FOC 



FCET 



so long as the arch of air the wing de- 

 scribes makes a resistance equal to the 

 excess of the specific gravity of the bird 

 above the air. If the air, therefore, be so 

 rare as to give way with the same velo- 

 city as it is struck withal, there will be 

 no resistance, and consequently the bird 

 can never mount. Birds never fly up- 

 wards in a perpendicular line, but always 

 in a parabola. In a direct ascent, the na- 

 tural and artificial tendency would oppose 

 and destroy each other, so that the pro- 

 gress would be very slow. In a direct 

 descent, they would aid one another, so 

 that the fall would be too precipitate. 



FLYING, artificial, that attempted by 

 men, by the assistance of mechanics. 

 The art of flying has been attempted by 

 several persons in all ages. The Leuca- 

 clians, out of superstition, are reported to 

 have had a custom of precipitating a man 

 from a high cliff into the sea, first fixing 

 feathers, variously expanded, round his 

 body, in order to break his fall. Friar 

 Bacon, who lived near five hundred years 

 ago, not only affirms the art of flying pos- 

 sible, but assures us, that he himself knew 

 how to make an engine, wherein a man, 

 sitting, might be able to convey himself 

 through the air, like a bird ; and further 

 adds, that there was then one who had 

 tried it with success ; but this method, 

 which consisted of a couple of large, thin, 

 hollow copper globes, exhausted of the 

 air, and sustaining a person who sat there- 

 on, Dr. Hook shows to be impracticable. 

 The philosophers of K. Charles the se- 

 cond's reign were mightily busied about 

 this art. Bishop Wilkins was so confi- 

 dent of success in it, that he says, he does 

 not question but, in future ages, it will be 

 as usual to hear a man call for his wings, 

 when he is going a journey, as it is now 

 to call for his boots. 



The art of flying has, in some measure, 

 been brought to bear in the construction 

 and use of balloons. See jEnosTATiox. 



FLYING army, a small body, under a 

 lieutenant or major general, sent to harass 

 the country, intercept convoys, prevent 

 the enemy's incursions, cover its own 

 garrisons, and keep the enemy in con- 

 tinual alarm, 



FLYING bridge. See BRIDGE. 

 FLYING^S/*, a name given by the Eng- 

 lish writers to several species of fish, 

 which, by means of their long fins, have 

 a method of keeping themselves out of 

 water some time. See EXOCOETUS, &c. 



FOCUS, in geometry and conic sec- 

 tions, is applied to certain points in the 

 parabola, ellipsis, and hyperbola, where 



the rays reflected from all parts of these 

 curves concur and meet. 



Foci of an ellipsis, are two points in the 

 longest axis, on which as centres the 

 figure is described. See ELLIPSIS. 



If from the foci two right lines are 

 drawn, meeting one another in the peri- 

 .phery of the ellipsis, their sum will be al- 

 ways equal to the longest axis; and there- 

 fore, when an ellipsis and its two axes are 

 given, and the foci are required, you need 

 only take half the longest axis in your 

 compasses, and setting one foot in the 

 end of the shorter, the other foot will cut 

 the longer in the focus required. 



Focus of an hyperbola, is that point in. 

 the axis, through which the latus rectum 

 passes ; from whence, if any two right 

 lines are drawn, meeting in either of the 

 opposite hyperbolas, their difference will 

 be equal to the principal axis. See HY- 

 PERBOLA. 



Focus of a parabola, a point in the axis 

 within the figure, distant from the vertex 

 one-fourth part of the latus rectum. See 

 PARABOLA. 



Focus, in optics, is the point wherein 

 rays are collected, after they have un- 

 dergone reflection or refraction. See 

 OPTICS. 



FODDER, any kind of meat for horses, 

 or other cattle. In some places, hay and 

 straw, mingled together, is peculiarly de- 

 nominated fodder. 



FODDER, in mining, a measure contain- 

 ing twenty-two hundred and an half 

 weight, though in London but twenty 

 hundred weight. 



FCETUS, in anatomy, a term applied to 

 the offspring of the human subject, or of 

 animals, during its residence in the ute- 

 rus. The term of ovum is applied to the 

 foetus, with its membranes and placenta 

 taken altogether. We shall consider, un- 

 der this article, the anatomy of the mem- 

 branes which cover the foetus during its 

 abode in the uterus ; of the placenta, 

 which forms the medium of connexion 

 between the systems of the mother and 

 child; and of the pregnant uterus itself, 

 since the peculiarities, distinguishing its 

 structure at this time, arise from the re- 

 sidence of the foetus in its cavity. The 

 following description applies to the uterus 

 and its contents in the ninth month of 

 gestation. 7'he size of the organ differs 

 much in different individuals ; and this 

 arises principal!}' from varieties in the 

 quantity of the liquor amnii. In shape it 

 is oviform ; the fundus answering to the 

 largest extremity of the egg, and the 

 cervix and os uteri to the small end. It 



