necessary to do the work. Our bridges are usually designed and built by the same company, so that the design within certain limits corresponds to the available plant of the manufacturer, and the expensive tools can be used over and over again. In English practice, however, the bridges are designed according to the ideas of the individual engineer, and then some firm has to build them in all their details to correspond with the design. If the construction necessitates expensive machinery and tools, no company would undertake them at any reasonable cost, as there would be very little chance of any other similar design being offered upon which they could use the same tools.
In riveted work, however, the tools required are within certain limits the same, regardless of the details of design. Pin-connected bridges are much more economical for large work than riveted ones; and this fact, taken in connection with the unrivaled facilities we have for doing the work, accounts for the fact that in the building of large bridges American firms can underbid any others, and not in any way lower the character of the work done.
By HORACE WHITE.
IN the second half of the eighteenth century there arose a school of thinkers in France to whom, at a later period, J. B. Say gave the name of physiocrats. The founder of the school was François Quesnay. Turgot was one of his disciples, and was the most distinguished member of the group. De Gournay, the elder Mirabeau, Morellet, and Dupont de Nemours are well-remembered names of the physiocratic school. Adam Smith was in Paris in the year 1764, and was much in the society of Quesnay and his friends. The exchange of thoughts among these great men must have been mutually beneficial, but the question that has since been raised and discussed with some heat, whether the author of the “Wealth of Nations” gained more from that intercourse than he gave in return, is a barren controversy.
At that time governmental interference with the business and livelihood of the people was incessant and almost universal, and
- Lattice riveted bridges and double intersection trusses have not been discussed, as their introduction would only have obscured the object of the paper.
In regard to the advantages of the American pin-connected bridges for long spans, we may say that from the most recent data the time required for the erection of the bridge, after everything is ready, is only about one twentieth of that required for the erection of the English riveted bridges.