330 THE AMERICAN MONTHLY [Dec 
Q. What did they show?—A. Each-~showed there was 
blood on both specimens. 
Q. Were allofthe tests applicable and conclusive?—A. 
Yes, sir. 
Notes on Microscopy. 
M. I. CROSS. 
THE MicroscopicAL EXAMINATION OF Metats.—lIt is a 
little singular that a study which has assumed such great 
importance as the examination of steel and iron under the 
microscope has done during recent years should not have 
received any treatment whatever in so exhaustive a work 
s the new edition of ‘‘Carpenter on the Microscope.” It 
is a highly technical and important subject and has become 
an absolute essential in all iron and steel works. In fact, 
there is probably no factory of standing that is not equip- 
ped with suitable instruments both for observing and 
photographing. 
Although much information regarding the chemical con- 
stitution of the metal is disclosed by the microscope, it is 
in ascertaining the mechanical properties that the special 
value of the examination lies. 
For instance, the structure of steel varies with the dif- 
ferent degrees of hardness andtheamount of heat to which 
it has been subjected, and it is possible to gain definite in- 
formation concerning the suitabiity of the metal for the 
purposes for which it is to be used by meansofthe micros- 
cope. 
In the manufacture of guns the microscope is invariably 
resorted to, and it can be definitely determined before the 
manufacture is proceeded with whether the metal is suit- 
able for the purpose, or any defect has taken place in the 
heating or quenching which would render the gun unsafe 
or unsatisfactory. 
Engineers can detect flaws, blow-holes, defective welds, 
etc., and in many ways are able in an early stage to avoid 
the trouble incident to the use of imperfect metal in the 
finished article. Microscopes for the exclusive purpose 
