368 



fleeted light, special means of illumination must be used, and it 

 is now customary with the highest powers to use a beam from a 

 powerful arc-lamp, which falls vertically on the surface of the 

 metal and is reflected through the microscope. Under these 

 conditions hardened steel is readily distinguishable from annealed 

 or even tempered specimens, and it is possible to distinguish all 

 the variations of thermal treatment to which the metal has been 

 subjected. This is of great value to the engineer, and the 

 " pathology " of injured specimens has become one of the chief 

 means of testing material which has shown signs of failure. All 

 this is clearly set forth and the photographic illustrations 

 throughout the book are beautifully reproduced on special paper. 

 In future editions, no doubt, Mr. Hiorns will be able to extend 

 and complete his work, but, taking it as it stands now, he 

 deserves the thanks of his fellow-workers for the useful aid 

 which he has given them. T. K. E. 



Journ. Qv.ekdt Microscopical Club, Scr. 2, Vol. VIII., Is'o. 51, iiovember 1902. 



