The Orbit of 61 Cygni.—This well-known double star has always attracted much attention from the wide distance between the components and the large proper motion; it was for the latter reason that Bessel selected it for parallax tests with the Königsberg heliometer, obtaining the first reliable stellar distance. Though it is such a near neighbour, the period is so long that its determination has baffled many investigators. In fact, at the end of the last century some American astronomers denied that it was a binary at all. However, Mr. T. Lewis, in his memoir on the Struve double stars, gave a diagram on a large scale of the observations up to 1900, which exhibited the curvature of the path in a palpable manner. At an even earlier date Dr. Peters had published an orbit in Astr. Nach., with a period of nearly eight hundred years.