"Firstly, we wish to know whence comes the comet and whither it goes. We wish to follow its path, as it sweeps its way through our solar system. As this orbit is controlled by the same law of gravity which controls all celestial motion, an exact knowledge of a comet's course among the planets, gives the basis of investigation regarding its relation to the solar system and to the realms of space beyond. Therefore one important line of investigation is the determination of the positions of the comet in the sky, from whence may be obtained its orbit in space. Secondly, the astronomer wished to know what are the nature and constitution of comets. The investigation of this question is of comparatively recent origin, and belongs to ."