LUARY 20, I'll') 



NATURE 



487 



capable instructors in advanc is threatened. 



At present teachers ol elementary scieno 

 paid, on the average, than those engaged in the 

 higher branches, and are additionally, in mosl cases, 

 entitled to pensions under the reachers' Superannua- 

 tion Act. rhe obvious result of this anomalous state 

 of tiling is that the ranks of higher scientific teachers 

 will be depleted unless strong and prompt '• 

 men I action is taken to place the universities and 

 < ■ illt j_^< -. .in .1 sound financial basis. Unless iliis be 

 done there is little prospect, of obtaining the research 

 workers necessary to secure the industrial future of 

 the country. ('has. K. Darling. 



( lity and • iuilds Technical < lollegi , 

 Finsbui , E.t 



The Indian Rope Trick. 



["hi rri spondence in the Daily Mail 



elating to the Ii rick is vei j similar to ih>-' 



roversies thai havi arisen from time to time in the 



- in India, but noth advance the 



■ jot further. I he man who does th ropi 



trick has yet to tx pi odui 1 .1 ! 



During a considerabli porl esidence ol mon 



than thirty years in India, I studied Indian conjuring 

 and made all the inquiries I could regarding this trick. 

 I knew main of the best conjurers between Calcutta 

 Delhi, but never found one who had seen the rope 

 trick. Several had heard ol it, some believed in it, 

 nunc 1 .ml. I sal isfai toi il) explain it. 



Personally, 1 am of opinion that the rope trick is 

 entirely mythical. I decline to accept the various 

 theories put forward !i in support of its 



practicability, such, for example, as hypnotism or sub- 

 stitution. The mosl likely explanation I have heard 

 is that the trick I in 10 mrtyard, that 



he \ ii w above, and that the rope is 

 ii\ thrown up to a confederate, who fastens it to 

 n whii li 1 annot be seen on account of the smoke; 

 a lad then climbs up the rope and is similarly Ins: to 

 view in the smoke, but even this theory is unlikely. 

 It would not be impossible to arrangi a scene on 



where the rope trick could be performed as an 

 illusion — not by a smoke screen, but bj other means 

 of hiding what happens above a certain height 



\- to Indian conjuring generally, I consider ii to 

 be far behind European, though the sleight of hand 

 is often extraordinaril) good, and the methods occa- 

 sionally ingenious, as, foi instance, when conjurers ap- 

 parently cause a fi w grains of wheat or gram to sprout 

 in a few moments .. fai better illusion than the over- 

 mango-tree trick. 

 Indian conjurers are ven conservative and seldom 

 produce new tricks, and they are very slow in dis- 

 covering how a trick, new to them, is done even when 

 irmed bj an amateur on well-known principles. 

 I . . HUDDLESTON. 

 1 1. 111. I I I. mpsl. ad, 1 1. 1 K. 



/ III- 1 si- Of HE1 II \l FOR URCRAFT 

 n RPOSES. 



SHORTLY alter the commencemenl of the war 

 it became evident that if helium were avail- 

 able in sufficient quantities to replace hydrogen in 

 naval and military airships, the losses in life and 

 equipment arising from the use of hydrogen would 

 be enormously lessened. Helium, as is known, 

 is most suitable as a filling for airship envelopes, 

 in that it is non-inflammable and non-explosive, 

 and, if desired, the engines may be placed within 

 2573, VOL. I02] 



the envelope. B) us use it is also possible to 

 additional buoyanc) b\ heating the gas 

 (electrically or otherwise), and ibis fact might 

 possibly lead to considi rable modifications in the 

 technique of airship manoeuvres and navigation. 

 The loss of gas from diffusion through the en- 

 velope is .ds.. less with helium than with hydrogen, 

 but, on the other band, the lifting power of helium 



is aboul 10 per cent, less than that of hydrogen. 



Proposals had been frequently put Forward b> 



men ol science in the British Empire and in enemy 

 es regarding the development ol supplies 

 of helium for airship purposes, but the lust 

 attempt to give practical 'Meet to these proposals 

 was initiated by Sir Richard Thrclfall, who re- 

 ceived strong support hum the Admiralty through 

 the Board of Invention and Research, under the 

 presidency of Admiral of the Fleet Lord Fisher. 



It was known that supplies of natural gas con- 

 taining helium in varying amounts existed in 

 America, and it became evident from the pre- 

 liminary investigations made by Sir Richard 

 Threlfall, and from calculations submitted bv him 

 as to cost of production, transportation, etc., that 

 there was substantial ground for believing that 

 helium could be obtained in large quantities at a 

 COSl which would not be prohibitive. 



Prof. J. C. McLennan was invited by the Board 

 of Invention and Research in 1915 to determine 

 the helium content of the supplies of natural gas 

 within the Empire, to carry out a scries of experi- 

 ments on a semi-commercial scale with the helium 

 supplies available, and also to work out all tech- 

 nical details in connection with the large-scale 

 production of helium and the large-scale purifica- 

 tion of such supplies as might be delivered and 

 become contaminated with air in service. In this 

 work Prof. McLennan received assistance from 

 his colleagues, Profs. John Satterly, E. F. 

 Burton, H. F. Dawes, Capt. McTaggart, and 

 Mr. John Patterson. 



In the course of their investigations, which 

 were carried out with the co-operation of L'Air 

 Liquide Co., it was found that large supplies of 

 helium were available in Canada, which could 

 be produced at a cost of about one shilling per 

 cubic foot. 



In the summer of 19 1 7, when the United States 

 of America had decided to enter the war on the 

 side of the Allies, and after the investigations re- 

 ferred to above were well under way, proposals 

 were made to the Navy and Army and to the 

 National Research Council of the U.S.A. to co- 

 operate by developing the supplies of helium avail- 

 able in the United States. These were made, on 

 behalf of the Admiralty, through the Board of 

 Invention and Research by Sir Ernest Rutherford 

 and a special Commission consisting of Com- 

 mander Bridge, R.N., Lt.-Col. Lowcock, and 

 Prof. John Satterly. 



The authorities cited agreed to co-operate with 

 vigour in supporting" these proposals, and large 

 ordeis were at once placed by them with the Air 

 lion Co. and the Lynde Co. for plant, equip- 

 ment, cylinders, etc. The Bureau of Mines also 



