And First, Every Feather has various Colours, and according to the Variety of the Weather, are apt to look brighter and clearer, or paler and fainter, as the Sun happens to look on them with a stronger or weaker Aspect. The Quill or Head of every Feather is or ought to be full of a vigorous Substance, which gives Spirit, and supports the brightness and colour of the Feather; and as this is more or less in quantity, the bright Colour of the Feather is increased, or turns languid and pale. Tis true, some of those Quills are exceeding empty and dry; and the Humid being totally exhal'd, those Feathers grow very useless and insignificant in a short time. Some again are so full of Wind, and puft up with the Vapour of the Climate, that there's not Humid enough to Condence the Steam; and these are so fleet, so light, and so continually fluttering and troublesome, that they greatly serve to disturb and keep the Motion unsteddy. Others either placed too near the inward concealed Fire, or the Head of the Quill being thin, the Fire causes too great a Fermentation; and the Consequence of this is so fatal, that sometimes it mounts the Engine up too fast, and indangers Precipitation: But 'tis happily observed, That these ill Feathers are but a very few, compar'd to the whole number; at the most, I never heard they were above 134 of the whole number: As for the empty ones, they are not very dangerous, but a sort of Good-for-nothing Feathers, that will fly when the greatest number of the rest fly, or stand still when they stand still. The fluttering hot-headed Feathers are the most dangerous, and frequently struggle hard to mount the Engine to extravagant heights; but still the greater number of the Feathers being stanch, and well fixt, as well as well furnisht, they always prevail, and check the Disorders the other would bring upon the Motion; so that upon the whole Matter, tho' there has sometims been oblique Motions, Variations, and sometimes great Wandrings out of the way, which may make the Passage tedious, yet it has always been a certain and safe Voyage; and no Engine was ever known to miscarry or overthrow, but that one mentioned before, and that was very much owing to the precipitate Methods the Prince took in guiding it; and tho' all the fault was laid in the Feathers, and they were to blame enough, yet I never heard any Wise Man, but what blam'd his Discretion, and particularly, a certain great Man has wrote three large Tracts of those Affairs, and call'd them, The History of the Opposition of the Feathers; wherein, tho' it was expected he would have curst the Engine it self and all the Feathers to the Devil, on the contrary, he lays equal blame on the Prince, who guided the Chariot with so unsteddy a hand, now as much too slack, as then too hard, turning them this way and that so hastily, that the Feathers could not move in their proper order; and this at last put the Fire in the Center quite out, and so the Engine over-set at once.