This calligraphy mounted on a hanging scroll was written by the Zen monk Sogan Kogetsu, who lived from November 8, 1574 to August 19, 1643, in the Momoyama period in the early Edo period. He was the chief priest of Daitokuji Temple. He was the son of Munenori Tsuda, a wealthy merchant in Sakai who served Oda Nobunaga and Toyotomi Hideyoshi as a tea master. In 1611, he took over the Kuroda family's family temple, sub-temple Ryuko-in which contains, Mittan, a national treasure tea room which I visited last year. Kogetsu's calligraphy is popular for tea ceremony hangings.
The calligraphy characters are: 斗指両辰間 - toshi ryoushin no kan
斗 means "dipper" and refers to the Big Dipper which always points to true north.
指 means "to point".
Together, they mean to point to true north.
両 means "both" and 辰 means "dragon" and "間" means space. "両辰間" mean the space between the two dragons. The two dragons represent extremes in a dichotomy such as good and evil, light and dark. The phrase means that you should find your true north and follow it and navigate between the extremes. The "middle way" is often described in Buddhism.
This hanging scroll is also very appropriate for this year because it is the Year of the Dragon and somehow relevant to my own life. It's currently hanging in the President's office at the Chiba Institute of Technology.
I was reading Souoku Sen's book on Tea recently and he writes about how when you look at the 茶会記 (tea ceremony logs) of the period, they describe the hanging scroll's colors, dimensions, etc. but usually don't record what the scroll actually says or means. It could be that most people couldn't read them. This was a bit heartening for me since Japanese calligraphy is very hard to read and understand, but often rewarding once you do. (Souoku is a descendant of Rikyu and the current head of the Mushanokoji School of Tea.)