of, and after, this brilliant display of hydrogen, which is proved by the spectrum analyses of its light during that time.
The "new star" lately discovered in the constellation of Cygnus seems to be a complete confirmation of this theory.
A very interesting account of this star, by Richard A. Proctor, may be found in The Popular Science Monthly for December, 1877. From this account the star seems to have passed through all the various changes which should naturally be expected from such a collision; first, a very great augmentation of light, with a continuous, rainbow-tinted spectrum arising from the intense pressure to which the rapidly expanding mass of gas was at first subjected; gradually passing through various changes and gradations, till, finally, it took on the "spectrum of a true nebula," which should naturally occur after a large part of the intense heat of percussion had taken on the form of latent heat of expansion.
"As the stars are moving with various velocities in various directions," it may be asked, "What would be the consequences if two of them should enter each other's sphere of sensible attraction with very great velocities?"
In order to secure definite results, in replying to this question let us assume definite conditions:
Suppose them to be equal, and of such mass and density that each would approach the point of meeting with a velocity of 400 miles a second, by virtue of their mutual gravitation alone; and, further, that each one had an original velocity of 300 miles a second toward that point, when they entered each other's sphere of sensible attraction.
Now, they would meet, not with a velocity of 700 miles a second, as might, at first, be supposed, but with the velocity represented by , or 500 miles a second.
According to a previous mode of reasoning, the heat-force generated by such a collision should be sufficient to throw these two bodies outward beyond the possibility of return; therefore, the greater portion of the resulting nebulous mass would be thrown out with a corresponding velocity, and be distributed among the surrounding stars, leaving but a small portion of it to occupy the place of meeting; which, consequently, without further additions, would make but a small solar system.
Conclusion.—Let us now consider what would most likely be the result of such collisions, if the matter of the universe were of finite instead of infinite extent.
For this purpose we may assume the last-named pair of stars to constitute the entire amount of ponderable matter in the universe. It is supposed, then, that they are both moving directly toward the point of future meeting with a velocity of 300 miles a second, when each begins to be affected by the other's accelerating force; which, consequently, increases that velocity to 500 miles a second at the time of meeting.
