Double Stars.

50. The work of cutting the stars will be infinitesimal in relation to their available energy before collision. It will not cause any appreciable lessening of the velocity of the escaping stars. But the middle body will exert a power- page 17 ful attraction. It will exercise a retarding influence, preventing the retreat of the two bodies, equal to that of three times the mass either body loses. Hence, when two equal bodies lose a third of each by impact, the attraction acting on each of the escaping bodies is doubled. Therefore they do not as a rule become free from the new central body unless the original proper motion were large.

51. If however, the original proper motion were large, and the graze small, the two stars would escape each other. If the original motion were small, and the graze, on an average, more than a tenth, then the two stars would become orbitally connected.

52. Such a pair, when thus connected, would form a permanent double star. It is the opinion of some astronomers that impacting stars becoming orbitally connected could not make double stars, as they think such stars would impact again. Rut they overlook the fact that the nebula that retarded their escape and formed an important factor after the first impact, will have dissipated before they return.

53. Hence the eccentricity will lessen greatly, and, as a rule, instead of impacting again they page 18 will be scores of millions of miles away at perihelion. In fact, they may have about the eccentricity that double stars are known to have.

54. There is a possibility of a second impact when the graze has been a very small fraction, or if one of the stars were multiple. But the period of the subsequent recurrence of impacts, after the first recurrence, would lessen in point of time. On calculating the dates of the apparently recurrent star, "The Pilgrim," viz., 945, 1264, and 1572, this is proved to be the case. The dark bodies producing these impacts must be of absolutely stupendous dimensions. The dark bodies producing Nova Auriga: were probably 8,000 and 4,000 times the mass of the sun respectively.

55. Double stars should be more often variable than single stars. Struvé has proved that they are hundreds of thousands of times more variable than ordinary stars.

56. We should expect them also to be more frequently coloured. This, too, is most strikingly the case.

57. We should look for them to be associated with nebulae. Herschell says the association of page 19 nebulae and double stars is most truly remarkable.

58. They should be highly eccentric. This is also well known to be the case.

59. A large number of agencies tend to render the orbit less eccentric. These are fully discussed in my papers of 1880.