=Effects of Weather.= The principal obstruction to economical construction work in the temperate zone, is due to _rain_. If it is raining at about the time when the men come upon the work, they will rarely fail to retire to their homes or to some point so far from the scene of operations as to make it difficult if not impossible to get them back upon the job if the weather should clear. If a rain comes on in the noon hour, they generally leave and do not return to work. If it should start to drizzle in the middle of the afternoon, and the men are under fairly good discipline, they stand a very good chance to stay the day out rather than miss getting a full day's pay. Next to rain as an obstacle is _freezing weather_. On concrete work, if the concrete is laid at temperatures below 22 degrees, and particularly when a slow─setting brand of cement is used, special precautions have to be taken, and even then the work is liable to be rejected. For work in which steam engines are employed, as dinkeys, steam shovels, steam drills, etc., continued cold weather is likely to result in the freezing of supply pipes, the freezing of valves, and the breaking of pipe connections, necessitating a good deal of frost protection and a well─disciplined and well─handled gang of pipe─fitters under a responsible foreman charged with the express duty of keeping the water lines clear. In very cold weather──say below zero──the freezing of water will seriously interfere with the economy of the work on the water end alone. Where steam drills are used and the weather is exceedingly cold, the steam from the drills blown upon the men condenses and freezes upon their clothes, involving great inconvenience and suffering. Under such conditions the men will not work so many hours per day as otherwise, and frequently they will not work at all at critical times in the progress of the work, to the great detriment of economy. It has been observed that a combination of stress of weather a few hours before the coming of the paymaster seems to be more discouraging than at any other time, and it is seized upon as an excuse to quit work. In very windy weather, more coal is burned than at other times; and sometimes a boiler which is capable of running seven or eight drills in ordinary weather will not be able to furnish steam for more than 70 or 80 per cent of this amount in the high, cold winds. For the above reasons it is essential to keep a record of the temperature and weather. =Accidental Conditions.= Besides the weather, there are a host of accidental conditions that may arise to influence the economy of the work and complicate a precise study of the performance. Some of these, named at random, are: 1. The blowing─out of the gasket in a main water supply pump. 2. A shipment of poor coal. 3. The wrecking of a trestle. 4. A derailment of cars. 5. The breaking of machinery on a shovel.