UNITED SERVICE MAGAZINE.-The April number of this monthly is just out. Devoted to army and navy affairs it is particularly interesting to men of a military turn of mind. It contains articles on the Egyptian campaign, by Gen. Stone; on Shiloh, by Gen. Jordon, late C. S. Army; on Gen. Gordon, etc. There are also two regular continued stories and two poems. An important and worthy feature of United Service is the editorial department, wherein are discussed the topics current in military affairs. Book notices and reviews close the number.