Page:Indian Journal of Economics Volume 2.djvu/34

?4 H. STANLEY JEFON$ they may be expected to last in good working order for some hundreds of years, so that no depreciation reserve is needed. Instances are quoted of Roman aqueducts which, with slight repairs, are serviceable and in use st the present day. To this view it may be replied that, whilst the lengthy physical endurance of great masonry works is not to be denied, rate of progress of modern civilization is such it is doubtful whether any the that of such works would be years. This should be taken, I think, as the limit of the period in which capital is to be recovered out of revenue. In ]nany eases, of course, invention will give to railways, and irrigation canals, a much shorter life than this. The electrical working of railways, particularly in ?hountain- ous countries, will so greatly decrease the cost of working that the existing steam lines may-be scrapped after a life. of only twenty or thirty years. Sneh an example is only a particular ease of a general economic law--'that of the evestment of capital from dying indus- tries. This may take place directly or indirectly. In the first ease the original owners of the capital recover it by insraiments from revenue; and, foreseeing that a new mechanical means of producing the same service (e.g. the change from horse-drawn vehicles to motor ears) is gaining the field, the capital. so recovered is re-invested in the new instrument instead of the old the progress of possibly to some found to be of sufficient utility a century hence to be worth maintaining in use. The invention of ne? engineering methods is likely to open up new ways of achieving the same results at a lower working cost. Whilst this cannot be confidently asserted, there is in it at least sufficient probability to make it unwise to assume that any kind of engineering work--rosA, railway, irrigation canal, or dock, will be worth main- taining in use or operation for more than a hundred