42 THE LAW AFFECTING ENGINEEKS 



must necessarily be a partisan. The engineer, therefore, who 

 is called to aid the Court with his professional knowledge 

 should not show bias in favour of one side or other. " Do not 

 fight the case ; leave that to me," is a piece of advice which 

 the writer once heard given to an engineer by an eminent 

 King's counsel. To deal with the awkward points which arise 

 is the function of the advocate ; it forms no part of the expert's 

 duty to try and explain them away. If the judge begins to 

 suspect that the expert witness is a partisan, he is more than 

 likely to attach little weight to the whole of his evidence. 



9. Views of an expert witness on expert evidence. The 

 author has been favoured by an eminent engineer who has 

 often given scientific evidence with the following statement of 

 the duties of an expert witness : " Concerning the art of 

 giving evidence, the expert must be able to comprehend what 

 is material to the vital points in the case as he understands it. 

 He must not only understand what is material, and its bearing 

 upon the points with regard to which there may be a differ- 

 ence of opinion, but he must be able to explain, as briefly as 

 possible, in what way the facts to which he can speak elucidate 

 the points raised, and clear away the ground for difference of 

 opinion. It is therefore necessary that he should see and 

 know how far any questions put to him in cross-examination 

 are framed upon a perverted knowledge of the scientific ques- 

 tion under consideration. Specious questions are often put 

 with a view to weaken his statements of fact, and to give 

 them the appearance of mere personal opinion. Again, 

 counsel will often endeavour to elicit a ' yes ' or ' no ' reply 

 which the witness knows is unsatisfactory and likely to be 

 misinterpreted, but which he does not at the moment see how 

 to reject or to expose." 



With regard to the last point, witnesses are often pressed to 

 say "yes" or " no " to questions which cannot be satisfac- 

 torily answered by either word. In such a case the witness is 

 always entitled to explain his answer. 



10. The use of documents to refresh the memory. Although 

 it is a general rule of law that a witness may not read his 

 evidence from a written document, it is most important for 

 the expert to remember that he is entitled to refresh his 

 memory from notes " made at the time." The rule has been 



