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THE Microscope. 189 
seems most likely to play is that of an adjunct to the testing- 
machine, and not (as some have supposed) a rival to the chem- 
ical laboratory. That it will be a most valuable accessory 
seems, to say the least, highly probable. 
As regards preparing the material for examination, the au- 
thor points out that Mr. J. C. Bayles has described the process 
in such a plain and comprehensive manner that if his instruc- 
tions are carefully followed, one need not encounter any serious 
obstacles after a little experience and the expenditure of a con- 
siderable amount of time and patience. Patience and cleanli- 
ness are the two most important attributes to be acquired by a 
student, if he desires success in a work of this character. A de- 
ficiency in either will be sure to spoil his work and in the end 
he will give it up in disgust, wondering what has been the cause 
of his failures. In grinding the specimens, it is quite unneces- 
sary that they should be ground to an extreme thinness and 
mounted in Canada balsam, as microscopical objects are usually 
preserved. This entails a vast amount of labor to no end what- 
ever. A good and accurate photograph, once obtained, is usually 
sufficient for any reference that may be desired in the future; 
besides, with a little care the etched surfaces of the objects can 
be preserved from rust by simply rubbing a few drops of kero- 
sene oil over them with a soft chamois-skin, and then placing 
them in a tightly corked phial. 
The size of the objects to be examined under the microscope 
may vary considerably; but the sizes found most convenient 
range from } in. down to about 1-16 in. in thickness and from 1 
in. to 1-5 in. in sectional area. If the specimens are extremely 
thin, there is often much difficulty in mounting them properly 
on a slide, and in getting the etched surface perfectly parallel 
to the object-glass. After the surface has been sufficiently 
treated with acid, and shows under the microscope no further 
traces of scratches made in the grinding, it should be carefully 
dried and cemented to a glass slide with wax or cement, great 
care being taken to have it in the proper plane parallel to the 
object-glass; otherwise, it will be impossible to make a satis- 
factory photograph. 
The great difficulty encountered in pursuing the study of 
the structure of materials is that of making accurate and satis- 
