Opinions entertained by astronomers of the last century: Gregory, Maupertuis, Lambert–Calculations of Lalande ; comets move too rapidly in the vicinity of the earth for the effects of their attraction to come into play–Opinion of Laplace– The collision of a comet with the earth; its effect according to the mechanical theory of heat.

It is interesting to note the opinions formed by savants a century ago respecting the probable effect of a collision between a comet and the earth. Further on we shall speak of the theological romance invented by Whiston for the scientific explanation of the Deluge. According to Whiston the famous comet of 1680, after having, 4000 years ago, produced the universal deluge, is destined to accomplish the destruction of the world, and our globe will be ultimately set on fire by the same comet which had previously inundated it.

Whiston wrote at the end of the seventeenth century. In the middle of the eighteenth century theological speculations engaged but very slightly the attention of astronomers ; but that a very exaggerated idea continued to prevail respecting the amount of injury which the proximity of a comet or its collision with the earth would be capable of producing is undoubted.

In 1742 Maupertuis, in his Lettre sur la Comète, writes as follows: ‘ With their variety of movements it is clearly possible for a comet to encounter some planet or even our earth upon its way; and it cannot be doubted that terrible results would ensue.