72 EXPERIMENTS, &c. 



I need not, I believe, offer to show, that the 

 fact here spoken of, is not owing to any of the 

 causes Mr. Melvill has specified. I shall there- 

 fore, in a few words, point out its dependance 

 upon the principles which have just been men- 

 tioned. 



It is generally known, I suppose, that when 

 a vessel at sea, in the language of sailors, is 

 said to pitch, its two extremities turn upon its 

 shorter axis, and that the term of rolling is con- 

 fined by them to its motions upon the longer 

 axis. In both pitching and rolling then, the 

 relative position of a vessel to a horizontal 

 plane is necessarily changed. Consequently, 

 though, in the abovementioned experiment, 

 Mr. Melvill's body and head were at rest with 

 respect to every object about him, still a dif- 

 ferent degree of muscular effort was required 

 to ]keep them so, in every such different posi- 

 tion of the vessel. But each degree of mus- 

 cular effort, to sustain his body against the 

 operation of its gravity, would suggest to him 

 its concomitant position with regard to the 

 plane of the horizon ; each deviation, there- 

 fere, of the vessel from its former situation, re- 

 latively to the same plane, would be perceived, 

 and the vessel itself be seen to move. In short, 

 nothing more takes place in this, than in the 

 following experiment: Let a pole be placed 



