Bacon anticipated, however, much more than merely destructive effects from the use of high explosives, and indeed it is almost amusing to see how closely he anticipated some of the most modern usages of high explosives for motor purposes. He seems to have realized that some time the apparently uncontrollable forces of explosion would come under the control of man and be harnessed by him for his own purposes. He foresaw that one of the great applications of such a force would be for transportation. Accordingly he said: "Art can construct instruments of navigation such that the largest vessels, governed by a single man, will traverse rivers and seas more rapidly than if they were filled with oarsmen. One may also make carriages which without the aid of any animal will run with remarkable swiftness." {323} When we recall that the very latest thing in transportation are motor-boats and automobiles driven by gasoline, a high explosive, Roger Bacon's prophecy becomes one of those weird anticipations of human progress which seem almost more than human. It was not with regard to explosives alone, however, that Roger Bacon was to make great advances and still more marvelous anticipations in physical science. He was not, as is sometimes claimed for him, either the inventor of the telescope or of the theory of lenses. He did more, however, than perhaps anyone else to make the principles of lenses clear and to establish them on a mathematical basis. His traditional connection with the telescope can probably be traced to the fact that he was very much interested in astronomy and the relations of the heavens to the earth. He pointed out very clearly the errors which had crept into the Julian calendar, calculated exactly how much of a correction was needed in order to restore the year to its proper place, and suggested the method by which future errors of this kind could be avoided. His ideas were too far beyond his century to be applied practically, but they were not to be without their effect, and it is said that they formed the basis of the subsequent correction of the calendar in the time of Pope Gregory XIII., about three centuries later.