The Royal Proclamation of May 13th, in which the neutrality of England is peremptorily laid down, and all British subjects are forbidden to take any part in the war "between the Government of the United States of America and certain States calling themselves the Confederate States of America," is a paper in many respects most offensive to the people of this country, though probably it was better in its intention than it is in its execution. That part of it which most concerns us is the recognition of "any blockade lawfully and actually established by or on behalf of either of the said contending parties." It is important to us that the British Government has admitted our right to blockade the ports of the rebels, provided we shall do so in force; and though Lord Derby has exhibited his ignorance of our naval power by saying that we cannot enforce the blockade we have declared and instituted, we shall show to the world, before the next cotton-crop shall be ready for exportation, that we are fully up to the work that is demanded of us, by having at least one hundred vessels, strongly armed and well manned, employed in watching every part of the Southern coast to which any foreign ship would think of going with a cargo or for the purpose of receiving one. The naval strength of the Union is as capable of vast and effective development as its military strength; and there is no reason why we should not have afloat, and ready for action, by the beginning of autumn, fleets sufficient to close up the Confederate ports as thoroughly as the Allies closed those of Russia in 1854-6, and the advanced guard of other fleets to be made ready to contend with the forces that insolent foreign nations may send into the waters of America for the purpose of fighting the battles of the slaveholders.