August 19, 1920] 



NATURE 



793 



< Im .weather-boarding and two Army huts converted 

 into permanent bungalows. With regard to the latter 

 exp)eriment, results show that no economy is effected 

 by using these huts. Another cottage has walls of 

 clay and gravel, while two single and one pair of 

 cottages are being erected in pis^-de-terre. One of 

 the single pis^ cottages is now being roofed — this is 

 the first two-storied pisd house erected in England. 



Pis^-de-terre walls are built by ramming nearly dry 

 soil between movable shutters arranged as a tem- 

 porarv mould. The method was known in England 

 a century ago, but had fallen into disuse, and a large 

 number of investigations have been carried out to 

 determine the best lines for its revival. All soils are 

 not suitable for pis6 work, for not only must the 

 particles cohere firmly when rammed and dried, but 

 also there must be no excessive shrinkage in the 

 drying process. Calcium carbonate helps to reduce 

 shrinkage, while organic constituents are particularly 

 liable to shrinkage, and therefore weaken coherence 

 in the soil as a whole. The amount of water present 

 in the soil at the time of use is an all-important 

 factor. Generally speaking, this water should be 

 between 7 per cent, and 14 per cent, of the weight 

 of the dried earth. The most suitable method of 

 shuttering and the best form of rammer have been 

 decided, while experiments are also being made to 

 find the most satisfactory material andl method 

 for rendering the exterior face of the wall. Pis6 

 building can be carried out in the winter if 

 there is sufficient protection from severe weather, 

 but consideration of the expenses involved in providing 

 tarpaulins, screens, etc., makes it evident that it is 

 not sound economv to undertake pis^ construction 

 in the winter months. When building in pis^ the 

 foundations have to be of brick or concrete ; the 

 pis^ work mav be started only at about 9 in. to i ft. 

 above the ground-level. This Is an important factor 

 in the consideration of the cost of pis^ building, 

 which, however, will probablv prove to be a con- 

 siderably cheaper process than building in brick. 



Cotton Growing. 



'X*HE Empire Cotton Growing Committee of the 

 -*■ Board of Trade, which presented its first report 

 on cotton growing in the British Empire in January 

 last (N.\TURE, February 26 and March 25), has now 

 published a note on "Future Organisation," which 

 may be regarded as an appendix to the report, \yhile 

 it is merely indicative of the trend of the Com- 

 mittee's ideas, in that such organisation is subject to 

 the appointment of the director and his staff, it makes 

 the situation more definite by estimating the probable 

 ixpenditure upon the various branches of work con- 

 templated. 



As in the case of the original report, all the 

 organisation proposed is for common service, since 

 the expenditure can bring no direct return, but it 

 should, in the Committee's opinion, indirectly bring 

 about an increase in the cotton supplies. The Com- 

 mittee concludes that in order to carrv out the work 

 adequately an annual sum of approximately 20o,oooZ. 

 ought to be assured. This amount may apjjear large 

 until we remember that cotton to the value of about 

 50.000,000?. is imported into this country annually. 



The note sketches the proposals for finance and 

 superior organisation, executive work, and the central 

 office; for staff abroad; for supplementing staffs of 

 agricultural departments oversea, and pioneering; for 

 education and information ; and for commercial 

 handling. In the last case the setting up of semi- 

 commercial experimental enterorises is excluded from 



the scope of the note. Amongst these headings the 

 Committee proposes an initial expenditure of 2o,oooi. 

 per annum upon its own research station abroad. It 

 also proposes to provide for a staff of ninety men, 

 including scientific workers and agricultural officers 

 of different grades, for the purpose of supplementing 

 local agricultural department staffs " after full con- 

 sultation with and on invitation by the local adminis- 

 tration." 



Under the heading of " Education " the Committee 

 makes proposals which take the initiative in a move 

 towards obtaining co-operation between all the plant- 

 using industries in order to increase the facilities for 

 training men in pure science, later to be of economic 

 value to the various agricultural services abroad. It 

 estimates that university staffs in this country should 

 be increased specially for this purpose by at least four 

 professorships, fifteen lectureships, and six adminis- 

 trative and technical lectureships, together with a 

 provision of twentv post-graduate studentships. The 

 annual cost is estimated at 27,000?., of which it is 

 su{?gested that thp rotton industry should contribute 

 i2,oocZ. as its share. 



Thermostatic Metal. 



THE British Thomson-Houston Co., Ltd., has sent 

 us specimens of a new bimetallic strip for use in 

 thermostatically controlled devices. The strip is pre- 

 pared by the permanent union over their entire length 

 of two metals with widely differing coefficients of 

 expansion. The union between the two component 

 metals is complete and durable, and the strip may be 

 bent, twisted, or hammered without causing the 

 separation of the metals at any point, and even on 

 heating the bond will not be broken so long as the 

 temperature remains below the melting point of the 

 softer of the two metals. Owing to this per- 

 manency of union the metal can Ix^ formed into any 

 desired shape, annealed after formation, and safely 

 employed at anv temperature below 500° F. The 

 component metals do not corrode under ordinary 

 conditions, and mav be used in any reasonable situa- 

 tion without fear of deterioration or change in 

 ooeratintr characteristics. The amount of deflection 

 obtained is alwavs the same in a strip of given length 

 and thickness for a given temperature chanjje. and 

 consequentlv the strip provides a trustworthy basis 

 for the operation of anv 'thermostatic device, and may 

 be emoloved for work of hieh precision. The deflec- 

 tion' due' to temperature change varies inversely as 

 the thickness, directlv as the square of the length, and 

 directly as the temperature change. With a strip 

 .' in. lonft, o-^i in. wide, and 003 in. thick the^deflec- 

 tion obtained for a temperature change of 100° F. is 

 about o :;7 in. The force exerted varies as the square 

 of th*- numb'^r of decrees of temperature change and as 

 the square of the thickness, and directlv as the width, 

 and is not affected bv chances of length. For a strip 

 of the '^ipif^ns'ons above-mentioned the force exerted 

 for Too° F. chan??e of temperature is about 3 oz. 

 weight, whereas for a strip of the same dimensions 

 but 01 in. thick the force exerted is about_ 24 oz. 

 weight. To produce a permanent set in a strio 4. in. 

 long-, 0-31 in. wide, and oot in. thick a force of about 

 7 oz.' weight would be required. The metal is manu- 

 factured in standard sizes ranging from ocwi, in. to 

 n-2.1^ in. in widths uo to 6 in. and leneths up to if^ in. 

 It can, however, generally be supplied cut to widths 

 and lengths to suit the purchaser, and in special cnses 

 thermostatic metal parts mav be completely formed to 

 the purchaser's specifications. 



NO. 2651, VOL. 105] 



