A^fXUAL OF SCIENTIFIC DISCOVERY. 



as that which the last-named comet had when nearest the earth. The 

 most striking phenomenon noticed in this comet was the evolution 

 from the head or nucleus of two sheaf-like streams of luminous mat- 

 ter in opposite directions, indicating two fixed centres of eruption. 

 M. Secchi, the distinguished Roman astronomer, in describing this 

 appearance, says : " The tail was simple, until the two reversed jets, 

 or aigrettes, were well developed, so that no doubt could remain that 

 it was really these nebulosities which, in reversing themselves, pro- 

 duced the tail." The periodicity of the jets at first suggested a rota- 

 tion of the comet about an axis, but the idea was not confirmed by 

 observation. The light of the nucleus and of the aigrettes was only 

 polarized once, and then very feebly. The nebulosities, on the con- 

 trary, were always strongly polarized. These facts indicate a differ- 

 ent molecular condition, and M. Secchi suggests that the nucleus and 

 the aigrettes may have been formed of vapor analogous to our clouds, 

 which do not polarize, while the nebulosities had passed into a state 

 of gas which polarizes like our atmosphere. He adds, " We might 

 also admit that the nucleus and the aigrettes were incandescent, but 

 the supposition is a little difficult. After the perihelion passage there 

 appeared vestiges of paraboloid surfaces enveloping the sheaves of 

 light, as if the matter was being deposited in layers as the comet 

 cooled." 



M. Chacornac, of the Paris Observatory, who observed this comet 

 carefully, thus describes its phenomena: " The nucleus of the comet 

 emits, in the direction of the sun, a vaporous jet, from which there 

 appear to proceed particles of cometary matter, in the same way as a 

 jet of steam escapes from a machine. This preserves, during a cer- 

 tain time, a rectilinear form, which seems to indicate a considerable 

 force of projection emanating from the nucleus. Soon after, it curves 

 slightly, and presents the appearance of an arched cone, exhibiting 

 a good deal of analogy to a cornucopia, such as they are generally 

 represented. At this moment the gaseous particles accumulate at the 

 extremity of the jet nearest the sun in the form of rounded clouds, 

 and this appearance seems to indicate that at this distance from the 

 nucleus the force of projection is subdued by some resistance opposed 

 to it. Some hours later this luminous jet assumes a diffuse aspect, and 

 shows that the emission from the nucleus has ceased to continue in 

 this direction. At the moment that it begins to change, and in an 

 angle inclined thirty degrees towards the east, one perceives the first 

 traces of a new ray, whose development presents the same phases as 

 the preceding one. Sixteen hours later one observes a new ray in 

 the direction of the first one seen the night before, and this last, con- 

 tinuing to change in this interval of time, appears dispersed in the 

 hemispherical ..envelope, like a fog, hardly preserving traces of its 

 original form and direction. In these successive transformations the 

 new ray presents afterwards the same appearance as the one parallel 

 to the radius vector." 



Since the disappearance of this comet, Mr. Safford, of Cambridge, 

 and other (European) observers have determined, from a discussion 

 of its elements, that this body is a member of the solar system, mov- 

 ing in an elliptical orbit, with a period of one hundred and thirty-one 

 and a half years. The ellipse has considerable inclination to the plane 



