In describing Newton's comet, with a tail ninety million miles long projected backward both from the sun and the comet, when it disappeared in the light of the sun, and exhibiting a similar tail, also ninety million miles long, when, less than four days afterwards, it reappeared from behind the sun, but with the tail now directed forward from the comet, but in both cases extended radially outward from the sun, it is obvious that this whole tail must have made a sweeping change of direction of nearly one hundred and eighty degrees upon the nucleus as its center. Professor Proctor says, "As Sir John Herschel remarks, we cannot look on the tail of a comet as something whirled round like a stick as the comet circles around its perihelion sweep. The tail with which the comet reappeared must have been an entirely new formation." It is true that a comet's tail cannot be conceived of as being whirled round like a stick, but we can very readily conceive of it as something like a flame composed of incandescent gases, and it may very easily be blown round a stick; and this is precisely what must happen in the case of a comet. Construct, for experiment, a little apparatus consisting of a blow-pipe adapted to deliver a current of air between two horizontal metal disks, say an eighth of an inch apart, one perforated at the center to admit the nozzle of the blow-pipe. By directing a constant current of air through the latter, it will be deflected so as to blow radially outward in all directions and in the same plane. Now take a stick with a flame on the end of it, or a lighted candle, and with it approach this center of repellent energy in the plane of the space between the disks and along an ellipse representing the orbit of a comet. As the flame approaches the improvised solar center it will be driven backward from the wick of the candle almost along the line of its approach, and as it passes around the center it will be constantly blown outward in a radial direction until, when it recedes after perihelion, the flame will be seen pointed almost directly ahead. At all times the direction of the flame will lie along the radial lines prolonged outward from the center through the wick of the candle, and it will not be a new flame generated at every change of its direction, but the same flame constantly forced outward by the repulsive force of the central atmosphere in this case or the solar electrosphere in the case of the sun. This experiment is an accurate and conclusive exhibit of the phenomena of solar repulsion in its action upon the tail of a comet. It is analogous in principle to the repulsion of the pith-balls and the electric wind and (in application) to the phenomena presented by comets in their movements to, around, and from the sun. This repulsion is not operative in effect against the wick of the candle,--that is to say, it is not the repulsion of the nucleus which determines the direction of the tail, but the repulsion