on Plant Growth. — This 

 fundamental subject has been entrusted to the 

 Rothamsted Experimental Station, which is con- 

 cerned, among other things, with the examination 

 of the soil in its relation to bacteria and protozoa, 

 and an account is given of the arduous nature of 

 the research along these lines. The nitrification of 



1 " Ministry of Agriculture and Fisheries. Agricultural Research and 

 the Farmer: A Record of Recent Achievement." Bv V. E. Wilkins. Pp. 

 168. (London : H.M. Stationery Office, 1922.) 2s. 6d. net. 



organic nitrogen alone has demanded the services 

 of eight research workers, who in many cases have 

 worked nigfit- and day-shifts. An interesting form 

 of investigation undertaken at this station is con- 

 cerned with the production of artificial farmyard 

 manure. During the later stages of the war, and 

 subsequently, until the agricultural policy of the 

 Government was altered, there was a prospect of a 

 superabundance of straw, more, in fact, than could 

 be dealt with as food and litter by farm animals. 

 The Rothamsted investigators set about devising a 

 means of converting this straw directly into farmyard 

 manure, and the results are most encouraging, 

 although now, with the reduced area of tillage land, 

 the necessity for such conversion is no longer pressing. 



At the same station much work has been done on 

 the influence of colloids on the water-content of soil, 

 and on the mechanical operations concerned with 

 tillage. Most ingenious electrical methods are also 

 being exploited to determine the relation between 

 soil acidity and crop production, and the list of 

 publications that have been issued from Rothamsted 

 during 1920 and 1921 shows the extraordinarily 

 varied character of the work being conducted at this 

 famous station. 



(b) Plant Breeding. — The problems that are being 

 investigated along this line are concerned with the 

 baking qualities or strength of English wheat, with 

 the production of cereals possessed of a straw stiff 

 enough to stand up under adverse circumstances, 

 with immunity to disease, with the increase of the 

 number of grains in the ear, with the production of 

 hardier varieties of winter oats, with the relationship 

 of nitrogen in barley grain to the quality of the 

 produce, and with the production of potatoes immune 

 to wart disease. These problems are being dealt 



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