that all Matter is Heavy. 265 



and natural history; and the mere metaphysician who without such 

 preparation and fitness sets himself to determine the grounds of mathe- 

 matical or mechanical truths, or the principles of classification, will be 

 liable to be led into error at eveiy step. He must speculate by means 

 of general terms, which he will not be able to use as instruments of 

 discovering and conveying philosophical truth, because he cannot, in 

 his own mind, habitually and familiarly, embody their import in special 

 examples. 



" Acting upon such views, I have already laid before the Philosophical 

 Society of Cambridge essays on such subjects as I here refer to ; espe- 

 cially a memoir " On the Nature of the Truth of the Laws of Motion," 

 which was printed by the Society in its Transactions. This memoir 

 appears to have excited in other places, notice of such a kind as to 

 shew that the minds of many speculative persons are ready for and 

 inclined towards the discussion of such questions. I am therefore the 

 more willing to bring under consideration another subject of a kind 

 closely related to the one just mentioned. 



" The general questions which all such discussions suggest, are (in 

 the existing phase of English philosophy) whether certain proposed 

 scientific truths, (as the laws of motion,) be necessary truths ; and if 

 they are necessary, (which I have attempted to shew that in a certain 

 sense they are,) on loliat ground their necessity rests. These questions 

 may be discussed in a general form, as I have elsewhere attempted to 

 shew. But it may be instructive also to follow the general arguments 

 into the form which they assume in special cases ; and to exhibit, in a 

 distinct shape, the incongruities into which the opposite false doctrine 

 leads us, when applied to particvilar examples. This accordingly is 

 what I propose to do in the present memoir, with regard to the propo- 

 sition stated at the head of this paper, namely, that all matter is heavy. 



" At first sight it may appear a doctrine altogether untenable to as- 

 sert that this proposition is a necessary truth : for it may be urged, we 

 have no difficulty in conceiving matter which is not heavy ; so that 

 matter without weight is a conception not inconsistent with itself; 

 which it must be if the reverse were a necessary truth. It may be 

 added, that the possibility of conceiving matter without weight was 

 shewn in the controversy which ended in the downfall of the phlogiston 

 theory of chemical composition ; for Some of the reasoners on this 

 subject asserted phlogiston to be a body with positive levity instead of 

 gravity, which hypothesis, however false, shews that such a supposition 

 is possible. Again, it may be said that weight and inertia are two sep- 

 arate properties of matter ; that mathematicians measure the quantity 

 of matter by the inertia, and that we learn by experiment only that the 



Vol. sLii, No. 2.— Jan.-March, 1842. 34 



