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XVIII. Remarks on Prof. Moseley's Principle of least Pres- 

 sure. By S. Earnshaw, B.A.^ Fellow of the Cambridge 

 Philosophical Society. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 TVTOT being fortunate enough to comprehend fully the de- 

 ■^ monstration of the new statical principle, distinguished as 

 " the Principle of least Pressure," which Mr. Moseley com- 

 municated in your Journal of last October, I have been wait" 

 ing since its appearance in the hope that some gentleman in 

 a subsequent Number would have taken notice of it: but this 

 not having happened, and there appearing in your Magazine of 

 the present month a further communication from Mr. Moseley 

 in continuation of the same principle, but not containing any 

 additional elucidation of the previous demonstration, I have 

 ventured, not wishing to remain longer in doubt of the truth of 

 a principle so curious and interesting, to make a few observa- 

 tions on the subject, in the hope of eliciting from Mr. Moseley 

 such a reply as may clear both the principle and its demon- 

 stration from the obscurity with which, to me at least, it ap- 

 pears to be somewhat clouded. The remarks I have to make 

 are principally upon the following sentence of Mr. Moseley's 

 first communication : " Now each force of the system C, under 

 these circumstances, just sustains and is equivalent to the pres- 

 sure propagated to its point of application by the forces of the 

 system A; or it is equivalent to that pressure, together with the 

 pressure propagated to its point of application by the other 

 forces of the system C." Now it appears to me that, speaking 

 generally, it is impossible that each force of the system C 

 shall just sustain only such pressures as are propagated to it 

 by the system A ; unless either that the system C consists of 

 but one force, or that all the forces of which it consists are 

 parallel. For if there be more forces than one in the system 

 C, and if they are not parallel, their actions must of necessity 

 mutually propagate pressures. Wherefore in either of these 

 cases (which to me appear the only ones to which the former 

 part of the paragraph quoted can apply,) it is manifest that 

 the remaining part of the paragraph cannot apply; for there is 

 no pressure propagated by the forces of the system C, under 

 those suppositions, to each other. As what I have quoted from 

 Mr. Moseley contains the premises of the syllogism of which 

 his demonstration consists, if what I have said upon it be 

 found to be correct, the problem of pressures must remain in 

 as great mystery as heretofore. Admitting, however, that I 



Third Series. Vol.4. No. 20. Feb. 18 34. ' N 



