James D. Waite: The National Guard of the State of New York is not a part of the regular army of the United States. It is under the State control, but may be mustered into the United States service through the action of the President, who calls upon the States, if need be, to furnish troops. If your father does not wish you to join the N. G. S. N. Y., do not do so. Hubbard Marsh, Groton, N. Y., wants to belong to some literary or similar society having corresponding members. Write him. Claude G. Smith: There are, just now, no prize offers open. New ones, when ready, will be announced on this page. The only contest awards in which have not yet been announced is the Illustration. In that about 300 young artists are trying to make a picture for a story, a proof of which has been mailed to them. This contest closes March 21st, but applications for proofs with permission to enter the contest have already closed. D. Blondheim: We fear it is a bit late for descriptions of Christmas entertainments. Better tell us about oysters and the oyster trade. E. M. Wallace, Monmouth, Ill., and Jay F. Hammond, Harford, N. Y., want to receive samples of amateur papers. * * * * * Daniel W. May: We should think old skates could well be made use of in constructing an ice-boat. Coils in use in the relay and sounder of telegraph instruments are two in number. The cores are soft iron bars, and around them there is wound, for the relay, very fine wire that is covered with silk thread, to perfectly insulate it. The finer the wire, the more its resistance. The large wire that you see on the poles connects directly with this fine relay wire. When the electric circuit is complete, the soft iron bars are magnets; when it is broken, they are not. Thus is produced a backward and a forward movement of the armature which opens and closes a second or local circuit, in which is placed the sounder, having two similar coils, but wound with comparatively coarse wire. The Century Dictionary describes an induction coil as being essentially in two parts, one wound over the other. The first, of coarse wire, is wound about the soft iron bar, and connected with a key for breaking and closing the circuit. Above it, on the same coil, is wound very fine wire, carefully insulated from the first, which becomes magnetic by induction every time the electric circuit is closed. We advise, for a first attempt, a single coil of fine wire. All wire used in making coils should be insulated. [Illustration: STAMPS] This Department is conducted in the interest of stamp and coin collectors, and the Editor will be pleased to answer any question on these subjects as far as possible. Correspondents should address Editor Stamp Department.