(12518) S. R W. asks: In your Railroad number 1 note iu one of the articles (page 590) that reference Is made to the fact that in some instances the train dispatcher is able to communicate with the conductor of the train by telephone. Will you please inform me as to the construction and methods employed in this system I A. Communication was made with moving trains a good many years ago. A system which bears the name of Mr. rdison has been used. It employs the induction of the current to prodLce a cLlTent in the telephone circuit on the car of the train. The main circuit is by the side of the road. The receiving circuit is on one of the cars of the train. The indnction of the current in the main circuit is sufficient to generate a current in the circuit on the car, and thus enable one to hear the message. By the same means a message can be sent from the train. and these circuits have been, used by passengers to send and receive messages en 'oute. (1251') A. H. M. asks: In regard to query 12470 of June 24th, 19]1, issue, I would like to state the following: It is u well-known fact among those who have seen service on submarine vessels, that it is possible to balance a submarine boat at any desired depth. The greater the depth at which It IS deSIred to balance the boat. then t I e greater the amount of negatIve buoyancy (in the form of water ballast) which must be carried. From this it would be inferred that the density of sea water uears a certain relation to the depth of the water, and I am of the opinion that lack 0j. circulation as the depth increases naturally results in greater concentration and density. Theory leads us to belIeve that an object that IS heavy enongh to sink will ' continue to sink to the bottom, but the fact that water is not throughout a medium ,of uniform density is often not considered. , A. The ,compressibility of water is auont 1/22000 part per atmosphere, and an increase of olle atmosphere is had at about 3,: feet below the surface of the sea. From this statement it is not difficult to calculate the number of pounds of water ballast requi red by a submarine of known volume and weight to balance the increase of buoyancy due to depth. This' is, however, not the question in the query referred to. The fact is that if a heavy bo?y sinks in water, it wIII : ?ntllue to slnk tIll It reaches the bottom If Its weIght IS nOt chang : d. ThIS the submarm, e would do If Its weIght was not changed by changing the quantity of water iu it. The difference in density due to the quantity of salts dissolved in the water is not grlat at different places and docs not affect the result to any great extent. The continuous sinking of a MCy In the sea is due to the fact that it is compressed more and made denser by its deeper submersion than the sea water is at the same depth. The submarine is not compressed in sinking to ordinary depths. but its volume and weight are changed by admitting water to make it sink and removing water to make it rise. (12520) R E. T. says: My house is frame with slate roof. I use electric light 115-volt old-style two-wire system, with the wires entering at the top of house. The wiring was put in some ycars ago. Would it be better to throw the main switch during an electrical storm or not? one side of the transformer is grounded, and I have combination gas and electric fixtures. A. If you have not a good lightning arrester at the point where the electric wires enter your building, you would better have one put on without delay. Even after this is done, the house is better protected from lightning if the main switch is open during a thunder storm. In some places the switch at the generating station is opened during a thunder storm and all lights are cut off. (12521) E. P. says: I am experimenting with electricity. and usc a lot of dry cell batteries in my work, and I fnd it very expensive to buy new batteries. Won't you kindly tell me a way by which I can restore my oId batteries again I A. We regret to have to say that there, is no way of fully restoring old dry cells. 'hey are generally thrown away when exhausted. Some have pnnched holes in the zinc cases, and put the whole in a glass jar with a solution of ammonium chlor ide. They will then giv e some more service, but not enough so that the operatiou is prOftable. Some have dug out the top and soaked the cell in the ammonium chloride solution. 'his is the better way. If time and labor are of little value, one can perhaps profitably work on old dry cells; otherwise, not.