"Stand by the union" is the fourth of "The Blue and Gray Series." As in the preceding volumes of the series, the incidents of the story are located in the midst of the war of the Rebellion, now dating back nearly thirty years, or before any of my younger readers were born. To those who lived two days in one through that eventful and anxious period, sometimes trembling for the fate of the nation, but always sustained by the faith and the hope through which the final victory was won, it seems hardly possible that so many years have flowed into the vast ocean of the past since that terrible conflict was raging over so large a portion of our now united country.  
Though it is said that the South "robbed the 6 cradle and the grave" to recruit the armies of the Confederacy, it is as true that young and old in the North went forth in their zeal to "Stand by the union," and that many and many a young soldier and sailor who had not yet seen twenty summers endured the hardships of the camp and the march, the broiling suns, and the wasting maladies of semi-tropical seas, fought bravely and nobly for the unity of the land they loved, and that thousands of them sleep their last sleep in unmarked graves on the sea and the land. The writer can remember whole companies, of which nearly half of the number could be classed as mere boys. These boys of eighteen to twenty, who survived the rain of bullets, shot, and shell, and the hardly less fatal assaults of disease, are the middle-aged men of to-day, and every one of them has a thrilling story to tell. The boys of to-day read with interest the narratives of the boys of thirty years ago, and listen with their blood deeply stirred to the recital of the veteran of forty-five years, or even 7 younger, who brought back to his home only one arm or one leg.
 
In his youth the author used to listen to the stories of several aged Revolutionary pensioners, one of whom had slept in the snows of Valley Forge, another who had been confined on board of the Jersey prison-ship, and a third who had been with Washington at the surrender of Cornwallis. Not one lives to-day who fought in the battles of the Revolution; but a multitude of those who trod the battle-fields of the war that was finished twenty-seven years ago have taken their places, and have become as interesting to the present generation as the heroes of former wars were to the fathers and grandfathers of the boys and girls of to-day.
 
In the official record of a certain regiment recruited up to the full standard, we find that 47.5 per cent of the non-commissioned officers and privates were under twenty-one years of age. We find a few in the list who were only sixteen and seventeen years. In this regiment, 8 we find two captains only twenty-one years of age, and three lieutenants who were only twenty. This regiment was exceptional in regard to age, though we find that over twenty-five per cent of several companies, taken at random, were under age. Even boys of fourteen and fifteen were enlisted as musicians, "drummer boys," and served out their full term. It can, therefore, be truthfully said, that those who were literally "boys" did their full and fair share in fighting for the union. Perhaps even a larger proportion of minors served in the navy than in the army; and the record of some of them could be recited to prove that in those days boys became men prematurely, and distinguished themselves by brave and daring deeds.
 
The incidents of the story contained in this volume are suggested by actual occurrence during the Rebellion, though they are not absolutely historical details, but are as probable as many real events of the war. The enemy were busy in some of the Northern cities, and there were 9 many daring operations undertaken by them which justify the story in its principal features. Most of the characters have been introduced in the preceding volumes of the series; and in the succeeding volume the hero will be presented in a somewhat different field of action, though in whatever sphere he moves he will continue to be engaged in "Fighting for the Right."
 
Dorchester, Mass., April 23, 1891.