The term "renewals of locomotives" applies only to the literal substitution of a new locomotive for one which has been sent to the scrap-heap. Repairs are divided into two classes: general repairs and current repairs which are usually made in a roundhouse. The term "general repairs" applies to the more expensive work of repairing which is done in one of the general repair-shops of the road rather than in the roundhouse. Some roads consider that the repairs to a locomotive should be considered as general repairs if the amount of work to be done at any one time exceeds a certain figure, say $750, but as such a method of classifying repairs is purely arbitrary and depends to some extent on the amount of work that is done at the roundhouse in keeping the engine in condition, any comparison between the figures of two roads are almost useless. It is ordinarily expected that a passenger-locomotive should make 120,000 miles and a freight-engine 80,000 miles between consecutive assignments to the shop for general repairs, but even such figures are of little significance, except that, if a locomotive should be sent to the shop without having made some such mileage since the last visit, it would imply that there had been some mismanagement (barring accidents) for which some one was responsible. The term "current repairs" includes all the smaller repairs which are not considered of sufficient importance to demand a general overhauling of the locomotive. The figures reported by various roads for the cost of current repairs per engine handled average something over $1 per engine. Taking the figures in connection with the mileage-run it would show an average cost of from one to two cents per mile-run. Under very unfavorable conditions the total cost of general and current repairs may amount to from 10 to 15 c. per mile-run. Considering the average figure for the country given in a previous section (Item 12, 6.983 c), if we deduct .6 c. (or even a little more) as the cost for renewals we have left about 6 c. as the total average cost of the country of the general repairs. This seems to agree very closely with the statistics given by a certain road that the average cost of engine repairs per freight-engine mile during a period of seven years varied from 5.88 to 6.82 c, or an average of 6.30 c. per freight-engine mile. Another road, which gives the cost of freight-engine repairs as 7.22 c. per engine-mile, quoted at the same time the cost of passenger-engine repairs as 5.60 c. per engine-mile. If, however, we consider these figures on the basis of the work accomplished by the locomotives, we have another indication of the large economy in the use of heavy engines hauling heavy trains. In the last-mentioned case the costs were 22.88 c. for passenger-engines and 7.73 c. for freight-engines per thousand ton-miles; but the freight-trains were more than four times as heavy as the passenger-trains, so that, although the freight-engines cost far more than the passenger-engines per engine-mile, the cost per ton-mile was far less. It is usually found that compound engines cost much more per engine-mile than simple engines of the same capacity, and that the comparison is made still worse because their annual mileage is apt to be less, owing to their standing so much time in the repair-shops. On account of the very great variety of engines, the cost of engine repairs per engine-mile is very different for different types of engines, and the cost per ton-mile is likewise very variable. Mr. G. R. Henderson has sug-gested that the cost of repairs may be represented by the very simple formula of 1 c. per ton of tractive force per mile plus 1 c. per engine-mile. In this statement, however, he considers the term "tractive force" to be the average force which is actually exerted, and not the maximum tractive power. For example, he considered a passenger-engine, whose tractive force amounts to ten tons, and assumed that the actual tractive force exerted by it will not average more than 40% of this maximum. For the above case the assumed cost of repairs would be 40% of 10 or 4X1 c. + l c. for each mile-run, making a total of 5 c. per mile. This method is applied to pusher-engine service as follows: He assumes an engine with 40,000 pounds tractive force, which is exerted to its full capacity in running up-hill, and which returns down the hill without the use of steam. Applying the principle to a grade twenty miles long, the item chargeable to repairs for the up-hill run would be 20X20 c + 20 c. or $4.20. For the down-hill trip we would have merely 20X1 or 20 c., making a total of $4.40 for the 40-mile round trip, or an average of 11 c. per mile. In the case of pusher service it is generally correct to assume that the engine is working to its full capacity in climbing the hill, and that it does not have to use steam in going down. When we apply such a formula to the undulating grades on an ordinary road, it becomes very difficult to determine the proportion of the total possible tractive force which is actually exerted. Usually we can only make a very approximate assumption.