THE EMERY MACHINE. 95 



as to their properties or size. In many of the 

 general testing laboratories, the machines have to cope 

 with a great variety of work, both in size, material, and the 

 nature of the tests. Some machines are primarily intended 

 to be used in carrying out important and specially accurate 

 research work ; others for educational work almost entirely. 

 In those machines which are provided in many college 

 laboratories, the work to be performed in them comprises 

 almost all the varieties which have been mentioned, 

 especially if commercial work is undertaken. 



In comparing the different kinds of testing machines, 

 it must therefore be borne in mind that every kind of 

 testing work does not demand the same qualities in the 

 machines used to carry it out. 



If it is impossible for it to be said that one testing 

 machine is better than all others, it is also difficult for 

 one observer to offer perfectly reliable opinions in regard 

 to them. It is given to very few men to have an adequate 

 experience in the use of all the chief types of testing 

 machines ; he is almost certain to have a preference for 

 one kind, not because he has a complete knowledge of all, 

 but from an unconscious mental bias, born of use 

 and intimate acquaintance with this one kind. 



Bearing these points in mind, therefore, the author 

 proposes to sum up the evidence and present it to the 

 readers, who must themselves be the judges. 



There are certain qualities possessed to a more or less 

 marked extent by all testing machines. These are : 



I. Simplicity. 

 II. Ease of access. 



III. Convenience of manipulation. 



IV. Adaptability. 

 Y. Sensitiveness. 



VI. Accuracy. 



The best plan will be to take them one by one, and see how 

 each of the types which have been described stands as 

 regards these qualities. 



50. Simplicity. Simplicity is one of the first and 

 most necessary of the qualities which a designer or a 

 purchaser of a testing machine should insist upon. A 

 multiplicity of parts, however good the result may be, is 

 always to be avoided and always objectionable. 



Simplicity is to be desired for several reasons. In the 

 first place the manipulation of a large number of parts in 

 place of a few means loss of time, mistakes are more likely 



