:''Hast thou ne'er seen the ધૂમકેતુ's flaming flight?''
[[Isaacઆઈઝ॓ક Newtonન્યૂટન]] described ધૂમકેતુsધૂમકેતુન્॓ as compact, ધન, fixed, andઅન્॓ durable bodies: in one word, a kind of planets, which move in very oblique ભ્રમણકક્ષા, every way, સંપૂર્ણ આઝાદીથી, persevering in their motions even against the course and direction of the planets; and their પૂંછ as a very thin, slender vapour, emitted by the head, or nucleus of the ધૂમકેતુ, ignited or heated by the સૂર્ય. ધૂમકેતુઓ also seemed to Newton absolutely requisite for the conservation of the પાણી તથા ભેજ of the planets; from their condensed vapours and exhalations all that moisture which is spent on vegetations and putrefactions, and turned into dry earth, might be resupplied and recruited; for all vegetables were thought to increase wholly from fluids, and turn by putrefaction into earth. Hence the quantity of dry earth must continually increase, and the moisture of the globe decrease, and at last be quite evaporated, if it have not a continual supply. Newton suspected that the spirit which makes the finest, subtilest, and best part of our air, and which is absolutely requisite for the life and being of all things, came principally from the ધૂમકેતુs.
Another use which he conjectured ધૂમકેતુs might be designed to serve, is that of recruiting the સૂર્ય with fresh fuel, and repairing the consumption of his light by the streams continually sent forth in every direction from that luminary —
