Salmasius cannot think himself into it, nor had he sufficient imagination to be inspired by Charles as Burke (who, nevertheless, has borrowed from him) was to be inspired by Marie Antoinette.
His book--entitled "Defensio Regia pro Carolo I."-- appeared in October or November, 1649.

On January 8, 1650, it was ordered by the Council of State "that Mr.Milton do prepare something in answer to the Book of Salmasius, and when he hath done it bring it to the Council." There were many reasons why he should be entrusted with this commission, and only one why he should not; but one which would have seemed conclusive to most men.

His sight had long been failing.

He had already lost the use of one eye, and was warned that if he imposed this additional strain upon his sight, that of the other would follow.

He had seen the greatest astronomer of the age condemned to inactivity and helplessness, and could measure his own by the misery of Galileo.