A case in the Court of King’s Bench: text of Lord Mansfield’s judgment follows in full. It gives a useful overview of early thinking on this topic.
Lord Mansfield delivered the opinion of the Court.
This case comes before the Court under the same circumstances as if it were an indictment for the continuance of a nuisance, and it is a question, therefore, whether the demolition of the bank would contribute to restore the harbour. The Court will not compel the removal of a nuisance where it does not appear to be a prejudice, but will set a small fine. Nor would the Court of Chancery, in this case, compel the pulling down of the bank for a damage which might be compensated by a shilling.
The facts in this case are not disputed. In 1758 the bank was erected, and soon afterwards the harbour went to decay.
The question is, to what has this decay been owing?
The defendant says, to this bank. Why? Because it prevents the back- water. That is matter of opinion:-the whole case is a question of opinion, from facts agreed upon. Nobody can swear that it was the cause; nobody thought that it would produce this mischief when the bank was erected. The commissioners themselves look on for above twenty years, until a property has been acquired which would be good by the Statute of Limitations. It is a matter of judgment, what has hurt the harbour.
The plaintiff says that the bank was not the occasion of it. On the first trial, the evidence of Mr. Milne, who has constructed harbours, and observed the effects of different causes operating upon them, was received ; and it never entered into the head of any man at the Bar that it was improper; nor did the Chief Baron, who tried the cause, think so.
On the motion for the new trial, the receiving Mr. Milne’s evidence was not objected to as improper; but it was moved for on the ground of that evidence being a surprise; and the ground was material, for, in matters of science, the reasonings of men of science can only be answered by men of science. The Court considering the evidence as proper, directed the opinions to be printed, and to be exchanged. Under the persuasion of this being right, the parties go down to trial again, and Mr. Smeaton is called.
A confusion now arises from a misapplication of terms. It is objected that Mr. Smeaton is going to speak, not as to facts, but as to opinion. That opinion, however, is deduced from facts which are not disputed -the situation of banks, the course of tides and of winds, and the shifting of sands. His opinion, deduced from all these facts, is, that, mathematically speaking, the bank may contribute to the mischief, but not sensibly. Mr. Smeaton understands the construction of harbours, the causes of their destruction, and how remedied. In matters of science no other witnesses can be called. An instance frequently occurs in actions for unskilfully navigating ships. The question then depends on the evidence of those who understand such matters; and when such questions come before me, I always send for some of the brethren of the Trinity House. I cannot believe that where the question is, whether a defect arises from a natural or an artificial cause, the opinions of men of science are not to be received. Hand-writing is proved every day by opinion; and for false evidence on such questions a man may be indicted for perjury. Many nice questions may arise as to forgery, and as to the impressions of seals; whether the impression was made from the seal itself, or from an impression in wax. In such cases I cannot say that the opinion of seal-makers is not to be taken.
I have myself received the opinion of Mr. Smeaton respecting mills, as a matter of science. The cause of the decay of the harbour is also a matter of science, and still more so, whether the removal of the bank can be beneficial. Of this, such men as Mr. Smeaton alone can judge. Therefore we are of opinion that his judgment, formed on facts, was very proper evidence. As to the evidence respecting the situation of other harbours on the same coast, we think that if there were no embankments it was admissible in illustration of Mr. Smeaton’s opinion : but as to harbours in which there were embankments, we think it was improper, since litem lite resolvit.
Cited in Rogers v Hoyle  EWCA Civ 257.
For the up to date law see the other posts under this tag.
Edited for ease of reading.