644 SCIENCE PROGRESS 



opterygian and the leg of the terrestrial vertebrate. In his recently pubUshed 

 book on embryology, Prof. Kerr has given an account of the origin of the 

 pentadactyle limb according to his theory. 



The retirement is announced of Mr. R. I. Pocock, of the Zoological Gar- 

 dens, Regent's Park. Dr. Pocock has been a well-knowTi figure in English 

 zoological circles for some years, and he has carried out his duties at the 

 Gardens with the greatest courtesy to everyone who has had reason to 

 consult him. He has published a large number of memoirs on the osteology 

 and morphology of mammals, and is a Fellow of the Royal Society. We offer 

 him our congratulations and our best wishes for the years of his retirement. 



He is being succeeded by Dr. Geoffrey Marr Vevers, who is at present Beit 

 Memorial Research Fellow at the London School of Tropical Medicine. Mr. 

 Seth-Smith and Mr. E. Boulenger will continue in their old positions, and 

 Miss I. Cheeseman will be curator of insects. 



The death is announced of Prof. Oscar Hertwig, of the University of 

 Berlin. He was one of the greatest of German biologists and had published 

 a number of important textbooks. It was Oscar Hertwig who worked out 

 the nature of the Polar bodies, and in the field of human embryology his 

 contributions were considerable. The brothers Hertwig first worked out 

 in 1875 the fertihsation process of the animal egg, accurately following the 

 behaviour of the nuclei. 



Our last number went to press too early to comment upon the presen- 

 tation to Sir Edward Sharpey-Schafer, by his associates and pupils, of the 

 bas-relief plaque of himseli, as a token of esteem by those who had been 

 trained under him, and who occupy important posts, not only in the British 

 Isles, but also in the Overseas Dominions, in the United States of America, 

 and in Japan. 



A pamphlet entitled Suggestions for the Prevention of the Decay of Building 

 Stones, by J. E. Marsh, M.A., F.R.S. (Oxford : Basil Blackwell, is. 6d. net), 

 contains a most interesting discussion of the causes of stone decay and of 

 the methods which have been suggested during the last seventy years to 

 check the process. Decay is usually attributed to frost or the action of 

 sulphuric acid fumes in the atmosphere, but the author considers that nitric 

 acid is by far the most destructive agent on account of the great solubility 

 of calcium nitrate in water. He suggests that the nitrate is formed from 

 atmospheric ammonia by the action of micro-organisms in the stone, and as 

 a remedy for decay proposes that it should be made sterile by washing every 

 five years with a dilute solution of caustic soda. It is not improbable that 

 the ef&cacy of limewash is due to its alkaline property. 



A certain amount of information is now becoming available concerning 

 the production of helium from natural gas. During the war Prof. Mc- 

 Lennan, with the assistance from the staffs of the Universities of Toronto and 

 Alberta, constructed and worked a semi-commercial plant at Calgary at a 

 cost of less than fivepence per cubic foot of helium. From this plant a 

 large quantity of hehum of high purity was obtained, and the experiments 

 were regarded as the beginning of an attempt to place the utilisation of the 

 gas, which constitutes one of the natural resources of Canada, on an industrial 

 footing. Quite recently Prof. McLennan has succeeded in liquefying 

 helium in the cryogenic laboratory of the University of Toronto — an achieve- 

 ment previously accomplished only in the world-famous laboratory at Lej'-den. 

 Large quantities of helium have also been produced in the United States, 

 and Dr. Richard B. Moore, chief chemist of the U.S. Bureau of Mines, states, 

 in Nature (January 20), that the Linde helium plant at Fort Worth, Texas, 

 is now producing 15,000 cu. ft. of 93 to 95 per cent, helium per day from the 

 natural gas obtained from the Petrolia field in Texas. It is expected that this 

 output will shortly be increased to 90,000 cu. ft. per day, and present research 

 is being directed to the decrease of the cost of production. Repurification of gas 



