The two-ohm relay is at least as safe as the four ohm. It should be thoroughly understood that it is as important with the four-ohm relay as it is with the two-ohm relay to have not less than the R.S.A. recommended limiting resistance between the battery and track. This is important with any kind of low internal resistance battery, and under certain conditions with gravity battery also. In one case assume a train to be passing from the relay end to the battery end of a track section and in the other case from the battery end to the relay end. The effect accomplished is the same except that the relay will not release so quickly when the train passes from the battery end towards the relay end, and this is in part due to the self-induction of the circuit through the relay coils, the rails and the axles of the train. It is due more, however, to small current leakage from the adjacent section and the effects of stray currents which are always present to a greater or less degree. A broken rail will also generally open the circuit and de-energize the relay. Circuits for the control of the various signal devices are broken through the contact points of the track relay. Track Circuit Maintenance Cross ties have a relatively high resistance to the passage of electric current, but when a large number connect the rails many multiple paths are introduced into the circuit through which the current may flow from one rail to the other, and, considering them as a whole, the resistance they offer to the passage of the current reaches a relatively low value. Consequently there is always a current leakage from rail to rail through the cross ties and ballast. Every effort should be made to secure and maintain the best ballast and drainage possible on d.c. as well as a.c. track circuits. Cinders, dirty sand, soft water-logged ties and ballast not well cleaned away from the base of the rail will produce track circuit trouble, particularly during wet weather, while good rock ballast, sound ties and clean track give the greatest efficiency. The use of ties freshly treated with zinc chloride also reduces the ballast resistance. If too many such ties are used in a track circuit the current leakage between rails becomes so great that not enough current reaches the relay to hold it closed, the effect being the same as if a train is on the track circuit shunting out the relay. For good results, the number of zinc-treated ties installed per year in any track circuit should not be greater than 15 per cent. of the total number of ties in that circuit. Track Circuit Troubles