ON AERIAL LOCOMOTION. 



311 



square iuclies per pouud. The auuexed tigiires are given approximatelj'^^ 

 iu order to avoid decimal fractious: 



* Nearly. 



The power required to drive was uearly the same in both experi- 

 ments — about equal to oue-sixteenth part of a horse-power, or the third 

 part of the strength of a inau as estimated by a constant force on the 

 handle of 12 poumls in the first experiment and 10 in the second, the 

 radius of the handle being 5^ inches, and making seventy revolutions 

 per minute in the first case and eighty iu the other. 



These experiments are so far satisfactory iu showing the small pitch 

 or angle or rise required for sustaining the weight stated, aud demon- 

 strating the principle before alluded to, of the slow descent of planes 

 moving horizontally' in the atmosphere at high velocities ; but the (jues- 

 tiou remains to be answered, concerning the disposal of the excessive 

 power consumed in raising a weight not exceeding that of a carrier- 

 pigeon, for unless thi.^j can be satisfactorily accounted for there is but 

 little prospect of finding au available power of sufficient energy in its 

 application to the mechanism for raising apparatus, either experimental 

 or otherwise, in the atmosphere. In the second experiment, the screw- 

 shaft made two hundred and forty revolutions, cousequeutly, oue vane 

 (there being two) was constantly passing over the same spot four hun- 

 dred and eighty times each minute, or eight times in a second. This 

 caused a descending current of air, moving at tiie rate of near 4 miles 

 per hour, almost sufficient to blow a caudle out placed 3 feet under 

 ueath. This is the result of "slip," and the giving both a downward 

 and rotary motion to this column of air will account for a great part of 

 the power employed, as the whole apparatus performed the work of a 

 blower. If the wings, instead of traveling iu a circle, could have been 

 urged continually forward in a straight line iu a fresh and uumoved 

 body of air, the "slip" would have been so inconsiderable, and the 

 pitch, consequently, reduced to such a small angle as to add but little 

 to the direct forward atmosi)heric resistance of the edge. 



The small tlyiug screws, sold as toys, are well known, it is au easy 

 matter to determine approximately the force expended iu raising and 

 maiutainiug them in the atmosphere. The following is au example of 

 one constructed of tin-plate with three equidistant vanes. This was 

 spun by means of a cord wound round a wooden spindle, fitted into a 

 forked handle as usual. The outer end of the coiled string was attached 



