The following is the official report of the death of Mr. Lincoln, Addressed to the Legation in London:--

WASHINGTON, April 15.

SIR:--It has become my distressing duty to announce to you that last night his Excellency Abraham Lincoln, President of the United States,  was assassinated, about the hour of half-past ten o'clock, in his private  box at Ford's Theatre, in this city. The President, about eight o'clock,  accompanied Mrs. Lincoln to the theatre. Another lady and gentleman  were with them in the box. About half-past ten, during a pause in the  performance, the assassin entered the box, the door of which was un guarded, hastily approached the President from behind, and discharged a  pistol at his head. The bullet entered the back of his head, and penetrated nearly through. The assassin then leaped from the box upon the  stage, brandishing a large knife or dagger, and exclaiming, "Sic semper  tyrannis!" and escaped in the rear of the theatre. Immediately upon  the discharge, the President fell to the floor insensible, and continued  in that state until twenty minutes past seven o'clock this morning, when  he breathed his last. About the same time the murder was being com mitted at the theatre, another assassin presented himself at the door of  Mr. Seward's residence, gained admission by representing he had a prescription from Mr. Seward's physician, which he was directed to see  administered, and hurried up to the third-story chamber, where Mr. Seward was lying. He here discovered Mr. Frederick Seward, struck him  over the head, inflicting several wounds, and fracturing his skull in two  places, inflicting, it is feared, mortal wounds. He then rushed into the  room where Mr. Seward was in bed, attended by a young daughter and a  male nurse. The male attendant was stabbed through the lungs, and it  is believed will die. The assassin then struck Mr. Seward with a knife or dagger twice in the throat and twice in the face, inflicting terrible wounds.  By this time Major Seward, eldest son of the Secretary, and another  attendant reached the room, and rushed to the rescue of the Secretary;  they were also wounded in the conflict, and the assassin escaped. No  artery or important blood-vessel was severed by any of the wounds  inflicted upon him, but he was for a long time insensible from the loss of  blood. Some hope of his possible recovery is entertained. Immediate ly upon the death of the President, notice was given to Vice-President  Johnson, who happened to be in the city, and upon whom the office of  President now devolves. He will take the office and assume the functions  of President to-day. The murderer of the President has been discovered,  and evidence obtained that these horrible crimes were committed in  execution of a conspiracy deliberately planned and set on foot by rebels,  under pretence of avenging the South and aiding the rebel cause; but it  is hoped that the immediate perpetrators will be caught. The feeling  occasioned by these outrageous crimes is so great, sudden, and overwhelming, that I cannot at present do more than communicate them to you.  At the earliest moment yesterday the President called a Cabinet meeting,  at which General Grant was present. He was more cheerful and happy  than I had ever seen him, rejoiced at the near prospect of firm and dura ble peace at home and abroad, manifested in a marked degree the kind ness and humanity of his disposition, and the tender and forgiving spirit  that so eminently distinguished him. Public notice had been given that  he and General Grant would be present at the theatre, and the opportunity of adding the Lieutenant-General to the number of victims to be  murdered was no doubt seized for the fitting occasion of executing the  plans that appear to have been in preparation for some weeks, but General Grant was compelled to be absent, and thus escaped the designs  upon him. It is needless for me to say any thing in regard of the influence which this atrocious murder of the President may exercise upon the  affairs of this country; but I will only add that, horrible as are the atrocities that have been resorted to by the enemies of the country, they are  not likely in any degree to impair the public spirit or postpone the complete final overthrow of the rebellion. In profound grief for the events  which it is my duty to communicate to you, I have the honor to be, very  respectfully, your obedient servant,

EDWIN M. STANTON.