The exceptionally low rate for printed matter for the blind has been given as a measure of philanthropy. By its means, although at some loss to postal revenue, the effect of the disadvantage of bulk and weight in such printed matter, which results from the affliction, is in a large degree removed.[642] * * * * * The question of the rate to be applied to parcels is one of considerable difficulty. While considerations of public utility would probably make it undesirable for the State to derive a profit from the business, they would hardly extend to the point of conducting a large transportation business at a loss, and the results in England and Germany show how important and difficult is the problem of fixing remunerative rates. The rates for newspapers, samples, ordinary printed matter, etc., have been accorded not solely with reference to the cost of the service, but on grounds more or less political and social as regards the fact of granting a privileged rate, and more or less empirical as regards the fixing of the actual amount of the charge. For the most part this method has answered sufficiently well, the reason being that the cost per packet is comparatively small, and the privileged traffic has not generally assumed large proportions relative to the letter traffic. These empirical methods cannot, however, be applied in the case of parcels. The expense of the service performed by the Post Office is not, as with a letter, actually small, and confined to that of collection at one end and delivery at the other end of the journey, with a negligible cost (per packet) for transmission between the points of origin and destination. Cost of transportation itself becomes an appreciable item in respect of every parcel. For this transportation the Post Office is in the main dependent on the railways, and in the determination of its cost the principles determining ordinary railway rates must necessarily apply. Those principles are complex and to a large degree indeterminate. On the problem of railway and other transport rates many volumes have been written, and many more will yet be written before a solution is arrived at.[643] Railways, like the Post Office, are unable to allocate the actual working costs with any degree of precision between the various kinds of service they perform. Like the Post Office, they have one general set of expenses, although they have diverse sources of revenue.[644] Even if the cost of service could in each case be definitely ascertained, its adoption as the sole basis of the rates would prove unsatisfactory.[645] For the most part the principles on which the rates are actually fixed resolve themselves into a consideration of "what the traffic will bear," that is to say, the test by actual observation and computation, strengthened, if need be, by actual experiment, of the rates which will yield the maximum advantage to the railway company.