Let us return to our supposition of two stations north and south, 6,000 miles apart. The two lines of transit, as seen from them, are separated about 35 of an arc. This is as the lines are seen from the earth. If we recur to Kepler’s proportion, as stated before—that the distance of the earth from the sun is to the distance of Venus from the sun as 10,000,000 is to 7,233,324—we can make use of a trigonometrical calculation, and easily ascertain that those same lines on the sun, seen by an observer on Venus, would appear about 48‐½" apart. Moreover, the lines from the sun to Venus, forming this angle, cross each other at the planet, and, if prolonged, will reach the two stations on the earth. Hence, since opposite interior angles are equal, this (48‐½") must be the angle at which the same observer on Venus, turning towards the earth, would see the two stations. We arrive thus at a triangle, in which the base is known—6,000 miles; the angle at the vertex on Venus is also known—48‐½"; and the angles at the base are easily ascertainable. A simple calculation leads to the distance of Venus from the earth—about 25,300,000 miles. Again, applying Kepler’s formula to this number, we obtain as the result, for the earth’s distance from the sun, about 91,450,000 miles. If we give here only rough approximations, we are, after all, as near the truth as the astronomers of to‐day can boast of being. In a minute calculation, subsidiary but important points are to be brought in, complicating the calculation and influencing the result. After this statement of the general character of Halley’s method, we may be brief in our notice of the yet more beautiful mode of Delisle. He proposed it before the transits of the last century. But its efficiency so entirely depends on an accurate knowledge of the longitudes of the stations, and the longitudes of distant stations were then so uncertain, that it could not then be used with success.