216 EIGHTH REPORT 1838. 



The object of the experiments of Robins was to obtain grounds 

 for a practical treatise on gunnery, and they were accordingly 

 limited for the most part to the motion of cannon balls at high 

 velocities. The result of these experiments was to prove, that 

 the law of the resistance being proportional to the square of- the 

 velocity was not true in comparing slow with very high speeds. 

 It was found, for example, to give a resistance in some cases 

 three times less than the actual resistance, showing, that when 

 extended to such limits, the resistance must vary in a much 

 higher proportion. 



Dr. Hutton was, so far as we are informed, the latest inquirer 

 who undertook a course of experiments with the view of de- 

 termining the amouint and the law of the atmospheric resistance. 

 Besides directing his inquiries to more varied velocities, he also 

 endeavoured to investigate the effects which the form of the 

 moving body produces upon the resistance. The experiments 

 were made with hemisphei*es moved alternately with the con- 

 vex and flat sides foremost, with cones moved alternately with 

 the point and base foremost, with cylinders moved with the end 

 foremost, and with spheres. 



It was found that at moderate velocities the resistance did not 

 sensibly vary from tlie law of the squares of the velocities ; but 

 in comparing slow speeds with high speeds, a gradual departure 

 from that law took place, the resistance increasing in a higher 

 ratio. ' 



In comparing together bodies exposing a frontage of different 

 magnitudes with the same speed, it was fovmd that the resist- 

 ance was not proportional to the magnitude of the frontage, but 

 in some higher unascertained ratio. 



It was also found that the resistance did not depend alone on 

 the magnitude of the transverse section, for that with the saiiie 

 transverse section different resistances were encountered accord- 

 ing to the form of the body. Thus, in general, a flat front pro- 

 duced more resistance than a round or pointed one. But on the 

 other hand, the resistance was not found to diminish in propor- 

 tion to the sharpness of the foremost end of the moving body; 

 but that, on the contrar}-, a body presenting a hemispherical 

 end was less resisted than one presenting a conical end, the 

 transverse section of both being the same. 



It was also found that the resistance did not depend alone on 

 the magnitude or form of the foremost end, but had some de- 

 pendence on the hinder part. Thus, a cone, hemisphere, and 

 cylinder, having equal bases, moved base foremost, with the same 

 velocity, suffered different resistances. 



No law was obtained from these experiments by which the- 



