WASHINGTON — The world saw brain power take a different form Saturday. From the Washington Monument to Germany’s Brandenburg Gate and even to Greenland, scientists, students and research advocates rallied on an often soggy Earth Day, conveying a global message about scientific freedom without political interference, the need for adequate spending for future breakthroughs and just the general value of scientific pursuits. They came in numbers that were mammoth if not quite astronomical. “We didn’t choose to be in this battle, but it has come to the point where we have to fight because the stakes are too great,” said Pennsylvania State University climate scientist Michael Mann, who regularly clashes with politicians. President Donald Trump, in an Earth Day statement hours after the marches kicked off, said that “rigorous science depends not on ideology, but on a spirit of honest inquiry and robust debate.” Denis Hayes, who co-organized the first Earth Day 47 years ago, said the crowd he saw from the speaker’s platform down the street from the White House was energized and “magical” in a rare way, similar to what he saw in the first Earth Day. “For this kind of weather this is an amazing crowd.