"It is true that the 'value' of a property is an unstable figure, subject to fluctuations due to natural or artificial causes, and that a material change in value may occur suddenly, but the 'value' of any given property on any given date is, or should be, from an engineering standpoint, a definite sum which may not be varied or changed to suit the whim or will of the people for whom the work is done." The fundamental conception of a value is so important in an investigation of this kind that it is worthy of careful and thorough discussion. The appraisals which the writer has had occasion to make have generally been for one or other of the following purposes, namely: (I) Taxation, in the interest of the community or corporation taxed; (II) Bonding, in the interest of the banker or representative of persons who contemplated lending money on the property; (III) Rate-making, in order to determine what was a fair amount of money that the property should be allowed to earn for the owners. Now, in general, a proper value for any property for any one of these purposes is different from its proper value for any of the others. This proposition is of immense significance, for the reason that, if the value for the property arrived at, on one basis, be accepted and applied for one of the other purposes, it will inevitably result in gross injury and financial loss to some one. In attacking this problem, one must be careful to take the correct standpoint, which is not necessarily that of engineering. Engineering science is indispensable for a large part of the work, but there are other indispensables, which would not ordinarily be recognized as engineering. The writer takes the view that engineering is a part of economics, rather than economics being a part of engineering. To illustrate this point, consider two objects, one of which is concrete and simple and the other more complex. (1) A steam shovel belonging to a railroad, costing $10,000, new; (2) The entire railroad as an operating entity. Assume for (1) that the shovel has been purchased recently, is in perfect condition, and that the railroad has some work for it to commence on as soon as it can be properly installed. What is its: (I) Taxable value, (II) Bonding value, and (III) Rate-making value?