The various parts of the system were held together by a combination of leases and stock control. The associates in 1877 held all or a majority of the stock of each railroad company which has been mentioned. Usually this stock had come to them in their capacity as shareholders in the various construction companies which had built the roads. In some cases, however, as with the California Pacific and the Northern Division of the Southern Pacific, the greater part of it had been acquired by purchase. But the associates in most instances preferred to add to their control by stock ownership the further security of a lease—a procedure which had the additional advantage of simplifying the conditions under which the companies were operated, by concentrating operations under a single management. Only in the case of the Northern Division of the Southern Pacific do they seem to have temporarily departed from this procedure, and this exception can probably be explained by the special circumstances of the case. So long as the same parties held all the securities of all the companies in the Central Pacific-Southern Pacific system, it made little difference how payments under the various leases were determined. Yet the possibility that the Central Pacific might sometime divest itself of some portion of its property, was kept in mind, and rentals were fixed so that in most cases they were materially less than the net earnings of the leased mileage. This was probably not true of the Southern Pacific in early years, but it had become so by 1880. In form, the leases showed surprising variety. The rental of the Northern Railway to the California Pacific in 1876 was at the rate of $1,500 per mile per year.[193] Mr. Stanford thought that this was based on an estimated cost of construction.[194] In 1879 the same property was leased to the Central Pacific for a payment of a given sum per mile for each piece of equipment passing over the road. That is to say, 25 cents per mile was paid for each passenger or freight locomotive, 20 cents for each passenger car, and 8 cents for each freight or caboose car.[195] This proved to be a very expensive rental, and was changed to a monthly payment of $47,500.[196]