It was a march, pure and simple; and inasmuch as men are the same now as they were then, it gives excellent data of the way in which purely military or army power can move from one place to another, _while still preserving its character and exercising its functions_.

Similarly, when Admiral Schroeder, in November, 1910, went from the east coast of the United States to the English Channel, his march was unopposed, its details are known, and it gave an excellent illustration of how naval power can move from one place to another, _while still preserving its character and exercising its functions_.
Now General Sherman was a man of world-wide fame, and so were some of his generals, and Sherman's fame will last for centuries.

Compared with Sherman, Admiral Schroeder was obscure; and compared with Sherman's officers, Admiral Schroeder's were obscure.

Sherman's soldiers, privates and all, were made glorious for the rest of their lives by having been in Sherman's march to the sea, while Admiral Schroeder's sailors achieved no glory at all.

So, the next paragraph is not intended to detract in the slightest from Sherman and his army, but simply to point out the change in conditions that mechanical progress has brought about.
The statement of comparison is simply that when General Sherman marched from Atlanta to the sea his army composed 62,000 men, and it took him twenty-five days to go about 230 land miles or 200 sea miles; and when Admiral Schroeder went from our coast to Europe he had 16 ships, and he made the trip of more than 3,000 sea miles in less than fourteen days.