REVIEW. 87 



making the ship pitcli ami send, will be less than if the weights 

 in the fore and after bodies are unequal, and their centres of gra- 

 vity at unequal distances from the centre of gravity of the whole. 



Capt. P. has however shewn by an illustration of a most 

 simple mechanical experiment, that, with the same distance 

 between the centres of gravity of the two weights in each body, 

 and when the two bodies are put in motion together by the same 

 momentary force, the vibrations of the one with equal weights, at 

 equal distances from the axis, are greater in extent and duration 

 than the vibrations of the body with unequal weights at unequal 

 distances from the axis. And this is shewn to proceed from the 

 momentum of the unequal weights being /ess than the momentum 

 of the equal weights. For, as Capt. P. observes, as the power 

 of the weights to generate motion, is /ess in the former case than 

 in the latter, and as the stability, or the power to resist motion, is 

 the mme in each, the motions of the former must necessarily be 

 l-ess in extent than those of the latter. 



Again, the sum of the ^^ moments of inertia^ of the equal 

 weights, is greater than the sum of the " moments of inertia" of 

 the unequal weights ; and, therefore, according to Mr. H.'s own 

 argument, "that, *by the moment of inertia' of a body, revolving 

 round an axis, is always understood, the force ^vith which the 

 body moves,*' the body with equal weights must move with 

 greater force than the one with unequal weights ; and, as the 

 power to resist motion is the same in each, the motions of the 

 former must be greater in extent than those of the latter. 



And, at page 77, Capt. P. says : "Mr. Henwood, in place of 

 taking the sum of the ^ moments of inertia' of the weights of the 

 fore and after bodies of the ship, to represent the ' force of inertia' 

 of the body ; and, in place of considering this force as proceeding 

 from the united efforts of those weights, and the whole force to 

 act in the same direction ; he actually considers, and asserts that 

 the tendencies of the * moments of inertia' of those weights are 

 always in opposition to each other. But this," as Capt. P. 

 observes, " is totally at variance with all known laws." 



Mr. Henwood erroneously imagines likewise, that the motions 

 of a body must be greater in extent one way than the other, when 

 equilibrium is produced by unequal weights, at unequal distances 

 from the axis, and merely because the " moments of inertia" of 

 such weights are unequal. But, as Capt. P. observes, " as it is 

 the su7n of the ^ moments of inertia' of the various weights of 

 which a body is composed, which represents the ^ force of inertia^ 



