1900] MICROSCOPICAL JOURNAL. 287 



a steel is of vital importance, especially in the case of 

 large masses of metal — e. g., the ingots used in the man- 

 ufacture of ordnance. If a gun-tube is quenched below its 

 critical point it will be soft, and consequently very unsafe 

 for firing purposes, on account of its low elastic limit. The 

 microscope would, however, be invaluable in such circum- 

 stances, as it would enable one to say definitely whether 

 the metal had been properly quenched and tempered or 

 not. 



If the proportion of carbon in a steel be high, say 1-5 

 per cent and if the cooling be rapidly effected in iced brine, 

 another constituent appears, which may be scratched with 

 a hard needle, and to which M. Osmond, who discovered 

 it, has given the name of "austenite," after Sir W. Rob- 

 erts-Austen. 



For the engineer, the microscope is especially useful in 

 determining the influence exerted by thermal treatment 

 on varieties of steel of different composition. It is also 

 useful for detecting slag patches, defective welds, and cold 

 rolling effects. 



In conclusion, I wish to point out that no attempt has 

 been made to deal at all exhaustively with this subject, 

 only typical cases having been shown, and the method of 

 working briefly described. Both the manipulation and the 

 interpretation of the results obtained require a consider- 

 able amount of practice. — Annual of Microscopy. 



Malaria and Mosquitoes. 



So many people have suffered from the attacks of mos- 

 quitoes, even in this country, that one of the most at- 

 tractive addresses delivered at the meeting of the British 

 Association, was that by Surgeon-Major Ronald Ross, the 

 president, Sir W. Turner, being present. Major Ross, in 

 the course of his remarks, said : The particular organism 

 in question belonged to the Hsemffimobida?, of which there 



