CHAPTER II. 

 CHARACTER AND METHOD OF E3XPERIMENTS. 



The experiments which 1 have devised and here describe, are made with one 

 specific object, namely, to elucidate the dynamic principles lying at the basis of 

 the aerial mechanical flight of bodies denser than the air in which they move, and 

 I have refrained as a rule from all collateral investigations, however important, 

 iint contributing to this end. These experiments, then, arc in no way concerned 

 with ordinary aeronautics, or the use of balloons, or objects lighter than tic air, 

 but solely with the mechanical SUStentation of bodies denser than the air, and tin- 

 reader will please note that only the latter are referred to throughout this 

 memoir when such expressions as "planes," "models," ••mechanical flight," 

 and the like, are used. 



The experiments in question, for obtaining first approximations to the power 

 and velocities needed to sustain in the air such heavy inclined planes or other 

 models in rapid movement, have been principally made with a very large 

 whirling table, located on the grounds of the Allegheny Observatory, Allegheny, 

 Pa. (lat.40°27'41.6"; long. 5 h 20 ra 2.93 s ; height above the sea-level, 1,1 15 feet). 



The site is a hill on the north of the valley of the Ohio and rising about 400 

 feet above it. At the time of these observations the hill-top was bare of trees 

 and of buildings, except those of the observatory itself. This hill-top is a plane 

 of about three acres, of which the observatory occupies the south side. The 

 ground slopes rapidly both toward the east and west, the latter being the quarter 

 from which come the prevailing winds. 



The general disposition of the grounds of the observatory buildings, of the 

 engine, and of the whirling table is shown in plate I. The whirling table is 

 shewn in plate II, in elevation and in plan, ami with details on an enlarged scale. 

 It has been constructed especially in view of the need of getting the greatest 

 continuous speed thus attainable, under circumstances which should render 

 corrections for the effects of circular motion negligible, in relation to the degree 

 of accuracy aimed at. 



The first disturbing effect of circular motion to present itself to the mind of 

 the reader will probably be centrifugal force; but in regard to this he may observe 

 that in all the pieces of apparatus hereafter to be described, the various parts are 

 so dispose.l that the centrifugal force proper, viz., the out ward thrust of the plane 



