each separate operation on the railroad, no matter how minute, such as talking over a telephone or spiking or unspiking a switch, is so far an exclusive property of a particular class of employee that if an employee of another class, in the course of his regular duties, performs such operations he must not only be paid an extra day’s wages for doing so, but at the same time the furloughed or unemployed members of the class held to be entitled to perform the operation must be paid a day’s wages for not having been called upon to perform it.
