For example, in nuclear fusion or fission only a small proportion of the mass is converted into energy so enormous quantities of material would be needed thus a nuclear starship would greatly deplete Earth of fissile and fusile material.

Again, when the fire goes out of the fusile substance, it does not pass into vacuum, but into the neighbouring air; and the air which is displaced forces together the liquid and still moveable mass into the place which was occupied by the fire, and unites it with itself.