It thus appears that the United States Courts have laid down a few rules, which may be regarded as fixed and definite and must be followed, but that many important questions have not yet been decided. The value to be determined must be a "fair value" of the property being used for the convenience of the public. The par value of stocks and bonds may not alone be considered (although it may be considered), the market value of stocks and bonds, original cost plus cost of additions, the probable earning capacity, the cost of reproduction, depreciation, appreciation, all these, and any others that will throw light on the "fair value" must be taken into account and given the weight to which they are entitled. Any fictitious book values due to over-issues of stock and bonds are to be given no weight, but the appraisal must give the fair value, in the light of all the facts, of the property in actual use at the time of the appraisal. There are several decisions of the State Supreme Courts which discuss these subjects, but an examination of a number of these gives practically nothing more, in the way of definite conclusions as to method, than has been cited. Perhaps the most complete and painstaking consideration of appraisal problems by any Court was that given by Judge Savage of the Supreme Court of Maine (97 Maine, 185, and 99 Maine, 371). These were neither rate cases nor taxation cases, but proceedings under statute to require from the Court instructions to a board of appraisers appointed to value the plants. In the later or Brunswick case, Judge Savage elucidates a number of points left not altogether clear in the Waterville case. The Brunswick decision contains some interesting views on "going value," and the Court's remarks on the general difficulties in making rules for an appraisement are exactly to the point: "There are many difficulties, if not dangers, in attempting to formulate rules which are to be applied to facts not yet ascertained. While it may be easy enough to state rules in the abstract, it is much more satisfactory in an opinion of the court, to express them in terms which are applicable to the facts in the precise case in hand.... It must be always understood that our answers to these questions are intended to be given only in the most general and comprehensive terms, which may, or may not, be found to be fitted to the facts which may subsequently be developed. No other course would be wise or safe.... A public service property may or may not have a value independent of the amount of rates, which for the time being may be changed. A public service company may, under some circumstances, be required to perform its services at rates prohibitive of a fair return to its stockholders, considering their property as an investment merely....