i\UGUST 14, 19 19] 



NATURE 



469 



the phase relationships between a number of 

 hydrophones distributed at regular intervals in 

 a straight line. It is obvious that in this case 

 sound-waves from a distant source arrive in phase 

 only when it is situated on the beam of the line 

 of hydrophones. By making use of a multiple 

 "compensator" the phases can be corrected for 

 all directions, and the bearing of the source read 

 off from the "compensator" when the observer 

 has determined the setting for maximum 

 intensity. 



One gratifying feature of the work on sub- 

 marine acoustics done during the war is the possi- 

 bility which it provides of rendering navigation 

 more safe in times of peace. Used in conjunction 

 with suitable sound signalling apparatus fitted to 

 vessels, and submarine bells moored near danger- 

 ous shoals and rocks, the improved hydrophones 

 developed for war service should greatly reduce 

 the dangers of collisions and shipwreck, due to 

 fog, etc. 



Already hydrographic surveys of the North Sea 

 are being carried out in which the position of 

 danger spots are located for charting purposes 

 by exploding depth charges and recording the 

 resulting disturbances at a number of hydro- 

 phones connected to land stations. This method 

 of submarine sound-ranging is by far the most 

 accurate method of locating such spots, and also 

 provides a means of enabling a ship at sea to 

 obtain its correct bearings. By dropping a bomb 

 hundreds of miles at sea, a ship can in a few 

 minutes communicate its position to the nearest 

 shore station and receive this information itself 

 ])ack again by wireless. 



F. Lloyd Hopwood. 



POWER ALCOHOL. 



THE annual importation of petrol into this 

 country rose to more than 100,000,000 

 gallons before the war. Most of this came from 

 the United States. At that time the consumption 

 in the States was about ten times this figure, but 

 in 19 19 will probably prove to be not less than 

 thirty times as much. With these values to face 

 it is impossible not to wonder whether the rapid 

 expansion of usage in the States will allow the 

 exportation — at any practicable price — of even 

 the small relative quantity used in the United 

 Kingdom before the war, to say nothing of any 

 additional supply to meet the growth of our own 

 needs for road, sea, and air. 



These considerations suffice to render inquiry 

 into the subject a matter of immediate moment, 

 but there is an additional argument available to 

 those who take a longer view. Any fuel product 

 flrawn from oil wells or coal mines has the nature 

 of a fortunate dip in a "lucky bag." No one 

 knows how long such supplies will last, nor what 

 untapped stores there yet may be (nor where they 

 are). Moreover, their renewal is a matter of 

 hundreds, if not thousands, of thousands of 

 } ears. For this reason it is wise for mankind to 

 prepare to supply its future needs by drawing 

 NO. 2598, VOL. 103] 



on the current account of the sun's radiant energy 

 and to touch the capital as little as may be. 



In most previous discussions on this subject it 

 has been assumed that alcohol obtained from the 

 potato crop is as feasible a source of supply as 

 any that could be named. It now appears from 

 the investigations of the Inter-Departmental Com- 

 mittee on Power Alcohol (Cmd. 218, 1919, price 

 2d. net) that whilst potatoes yield 20 gallons of 

 alcohol per ton, the sun-dried flowers of the Indian 

 mahua tree (costing about 305. per ton delivered 

 at the factory) will yield as much as 90 gallons of 

 alcohol per ton. Here, as in so many other cases, 

 it seems that raw material comes most abun- 

 dantly and most economically from the tropics, 

 which, indeed, in the present instance is not to be 

 wondered at, seeing that it is the daily solar 

 radiation the energy of which it is desired to tap. 



The Government Committee above mentioned, 

 with most praiseworthy energy, has also taken 

 a decided step forward in probing the problems 

 relating to the best use of the alcohol when 

 produced. With this in view it has arranged 

 with the London General Omnibus Co. for a com- 

 plete fleet of motor omnibuses to be run for six 

 months on both alcohol-benzol and alcohol-benzol- 

 petrol mixtures, and for the results to be com- 

 pared with running on petrol or other fuel. To 

 use alcohol without any admixture might prove 

 difficult owing to its reluctance to fire in a cold 

 engine ; moreover, for good thermal efficiency a 

 high-compression pressure would be needed, and 

 this again makes starting difficult. That, howr 

 ever, is but one of a series of problems which 

 the Committee has arranged to have investigated 

 at Manchester in the laboratory of Prof. H. B. 

 Dixon, whose work on similar lines is well 

 known. Both these investigations — scientific and 

 commercial — should begin to bear fruit very 

 shortly, and by Christmas it may not be too much 

 to hope that the Committee will be able to 

 publish information of such value as to enable 

 the Government to take definite steps towards 

 rendering power alcohol available for all internal- 

 combustion engine users. 



THE FORESTRY BILL. 

 '"PHE Forestry Bill came before the Commons 

 -1- in Committee of the whole House on 

 August 8, when amendments to several of the 

 clauses were suggested. An important amend- 

 ment increased the number of Commissioners 

 from seven to eight, with the object of having one 

 unpaid Commissioner sitting in the House of 

 Commons, thus enabling the House to keep itself 

 acquainted with the prepress of the afforestation 

 work. This amendment was agreed to, as was 

 also another by Major W. Murray that not fewer 

 than two of the Commissioners should have 

 special knowledge and experience of plantation 

 and forestry in Scotland. 



Sir Philip Magnus strongly advocated the view 

 put forward by the British Science Guild that at 

 least one of the Commissioners should be a person 



