The fact that there has been a popular tendency in the past to measure the reasonableness of rates of one public utility plant, or even to fix rates for a new plant, by a comparison of those in force in other cities seems to warrant a little consideration of the differences between various plants of like kind and between the conditions under which they are constructed and operated. These differences seem generally far from being fully appreciated except by the comparatively few who have had something to do with a considerable number of such properties and had occasion to make comparison between them. The popular comparison of rates of different water or other utility plants appears to be merely a superficial one, due to the lack of knowledge and appreciation of the great differences that may exist even in cities of similar size. Certain water works franchises have specified that the rates to be charged by the grantees under those franchises should not exceed the average of those in certain other cities named therein. Those who have had experience in construction and valuation of railroad property, and doubtless others as well, are aware of the existence of a wide range of values per mile of roadbed or track, which are the common bases of comparison of different roads. The heavier types of construction on heavy traffic roads is by no means the only cause of the differences in costs or values per mile. Construction difficulties may be relatively so serious in the case of a so-called small road, or light traffic road, as to offset the extra expenses for stiffer construction in the cases of certain higher class lines. These relative construction difficulties may, in other cases, operate to augment, instead of to offset, the differences in cost that are due merely to construction standards. Topography and geology of the country traversed are important factors in the results.