30051902A Science Christian Hansen for the New York TimesThe Secret Science Club meets once a month in the basement of a Park Slope bar called Union Hall. The club is more of a loose assortment of twenty-somethings (as well as some older folks) who come to see free science lectures presented by real scientists. The people who come are not scientists, but really love science. The last time the Secret Science Club got together, Wednesday Nov. 7, there were two hour long presentations. The first to present was David Maiullo, of the Rutgers University Physics Dept. He used a cannon that shot out smoke rings to demonstrate fluid mechanics. The cannon was made out of an old metal garbage can.